Citation
Testing shear strength of concrete cylinders using the Iosipescu method

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Title:
Testing shear strength of concrete cylinders using the Iosipescu method
Creator:
Cardillo, Christopher James
Place of Publication:
Denver, CO
Publisher:
University of Colorado Denver
Publication Date:
Language:
English

Thesis/Dissertation Information

Degree:
Master's ( Master of science)
Degree Grantor:
University of Colorado Denver
Degree Divisions:
Department of Civil Engineering, CU Denver
Degree Disciplines:
Civil engineering
Committee Chair:
Rutz, Frederick R.
Committee Members:
Rens, Kevin
Nogueira, Carnot

Notes

Abstract:
The Iosipescu shear test uses two force couples to create an area of high shear near the mid-length of a test specimen. While concrete specimens that are prepared in in a laboratory can be formed to virtually any desired shape, field specimens, which are most-commonly procured through core drilling, typically possess circular cross-sections. The purpose of this research was to develop an Iosipescu-inspired test apparatus for testing circular specimens. In this case, the apparatus was designed for testing of core samples that were taken with a 76.2 mm (3-in) nominal diameter wet coring drill. The vertical steel plates that applied the force couples were fabricated with semicircular cutouts lined in neoprene. The test specimens included bonded overlays with four different surface treatments as well as monolithically-cast concrete. Results from the Iosipescu core testing were compared to other direct shear tests.

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University of Colorado Denver
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Auraria Library
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Copyright Christopher James Cardillo. Permission granted to University of Colorado Denver to digitize and display this item for non-profit research and educational purposes. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder.

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TESTING SHEAR STRENGTH OF CONCRETE CYLINDERS USING THE IOSIPESCU METHOD b y: CHRISTOPHER JAMES CARDILLO B.A. University of Northern Colorado, 1993, B.S. University of Colorado at Denver, 2005 A thesis submitted to the Faculty of the Graduate School of the University of Colorado in partial fulfillment of the requirements for the degree of Master of Science, Civil Engineering 2018

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ii A thesis for the Master of Science in Civil Engineering degree by Christopher James Cardillo has been approved for the Civ il Engineering Program by Fredrick R. Rutz Kevin Rens Carnot Nogueira Date: December 10, 2018

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iii Cardillo, Christopher James (MS Civil Engineering) Testing Shear Strength of Concrete Cylinders Using the Iosipescu Method Thesis directed by Frede rick R. Rutz. ABSTRACT The Iosipescu shear test uses two force couples to create an area of high shear nea r the mid length of a test specimen. While concrete specimens that are prepared in in a laboratory can be formed to virtually any desired shape, field specimens, which are most commonly procured through core drilling, typically possess circular cross sections. The purpose of this research was to develop an Iosipescu inspired test apparatus for testing circular specimens . In this case, the apparatus was designed for testing of core samples that were taken with a 76.2 mm (3 in ) nominal diameter wet coring drill . The vertical steel plates that applied the force couples were fabricated with semicircular cutouts lined in neoprene. The test specimens included bonded overlays with four different surface treatments as well as monolithically cast concrete. Results from the Iosipescu core testing were compared to other direct shear tests. The form and content of this abstract are approved. I recommend its publicat ion Approved: Fredrick R. Rutz

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iv ACKNOWLEDGEMENTS There were a number of individuals and organizations that contributed greatly to the successful completion of this research. I would, first, like to express my deepest gratitude to Dr. Fredrick Rutz. Dr. Rutz continually shared his time, knowledge, wisdom and enthusiasm through out the course of this project. His mentorship was instrumental in the completion of this research. I would also like to thank the University of Colorado at Denver and especially, D r. Kevin Rens , and Dr. Carnot Nogueira for serving with Dr. Rutz on the research committee. My sincerest thanks also goes to Tom Thuis of the electronic calibration laboratory at UC Denver for his continued assistance with the various tools used for the ex traction of the test specimens, training on the laboratory testing machines and overall great advice, to Jac Coreless and Adam Niesen of the machine shop at UC Denver for fabricating the test apparatus , to Bud Werner and CTL Thompson, Inc., for use of the guillotine device, and to Pam Mettler for her frequent assistance in arranging for needed materials and equipment . My deepest thanks also goes out to my fellow students, including Andrew Pultorak, Christian Rosen, and Anne Swan for assisting with mixing and placement of concrete, and especially to Nabeal (Newton) Khatib , who not only assisted with the placement of concrete, but also helped with the extraction of cores and the continual maintenance and cleanup of the test pads. Finally, I wish to express m y gratitude to my wife, Amy and my sons, Pasquale and Ezekiel for their love, continual support and sacrifices made throughout this project.

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v TABLE OF CONTENTS CHAPTER OVERVIEW ................................ ................................ ................................ ................. 1 1.1 Introduction ................................ ................................ ................................ ........... 1 1.2 Research Goal and Significance ................................ ................................ ............ 2 1.3 Outline ................................ ................................ ................................ ................... 2 BACKGROUND INFORMATION ................................ ................................ ............. 3 2.1 Introduction ................................ ................................ ................................ ........... 3 2.2 Shear in Monolithic Concrete ................................ ................................ ............... 4 2.3 Shear in Bonded Concrete ................................ ................................ ..................... 7 2.4 History of Iosipescu Test ................................ ................................ ....................... 7 2 .5 Other Recent Direct Shear Tests ................................ ................................ ......... 14 RESEARCH PROGRAM ................................ ................................ ........................... 15 3.1 Development of Test Apparatus for This Research ................................ ............ 15 3.2 Preparation of Primary Test Specimens ................................ .............................. 20 3.3 Preparation of Specimens Associated with Other Research ............................... 27 3.4 Testing ................................ ................................ ................................ ................. 28 3.4.1 Slump Test ................................ ................................ ................................ ..... 29 3.4.2 Compression Cylinder Test ................................ ................................ ............ 29

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vi 3.4.3 Direct Shear with Iosipescu Test Apparatus ................................ .................. 31 3.4.4 Direct Shear with Guillotine Test Apparatus ................................ ................. 33 TEST RESULTS FOR PRIMARY SPECIMENS ................................ ..................... 37 4.1 Slump Test Results ................................ ................................ .............................. 37 4.2 Compression Cylinder Test Results ................................ ................................ .... 37 4.3 Direct Shear Test Results Iosipescu Apparatus ................................ ................ 40 4.3.1 Direct Shear Test Results on Primary Layered Cylinders ............................. 40 4.3.2 Direct Shear Test Results on Primary Monolithic Cylinders ......................... 45 4.4 Direct Shear Test Results Guillotine Device ................................ .................... 46 TEST RESULTS FOR SECONDARY SPECIMENS ................................ ............... 50 5.1 Results of Iosipescu Inspired Testing of Pultorak Specimens ............................ 50 5.2 Results of Iosipescu Inspired Testing of Longmont Specimens ......................... 52 DISCUSSION ................................ ................................ ................................ ............. 56 6.1 Breakage of Layered Specimens ................................ ................................ ......... 56 6.1.1 Effect of Surface Treatment on Shear Strength Pultorak Specimens ......... 57 6.1.2 Effect of Degree of Surface Roughness on Shear Strength ........................... 58 6.2 Breakage of Monolithic Specimens ................................ ................................ .... 62 6.2.1 Examination of Crack Patterns ................................ ................................ ...... 63 6.2.2 Effect of flexural tension on monolithic specimens ................................ ...... 64 6.2.3 Relationship between Compressive Strength and Shear Strength ................. 64

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vii 6.3 Comparing Direct Shear Strength from Iosipescu and Guillotine Testing ......... 66 6.4 Effect of Geometry on Iosipescu Test ................................ ................................ . 67 6.4.1 Size Effect ................................ ................................ ................................ ...... 67 6.4.2 Test Fixture Geometry ................................ ................................ ................... 68 6.5 Sources of Error/Improvements ................................ ................................ .......... 69 CONCLUSIONS AND RECOMMENDATIONS ................................ ..................... 71 7.1 Summary and Conclusions ................................ ................................ .................. 71 7.2 Recommendations ................................ ................................ ............................... 72 REFERENCES ................................ ................................ ................................ ................. 73 APPENDIX ................................ ................................ ................................ ..................... A 1

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vii i LIST OF FIGURES Figur e 2 1 Idealized direct shear ................................ ................................ ...................... 5 Figure 2 2 Flexural Shear ................................ ................................ ................................ 5 Figure 2 3 Torsional Shear ................................ ................................ .............................. 6 Figure 2 4 Iosipescu loading and notching (adapted from Iosipescu 1967) .................... 8 Figure 2 5 Assumed shear failure in narrow band of high shear stress (adapted from Bazan t & Pfeiffer 1986) ................................ ................................ ................................ .... 10 Figure 2 6 Observed principal tension cracking in wide band of high shear stress (adapted from Bazant & Pfeiffer (1986) ................................ ................................ ........... 10 Figure 2 7 Diagram of Iosipescu test on bonded concrete (adapted from Swan 2016) . 13 Figure 3 1 Design drawing from which the fixture was fabricated. .............................. 16 Figure 3 2 Longitudinal view of test apparatus ................................ .............................. 17 Figure 3 3 Transverse view of test apparatus ................................ ................................ . 17 Figure 3 4 Distribution of forces and shear and moment on specimen .......................... 19 Figure 3 5 Section view of a typical pad ................................ ................................ ........ 21 Figure 3 6 Photograph of the forms ................................ ................................ ............... 22 Figure 3 7 Photograph of first casting in progress ................................ ......................... 23 Figure 3 8 Raked surface ................................ ................................ ................................ 24 Figure 3 9 Acid etched surface ................................ ................................ ...................... 25 Figure 3 10 Bush hammered surface ................................ ................................ .............. 25 Figure 3 11 Placement of colored overlay ................................ ................................ ..... 26 Figure 3 12 Retaining wall overlay ................................ ................................ ................ 28 Figure 3 13 Typical slump test ................................ ................................ ....................... 29

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ix Figure 3 14 Typical compression test ................................ ................................ ............ 30 Figure 3 15 Test fixture prior to loading ................................ ................................ ........ 32 Figure 3 16 Test fixture following loading ................................ ................................ .... 33 Figure 3 17 Sketch of guillotine with loading, shear and moment diagrams ................. 34 Figure 3 18 View of the guillotine fixture ................................ ................................ ...... 35 Figure 3 19 View of a specimen in the guillotine prior to loading ................................ 35 Figure 4 1 Initial fracture of B 7 in guillotine device ................................ .................... 47 Figure 4 2 Double shear failure of S 9 in guillotine device ................................ .......... 48 Figure 6 1 Typical appearance of a layered specimen following Iosipescu test ........... 56 Figure 6 2 Plot of Iosipescu mean shear strengths vs. surface treatment with standard deviation where suffi cient specimens were available for statistical analysis ................... 58 Figure 6 3 Relationship between surface roughness and average shear strength of retaining wall cores by Iosipescu method ................................ ................................ ......... 59 Figure 6 4 Relationship between surface roughness and average shear strength of Longmont cores by guillotine method ................................ ................................ .............. 60 Figure 6 5 Rela tionship between surface treatments and Iosipescu tested average shear strengths ................................ ................................ ................................ ............................ 61 Figure 6 6 Typical crack patterns in Iosipescu tested monolithic specimens ............... 63 Figure 6 8 Comparison between Iosipescu and Guillotine Tests ................................ .. 66 Figure 6 9 Test fixture with guide rods ................................ ................................ ......... 70

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x LIST OF TABLE S Table 4.1 1 Slump cone test results ................................ ................................ ................ 37 Table 4.2 1 Substrate compression test results (SI units) ................................ ............... 38 Table 4.2 2 Substrate compression test data (US Customary Units) ............................. 38 Table 4.2 3 Overlay compression test data (SI Units) ................................ .................... 39 Table 4.2 4 Overlay compression test data (US Customary units) ................................ 39 Table 4.3 1 Acid etch Iosipescu shear strength data (SI Units) ................................ ..... 41 Table 4.3 2 Acid etch Iosipescu shear strength data (US Customary units) ................. 41 Table 4.3 3 Bush hammer Iosipescu shear strength data (SI units) .............................. 42 Table 4.3 4 Bush hammer Iosipescu shear strength data (US Customary units) ........... 42 Table 4.3 5 Raked overlay Iosipescu shear strength data ( SI units) .............................. 43 Table 4.3 6 Raked Iosipescu shear strength data (US Customary Units) ...................... 43 Table 4.3 7 Smooth Iosipescu shear streng th data (SI units) ................................ ......... 44 Table 4.3 8 Smooth Iosipescu shear strength data (US Customary units) ..................... 44 Table 4.3 9 Iosipescu test on p rimary monolithic specimens (SI Units) ....................... 45 Table 4.3 10 Iosipescu test on primary monolithic specimens (US Customary Units) . 46 Ta ble 4.4 1 Guillotine test results on primary layered specimens (SI Units) ................. 49 Table 4.4 2 Guillotine test results on primary layered specimens (US Customary Units) ................................ ................................ ................................ ................................ ........... 49 Table 5.1 1 Descriptions of specimens extracted from Pultorak pads ........................... 50 Table 5.1 2 Iosipescu shear strength on Pultorak cores (SI units) ................................ . 51 Table 5.1 3 Iosipescu shear strength on Pultorak cores (US Customary Units) ............ 52 Table 5.2 1 Iosipescu tests on Longmont retaining wall sp ecimens (SI Units) ............. 53

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xi Table 5.2 2 Iosipescu testing on retaining wall specimens (US Customary Units) ....... 54 Table 5.2 3 Iosipescu test on monolithic retaining wall cores (SI Units) ...................... 55 Table 5.2 4 Iosipescu test on monolithic retaining wall cores (US Customary Units) .. 55 Table 6.2 1 Relationships between average shear strength and compressive strength in monolithic specimens ................................ ................................ ................................ ........ 65

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1 OVERVIEW 1.1 Introduction Whether concrete is cast monolithically (all at one time) or in phases tha t require an overlay of new concrete onto an existing concrete substrate, an understanding of the shear strength in concrete is instrumental in design. Concrete shear strength often influences shear design in monolithically cast beams and footings as well as precast members subject to concentrated loads at their supports. There are numerous structural applications that require the placement of new concrete on to an existing concrete substrate , many of which also necessitate composite action between the over lay and substrate . Whether a bonded concrete overlay is performed to make repairs to a structural member or pavement, or used to achieve composite action in new construction, such as between beams and slabs that have been cast at different times, an accura te model of the shear strength along the bonded interface is needed so that engineers can make reliable predictions related to the future performance of a composite section . In determining the expected performance, evaluation and assessment of the struct ure is needed. Evaluation, by its nature implies the use of personal and subjective judgment by those functioning in the capacity of experts, while structural assessment is a systematic collection and analysis of data (Stevens & Kesner, 2016) . It follows that the execution of an assessment on a completed structure necessitates extraction of s amples for testing. Given that shear transfer is of particular interest in monolithic and composite concrete sections, as well as bonded pa vement overlays , direct shear testing of specimens is desirable. The Iosipescu test is one such direct shear test, in which a specimen is subjected to two force couples that produce a high shear zone near the center of the specimen. Initially used on spec imens with rectangular cross sections, test

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2 specimens from completed structures are o ften obtained by core drilling, and, consequently, possess circular cross sections. 1.2 Research Goal and Significance This research was performed with the objective of deve loping an Iosipescu inspired test apparatus for specimens with circular cross sections that could be easily fit into a unive rsal materials testing machine and could be inexpensively fabricated. The results of this research may be adapted to numerous constr uction projects where direct shear tests on field obtained specimen s are needed . 1.3 Outlin e This thesis is divided into seven chapters. The first chapter provided an introduction of research topic and the goals of the study. Chapter 2 provides background in formation inclusive of literature review of shear strength of concrete. A discussion of the history of the Iosipes c u test and other direct shear tests for concrete specimens is also provided. Chapter 3 includes a discussion of the development of the test a pparatus, the preparation of the test specimens and tests that were performed. Chapter 4 provides tabulated results of the various tests that were conducted on the primary specimens that were created specifically for this research . Chapter 5 provides tabul ated results of the various tests that were conducted on the specimens obtained from secondary sources. Chapter 6 provides a discussion of the results and influencing factors . Comparisons between the results of this test and other direct shear testing are also provided. Chapter 7 offers a summary and conclusions reached as a result of this research.

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3 BACKGROUND INFORMATION 2.1 Introduction Development of test methods for shear strength of both monolithic and bonded concrete has numerous applications. In concre te beam design, the nominal shear strength is the combined shear strength of the concrete and , where specified, the transverse reinforcement . Nominal shear strength in concrete also often influences the design of one way and two way footings. Moreover, kno wledge of the transfer of shear across various c oncrete interfaces, including expected cracks in monolithic concrete and a long the plane between concrete elements that were cast at different times, i s instrumental for the design of many common structures, such as shear walls, ends of precast beams and corbels . strength of the concrete, the need for an accurate determination of that strength is clear. Existing concrete structures and pavements can be expected to sustain varying distresses throughout their service lives. In many cases, the magnitude of such distresses does not warrant large scale rehabilitation or replacement. Rather, repairs and/or maintenance can be performed to restore the structure or paveme nt to its pre distressed state. Often, these repairs necessitate bonding of new concrete to old in such a manner that the repaired structure behaves as if the concrete was monolithically cast. In order for the repaired structure to behave in this manner, t here can be no slippage between the substrate concrete and the overlay. For pavements, perhaps the most important construction and performance aspect of bonded overlays is achievement of an effective bond between the overlay and existing pavement (American Concrete Institute, 2006) . Although the need for direct shear testing is understood, research to date has met limited success in testing specimens in purely shear loading condition. Indeed, concerns regarding how to measure shear in concrete existed almost one hundred years ago (Nogueira & Rens, 2018) .

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4 However, Nicolae Iosipescu (1967) developed a procedure that allowed for direct shear testing in metals. Iosipescu posited that his apparatus would effectively eliminate the effects of longitudinal forces induced by moment as well as the normal forces from the loading plates. That procedure had subsequently been applied to other materials, including wood and plastics, and was formalized in ASTM D5379 Composite Materials by the V Subsequ ent research on the application to concrete specimens has been conducted; however, there is no standard Iosipescu inspired direct s hear test f or concrete as of this writing . 2.2 Shear in Monolithic Concrete There are three general sources of shear stress in concrete members to be considered: direct shear, flexural shear an d torsional shear. In members subjected to opposing and offset forces, direct shear stress occurs parallel to the load. Direct shear commonly affects simple beams near their supports as well as interfaces between spread footings and columns and strip footings and ste m walls. In an idealized, pure direct shear state, with no flexura l or axial stresses, direct shear stress, as well as the transformed principal stresses, can be illustrated as in Figure 2.1 . Flexural shear in beams occurs due to variations of moment stress with respect to the distance from the neutral axis. In typical b eams, flexural shear is horizontal, and is greatest near the neutral axis. With flexural shear, the stress block is also subjected to appreciable flexural tension or compression, which is variable along the length and depth of the beam. As a consequence, t he angle at which a stress block is subject to principal stresses only is also variable along the length and depth of the beam. F lexural shear stress and the transformed principal stresses are illustrated in Figure 2.2.

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5 Figure 2 1 Idealized direct shear Figure 2 2 Flexural Shear Torsional shear occurs in concrete members that are subjected to a twisting moment about the longitudinal axis of the member. If no other loads are applied to that member, then the

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6 principal stresses are similar to those seen for a pure direct shear case on all faces of the member . A diagram illustrating torsional stress and the transformed principal stresses is provided in Figu re 2 3. Figure 2 3 Torsional Shear I f a pure shear loading state can be achieved i n mono lithic plain concrete sections, failure of the concrete typical ly develops along lines that are at some acute angl e with respect to the direction of the shearing forces. This can be seen in the propagation of diagonal cracks in simply supported, beams subject to uniaxial bending; where the angle of the cracks with respect to the shearing forces tends to decrease with respect to distance from the supports . Similarly, helical cracks form in sections that are subject to torsion. As such, it can be qualitatively concluded that shear affects the behavior of beams without reinforcement through the formation of diagonal tensi on cracks. While tensile splitting is the expected mode of failure for monolithic concrete members with high shear stresses , there have been occasions where direct shear failures have occurred. Shear failures have been reported in reinforced concrete slab s subjected to a short pulse blast ,

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7 which resulted in shearing off of the slab along a plane that was normal to the surface of the slab. Similarly oriented failures have also been reported in concrete that was penetrated by projectiles (Z.P. Bazant and P.A. Pfeiffer, 1986) . The geometry of the shear plane affects the occurrence of shear cracks . If shear keys develop, such as through aggregate interlock, then the behavior of the concrete along the shear plane will vary and may no t solely coincide with principal tensile stress . Rather, initial cracking from principal tension may develop, but final continuous cracks may necessitate a shearing force (Z.P. Bazant and P.A. Pfeiffer, 1986) . 2.3 Shear in Bonded Concrete In bonded concrete overlays, such as composite beams and pavement overlays, it is often desirable for the finished section (substrate and overlay) to behave as a monolithic section. In order to achieve that behavior, there can be no slippage betwe en the substrate and overlay; shear transfer must be contin uous across the interface. In bonded concrete without shear ties and where the surface of the substrate is intentionally roughened to a full amplitude of 6 .35 mm (0.25 in), ACI 318 indicates that the shear strength across the interface is 552 kPa (80 psi) (American Concrete Institute, 2014) . 2.4 History of Iosipescu Test In order to adequately test shear in concrete specimens, a test specimen must be subjected to pure shea r across its face without any longitudinal or normal stresses. To produce such a condition, there can be no bending moment which would produce longitudinal tension and compression ( x ) in the specimen. Similarly, there cannot be any localized effects from the testing apparatus that would produce normal stresses ( y ) in the material adjacent to the section under review (Iosipescu, 1967) .

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8 In beams, I osipescu (1967) posited that the solution to the problem of effects of longitudin al and normal stresses on pure shear loading was loading of a straight beam to produce linearly varying bending moment with a zero moment region at the mid span. The corresponding beam shear would be constant between the points of applied force , and by pla cement of forces that produced two opposing couples, a predictable region of high shear and negligible (theoretically zero) moment can be made to occur. In order to ensure that the shear failure occurred at the zero moment location, weakening of the specim ens at the desired failure location was needed. A sketch of the proposed loading is in Figure 2 4. Figure 2 4 Iosipescu loading and notching (adapted from Iosipescu 1967) Subsequent research using a syst em of steel beams to apply point forces to variably sized rectangular concrete specimens was performed by Bazant and Pfeiffer (1986) . The beams were arranged such that the concentrated transverse loads were applied onto the top and bottom faces of the specimens at 1/12 of the beam depth left and right of the beam center, respectively to produce the Iosipescu type force couple and high shear zone. Additional steel beams located near

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9 the outboard edges of the specimens stab ilized the system when loaded. All of the tested specimens were the same width, but varied in depth. Three notable outcomes were derived from this testing. First, for the same concrete mix, shear stress at fracture was greater in smaller test specimens. Sp ecifically, the average shear stress across the failure plane in the specimen whose depth was 38.1 mm (1.5 in) was approximately 6.7 MPa (973 psi), while the average stress across the failure plane of a 305 mm (12 in) specimen was 5.8 MPa (840 psi). From the test data, the authors concluded that structural size effect was applicable to shear fracture in concrete , in that larger specimens fractured at a lower shear stress than geometrically similar smaller specimens . In addition to the effects of specimen size on total shear stress a t fa ilure, Bazant and Pfeiffer (1986 ) testing revealed differences in the failure modes that were largely dependent upon the distances between the center point forces and the intended failure plane of the specimens. Where those distances were generally small , crack patterns were most consistent with shear fractures. However, as the distance between the point loads was increased, the crack patterns were more consistent with cracking perpendicular to the principal tensile stress. T he authors concluded that the reason for the difference was that in a narrow band of high shear, diagonal principal tensile cracks would propagate a short distance before reaching a low shear stress zone (Figure 2 5) . With a wider band of high shear, tensi le splitting cracks would continue to progress within that band of high shear stress (Figure 2 6) . In contrast, vertical shear cracks would remain in the high stress zone in a narrow case only .

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10 Figure 2 5 Assumed shear failure in narrow band of high shear stress ( adapted from Bazant & Pfeiffer 1986 ) Figure 2 6 Observed principal tension cracking in wide band of high shear stress ( adapted from Bazant & Pfeiffer 1986 )

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11 Fi nally, Bazant and Pfeiffer (1986 ) testing revealed that the shea r stress controlled failure occurred at loads that were approximately four to six times that of the principal tension splitting controlled failure. In terms of fracture energy , th at ratio appeared to be about 24 for concrete . The authors concluded that in the narrow band test, tensile cracks were not all that was needed for failure. Rather, discontinuous tensile cracks developed through the band, whose angle relative to the hor izontal plane was approximately 31 degrees. A connection of inclined concrete compression struts remained after the tensile cracks form ed . As such, in order for full shear failure to occur, compression crushing of these struts was necessary, greatly increa sing the overall force required to produce failure. Finite element analysis of concrete beams was also performed by Ingraffea and Panthaki (1985) , which indicated that narrow high shear band test specimens did not sustain shear fractures . Rather, those s pecimens had fa iled due to principal tension that developed within the high shear zone between the two innermost loading plates. Ingraffea and Panthaki (1985) posited that the failure in the higher shear zone was analogous to the splitting tensile strength test, and that the principal tensile stresses were nearly horizontal at the center of the test specimens in the critical stress zone. Additional comparisons between modulus of rupture, splitting tensile strength and Iosipescu tests (Helmick, Toker Beeson, & Tanner, 2016) also found that the Iosipescu beam test is more a measure of tension than of shear failure, further casting doubt on whether experimental shear failures can be achieved. The authors concluded that the failure surface roughness of Iosipescu test specimens was similar to that which was present on split cylinder and prism tests, indicating that all of these failures were caused by tension. Moreover, their finite element results also revealed that the calculated di agonal tensile stress along the failure plan e in an Iosipescu test

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12 specimen was similar to the maximum principal stress. However, despite the evidence that indicated that the failure wa s caused by tensile stress, it was also concluded that the Iosipescu be am test would be a suitable standard method for predicting the direct shear strength of plain concrete. Recently, additional Iosipescu inspired testing of rectangular concrete beams consisting of two bonded concrete sections was undertaken at the Universit y of Colorado at Denver (Swan, 2016) . For this testing, concrete beams were cast vertically in two different lifts using a commercially available sack concrete mix. Following curing of the first concrete placement, which filled one half of the forms, the exposed faces of the beams received various surface treatments: four were left smooth, four were roughened with a bush hammer and four were rou ghened with a jackhammer. The final surface profiles of the roughened concrete was sim ilar to C oncrete Surface Profile 6 (CSP 6 ) for the bush hammered specimens, and CSP 10 for the jackhammered sections, as specified by the International Concrete Repair Institute (2013) . Subsequent to the surface treatmen ts described above, additional concrete was placed atop the prepared surfaces, filling the forms. To facilitate identification of locations of the interfaces between the substrate and overlay concrete, colorant was added to the substrate mix. Following pl acement of the overlays, t he beams were allowed to cure for an additional 28 days prior to form removal and testing. When oriented horizontally, the interfacial plane was oriented vertically . Iosipescu testing was then conducted, with the interfacial plane situated between the two primary loads, as illustrated in Figure 2.7.

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13 Figure 2 7 Diagram of Iosipescu test on bonded concrete ( adapted from Swan 2016) At the conclusion of the testing, Swan concluded t hat the Iosipescu testing was generally successful, though potential factors that could have introduced error into the tests were present. Those potential sources of error included deformation of the forms during concrete placement, resulting in non unifor m cross sections, bruising from roughening activities, and differing lengths of substrate and overlay concrete in the forms. Swan noted other potential sources of error, including potential misalignment of the apparatus and non concentric loading. Furtherm ore, the author noted that the test specimens were large and cumbersome. It would follow that testing of numerous specimens and/or conducting this test in the field would be an arduous process. Iosipescu type tests were also conducted on notched beams wit h square cross sections in conjunction with the measurement of ultrasonic waveforms through the specimens (Nogueira & Rens, 2018) produced she ar stress concentrations at the notches and increased the likelihood of shear failure at that location. The results of the Iosipescu type tests were compared with specimens that were subjected to tension. Among the relationships that this research establis hed with respect to

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14 ultrasonic wave transmission and shear strength, the authors concluded that the fracturing process and failure of specimens in shear and splitting tension tests are different (Nogueira & Rens, 2018) . 2.5 Other Re cent Direct Shear Tests Research related to non Iosipescu testing has also recently been undertaken at the University of Colorado at Denver. Testing of the shear strength in bonded concrete overlays was performed by Rosen (2016) and Pultorak (2016) using various methodologies. These methods included direct shear testing on specimens obtained by 90 degree coring into pads consisting of substrate and overlay concrete. Additional core specimens were obtained from the same pa ds, but with the coring drill set at a prescribed angle. The intent was to then load those cores in compression, thereby causing a shearing component along the inclined interface, with the hope that the bond between the substrate and overlay would be suffi cient to produce a failure that was similar to that which occurs in monolithic cylinders under compression. Shear testing was also performed by the direct application of the shearing force to the overlay section of the pads with a mounted jack.

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15 RES EARCH PROGRAM 3.1 Development of Test Apparatus for This Research The test apparatus that was developed for this research was inspired by the model used by Ba zant and Pfeiffer (1986 ), Helmick, Toker Beeson and Tanner (2016) and Swan (2016) . Specifically, poin t loading was distributed from the center of the apparatus to specimens through vertical plates that were situated at 76.2 mm (3 in) apart as illustrated in Figure 3 1 . The top and bottom sections of the apparatus were aligned such that the center to cente r distance between the inner loading plates of the apparatus was 12.7 mm (0.5 in), with the point force from the uniaxial testing machine centered between them. The final design drawing from which the test fixture was fabricated can be found in Figure 3 1. Photographs of the test fixture from its side and end are also provided in Figure 3 2 and Figure 3 3, respectively. Although the nominal outside diameter of the drill bits that were utilized to extract the core samples was 76.2 mm (3 in), the diameters of the cores were variable, ranging from 67.6 mm (2.66 in) to 69.1 mm (2.72 in). Additionally, although it was intended for the specimens to be cylindrical, the cross sections were found to be slightly elliptical. As such, the application of force from the r ound cutouts in the loading plates could produce localized stress concentrations, elevating the potential for transverse tensile splitting. To address both of these concerns, the test apparatus was designed with cutouts that were 73.7 mm (2.90 in) in diame ter and lined with neoprene. The neoprene thicknesses were variable to allow for different specimen diameters as illustrated in the transverse view of the fixtu re at the bottom of Figure 3 1.

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16 Figure 3 1 Design drawing from which the fixture was fabricated.

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17 Figure 3 2 Longitudinal view of test apparatus Figure 3 3 Transverse view of test apparatus

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18 The geometry of the test apparatus was designed such that the force couples would produce a high shear zone near the center of the specimens that coincided with an area of zero moment. In this way, longitudinal stresses associated with the flexural couple would not be expected to have an appreciable effect on the test results. Moreover, given that data collection from the materials testing machine would provide the loads applied to the apparatus, the geometry allowed for easy calculation of the forces that the apparatus applied onto the specimens. A diagram depicting the applied forces as well as shear and moment diagrams, as functions of the external applied force and distance between loading plates for the particular geometry used, is provided in Figure 3 4. The apparatus geometry was such that the following forces could be calculated: (2 1) (2 2) Where: V = the maximum shear force on the specimen, M = the maximum moment on the specimen, a = the distance between t he inner loading plates (for this experiment a = ), b = the distance between inner and outer loading plates (for this experiment b = ), P = the force applied to the test apparatus by the testing machine, and l = the distance between the outer loading plates.

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19 Figure 3 4 Distribution of forces and shear and moment on specimen As indicated by Figure 3 4 , some internal moment will be induced by the test fixture with the peak moments occurr ing at the loading plates, though the point of greatest shear stress coincides with the point at which the moment is theoretically zero.

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20 The subject test apparatus was fabricated at the University of Colorado at Denver, machine shop using 19.1 mm (0.75 in ) and 95.3 mm (0.38 in) ASTM A36 steel plates. The thicker plates comprised the horizontal bases on which the vertical loading plates were mounted. It was determined that the greater thickness of these bases was needed in order to avoid excessive deflectio n and potential fatigue related failures with repeated use. For additional stability, the vertical plates were also set in recesses within the horizontal plates. To avoid warping that could occur with welding, the vertical plates were fastened to the hori zontal plates with screws. Based upon preliminary shear force calculations, it was determined that the apparatus would be used in conjunction with the 89 kN (20 kip) load frame manufactured by MTS Systems Corporation. Compressive forces from the load fram e would be transferred to the test fixture via semicircular rods that were centered between the inner load plates to replicate point loading onto the fixture . For added stability and more consistent placement of the loads onto the fixture, these rods were set into recesses in the plates. Additionally, although the system would be stable once loaded, it was necessary to provide a secondary base plate (bottom plate) that was flush with the lower platen on the load frame in order to stabilize the system prior to the application of loads. Collapsible tubing was placed beneath the lower base and the bottom plate, which would hold the system level prior to loading, but would not transfer any appreciable loads to the system once loaded. 3.2 Preparation of Primary Test Specimens To provide a primary source of specimens f or this research, four concrete pads were cast from which the cylindrical samples were removed. Prior to concreting, wooden forms were made with two tiers, allowing for casting of sections with thicknes ses of 102 mm (4 in) and 203 mm (8

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21 in); the f ormer would be overlain after the concrete had cured for the bonded overlay specimens while the latter would be used for monolithic samples . Each pad measured 1.83 m x 0.61 m (6 ft by 2 ft) and the offset in el evation occurred at the pad mid spans. The sizes of the pads were largely dependent upon available working space as well as allowance for sufficient surface area on which a coring drill could be mounted. Each form was also constructed to allow for placeme nt of 102 mm (4 in) thick rigid insulation boards at the base of the pad. The insulation boards protected the underlying concrete floor from damage when coring. Figure 3 5 Section view of a typical pad The concrete used for the pads was Quikrete® 5000 Concrete Mix ( Quikrete), a commercially available pre blended mix of aggregates and portland cement that was designed to be mixed only with water and would achieve high early strength. According to a manuf representative, the largest aggregate in the mix was 12.7 mm (0.5 in). The Quikrete was packaged in 36.3 kg (80 lb) bags and would, a ccording to the label, attain a 28 day compressive strength of 34.5 MPa (5,000 psi) .

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22 Figure 3 6 Photograph of the forms Concreting for the substrate and monolithic sections took place on November 12, 2016. Mixing was performed using an electric drum mixer in eight separate batches consisting of fou r to five bags of Quikrete and water. s recommended proportion of water per bag was 2.8 L (0.75 gal) to 4.7 L (1.25 gal). With a dry mixer, the first batch was made with four bags of Quikrete and 15.1 L (4 gal) of water. The amount of wat er was adjusted for subsequent batches, until it was found that the desired workability and slump could consistently be achieved when four bags of Quikrete were mixed with 13.6 L (3.6 gal) of water. Consolidation of the concrete was achieved using an elect ric flexible internal vibrator .

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23 Figure 3 7 Photograph of first casting in progress Three of the four substrate pads that were to be overlain received various surface treatments prior to overlay including raking, bush hammering and acid etching. Raking was performed on the same day that the substrate concrete was placed. The concrete was allowed to cure for at least 28 days prior to the commencement of the other surface treatments. Labeling of the pads cor related to their surface treatments: Pad R was raked, Pad B was bush hammered, Pad A was acid etched, and Pad S was left smooth prior to overlay. Raking of Pad R was performed with a typical garden rake. Grooves were made that were generally 25.4 mm (1 in) apart and approximately 19.1 mm (0.75 in) deep .

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24 Figure 3 8 Raked surface Acid etching of Pad A was performed using undiluted, commercially available muriatic acid. The process was performed on two occasions that were seven days apart. The acid was allowed to remain on the surface until it was generally neutralized through its reaction with alkali in the concrete, as indicated by litmus paper testing. Following neutralization of the acid, the pad was rinsed with clean water. The final surface profile was similar to Concrete Surface Profile 1 (CSP 1) as specified by the International Concrete Repair Institute (2013) .

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25 Figure 3 9 Acid etched surface Bush hammering of Pad B was performed using an electric 133 N (30 lb) jackhammer with a bush hammer attachment. Following bush hammering, the surface profile of the concrete was similar to CSP 6 Medium Scarification, as s pecified by the International Concrete Repair Institute (2013) . Figure 3 10 Bush hammered surface

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26 Placement of concrete overlays was performed on February 11, 2017. Pr ior to placement of the overlays, the substrate surfaces were thoroughly cleaned with compressed air and water . The same commercial concrete mix used for the substrates was also used in the overlays. However , to facilitate identification of the interfaces between the substrate concrete and the overlay, red and terra cotta colored Sakrete® brand cement color was added to the overlay mix. Four batches were mixed in the drum mixer, each of which consisted of four bags of Quikrete and water. In order to achieve similar slump and workability in the overlay concrete, the amount of water per batch was marginally higher than that which was used in placement of the substrate concrete. On average, approximately 14.4 L (3.8 gal) of water was used for every four bags of Quikrete for the overlay batches of concrete. It is likely that the additional water was needed as a result of the added dry material for coloring of the concrete. Like the substrates, the overlay concrete was consolidated using an electric internal vibra tor. Figure 3 11 Placement of colored overlay

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27 3.3 Preparation of Specimens Associated with Other Research L ayered concrete pads that were associated with other research provided a second source from which spe cimens were extracted for this research . Specifically, i n researching the effects of various surface pretreatments on the shear strength of bonded concrete overlays (Pultorak, 2016) , three concrete pads were cast, each of which consisted of a single 8.3 c m (3.25 in) thick substrate and two 8.9 cm (3.50 in) overlay slabs. All of these pads were placed using a similar commercially available sack concrete mix to that which was used to prepare the primary sp ecimens for this research . Prior to the placement of the overlay concrete, the surfaces of the substrate s were roughened to Concrete Surface Profile 6 ( CSP 6 ) as specified by the International Concrete Repair Institute (2013) . The substrates fo r four of the six overlays received various bonding agents, and each of the substrates exhibited different moisture co nditions prior to the overlays. For testing in the Iosipescu inspired test fixture, 14 cores were extracted from these pads. Like the prim ary specimens that were specifically developed for this research, the overlay concrete in these cores was colored. An extant concrete retaining wall located in Longmont, Colorado provided a third source of test specimens that were extracted for this resea rch . The subject retaining wall was nomi nally 20.3 cm (8.0 in) thick , and consisted of concrete with a compressive strength of approximately 27.8 MPa (4,000 psi). An approximately 10.2 cm (4 in) thick overlay of self consolidating concrete (SCC) was applie d to the face of the retaining wall after the surface was roughened . Three different surface profiles, CSP 6, CSP 8, and CSP 10 in accordance with the Internati onal Concrete Repair Institute (2013) , were produced in the substrate material of the retaining wall prior to placement of the SCC overlay.

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28 Figure 3 12 Retaining wall overlay 3.4 Testing Testing was performed at the University of Colorado at Denver materials and soi ls laboratory. For the primary specimens that were specifically prepared for this research, slump and compressive strength were tested. Slump was measured during placement of the substrate and overlay concrete and compression testing was performed at three , ten and 28 days after concrete placement. Direct shear testing using the Iosipescu inspired fixture was performed on specimens that were specifically prepared for this research as well as those specimens obtained from the Pultorak pads and the retaining wall in Longmont, Colorado. Direct shear testing using the Guillotine device was performed on the primary specimens that were specifically procured for this research . Guillotine testing was also performed by others on the cores extracted from the Longmont retaining wall overlay , and was included in the research performed by Pultorak (2016) .

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29 3.4.1 Slump Test Slu mp testing was performed during placement of the primary substrate and overlay concrete using a standard stainless steel slump cone. Slump was measured on seven of the eight batches that were used for the substrate concrete and on all four of the batches needed for the overlay. The targeted slump for this research was between 50 and 76 mm (2 and 3 in). Slump results for the primary specimen pads are tabul ated in Chapter 4. Figure 3 13 Typical slump test 3.4.2 Compression Cylinder Test During concrete placement for the primary specimens , cylinders measuring 203 mm (8 in) in length and 102 mm (4 in) in diameter were cast in plastic molds for compression testing. For the substrate concrete, three cylinders were cast for each of the pads (a total of twelve cylinders). Nine cylinders were cast for the overlay concrete from randomly selected batches .

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30 Alt hough testin g was targeted for three, seven and 28 days after concrete placement, unforeseen equipment difficulties delayed the second round of testing on the substrate cylinders. As such, testing was performed at three, ten and 28 days. Compression testing was perfo rmed using a Forney compression machine with an attached Ad met data collection unit. Prior to testing, a neoprene cap with a steel surround was placed onto each end of the cylinders. Loading was controlled by hand and was adjusted such that the rate of loa d application was maintained at 19.6 ± 0.4 kN/s (440 ± 88 lbs/s). Results of the compression tests for the primary pads are provided in Chapter 4. Figure 3 14 Typical compression test

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31 3.4.3 Direct Shear with I osipescu Test Apparatus As indicated throughout this thesis , four test pads were cast specifically for the purpose of this research, with half of each pad consisting of layered (substrate and overlay) concrete and the other half consisting of monolithic co ncrete . For testing in the Iosipescu inspired test apparatus, eight cores from each of the layered portions, and 20 cores from the monolithic portions of the se primary test pads were selected. Additionally, 14 cores that were extracted from the pads devel (Pultorak, 2016) and nine cores that were extracted from the Longmont retaining wall overlay were tested. Prior to placement into the fixture, the core diameters were measured using an electronic mi crometer, and the cores were marked such that the interface between substrate and overlay concrete would be centered between the load plates on the fixture. Diameters were measured in two directions at the substrate/overlay interfaces, and the average of t h ose measurements was recorded for each specimen. Each of the load plates in the text fixture was lined in neoprene, which was adhered to the l oad plates with two sided tape. Since the fraction of the total load was minimal at the outside load plates (1/12 of the total load), the neoprene liners sustained little distress and, as such, could be re used for approximately ten to 15 test cycles. However, at the inner load plates, distress in the neoprene liners became visible after as few as three test cycles, necessitating their frequent replacement. The liners were cut from 6.35 mm (0.25 in ) and 3.18 mm (0.125 in) rolls to fit the load plates. Once the test specimens were fit into the test fixture, the fixture was loaded onto the bottom platen of the 89 kN (20 kip) load frame at the University of Colorado at Denver laboratory. Loading on the test fixture was achieved by displacement controlled compression

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32 applied by the load frame onto the test fixture. The rate of displacement was 0.05 08 mm/s (0.002 in/s). The data collection software also recorded displacements in addition to applied force. However, those d isplacements were likely inclusive of deflection of the test fixture itself and crushing of the neoprene liners . For this reason, the results presented in C hapter 4 (primary specimens) and Chapter 5 (Pultorak and Longmont specimens) of this thesis are based upon peak force at failure only. For reference, load deflection graphs can be found in the appendix. As indicated by the diagrams in Figure 3 4 , the peak shear force on the specimens was 5/6 of the peak load recorded by the testing machine. Given that this test is a direct shear test, the peak shear force was divided by the gross cross sectional area to obtain a n average shear stress at failure. For this di rect shear testing, the non uniform nature of the distribution of shear stress across a beam element was not considered. The results of the direct shear test using the Iosipescu inspired fixture on the primary specimens are presented in Chapter 4 while the results of Iosipescu inspired testing of the Pultorak and Longmont specimens are presented in Chapter 5. Figure 3 1 5 Test fixture prior to loading

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33 Figure 3 16 Test fixture following loading 3.4.4 Direct Shear with Guillotine Test Apparatus A guillotine style test apparatus was furnished for this research by CTL Thompson, Inc. Guillotine testing was utilized to allow for a comparison of results to those reach ed with the Iosipescu inspired device that was developed for this research. The guillotine device consisted of two steel boxes with semicircular cu touts on their sides that served to cradle the test specimens. Unlike the Iosipescu fixture, no neoprene was used in conjunction with the guillotine fixture, which was expected to result in some stress concentrations on the faces of the specimens. Compressive loading on the boxes was supplied by the same 89 kN (20 kip) load frame used with the Iosipescu fixture w ith t he same rate of load application , which induced double shear at the interfaces between the upper and lower boxes.

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34 Figure 3 17 Sketch of g uillotine with loading, shear and moment diagrams As indicat ed in Figure 3 17 , the guillotine fixture also produces moment that is proportional to the distance between the vertical loading plates within the boxes. The moment diagram presented in Fi gure 3 17 was based upon an assumption that there was no rotational fixity in the guillotine fixture. This is an idealized case, since some fixity would be introduced by clamping at the plate interfaces. The distance between the shearing plates on the guillotine boxes when loaded is approximately 3.2 mm (1/8 in). With the observed geometry, the maximum idealized moment in the guillotine fixture is approximately 60 percent of the moment induced by the Iosipescu fixture. However, with the Iosipescu fixture, the location of maximum shear corresponds to a location of zero mome nt, a difference between it and the guillotine fixture .

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35 Figure 3 18 View of the guillotine fixture Figure 3 19 View of a specimen in the guillotine pr ior to loading

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36 Guillotine testing was performed on eight test specimens that were selected from the primary layered pads. Two specimens for each overlay type were tested using the guillotine device. Additionally, prior CU Denver research (Pultorak, 2016) included guillotine testing on specimens from the same pads from which 14 test specimens were removed for Iosipescu testing , and guillotine testing was performed by others on additional specimens obtained from the Longmont reta ining wall . Consequently, comparisons can be made between shear strengths derived from Iosipescu testing and guilloti ne testing for the primary specimens that were specifically procured for this research as well as those that were obtained from secondary s ources . Like the Iosipescu fixture, the guillotine fixture is a direct shear device. As such, the average shear strength of the specimens is calculated by dividing the maximum shear force by the gross cross sectional area. Th e results of guillotine testi ng on the primary specimens that was performed by this author can be found in Chapter 4.

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37 TEST RESULTS FOR PRIMARY SPECIMENS 4.1 Slump Test Results Slump cone testing was performed on samples taken from seven of the eight substrate batches and from all four of the batches of concrete used for the overlays. The results of the slump cone testing are tabulated in Table 4.1 1 Table 4.1 1 Slump cone test results Batch No. Pad Date of Placement Slump 1 R Substrate Nov. 12, 2016 63.5 mm (2.5 in) 3 R Substrate Nov. 12, 2016 152 mm (6.00 in) 4 S Substrate Nov. 12, 2016 57.2 mm (2.25 in) 5 A Substrate Nov. 12, 2016 25.4 mm (1.00 in) 6 A Substrate Nov. 12, 2016 25.4 mm (1.00 in) 7 B Substrate Nov. 12, 201 6 57.2 mm (2.25 in) 8 1 O B Substrate R Overlay Nov. 12, 2016 Feb. 11, 2017 44.5 mm (1.75 in) 76.2 mm (3.00 in) 2 O S Overlay Feb. 11, 2017 50.8 mm (2.00 in) 3 O A Overlay Feb. 11, 2017 63.5 mm (2.50 in) 4 O B Overlay Feb. 11, 2017 44.5 mm (1 .75 in) 4.2 Compression Cylinder Test Results Compression testing of the prepared cylinders was performed using a Forney testing machine with a n Admet data collection device. As an unforeseen malfunction in the testing equipment coincided with the seventh day following placement of the substrate concrete, the

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38 second round of testing took place at ten days after concrete placement. For conformity, the second round of compression testing of the overlay cylinders was also performed at ten days. The results of those tests are provided in Tables 4.2 1 through 4.2 4 . Table 4.2 1 Substrate compression test results (SI units) Substrate Compression Testing Concrete Placed on November 12, 2016 Day 3 Day 10 Day 28 Pad ID Load Stress Load Stress Load Stress B 188 kN 23.1 MPa 231 kN 28.5 MPa 247 kN 30.5 MPa R 123 kN 15.2 MPa 172 kN 21.1 MPa 235 kN 29.0 MPa A 165 kN 20.3 MPa 216 kN 26.7 MPa 240 kN 29.6 MPa S 189 kN 23.2 MPa 249 kN 30.7 MPa 238 kN 29.4 MPa Ave 166 kN 20.5 MPa 217 kN 26.8 MPa 240 kN 29.6 MPa Table 4.2 2 Substrate compression test data (US Customary Units) Substrate Compression Testing Concrete Placed on November 12, 2016 Day 3 Day 10 Day 28 Pad ID Load Stress Load Stress Load Stress B 42.2 kips 3,360 psi 52.0 kips 4,140 psi 55.6 kips 4,430 psi R 27.7 kips 2,200 psi 38.6 kips 3,070 psi 52.8 kips 4,200 psi A 37.1 kips 2,950 psi 48.6 kips 3,870 psi 53.9 kips 4,290 psi S 42.4 kips 3.370 psi 55.9 kips 4,450 psi 53.6 kips 4,260 psi Ave 37.3 kips 2,970 psi 48.8 kips 3,890 psi 54.0 kips 4,290 psi

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39 Table 4.2 3 Overlay compression test data (SI Units) Overlay Compression Testing Concrete Placed on Feb ruary 11, 2017 Day 3 Day 10 Day 28 Sample Load Stress Load Stress Load Stress 1 193 kN 23.7 MPa 308 kN 38.0 MPa 368 kN 44.7 MPa 2 166 kN 20.5 MPa 251 kN 31.0 MPa 324 kN 40.0 MPa 3 180 kN 22.2 MPa 287 kN 35.4 MPa 359 kN 44.3 MPa Ave 180 kN 22.1 MPa 2 82 kN 34.8 MPa 350 kN 43.0 MPa Table 4.2 4 Overlay compression test data (US Customary units) Overlay Compression Testing Concrete Placed on November 12, 2016 Day 3 Day 10 Day 28 Sample Load Stress Lo ad Stress Load Stress 1 43.3 kips 3,440 psi 69.2 kips 5,500 psi 81.4 kips 6,480 psi 2 37.3 kips 2,970 psi 56.5 kips 4,500 psi 72.9 kips 5,800 psi 3 40.5 kips 3,220 psi 64.6 kips 5,140 psi 80.7 kips 6,420 psi Ave 40.3 kips 3,210 psi 63.4 kips 5,050 psi 78.3 kips 6,230 psi As indicated in the data above, the strength of the overlay concrete was higher than that of the substrate. For the 28 day tests, the average compressive strength of the overlay concrete was approximately 150 percent of the 28 day st ren gth for the substrate concrete. ( Moreover, the ) .

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40 4.3 Direct Shear Test Results Iosipescu Apparatus Direct shear testing was performed using the Iosipescu in spired device that was developed for this research. Testing on the primary layered core specimens was performed on five dates during the spring and summer of 2018. Testing on the solid cores was performed on two dates during the summer of 2018. 4.3.1 Direct Sh ear Test Results on Primary L ayered Cylinders Iosipescu testing was performed on 32 cores that were extracted from the test pads. Eight cores that represented each pre overlay surface treatment were tested in the fixture. Each specimen was placed into the fixture such that the interface between substrate and overlay concrete was situated at the center between the two interior loading plates. The results of those tests are provided in Tables 4.3.1 through 4.3.8.

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41 Table 4.3 1 Acid etch Iosipescu shear strength data (SI Units) Core ID Gross Area Max. Load Max. Shear Shear Strength A 1 37.21 cm 2 15.8 kN 13.1 kN 3.53 MPa A 3 37.30 cm 2 12.4 kN 10.4 kN 2.78 MPa A 4 37.27 cm 2 24.8 kN 20.6 kN 5.53 MPa A 5 3 7.24 cm 2 25.2 kN 21.0 kN 5.65 MPa A 6 36.94 cm 2 10.3 kN 8.6 kN 2.32 MPa A 7 37.19 cm 2 22.6 kN 18.9 kN 5.08 MPa A 8 36.64 cm 2 19.6 kN 16.3 kN 4.45 MPa A 9 36.64 cm 2 26.4 kN 22.0 kN 6.01 MPa Mean 4.42 MPa SD 1.39 MPa COV 31.5% Table 4.3 2 Acid etch Iosipescu shear strength data (US Customary units) Core ID Gross Area Max. Load Max. Shear Shear Strength A 1 5.77 in 2 3,544 lbs 2,953 lbs 512 psi A 3 5.78 in 2 2,795 lbs 2,329 lbs 403 psi A 4 5.78 in 2 5,566 lbs 4,638 lbs 802 psi A 5 5.77 in2 5,673 lbs 4,728 lbs 819 psi A 6 5.73 in 2 2,317 lbs 1,931 lbs 337 psi A 7 5.76 in 2 5,091 lbs 4,243 lbs 737 psi A 8 5.68 in 2 4,402 lbs 3,668 lbs 646 psi A 9 5.68 in 2 5,935 lbs 4,946 lbs 871 psi Mea n 641 psi SD 202 psi COV 31.5%

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42 Table 4.3 3 Bush hammer Iosipescu shear strength data (SI units) Core ID Gross Area Max. Load Max. Shear Shear Strength B 1 35.42 cm 2 14.0 kN 11.6 kN 3.29 MPa B 2 35.53 cm 2 13.4 kN 11.2 kN 3.14 MPa B 3 35.50 cm 2 14.5 kN 12.1 kN 3.41 MPa B 4 35.53 cm 2 13.0 kN 10.8 kN 3.05 MPa B 5 35.61 cm 2 15.6 kN 13.0 kN 3.66 MPa B 8 36.66 cm 2 13.5 kN 11.3 kN 3.16 MPa B 9 36.61 cm 2 17.7 kN 14.7 kN 4.03 MPa B 10 36.58 cm 2 16.8 kN 14.0 kN 3.83 MPa Mean 3.45 MPa SD 0.36 MPa COV 10.4 % Table 4.3 4 Bush hammer Iosipescu shear strength data (US Customary units) Core ID Gross Area Max. Load Max. Shear Shear Strength B 1 5.49 in 2 3, 142 lbs 2, 618 lbs 477 psi B 2 5.51 in 2 3,014 lbs 2, 512 lbs 4 56 psi B 3 5.50 in 2 3,267 lbs 2,723 lbs 495 psi B 4 5. 51 in2 2,924 lbs 2,437 lbs 443 psi B 5 5. 52 in 2 3,518 lbs 2,932 lbs 531 psi B 8 5. 53 in 2 3,040 lbs 2,533 lbs 458 psi B 9 5.67 in 2 3,978 lbs 3, 315 lbs 584 psi B 10 5.6 7 in 2 3,785 lbs 3,154 lbs 556 psi Mean 500 psi SD 52 psi COV 10.4 %

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43 Table 4.3 5 Raked overlay Iosipescu shear strength data (SI units) Core ID Gross A rea Max. Load Max. Shear Shear Strength R 1 35.83 cm 2 25.7 kN 21.4 kN 5.98 MPa R 2 35.45 cm 2 18.7 kN 15.6 kN 4.40 MPa R 3 35.56 cm 2 18.1 kN 15.1 kN 4.25 MPa R 4 35.74 cm 2 18.0 kN 15.0 kN 4.19 MPa R 9 35.77 cm 2 22.8 kN 19.0 kN 5.31 MPa R 10 35.80 cm 2 16.8 kN 14.0 kN 3.92 MPa R 11 35.56 cm 2 17.0 kN 14.1 kN 3 .98 MPa R 12 35.61 cm 2 17.6 kN 14.7 kN 4.12 MPa Mean 4.52 MPa SD 0.73 MPa COV 16.2 % Table 4.3 6 Raked Iosipescu shear strength data (US Customary Units) Core ID Gross Area Max. Load Max. Shear Shear Strength R 1 5.55 in 2 5,784 lbs 4,820 lbs 868 psi R 2 5.49 in 2 4,209 lbs 3,508 lbs 638 psi R 3 5.51 in 2 4,076 lbs 3,397 lbs 616 psi R 4 5. 54 in2 4,043 lbs 3,369 lbs 608 psi R 9 5. 54 in 2 5,123 lbs 4,269 lbs 770 psi R 10 5. 55 in 2 3,782 lbs 3,152 lbs 568 psi R 11 5.51 in 2 3,816 lbs 3, 180 lbs 577 psi R 12 5.52 in 2 3,961 lbs 3,301 lbs 598 psi Mean 655 psi SD 107 psi COV 16.3 %

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44 Table 4.3 7 Smooth Iosipescu shear strength data (SI units) Core ID Gross Area Max. Load Max. Shear Shear Strength S 1 37.54 cm 2 11.7 kN 9.8 kN 2.61 MPa S 2 37.38 cm 2 16.1 kN 13.5 kN 3.60 MPa S 3 37.16 cm 2 7.0 kN 5.8 kN 1.57 MPa S 7 36.50 cm 2 25.7 kN 21.4 kN 5.85 MPa S 8 36.69 cm 2 19.5 kN 16.2 kN 4.42 MPa S 11 36.86 cm 2 11.8 kN 9.8 kN 2.67 MPa S 12 36.75 cm 2 22.5 kN 18.8 kN 5.11 MPa S 13 36.77 cm 2 17.9 kN 14.9 kN 4.05 MPa Mean 3.74 MPa SD 1.42 MPa COV 37.9 % Table 4.3 8 Smooth Iosipescu shear strength data (US Customary units) Core ID Gross Area Max. Load Max. Shear Shear Strength S 1 5.82 in 2 2,640 lbs 2,200 lbs 378 psi S 2 5.79 in 2 3,630 lbs 3,025 lbs 522 psi S 3 5.76 in 2 1,577 lb s 1,314 lbs 228 psi S 7 5. 66 in 2 5,767 lbs 4,806 lbs 849 psi S 8 5.69 in 2 4,376 lbs 3,647 lbs 641 psi S 11 5. 71 in 2 2,656 lbs 2,213 lbs 387 psi S 12 5.70 in 2 5,066 lbs 4,222 lbs 741 psi S 13 5.70 in 2 4,013 lbs 3,344 lbs 587 psi Mean 542 psi S D 205 psi COV 37.9 %

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45 4.3.2 Direct Shear Test Results on Primary Monolithic Cylinders Iosipescu testing was performed on monolithic core samples that were extracted from the primary pads. Of the 20 core samples that were extracted from the pads, 19 of those cores were successfully tested in the Iosipescu fixture . Tables 4.3 9 and 4.3 10 provide the data obtained from the monolithic cylinders. As one specimen (designated as B 15) was improperly loaded, its data was not included in the statistical analysis for the monolithic cores. Table 4.3 9 Iosipescu test on primary monolithic specimens (SI Units) Core ID Gross Area Max. Load Max. Shear Shear Strength A 12 36.94 cm 2 27.2 kN 22.7 kN 6.14 MPa A 13 36.83 cm 2 29 .0 kN 24.2 kN 6.56 MPa A 14 36.99 cm 2 34.0 kN 28.4 kN 7.67 MPa A 15 36.86 cm 2 32.4 kN 27.0 kN 7.32 MPa B 10 35.83 cm 2 29.8 kN 24.8 kN 6.92 MPa B 11 36.1 cm 2 24.2 kN 20.2 kN 5.59 MPa B 13 35.85 cm 2 27.6 kN 23.0 kN 6.41 MPa B 14 35.96 cm 2 26.6 kN 22.2 kN 6.17 MPa R 5 36.64 cm 2 26.2 kN 21.8 kN 6.13 MPa R 6 35.64 cm 2 22.5 kN 18.8 kN 5.27 MPa R 7 35.99 cm 2 24.8 kN 20.7 kN 5.74 MPa R 8 25.85 cm 2 23.8 kN 19.9 kN 5.54 MPa R 13 35.96 cm 2 24.1 kN 20.1 kN 5.59 MPa R 14 35.99 cm 2 23.2 kN 19.3 kN 5.36 MPa R 15 37.21 cm 2 26.6 kN 22.1 kN 5.95 MPa S 8 37.13 cm 2 24.9 kN 20.8 kN 5.59 MPa S 9 36.97 cm 2 29.5 kN 24.6 kN 6.65 MPa S 14 36.86 cm 2 25.0 kN 20.8 kN 5.64 MPa S 15 36.94 cm 2 28.0 kN 23.4 kN 6.33 MPa B 15 35.88 cm 2 30.4 kN Inconclusive Mean 6.14 MP a SD 0.66 MPa COV 10.8 %

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46 Table 4.3 10 Iosipescu test on primary monolithic specimens (US Customary Units) Core ID Gross Area Max. Load Max. Shear Shear Strength A 12 5.73 in2 6,118 lbs 5,098 lbs 89 0 psi A 13 5.71 in2 6,518 lbs 5,432 lbs 951 psi A 14 5.73 in2 7,652 lbs 6,377 lbs 1,112 psi A 15 5.71 in2 7,281 lbs 6,068 lbs 1,062 psi B 10 5.55 in2 6,691 lbs 5,576 lbs 1,004 psi B 11 5.59 in2 5,448 lbs 4,540 lbs 811 psi B 13 5.59 in2 6,199 lbs 5,16 6 lbs 930 psi B 14 5.57 in2 5,998 lbs 4,990 lbs 895 psi R 5 5.52 in2 5,890 lbs 4,908 lbs 889 psi R 6 5.52 in2 5,068 lbs 4,223 lbs 765 psi R 7 5.58 in2 5,577 lbs 4,648 lbs 833 psi R 8 5.56 in2 5,361 lbs 4,468 lbs 804 psi R 13 5.57 in2 5,421 lbs 4,518 lbs 810 psi R 14 5.58 in2 5,206 lbs 4,338 lbs 778 psi R 15 5.77 in2 5,969 lbs 4,974 lbs 862 psi S 8 5.76 in2 5,598 lbs 4.665 lbs 811 psi S 9 5.73 in2 6,632 lbs 5,527 lbs 965 psi S 14 5.71 in2 5,612 lbs 4,677 lbs 819 psi S 15 5.73 in2 6,303 lbs 5,253 lbs 917 psi B 15 5.56 in2 6,830 lbs Inconclusive Mean 890 psi SD 96 psi COV 10.8 % 4.4 Direct Shear Test Results Guillotine Device Eight of the layered specimens that were extracted from the primary pads were set aside for testing in the guil lotine device to allow for comparisons between average shear strengths obtained with the two direct shear test fixtures. Two specimens from each of the pads were tested using the guillotine device. On two occasions, failure of the specimens did not occur e xclusively at the interface. Specifically, on the initial test for the specimen designated as B 7, failure

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47 occurred in the high shear zone that was on the opposite side of the text fixture from the interface (Figure 4 1). A subsequent test of that specimen was performed, which produced failure at the interface. Additionally, the specimen designated as S 9 failed at both high shear zones during one test (Figure 4 2). Furthermore, with the initial test of S 9 and the second test of B 7, the system continued t o resist the compressive displacement of the materials testing machine with increasing force. As a consequence, the recorded loads at failure were estimated based upon observation of the apparatus during the test and the approximate applied load at the tim e of observed breakage of the concrete. The data is provide d in Tables 4.4 1 and 4.4 2 . Figure 4 1 Initial fracture of B 7 in guillotine device

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48 Figure 4 2 Double shear failure of S 9 in guillotine device

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49 Table 4.4 1 Guillotine test results on primary layered specimens (SI Units) Core ID Gross Area Max. Load Max. Shear Shear Strength A 10 36.4 5 cm 2 25.8 kN 12.9 kN 3.53 MPa A 12 36.83 cm 2 6.1 kN 3.1 kN 0.83 MPa Average 2.18 MPa B 6 35.56 cm 2 16.3 kN 8.2 kN 2.30 MPa B 7 34.52 cm 2 11.1 kN 5.6 kN 1.61 MPa Average 1.95 MPa R 17 36.64 cm 2 28.2 kN 14.1 kN 3.85 MPa R 18 36.58 cm 2 24.8 kN 12.4 kN 3.39 MPa Average 3.62 MPa S 9 36.72 cm 2 26.7 kN 13.3 kN 3.63 MPa S 10 36.50 cm 2 26.6 kN 13.3 kN 3.65 MPa Average 3.64 MPa Table 4.4 2 Guillotine test results on primary layered specimens (US Customary Units) Core ID Gross Area Max. Load Max. Shear Shear Strength A 10 5.65 in 2 5,793 lbs 2,897 lbs 513 psi A 12 5.71 in 2 1,380 lbs 690 lbs 121 psi Average 317 psi B 6 5.51 in 2 3,673 lbs 1,837 lbs 333 psi B 7 5.35 in 2 2,500 lbs 1,250 lbs 234 psi Average 283 psi R 17 5.68 in 2 6,340 lbs 3,170 lbs 558 psi R 18 5.67 in 2 5,579 lbs 2,790 lbs 492 psi Average 525 psi S 9 5.69in 2 6,000 lbs 3,000 lbs 527 psi S 10 5.66 in 2 5,987 lbs 2,994 lbs 529 psi Average 528 psi

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50 TEST RESULTS FOR SECONDARY SPECIMENS Additional cored specimens were provided in the course of this research from two secondary sources: pads that had been placed as part of prior research at the University of Colorado at Denver (Pultorak, 2016) and from a retaining wa ll in Longmont, Colorado. The specimens were tested in the Iosipescu inspired fixture developed for this research. 5.1 Results of Iosipescu Inspired Testing of Pultorak Specimens Direct shear tests using the Iosipescu fixture were performed on 14 core samples that were extracted from the Pultorak pads. The cores were extracted from f ive different layered pads, with different overlay pre treatments. Table 5.1 1 provides the descriptions of each of the specimens and their designations and the results of the Iosipe scu testing on these cores is provided in Tables 5.1 2 and 5.1 3 . Table 5.1 1 Descriptions of specimens extracted from Pultorak pads Pad Designation Wet or dry prior to overlay Bonding agent 1A Dry None 1B Dry Wet bonding agent 2B Saturated Surface Dry Dried bonding agent 3A Wet Wet bonding agent 3B Saturated Surface Dry No bonding agent

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51 Table 5.1 2 Iosipescu shear strength on Pultorak cores (SI units ) Core ID Gross Area Max. Load Max. Shear Shear Strength 1A 1 36.75 cm 2 17.8 kN 14.8 kN 4.03 MPa 1A 2 36.86 cm 2 15.8 kN 13.2 kN 3. 58 MPa 1A 3 35.05 cm 2 10.1 kN 8.4 kN 2.40 MPa 1A 4 35.32 cm 2 11.8 kN 9.9 kN 2.79 MPa 1A 5 35.13 cm 2 13.2 kN 11.0 kN 3.12 MPa Mean 3.19 MPa SD 0.64 MPa COV% 20.1% 1B 1 37.71 cm 2 13.9 kN 11.6 kN 3.06 MPa 1B 2 37.65 cm 2 15.2 kN 12.7 kN 3.36 MPa 1B 3 36. 97 cm 2 1 5 .9 kN 13.3 kN 3.59 MPa Mean 3.34 MPa SD 0.26 MPa COV% 7.9% 2B 3 36.07 cm 2 10.8 kN 9.00 kN 2.50 MPa 3A 1 35.21 cm 2 18.3 kN 15.2 kN 4.32 MPa 3A 2 35.32 cm 2 12.8 kN 10.6 kN 3.01 MPa Average 3.67 MPa 3B 1 34.62 cm 2 17.3 kN 14.4 kN 4.16 MPa 3B 2 34.78 cm 2 13.8 kN 11.5 kN 3.31 MP a 3B 3 34.73 cm 2 12.4 kN 10.3 kN 2.98 MPa Mean 3.48 MPa SD 0.61 MPa COV 17.5 %

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52 Table 5.1 3 Iosipescu shear strength on Pultorak cores (US Customary Units) Core ID Gross Area Max. Load Max. Shear Shear Strength 1A 1 5.70 in 2 4,001 lbs 3,334 lbs 585 ps i 1A 2 5.71 in 2 3,556 lbs 2,963 lbs 519 psi 1A 3 5.43 in 2 2,269 lbs 1,891 lbs 348 psi 1A 4 5.47 in 2 2,663 lbs 2,219 lbs 405 psi 1A 5 5.44 in 2 2,961 lbs 2,468 lbs 453 psi Mean 462 psi SD 93 psi COV% 20.1% 1B 1 5.84 in 2 3,116 lbs 2,597 lbs 4 44 psi 1B 2 5.84 in 2 3,421 lbs 2,851 lbs 488 psi 1B 3 5.73 in 2 3,577 lbs 2,981 lbs 520 psi Mean 484 psi SD 38 psi COV% 7.9% 2B 3 5.59 in 2 2,430 lbs 2,025 lbs 362 psi 3A 1 5.46 in 2 4,104 lbs 3,420 lbs 627 psi 3A 2 5.47 in 2 2,872 lbs 2,393 lbs 437 psi Average 532 psi 3B 1 5.37 in 2 3,881 lbs 3,234 lbs 603 psi 3B 2 5.39 in 2 3,105 lbs 2,588 lbs 480 psi 3B 3 5.38 in 2 2,790 lbs 2,325 lbs 432 psi Mean 505 psi SD 88 psi COV 17.5 % 5.2 Results of Iosipescu Inspired Testing of Longmo nt Specimens Nine layered specimens, which were extracted from an existing retaining wall that received an overlay of self consolidating concrete, were also tested. Prior to placement of the overlay, the face of the retaining wall was roughened to varying degrees, which corresponded to CSP 6, CSP 8, and CSP 10 in accordance with the ICRI specifications (International Concrete

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53 Repair Institute, 2013) . Three cores that were representative of each of the degrees of surface roughne ss were tested. Unfortunately, an error in the setup of the test for specimen 10 3 was made and was not discovered unt il the specimen reached failure . Consequently, the standard deviation and coefficient of variation could not be calculated for the CSP 10 cores. The results are p rovided in Tables 5.2 1 and 5.2 2 . Table 5.2 1 Iosipescu tests on Longmont retaining wall specimens (SI Units) Core ID Gross Area Max. Load Max. Shear Shear Strength 6 1 37.74 cm 2 1 3.8 kN 11.5 kN 3.04 MPa 6 2 37.43 cm 2 19.8 kN 16.5 kN 4.42 MPa 6 3 37.32 cm 2 16.5 kN 13.8 kN 3.69 MPa Mean 3.72 MPa SD 0.69 MPa COV% 18.5 % 8 1 37.49 cm 2 18.8 kN 15.7 kN 4.18 MPa 8 2 37.71 cm 2 16.6 kN 13.9 kN 3.68 MPa 8 3 37.46 cm 2 20.5 kN 17.0 kN 4.55 MPa Mean 4.10 MPa SD 0.40 MPa COV% 10.6 % 10 1 37.38 cm 2 22.7 kN 18.9 kN 5.07 MPa 10 2 37.57 cm 2 21.9 kN 18.3 kN 4 .87 MPa 10 3 34.73 cm 2 19.1 kN Inconclusive Mean 4.97 MPa SD COV

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54 Table 5.2 2 Iosipescu testing on retaining wall specimens (US Customary Units) Core ID Gross Area Max. Load Max. Shear Shear Strength 6 1 5.85 in 2 3,093 lbs 2,578 lbs 441 psi 6 2 5.80 in 2 4,459 lbs 3,716 lbs 640 psi 6 3 5.79 in 2 3,7 17 lbs 3,098 lbs 535 psi Mean 539 psi SD 100 psi COV% 18.5% 8 1 5.81 in 2 4,226 lbs 3,522 lbs 606 psi 8 2 5.84 in 2 3,740 lbs 3,117 lbs 533 psi 8 3 5.81 in 2 4,598 lbs 3,832 lbs 660 psi Mean 600 psi SD 64 psi COV% 10.6% 10 1 5.79 in 2 5,108 lbs 4,257 lbs 735 psi 10 2 5.82 in 2 4,933 lbs 4,111 lbs 706 psi 10 3 5.81 in 2 4,303 lbs Inconclusive Mean 720 psi SD COV Following direct shear testing of the layered specimens obtained from the aforementioned retaining wall o verlay, the substrate concrete section from three of those specimens that remained after testing was of sufficient length to perform Iosipescu tests using the developed fixture. The data from those tests is provided in Tables 5.2 3 and 5.2 4 .

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55 Table 5.2 3 Iosipescu test on monolithic retaining wall cores (SI Units) Core ID Gross Area Max. Load Max. Shear Shear Strength 8 2 s 37.54 cm 2 23.6 kN 19.6 kN 5.23 MPa S 3 s 37.27 cm 2 20.8 kN 17.4 kN 4.66 MPa 10 3 s 37.08 cm 2 20.8 kN 17.3 kN 4.68 MPa Mean 4.86 MPa SD 0.33 MPa COV 6.7 % Table 5.2 4 Iosipescu test on monolithic retaining wall cores (US Customary Units) Core ID Gross Area Max. Load Max. Shear Shear Strength 8 2 s 5.82 in 2 5,299 lbs 4,416 lbs 759 psi 8 3 s 5.78 in 2 4,682 lbs 3,902 lbs 675 psi 10 3 s 5.75 in 2 4,678 lbs 3,898 lbs 678 psi Mean 704 psi SD 47 psi COV 6.7 %

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56 DISCUSSION 6.1 Breakage of Layered Specimens In general , Iosipe scu tests that were conducted on layered specimens resulted in breakage of those specimens along the interface between substrate and overlay concrete. As indicated in Figure 6 1 below, material from both the overlay and substrate w as visible along the frac tured face of the layered specimens. Figure 6 1 Typical appearance of a layered specimen following Iosipescu test As indicated in Figure 3 4, some moment w as applied to the specimens by the Iosipescu i nspired test fixture, with peak moments occurring at the inner loading plates. The point of greatest shear stress, however, does coincide with the point at which the applied moment is theoretically zero. Given that the failure of the layered specimens occu rred at the interfacial plane, as long as that interface was centered between the inner loading plates of the test fixture, the effects of moment on specimen failure were likely negligible.

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57 6.1.1 Effect of Surface Treatment on Shear Strength Pultorak Specime ns As indicated earlier, a number of specimens were extracted from l ayered pads that had been previously placed in the outdoor chute at the University of Colorado at Denver structures l aboratory . Prior to overlay placement, the substrate concrete in the pa ds from which these specimens were extracted was roughened with jackhammer using a bush hammer attachment, and various surface treatments were applied prior to placement of the overlay concrete (Pultorak, 2016) . Direct shear (g uillotine) testing of these specimens found that the greatest nominal shear strength at the interface occurred in specimens whose substrate was treated with a wet bonding agent and was dry prior to overlay (designated as 1B). The lowest shear strength occu rred with specimens taken from the pad designated as 2B, which were saturated but dry at the surface prior to overlay, and received dry bonding agent. Regarding the latter, only one specimen from the pad designated as 2B (SSD with dried bonding agent) wa s available for Iosipescu testing. Iosipescu testing of that specimen found the shear strength at the interface to be lower than the average shear strengths of all of the other specimens that were taken from those pads ults (2016) . However, relative to one another, the relationship between average shear strength and surface treatments in all other tested specimens was different for Iosipescu inspired testing than in guillotine tests. Although the Iosipescu test results on these specimens found somewhat different relationships between surface treatments and bond strengths as compared with prior guillotine testing, where sufficient Iosipescu tested specimens were available for statistic al analysis, the mean shear strengths w ere similar . The greatest difference between shear strengths was approximately 0.29 MPa (43.0 psi). T his difference was less than one standard deviation for the

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58 1A and 3A pad data, and was approximately 13 percent greater than the standard deviation for the 1B data as shown in Figure 6 2 . Given the similarities in interfacial shear strengths in specimens from these pads, if testing were to be performed on substantially larger sample sizes, the differences in resultant strengths between the pads and/or bet ween the testing methods may decrease. Figure 6 2 Plot of Iosipescu mean shear strengths vs. surface treatment with standard deviation where sufficient specimens were available for statistical analysis 6.1.2 Effect of Degree of Surface Roughness on Shear Strength The shear strength along the interface between substrate and overlay concrete is greatly affected by the roughness of the substrate surface prior to the placement of the overlay. This is recogniz ed in Chapter 16 of ACI 318 ( 2014), which o nly allows for consideration of shear across an unreinforced interface in cases where the substrate had been intentionally roughened. Moreover, not only does the code require surface roughening, it specifies the a mplitude to which the surfaces must be roughened. 3 3.05 3.1 3.15 3.2 3.25 3.3 3.35 3.4 3.45 3.5 3.55 300 350 400 450 500 550 600 650 1A 1B 3B Shear Strength (MPa) Shear Strength (psi) Pad

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59 Iosipescu testing of the retaining wall cores that were extracted from Longmont, Colorado illustrated the positive effects of surface roughening on shear strength along the bonded interface. Specifically, a s indicated in Figure 6 3 , the average interfacial shear strength increased with respect to the degree to which the surface was rou ghened. Figure 6 3 Relationship between surface roughness and average she ar strength of retaining wall cores by Iosipescu method Although nine specimens were procured for Iosipescu testing, nine additional specimens from the retaining wall had also been extracted for guillotine testing. That testing was performed by others, an d also revealed increasing shear strength with respect to surface rou ghness, as indicated in Figure 6 4 . 0 1 2 3 4 5 6 0 100 200 300 400 500 600 700 800 CSP-6 CSP-8 CSP-10 Shear Strength (MPa) Shear Strength (psi) Specimens

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60 Figure 6 4 Relationship between surface roughness and average shear strength of Longmont cores by g uillotine method The effects of surface roughness were also evaluated for the specimens that were procured from the primary pads . Unlike the retaining wall cores, however, the resulting average shear strengths across the interfaces were different than exp ected. Based upon surface roughness, it was expected that the average shear strengths across the interfaces would rank as: 1 raked, 2 bush hammered, 3 acid etched, and 4 smooth. However, Iosipescu testing of these specimens did not yield that surfa ce roughness/strength relation ship, as illustrated in Figure 6 5 . 0 1 2 3 4 5 6 7 0 100 200 300 400 500 600 700 800 900 1000 CSP-6 CSP-8 CSP-10 Shear Strength (MPa) Shear Strength (psi) Specimens

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61 Figure 6 5 Relationship between surface treatments and Iosipescu tested average shear strengths As expected, the specimens whose substrat e concrete was raked did possess the highest average shear strengths across their interfaces. However, based solely upon surface roughness, it would have been expected that the second highest strength would have come from the bush hammered cores. In contra st, the bush hammered specimens had the lowest average shear strength of all of the prepared specimens . The use of a bush hammer for surface roughening can lead to bruising, the development of microcracking near the prepared surface that can weaken the ove rall bond strength. Given that these microcracks are generally not visible to the naked eye, it is likely that they would go unnoticed, leading to weak bond strength in the bush hammered specimens. The vertical bars in Figure 6 5 indicate shear strengths a t one standard deviation from the mean shear strengths that were obtained by Iosipescu testing . It can be seen that the variance in the data for the bush hammered and raked specimens was much smaller than that of the acid etched and smooth specimens. As discussed in the next section, a lower variance can also be 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 0 100 200 300 400 500 600 700 800 900 Smooth Acid Etch Bush Hammer Raked Shear Strength (MPa) Shear Strength (psi) Surface Treatment

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62 found in the data from Iosipescu testing of monolithic specimens, for which more than double the number of specimens were tested. As such, it can be reasonably concluded that the wide variations i n data from the acid etched and smooth specimens likely stems from actual variations in interfacial shear strength with respect to the locations on the pads from which cores were extracted , not variations in the testing apparat us. Moreover, inexperience in providing a smooth finish on the part of this author may have produced location specific variations in interfacial shear strength in cores taken from the smooth pad. It is also possible that larger sample sizes may yield results that more closely align wi th the expected relationship between surface roughness and average interfacial shear strength. Like the Iosipescu testing, average shear strengths across the interfaces of the primary specimens prepared for this research and tested in the guillotine devi ce also did not increase with respect to surface roughness. In this case, the highest average shear strength was found in the specimens whose substrate concrete wa s left smooth prior to overlay, with bush hammered specimens having the lowest average shear strengths. For guillotine testing, the data was based on only two specimens per test pad, and two of those specimens, one from the acid etched pad, and one from the smooth pad, failed on the opposite side of the fixture from the interface. With limited dat a from the guillotine device and unintended failure locations, it is unlikely that the data on these specimens obtain ed from the guillotine device was reliable. 6.2 Breakage of Monolithic S pecimens There were 19 successful tests of monolithic specimens obtaine d from the pads that were cast specifically for this research, and three additional test of monolithic specimens of substrate concrete obtained from the retaining wall in Longmont, Colorado. As indicated in the tabulated results in Chapter 4 and Chapter 5 , variation of shear strengths in these specimens was lower

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63 than many of the layered specimens, indicating consistency and repeatability in this testing method. 6.2.1 Examination of Crack Patterns While cracks in the la yered specimens generally occurred along th e interface between the overlay and the substrate, cracks in the monolithic sections were generally diagonal near the centers of the specimens and vertical near the load ing plates, as shown in Figure 6 6 . The crack patterns in the monolithic specimens test ed for this research were also consistent with those from prior Iosipescu tests on monolithic sections (Helmick, Toker Beeson, & Tanner, 2016) . Moreover, the experimental and analytica l study performed by Tanner et al. (2016) a l so indicated that the calculated diagonal tensile stress along the failure plane in Iosipescu tested beams was close to the maximum principal tensile stress. Thus, the observed cracks in these specimens were also most consistent with principal tensile spli tting . Figure 6 6 Typical crack patterns in Iosipescu tested monolithic specimens

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64 6.2.2 Effect of flexural tension on monolithic specimens Unlike the layered specimens , the placement of monolithic specimens i nto the fixture did not necessarily align the weakest concrete section at the central point between the two inner loading plates. Specifically, despite consolidation efforts made during concrete placement, the in situ concrete is not necessarily completely homogeneous. Some variations in strength with respect to location should be expected. If, therefore, the weakest point in a specimen is not aligned with the center point of the fixture, flexural tension may have contributed to fracture, resulting in a low er peak force on the fixture and a correspondingly lower calculated shear strength. One way to counter this phenomenon is the intentional weakening of the section at the peak shear location by notching, was the case for some of the prior Iosipescu inspire d testing of concrete specimens. 6.2.3 Relationship between Compressive Strength and Shear Strength ACI 318 (2014) provides numerous formulas for calculating a design shear strength in concrete for various applications. In these formulas, the design shear streng th is presented as a function of the square root of concrete compressive strength. For this research, compressive strength testing was performed at three, ten, and 28 days after concrete placement. However, shear testing was performed more than one year af ter concrete placement. Consequently, in order to look into the relationship between shear strength and compressive strength, it was necessary to estimate the compressive strength at the time of the testing. The estimated average compressive strength was b ased upon an extension of the average compressive strength curve to 524 and 538 days (by this method, the estimated compressive strength was virtually the same at approximately 31.0 MPa (4,500 psi) ) . Table 6.2 1 provides the relationships between average s hear strength and the compressive strength .

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65 Table 6.2 1 Relationships between average shear strength and compressive strength in monolithic specimens Specimen ID Ave. Shear Strength ( ) / c c MPa p si % S.I. U.S. A 12 6.14 890 19.8% 1.10 13.3 A 13 6.56 951 21.1% 1.18 14.2 A 14 7.67 1,112 24.7% 1.38 16.6 A 15 7.32 1,062 23.6% 1.31 15.8 B 10 6.92 1,004 22.3% 1.24 15.0 B 11 5.59 811 18.0% 1.00 12.1 B 13 6.41 930 20.7% 1.15 13.9 B 14 6.17 895 19. 9% 1.11 13.3 R 13 5.59 810 18.0% 1.00 12.1 R 14 5.36 778 17.3% 0.96 11.6 R 15 5.95 862 19.2% 1.07 12.9 R 5 6.13 889 19.7% 1.10 13.2 R 6 5.27 765 17.0% 0.95 11.4 R 7 5.74 833 18.5% 1.03 12.4 R 8 5.54 804 17.9% 1.00 12.0 S 14 5.64 819 18.2% 1.01 12.2 S 15 6.33 917 20.4% 1.14 13.7 S 8 5.59 811 18.0% 1.00 12.1 S 9 6.65 965 21.4% 1.19 14.4

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66 6.3 Compari ng Direct Shear Strength from Iosipescu and Guillotine Testing A number of cylindrical bonded overlay specimens obtained from the various sources discussed in this thesis were tested via the Iosipescu method and the guillotine method. Given that the specimens were extracted from the same materials, and, with the exception of the Pultorak specimens, were tested at around the same time, it was prudent to direc tly compare the results of these test methods. That c omparison is shown in Figure 6 7 . Figure 6 7 Comparison between Iosipescu and Guillotine Tests As the data indicate s , there were occasions at which t he guillotine test yielded higher shear strengths than the Iosipescu device, and those where the guillotine test data was lower. The general trends in the curves were similar, but variation between specimen types was gr eater 0 1 2 3 4 5 6 7 0 100 200 300 400 500 600 700 800 900 1000 Acid Etch Bush Hammer Raked Smooth CSP-6 CSP-8 CSP-10 1A 1B 2B 3A 3B Primary Specimens (Quikrete) Longmont (SCC) Pultorak (Quikrete) Avg. Shear Strength (Mpa) Avg. Shear Strength (psi) Iosipescu Guillotine

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67 with the Guillotine test. Addi tionally, if concrete compressive strength is directly related to shear strength across a bonded interface, then the data for the Pultorak cores is as expected. Specifically, Iosipescu testing of the Pultorak cores took place nearly two years after guillot ine tests were conducted. It stands to reason that some time dependent strength gain in the concrete had occurred in that timeframe. The difference in guillotine a nd Iosipescu shear strength data for the other specimens, however, cannot be explained by tim e dependent changes in concrete strength, given that those tests were conducted at around the same time . With regard to the comparison of data conducted at nearly the same time, Figure 6 7 also shows that the Iosipescu shear strengths were higher for the p rimary specimens , for which both tests were performed by this author . In contrast, the shear strength was higher for guillotine testing on the Longmont retaining wall specimens, for which Iosipescu testing w as conducted by this author at the UC Denver labo ratory, and g uillotine testing was performed by others at a different location . This indicate s that minor differences in testing methods may have influenced results. One difference in those methods was with respect to the rate of load application. At the U C Denver laboratory, the rate of loading on the guillotine fixture was the same as that which was used for the Iosipescu fixture. That load rate was displacement controlled and was at 0.0508 mm/sec (0.002 in/sec). In contrast, loading of the guillotine fix ture performed by others was force controlled , at a rate of 222 N/s (50 lb/s). It is possible that differences in load rate affected the guillotine results and their comparison to Iosipescu results. 6.4 Effect of Geometry on Iosipescu Test 6.4.1 Size Effect Size eff ect, as descri bed by Bazant an d Pfeiffer (1986 ), highlights the contrast between failure stress under elastic or yi eld stress analysis , where failure stress is assumed to be constant

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68 regardless of specimen geometry, and failure stress derived from fracture mechanics. For the latter, the nominal stress at failure decreases as specimen sizes increase. In this research, the sizes of all tested specimens were effectively the same, notwithstanding minor variations in core diameters , which were less than 5 percen t of the average core diameter. As such, the potential research was performed on monolithic sections, it is unclear if this size effect phenomenon would also pertai n to the interfacial shear strength across a bonded concrete overlay. Consequently, it would be beneficial for future Iosipescu testing on cylindrical specimens (cores) to include many cores of varying sizes. 6.4.2 Test Fixture Geometry T he literature review per formed in the course of this research also found that t he geometry of the test fixture affected the shear stress at failure. Bazant and Pfeiffer (1986) found an inverse relationship between the distance between the primary loading plates and shear stress a t failure. As the distance between points of application of the loads increased, the shear stress at failure decreased. Ingraffea and Panthaki (1985) , however , co ncluded that moving the primary loads closer together decreased the shear stress at failure. W ith these arguments, it would also be beneficial to conduct Iosipescu inspired tests with varying test fixture geometry. With regard to overlay specimens, changes in fixture geometry may also prove beneficial for cases in which the interface between substr ate concrete and overlay concrete is irregular and/or difficult to see. As an example, in the testing for this research, it was not always possible to contain the entire raked interface in the narrow space between the primary loading plates. Spacing those plates further apart would better allow for testing of the interface rather than that of the solid concrete astride of that interface. Additionally, although the primary test specimens

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69 that were fabricated solely for this research included colorant that al lowed for relatively easy identification of substrate concrete versus overlay concrete, it is likely that most actual construction projects would not include colored concrete overlays . Cores extracted in those projects, therefore, may have interfacial plan es that are more difficult to see. With wider spacing of the primary loading plates, testing personnel can be more confident that the interfacial plane lies completely between the primary loading plates when testing such specimens. 6.5 Sources of Error/Improv ements The Iosipescu inspired tests conducted for this research produced promising results, but not without some inconsistencies. During the testing and data analysis, sources of error were encountered. First, the top and bottom sections of the fixture w er e independent of one another. In order to align the sections such that the desired load distribution was established, marks were made on the specimens, and the primary loading plates were aligned with those marks. Naturally, some, albeit minor, variations in the alignments will be introduced due to normal human error. In order to improve the process, p ermanent vertical guide rods could be added to the fixture that are fixed in the bottom section and with vertical slip allowed in the top section to accommoda te the displacement of the top section during testing (Figure 6 8 ).

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70 Figure 6 8 Test fixture with guide rods In addition to the potential variable geometry with the independent top and bottom sections, th e independence of those sections also allowed for reversal of the top section on one occasion when loading. Specifically, the top section was errantly placed backwards onto the specimen, eliminating the opposing force couples needed for Iosipescu inspired testing. This, obviously, produced inconclusive results. Error was also added to another specimen due to omission of the topmost half round rod. These errors can be alleviated with more careful use of the test apparatus.

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71 CONCLUSIONS AND RECOMMENDATIONS 7.1 S ummary and Conclusions Testing of field obtained specimens can often be an instrumental part of a construction project. In concrete, a common means for obtaining specimens from hardened concrete is coring. Consequently, the adaptation of test methods to ac commodate cylindrical specimens is desirable. In this research, a fixture for direct shear testing of cylindrical concrete specimens was designed, fabricat e d and successfully utilized to perform direct shear testing on 73 cored concrete specimens. The appa ratus was inexpensive to fabricate and was relatively easy to fit into a standard testing machine. Moreover, given the relatively small size of the apparatus and the specimens for which it was utilized, testing of numerous specimens in one testing session could be performed with little difficulty. The results of the testing confirmed that the use of this fixture is a viable method for direct shear testing on monolithic and layered concrete. Variation in results on monolithic specimens was relatively low, i ndicating that the test was consistent and repeatable. Similarly low variation in results on specimens obtained from the Longmont retaining wall, bush hammered and raked specimens also proved promising with respect to this test apparatus being applicable t o concrete overlays. Higher variation in acid etched and smooth specim ens warrants additional testing. However, given the low variation in monolithic, Longmont retaining wall, bush hammered and raked specimens, it is apparent that the variation is in the s hear strength of the surface treatments, not the device. As such, these variations do not preclude the use of this test apparatus as a viable means for testing the shear strength on bonded concrete overlays.

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72 7.2 Recommendations The Iosipescu inspired test app aratus used in this research was subject to limited human error due to separate top and bottom sections, which allowed for minor variations in the geometry of the fixture from test to test. As such, the addition of new components to the fixture that will e nsure the same geometry for every test, is recommended. One potential method for fixing that geometry is the addition of permanent guide rods, as shown in Figure 6 8 . Other methods may be available. It is as sumed that this testing method could be utilized on large scale projects, despite the relatively small size of the test fixture and coinci ding test specimens. Given prior research revealed that specimen size is a factor that influences the shear stress, this author also recommends that future research i nclude testing of specimens with variable sizes. Similarly, with prior research indicating that the spacing between primary loading plates influences shear strength, future research should also include test fixtures variable distances between the primary l oading plates. Given the ease and relatively low cost of fabrication of this test fixture, the fabrication of multiple fixtures of varying sizes and geometries should not be cost prohibitive or overly burdensome. It was apparent from the review of prior r esearch that a debate is ongoing as to whether failure of concrete that is loaded in shear occurs as a result of shear stress, tensile stre ss, or some combination of both . Consequently, this author believes that future testing should include close measurem ent of specimen behavior during loading in conjunction with finite element modeling. Combining laboratory and analytical data may prove fruitful in more precisely identifying the mechanics behind fractures in concrete under direct shear loading.

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73 REFERE NCES ACI Committee 326. (1962). Shear and Diagonal Tension. Journal of the American Concrete Institute , 1 30. American Concrete Institute. (2006). ACI 325.13R Concrete Overlays for Pavement Rehabilitation . Farmington Hills, Michigan: American Concrete Institute. American Concrete Institute. (2014). Building Code Requirements for Structural Concrete . Farmington Hills, MI: American Concrete Institute. Helmick, C. G., Toker Beeson, S., & Tanner, J. (2016). "Eva luation of Shear and Diag onal Tension in Plain Concrete," Concrete International , 39 48. Ingraffea, A. R., & Panthaki, M. J. (1985). "Analysis of Shear Fr acture Tests of Concrete Beams , " Finite Element Analysis of Reinforced Concrete Structures: Proceeding s of the Seminar Sponsored by the Japan Society for the Promotion of Science and the U.S. National Science Foundation (pp. 151 183). New York: American Society of Civil Engineers. International Concrete Repair Institute. (2013). Guideline No. 310.2R 2013 S electing and Specifying Concrete Surface Preparation for Sealers, Coatings, Polymer Overlays, and Concrete Repair. Rosemont, IL: International Concrete Repair Institute. Iosipescu, N. (1967). "New Accurate Procedure for Single Shear Testing of Metals , " Jou rnal of Materials , 537 566. Nogueira, C., & Rens, K. (2018). " Experimental Analysis of Cement Bas ed Materials Under Shear Stress," Construction and Building Materials , 392 401. Pultorak, A. S. (2016). The Effects of Common Surface Pretreatments on the Shear Strength of Bonded Concrete Overlays. MS thesis, Civil Engineering, University of Colorado, Denver, Denver, CO. Rosen, C. J. (2016). Shear Strength at the Interface of Bonded Concrete Overlays. MS thesis, Civil Engineering, University of Colorado, Denver, Denver, CO. Stevens, G., & Kesner, K. (2016). "Evolutio ns of the ACI 562 Code, Part 1 , " Concrete International , 53 56. Swan, A. (2016). Alternate Methods for Testing Shear Strength at a Bonded Concrete Interface. MS thesis, Civil Engineering, University of Colorado, Denver, Denver, CO. Z.P. Bazant and P.A. Pfeiffer. (1986). "Sh ear Fracture Tests of Concrete , " Materials and Structures , 111 121.

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A 1 APPENDI X The following pages include load displacement curves and photographs of the specimens that were tested for this thesis.

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A 2 Figure A 1 Acid etched layered specimen, A 1, taken from UC Denver pads and tested in Io sipescu inspired test app aratus 0 500 1000 1500 2000 2500 3000 3500 4000 4500 0 0.05 0.1 0.15 0.2 0.25 Load (lbf) Displacement (in) A 1

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A 3 Figure A 2 Acid etched layered specimen A 3, taken from UC Denver pads and tested in the Iosipescu inspired test fixture. 0 500 1000 1500 2000 2500 3000 0 0.05 0.1 0.15 0.2 0.25 MTS Load (lbf) Displacement (in) A 3

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A 4 Figure A 3 Acid etched layered test specimen A 4, taken from UC Denver pads and tested in the Iosipescu inspired te st fixture. 0 1000 2000 3000 4000 5000 6000 0 0.05 0.1 0.15 0.2 0.25 0.3 MTS Load (lbf) Displacement (in) A 4

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A 5 Figure A 4 Acid etched layered specimen, taken from UC Denver pads and tested in the Iosipescu inspired test fixture. 0 1000 2000 3000 4000 5000 6000 0 0.05 0.1 0.15 0.2 0.25 0.3 MTS Load (lbf) Displacement (in) A 5

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A 6 Figure A 5 Acid etched l ayered specimen A 6, taken from UC Denver pads and tested in the Iosipescu inspired test fi xture. 0 500 1000 1500 2000 2500 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 MTS Load (lbf) Displacement (in) A 6

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A 7 Figure A 6 Acid etched layered specimen, taken from UC Denver pads and tested in the Iosipescu inspired test fixture. 0 1000 2000 3000 4000 5000 6000 0 0.02 0.04 0.06 0.08 0.1 MTS Load (lbf) Displacement (in) A 7

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A 8 Figure A 7 Acid etched la yered specimen A 8, taken from UC Denver pads and tested in the Iosipescu inspired test fixtur e. -500 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 0 0.02 0.04 0.06 0.08 0.1 MTS Load (lbf) Displacement (in) A 8

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A 9 Figure A 8 Acid etched la yered specimen A 9, taken from UC Denver pads and tested in the Iosipescu inspired test apparatus. 0 1000 2000 3000 4000 5000 6000 7000 0 0.02 0.04 0.06 0.08 0.1 0.12 MTS Load (lbf) Displacement (in) A 9

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A 10 Figure A 9 Bush hammered l ayered specimen B 1, taken from UC Denver pads and tested in the Iosipescu inspired test ap paratus. 0 500 1000 1500 2000 2500 3000 3500 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 MTS Load (lbf) Displacement (in) B 1

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A 11 Figure A 10 Bush hammered la yered specimen B 2, taken from UC Denver pads and tested in the Iosipescu inspired test apparatus. 0 500 1000 1500 2000 2500 3000 3500 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 MTS Load (lbf) Displacment (in) B 2

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A 12 Figure A 11 Bush hammered l ayered specimen, B 3 , taken from UC Denver pads and tested in the Iosipescu inspi red test apparatus. 0 500 1000 1500 2000 2500 3000 3500 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 MTS Load (lbf) Displacement (in) B 3

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A 13 Figure A 12 Bush hammered l ayered specimen B 4, taken from UC Denver pads and tested in the Iosipescu inspired test apparatus. 0 500 1000 1500 2000 2500 3000 3500 -0.02 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 MTS Load (lbf) Displacement (in) B 4

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A 14 Figure A 13 Bush hammered l ayered specimen B 5, taken from UC Denver pads and tested in the Iosip escu inspired test fixture. 0 500 1000 1500 2000 2500 3000 3500 4000 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 MTS Load (lbf) Displacement (in) B 5

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A 15 Figure A 14 Bush hammered l ayered specimen B 8, taken from UC Denver pads and tested in the Iosipescu inspired test apparatus. 0 500 1000 1500 2000 2500 3000 3500 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 MTS Load (lbf) Displacement (in) B 8

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A 16 Figure A 15 Bush hammered l ayered specimen B 9, taken from UC Denver pads and tested in t he Iosipescu inspired test apparatus. 0 500 1000 1500 2000 2500 3000 3500 4000 4500 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 MTS Load (lbf) Displacement (in) B 9

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A 17 Figure A 16 Bush hammered la yered specimen B 10, taken from the UC Denver pads and tested in the Iosipescu inspired test apparatus. 0 500 1000 1500 2000 2500 3000 3500 4000 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 MTS Load (lbf) Displacement (in) B 10

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A 18 Figure A 17 Raked la yered specimen R 1, taken from UC Denver pads and test ed in the Iosipescu inspired test apparatus. 0 1000 2000 3000 4000 5000 6000 7000 0 0.05 0.1 0.15 0.2 0.25 MTS Load (lbf) Displacement (in) R 1

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A 19 Figure A 18 Raked la yered specimen R 2, taken from UC Denver pads and tested in the Iosipescu inspired test apparatus. 0 500 1000 1500 2000 2500 3000 3500 4000 4500 0 0.05 0.1 0.15 0.2 0.25 MTS Load (lbf) Displacement (in) R 2

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A 20 Figure A 19 Raked la yered specimen R 3, taken from UC Denver pads and tested in the Iosipescu inspired test apparatus. 0 500 1000 1500 2000 2500 3000 3500 4000 4500 0 0.05 0.1 0.15 0.2 MTS Load (lbf) Displacement (in) R 3

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A 21 Figure A 20 Raked la yered specimen R 4, taken from UC Denver pads and tested in the Iosipescu inspired test apparatus. 0 500 1000 1500 2000 2500 3000 3500 4000 4500 0 0.05 0.1 0.15 0.2 MTS Load (lbf) Displacement (in) R 4

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A 22 Figure A 21 Raked la yered specimen R 9, taken from UC Denver pads and tested in the I osipescu inspired test apparatus. 0 1000 2000 3000 4000 5000 6000 0 0.05 0.1 0.15 0.2 MTS Load (lbf) Displacement (in) R 9

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A 23 Figure A 22 Raked la yered specimen R 10, taken from UC Denver pads and tested in the Iosipescu inspired test apparatus. 0 500 1000 1500 2000 2500 3000 3500 4000 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 MTS Load (lbf) Displacement (in) R 10

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A 24 Figure A 22 Raked la yered specimen R 11, taken from UC Denver pads and tested in the Ios ipescu inspired test apparatus. 0 500 1000 1500 2000 2500 3000 3500 4000 4500 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 MTS Load (lbf) Displacement (in) R 11

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A 25 Figure A 24 Raked la yered specimen R 12, taken from UC Denver pads and tested in the Iosipescu inspired test apparatus. 0 500 1000 1500 2000 2500 3000 3500 4000 4500 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 MTS Load (lbf) Displacement (in) R 12

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A 26 Figure A 25 Smooth la yered specimen S 1, taken from UC Denver pads and tested in the Iosip escu inspired test apparatus. 0 500 1000 1500 2000 2500 3000 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 MTS Load (lbf) Displacement (in) S 1

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A 27 Figure A 26 Smooth l ayered test specimen S 2, taken from UC Denver pads and tested in the Iosipescu inspired test apparatus. 0 500 1000 1500 2000 2500 3000 3500 4000 0 0.05 0.1 0.15 0.2 MTS Load (lbf) Displacement (in) S 2

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A 28 Figure A 27 Smooth la yered specimen S 3, taken from UC Denver pads and tested in the Ios ipescu inspired test apparatus. 0 200 400 600 800 1000 1200 1400 1600 1800 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 MTS Load (lbf) Displacement (in) S 3

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A 29 Figure A 28 Smooth la yered specimen S 7, taken from UC Denver pads and tested in the Iosipescu inspired test apparatus. 0 1000 2000 3000 4000 5000 6000 7000 0 0.05 0.1 0.15 0.2 0.25 MTS Load (lbf) Displacement (in) S 7

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A 30 Figure A 29 Smooth la yered specimen S 8, taken from UC Denver pads and tested in the Iosip escu inspired test apparatus. 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 MTS Load (lbf) Displacement (in) S 8

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A 31 Figure A 30 Smooth la yered specimen S 11, taken from UC Denver pads and tested in the Iosipescu inspired test apparatus. 0 500 1000 1500 2000 2500 3000 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 MTS Load (lbf) Displacement (in) S 11

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A 32 Figure A 31 Smooth la yered specimen S 12, taken from UC Denver pads and tested in the Iosip escu inspired test apparatus. 0 1000 2000 3000 4000 5000 6000 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 MTS Load (lbf) Displacement (in) S 12

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A 33 Figure A 32 Smooth la yered specimen S 13, taken from UC Denver pads and tested in the Iosipescu inspired test apparatus. 0 500 1000 1500 2000 2500 3000 3500 4000 4500 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 MTS Load (lbf) Displacement (in) S 13

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A 34 Figure A 33 Monolithic specimen A 12, taken from UC Denver pads and tested in the Iosipescu inspired test apparatus. 0 1000 2000 3000 4000 5000 6000 7000 0 0.02 0.04 0.06 0.08 0.1 0.12 MTS Load (lbf) Displacement (in) A 12 (solid)

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A 35 Figure A 34 Monolithic specimen A 13, taken from UC Denver pads and tested in the Iosipescu inspired test apparatus. 0 1000 2000 3000 4000 5000 6000 7000 0 0.02 0.04 0.06 0.08 0.1 0.12 MTS Load (lbf) Displacement (in) A 13 (solid)

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A 36 Figure A 35 Monolithic specimen A 14, taken from UC Denver pads and tested in the Iosipes cu inspired test apparatus. 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 MTS Load (lbf) Displacement (in) A 14 (Solid)

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A 37 Figure A 36 Monolithic specimen A 15, taken from UC Denver pads and tested in the Iosipescu inspired test apparatus. 0 1000 2000 3000 4000 5000 6000 7000 8000 0 0.02 0.04 0.06 0.08 0.1 0.12 MTS Load (lbf) Displacement (in) A 15 (solid)

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A 38 Figure A 37 Monolithic specimen B 10, taken from UC Denver pads and tested in the Iosipescu inspired test apparatus. 0 1000 2000 3000 4000 5000 6000 7000 8000 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 MTS Load (lbf) Displacement (in) B 10 (solid)

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A 39 Figure A 38 Monolithic specimen B 11, taken from UC Denver pads and tested in the Iosipescu inspired test apparatus. 0 1000 2000 3000 4000 5000 6000 7000 0 0.02 0.04 0.06 0.08 0.1 0.12 MTS Load (lbf) Displacement (in) B 11 (solid)

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A 40 Figure A 39 Monolithic specimen B 12), taken from UC Denver pads and tested in the Iosipescu inspired test apparatus. 0 1000 2000 3000 4000 5000 6000 7000 0 0.02 0.04 0.06 0.08 0.1 0.12 MTS Load (lbf) Displacement (in) B 13 (Solid)

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A 41 Figure A 40 Monolithic specimen B 14, taken from UC Denver pads and tested in the Iosipescu inspired test apparatus. 0 1000 2000 3000 4000 5000 6000 7000 0 0.02 0.04 0.06 0.08 0.1 MTS Load (lbf) Displacement (in) B 14 (Solid)

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A 42 Figure A 41 Monolithic specimen R 5, taken from UC Denver p ads and tested in the Iosipescu inspired test apparatus. 0 1000 2000 3000 4000 5000 6000 7000 0 0.02 0.04 0.06 0.08 0.1 0.12 MTS Load (lbf) Displacement (in) R 5 (solid)

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A 43 Figure A 42 Monolithic specimen R 6, taken from UC Denver pads and tested in the Iosipescu inspired test apparatus. 0 1000 2000 3000 4000 5000 6000 0 0.02 0.04 0.06 0.08 0.1 MTS Load (lbf) Displacement (in) R 6 (solid)

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A 44 Figure A 43 Monolithic specimen R 7, taken from UC Denver pads and tested in the Iosipescu inspired test apparatus. 0 1000 2000 3000 4000 5000 6000 0 0.02 0.04 0.06 0.08 0.1 0.12 MTS Load (lbf) Displacement (in) R 7 (Solid)

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A 45 Figure A 44 Monolithic specimen R 8, taken from UC Denver pads and tested in the Iosipescu inspired test apparatus. 0 1000 2000 3000 4000 5000 6000 0 0.02 0.04 0.06 0.08 0.1 0.12 MTS Load (lbf) Displacement (in) R 8 (solid)

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A 46 Figure A 45 Monolithic specimen R 13, taken from UC Denver pads an d tested in the Iosipescu inspired test apparatus. 0 1000 2000 3000 4000 5000 6000 0 0.02 0.04 0.06 0.08 0.1 MTS Load (lbf) Displacement (in) R 13 (solid)

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A 47 Figure A 46 Monolithic specimen R 14, taken from UC Denver pads and tested in the Iosipescu inspired test apparatus. 0 1000 2000 3000 4000 5000 6000 0 0.02 0.04 0.06 0.08 0.1 0.12 MTS Load (lbf) Displacement (in) R 14 (Solid)

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A 48 Figure A 47 Monolithic specimen R 15, taken from UC Denver pads and tested in the Iosipescu inspired test apparatus. 0 1000 2000 3000 4000 5000 6000 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 MTS Load (lbf) Displacement (in) R 15 (Solid)

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A 49 Figure A 48 Monolithic specimen S 9, taken from UC Denver pads and tested in the Iosipescu inspired test apparatus. 0 1000 2000 3000 4000 5000 6000 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 MTS Load (lbf) Displacement (in) S 8 (solid)

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A 50 Figure A 49 Monolithic specimen S 9, taken from UC Denver pads and tested in the Iosipescu inspired test apparatus. 0 1000 2000 3000 4000 5000 6000 7000 0 0.02 0.04 0.06 0.08 0.1 MTS Load (lbf) Displacement (in) S 9 (solid)

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A 51 Figure A 50 Monolithic specimen S 14, taken from UC Denver pads and tested in the Iosipescu inspired test apparatus. 0 1000 2000 3000 4000 5000 6000 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 MTS Load (lbf) Displacement (in) S 14 (solid)

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A 52 Figure A 51 Monolithic specimen S 15, taken from UC Denver pads and teste d in the Iosipescu inspired test apparatus. 0 1000 2000 3000 4000 5000 6000 7000 0 0.02 0.04 0.06 0.08 0.1 MTS Load (lbf) Displacement (in) S 15 (solid)

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A 53 Figure A 52 These cores were extracted from the retaining wall in Longmont and tested in the Iosipescu test fixture . Separate images of the cores were not taken.

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A 54 Figure A 53 Load displacement r elationship for Longmont retaining wall specimen designated as 6 1, tested in Iosipescu inspired test apparatus. Figure A 54 Load displacement relationship for Longmont retaining wall specimen designated as 6 2, tested in Iosipescu inspired test app aratus. 0 500 1000 1500 2000 2500 3000 3500 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 MTS Load (lbf) Displacement (in) Retaining Wall Specimen 6 1 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 0 0.02 0.04 0.06 0.08 0.1 MTS Load (lbf) Displacement (in) Retaining Wall Specimen 6 2

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A 55 Figure A 55 Load displacement relationship for Longmont retaining wall specimen designated as 6 3, tested in Iosipescu inspired test apparatus. Figure A 56 Load displacement relationship for Longmont retaining wall specimen designated as 8 1, tested in Iosipescu inspired test apparatus. 0 500 1000 1500 2000 2500 3000 3500 4000 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 MTS Load (lbf) Displacement (in) Retaining Wall Specimen 6 3 0 500 1000 1500 2000 2500 3000 3500 4000 4500 0 0.02 0.04 0.06 0.08 0.1 MTS Load (lbf) Displacement (in) Retaining Wall Specimen 8 1

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A 56 Figure A 57 Load displacement relationship for Longmont retaining wall specimen designated as 8 2, tested in Iosipescu inspired test apparatus. Figure A 58 Load displacement relationshi p for Longmont retaining wall specimen designated as 8 3, tested in Iosipescu inspired test apparatus. 0 500 1000 1500 2000 2500 3000 3500 4000 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 MTS Load (lbf) Displacement (in) Retaining Wall Specimen 8 2 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 0 0.01 0.02 0.03 0.04 0.05 0.06 MTS Load (lbf) Displacement (in) Retaining Wall Specimen 8 3

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A 57 Figure A 59 Load displacement relationship for Longmont retaining wall specimen designated as 10 1, tested in Iosipescu inspired test apparatus. Figure A 60 Load displacement relationship for Longmont retaining wall specimen designated as 10 2, tested in Iosipescu inspired test apparatus. 0 1000 2000 3000 4000 5000 6000 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 MTS Load (lbf) Displacement (in) Retaining Wall Specimen 10 1 0 1000 2000 3000 4000 5000 6000 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 MTS Load (lbf) Displacement (in) Retaining Wall Specimen 10 2

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A 58 Figure A 61 Load displacement relationship for Longmont retaining wall specimen designated as 10 3, tested in Iosipescu inspired test apparatus. 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 MTS Load (lbf) Displacement (in) Retaining Wall Specimen 10 3

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A 59 The graphs and images that follow provide the raw loading/displacement data for Iosipescu testing of the specimens extracted from the Pultorak pads Figure A 62 L ayered spec imen 1A 1, taken from Pultorak pads and tested in the Iosipescu inspired test apparatus. 0 500 1000 1500 2000 2500 3000 3500 4000 4500 0 0.02 0.04 0.06 0.08 0.1 MTS Load (lbf) Displacement (in) Pultorak 1A 1

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A 60 Figure A 63 La yered specimen 1A 2, taken from Pultorak pads and tested in the Iosipescu inspired test apparatus. 0 500 1000 1500 2000 2500 3000 3500 4000 0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045 MTS Load (lbf) Displacement (in) Pultorak 1A 2

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A 61 Figure A 64 La yered specimen 1A 3, t aken from Pultorak pads and tested in the Iosipescu inspired test apparatus. 0 500 1000 1500 2000 2500 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 MTS Load (lbf) Displacement (in) Pultorak 1A 3

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A 62 Figure A 65 La yered specimen 1A 4, taken from Pultorak pads and tested in the Iosipescu inspired test apparatus. 0 500 1000 1500 2000 2500 3000 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 MTS Load (lbf) Displacement (in) Pultorak 1A 4

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A 63 Figure A 66 La yered specimen 1A 5, taken from P ultorak pads and tested in the Iosipescu inspired test apparatus. 0 500 1000 1500 2000 2500 3000 3500 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 MTS Load (lbf) Displacement (in) Pultorak 1A 5

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A 64 Figure A 67 La yered specimen 1B 1, taken from Pultorak pads and tested in the Iosipescu inspired test apparatus. 0 500 1000 1500 2000 2500 3000 3500 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 MTS Load (lbf) Displacement (in) Pultorak 1B 1

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A 65 Figure A 68 La yered specimen 1B 2, taken from Pultorak pads and tested in the Iosipescu inspired test apparatus. 0 500 1000 1500 2000 2500 3000 3500 4000 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 MTS Load (lbf) Displacement (in) Pultorak 1B 2

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A 66 Figure A 69 Layered specimen 1A 1, taken from Pultorak pads and tested in the Iosipescu inspired test apparatus. 0 500 1000 1500 2000 2500 3000 3500 4000 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 MTS Load (lbf) Displacement (in) Pultorak 1B 3

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A 67 Figure A 70 La yered specimen 2B 3, taken from Pultorak pads and tested in the Iosipescu inspired test apparatus. 0 500 1000 1500 2000 2500 3000 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 MTS Load (lbf) Displacement (in) Pultorak 2B 3

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A 68 Figure A 71 La yered specimen 3A 1, taken from Pultorak pads and tested in the Iosipescu inspired test apparatus. 0 500 1000 1500 2000 2500 3000 3500 4000 4500 0 0.02 0.04 0.06 0.08 0.1 MTS Load (lbf) Displacement (in) Pultorak 3A 1

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A 69 Figure A 72 La yered specimen 3A 2, taken from Pultorak pads and tested in the Iosipescu inspired test apparatus. 0 500 1000 1500 2000 2500 3000 3500 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 MTS Load (lbf) Displacement (in) Pultorak 3A 2

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A 70 Figure A 73 La yered specimen 3B 1, taken from Pultorak pads and tested in the Iosipescu inspired test apparatus. 0 500 1000 1500 2000 2500 3000 3500 4000 4500 0 0.02 0.04 0.06 0.08 0.1 MTS Load (lbf) Displacement (in) Pultorak 3B 1

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A 71 Figure A 74 La yered specimen 3B 2, taken from Pultorak pads and tested in the Iosipescu inspired test ap paratus. 0 500 1000 1500 2000 2500 3000 3500 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 MTS Load (lbf) Displacement (in) Pultorak 3B 2

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A 72 Figure A 75 La yered specimen 3B 3, taken from Pultorak pads and tested in the Iosipescu inspired test apparatus. 0 500 1000 1500 2000 2500 3000 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 MTS Load (lbf) Displacement (in) Pultorak 3B 3

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A 73 The images and charts that follow are from guillotine tests on overlay cores Figure A 76 Acid etch la yered specimen A 10, tested in guillotine device. 0 1000 2000 3000 4000 5000 6000 7000 0 0.005 0.01 0.015 0.02 0.025 MTS Load (lbf) Displacement (in) Guillotine A 10

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A 74 Figure A 77 Acid etch la yered specimen A 11, tested in guillotine device. 0 200 400 600 800 1000 1200 1400 1600 0 0.005 0.01 0.015 0.02 0.025 MTS Load (lbf) Displacement (in) Guillotine A 11

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A 75 Figure A 78 Bush hammer la yered specimen B 6 , tested in guillotine device. -500 0 500 1000 1500 2000 2500 3000 3500 4000 0 0.01 0.02 0.03 0.04 0.05 0.06 MTS Load (lbf) Displacement (in) Guillotine B 6

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A 76 Figure A 79 Bush hammer la yered s pecimen B 7, tested in guillotine device; failure on opposite side of interface corresponds to chart above 0 1000 2000 3000 4000 5000 6000 7000 0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 MTS Load (lbf) Displacement (in) Guillotine B 7

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A 77 Figure A 80 Specimen B 7 after second test. Breakage at interface occurred at first peak in chart 0 500 1000 1500 2000 2500 3000 3500 4000 4500 0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 MTS Load (lbf) Displacement (in) Guillotine B 7 Second Run

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A 78 Figure A 81 Raked la yered specim en R 17 , tested in guillotine device. 0 1000 2000 3000 4000 5000 6000 7000 0 0.01 0.02 0.03 0.04 0.05 0.06 MTS Load (lbf) Displacement (in) Guillotine R 17

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A 79 Figure A 82 Raked la yered specimen R 18 , tested in guillotine device. 0 1000 2000 3000 4000 5000 6000 0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 MTS Load (lbf) Displacement (in) Guillotine R 18

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A 80 Figure A 83 Smooth l ayered specimen S 9 , tested in guillotine device. 0 1000 2000 3000 4000 5000 6000 7000 0 0.01 0.02 0.03 0.04 0.05 MTS Load (lbf) Displacement (in) Guillotine S 9

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A 81 Figure A 84 Smooth la yered specimen S 10 , test ed in guillotine device. 0 1000 2000 3000 4000 5000 6000 7000 0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 MTS Load (lbf) Displacement (in) Guillotine S 10