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Beneficial use of ultra-fine fly ash and silica fume for concrete strength, durability, and restrained shrinkage

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Title:
Beneficial use of ultra-fine fly ash and silica fume for concrete strength, durability, and restrained shrinkage
Creator:
Merritt, Andrew William
Publication Date:
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English
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xvii, 119 leaves : ; 28 cm

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Subjects / Keywords:
Fly ash ( lcsh )
Concrete ( lcsh )
Silica fume ( lcsh )
Concrete ( fast )
Fly ash ( fast )
Silica fume ( fast )
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bibliography ( marcgt )
theses ( marcgt )
non-fiction ( marcgt )

Notes

Bibliography:
Includes bibliographical references (leaves 118-119).
General Note:
Department of Civil Engineering
Statement of Responsibility:
by Andrew William Merritt.

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|University of Colorado Denver
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|Auraria Library
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All applicable rights reserved by the source institution and holding location.
Resource Identifier:
710044125 ( OCLC )
ocn710044125
Classification:
LD1193.E53 2010m M47 ( lcc )

Full Text
BENEFICIAL USE OF ULTRA-FINE FLY ASH AND SILICA FUME FOR
CONCRETE STRENGTH, DURABILITY, AND RESTRAINED SHRINKAGE
By
Andrew William Merritt
B.S., North Dakota State University, 2006
A thesis submitted to the
University of Colorado Denver
in partial fulfillment
of the requirements for the degree of
Master of Science
Civil Engineering
2010


This thesis for the Master of Civil Engineering
degree by
Andrew William Merritt
has been approved
by
Stephan A. Durham, Ph.D., P.E.
Kevin L. Rens, Ph.D., P.E.
Chengyu Li, Ph.D., P.E.
Date


Merritt, Andrew William (M.S., Civil Engineering)
Beneficial use of Ultra-Fine Fly Ash and Silica Fume for Concrete Strength,
Durability, and Restrain Shrinkage
Thesis directed by Assistant Professor Stephan A. Durham
ABSTRACT
Research has shown that ultra-fine fly ash (UFFA) can be used as a substitute
to silica fume and provide many of the desirable properties that silica fume gives to
concrete.
Silica fume has been used in concrete as a supplementary cementitious
material (SCM) to increase compressive strength and durability and to decrease
permeability for many years. Though, silica fume improves many concrete properties
it causes many undesirable effects to the concrete mixtures. Silica fume increase
water demand, causes the fresh concrete to be very sticky and difficult to finish, and
increases concrete shrinkage.
UFFA has shown to increase concrete compressive strength and durability and
decrease permeability without increasing water demand or shrinkage. In fact, UFFA
increases concrete workability and decreases shrinkage. However, past research has
shown that a greater volume of UFFA is required to provide the same positive benefits
m


of silica fume. A majority of this research was completed on concrete mixtures with a
higher w/cm (water-to-cementitious ratio).
This study examined the benefits of using UFFA and silica fume in concrete
mixtures at low w/cm and in a CDOT Class H bridge deck mixture. This study
examined and compared the effects of UFFA and silica fume on the concrete
properties of slump, compressive strength, concrete permeability, freeze/thaw
durability, and restrained shrinkage in these mixtures.
Results from this study demonstrate that at low w/c mixtures, the UFFA
performed equal to or greater than the silica fume mixtures in compressive strength.
However, the silica fume mixtures out performed the UFFA mixture in permeability
and durability. The concrete mixture containing UFFA experienced less shrinkage
than the silica fume in the CDOT Class H Mixture.
This abstract accurately represents the content of the candidates thesis. I recommend
its publication.
Signed
Stephan A. Durham, Ph.D., P.E.
IV


DEDICATION
I dedicate this thesis to my family and friends for their never ending support during the
time while I was completing this thesis. To Nikky for your understanding and support
throughout this entire process of pursuing a master degree. Also, to my parents for
their endless support and giving me the desire to learn.
v


ACKNOWLEDGEMENT
I would like to thank my advisor, Dr. Stephan Durham, for his support and guidance
throughout my research. In addition I would like to thank Dr Kevin Rens and Dr
Chengyu Li for their assistance in my research. Thank You Mr. Adam Kardos for all
of your help in the laboratory and batching and Mr. Robert Cavaliero I greatly
appreciate all your help batching concrete mixtures and assistance with the AASHTO
P334 shrinkage test.
vi


TABLE OF CONTENTS
Figures......................................................................xiii
Tables.......................................................................xv
Chapter
1. Introduction................................................................1
1.1 Research Objective.........................................................2
2. Background..................................................................4
2.1 Research Interest..........................................................4
2.2 Bureau of Reclamation High Strength Mix Design Summary....................4
2.3 Comparison of Ultra-Fine Fly Ash and Silica Fume in Concrete Mixtures.....4
2.4 Evaluation of Crack Resistant Concrete for Colorado Bridge Decks..........6
3. Literature Review...........................................................8
3.1 Concrete Properties........................................................8
3.1.1 Fresh Concrete Properties................................................8
3.1.1.1 Workability............................................................8
3.1.1.2 Air Content............................................................8
3.1.2 Hardened Concrete Properties...........................................9
3.1.2.1 Compressive Strength...................................................9
Vll


3.1.2.2 Permeability............................................................10
3.1.2.3 Durability..............................................................11
3.1.2.4 Shrinkage...............................................................12
3.2 Supplementary Cementitious Materials.......................................13
3.2.1 Ultra-Fine Fly Ash.......................................................13
3.2.1.1 Fresh Concrete Properties...............................................15
3.2.1.1.1 Slump.................................................................15
3.2.1.2 Hardened Concrete Properties............................................15
3.2.1.2.1 Compressive Strength..................................................15
3.2.1.2.2 Permeability..........................................................16
3.2.1.2.3 Shrinkage and Restrained Shrinkage....................................17
3.2.2 Silica Fume.............................................................17
3.2.2.1 Fresh Concrete Properties...............................................18
3.2.2.1.1 Workability...........................................................18
3.2.2.2 Hardened Concrete Properties............................................19
3.2.2.2.1 Compressive Strength..................................................19
3.2.2.2.2 Permeability..........................................................19
3.2.2.4 Restrained Shrinkage....................................................20
3.3 CDOT Class H Mixture..................................................20
viii
3.3.1 History
21


3.3.2 UCD Finding/Recommendations............................................22
3.4 Summary.................................................................23
4. Problem Statement.........................................................25
4.1 Statement................................................................25
5. Research Plan.............................................................29
5.1 Preface..................................................................29
5.2 Materials Used..........................................................29
5.2.1 Coarse Aggregate.......................................................29
5.2.2 Fine Aggregate.........................................................31
5.2.3 Portland Cement........................................................31
5.2.4 Fly Ash................................................................32
5.2.5 Ultra-Fine Fly Ash.....................................................33
5.2.6 Silica Fume............................................................34
5.2.7 Chemical Admixtures....................................................35
5.2.7.1 High Range Water Reducing Admixture..................................35
5.2.7.2 Air-Entraining Admixture.............................................35
5.3 Mixture Designs..........................................................36
5.3.1 Phase 1................................................................36
5.3.2 Phase II...............................................................37
5.4 Method for Testing Concrete Properties..................................40
ix


5.4.1 Fresh Concrete Properties................................................40
5.4.2 Hardened Concrete Properties.............................................41
5.4.2.1 Compressive Strength....................................................42
5.4.2.2 Rapid Chloride Ion Permeability.........................................42
5.4.2.3 Freeze-Thaw Durability..................................................45
5.4.2.4 Restrained Shrinkage....................................................47
5.5 Curing......................................................................49
6. Phase I Experimental Results.................................................50
6.1 Fresh Concrete Properties...................................................50
6.1.1.1 Slump...................................................................50
6.1.1.2 Concrete Temperature....................................................52
6.1.1.3 Air Content.............................................................54
6.1.1.4 Unit Weight.............................................................55
6.1.2 Hardened Concrete Properties.............................................56
6.1.2.1 Compressive Strength....................................................57
6.1.2.2 Permeability............................................................63
6.1.2.3 Durability..............................................................67
7. Phase II Experimental Results................................................81
7.1 Fresh Concrete Properties...................................................81
7.1.1 Slump....................................................................81
x


7.1.2 Concrete Temperature....................................................82
7.1.3 Air Content.............................................................84
7.1.4 Unit Weight.............................................................85
7.2 Hardened Concrete Properties.............................................85
7.2.1 Compressive Strength....................................................86
7.2.2 Permeability............................................................89
7.2.3 Restrained Shrinkage....................................................92
8. Conclusions and Recommendations............................................98
8.1 Phase 1...................................................................98
8.1.1 Fresh Concrete Properties...............................................98
8.1.1.1 Slump.................................................................98
8.1.1.2 Concrete Temperature..................................................99
8.1.1.3 Air Content...........................................................99
8.1.1.4 Unit Weight...........................................................99
8.1.2 Hardened Concrete Properties............................................99
8.1.2.1 Compressive Strength..................................................99
8.1.2.2 Permeability.........................................................100
8.1.2.3 Durability...........................................................101
8.2 Phase II................................................................101
8.2.1 Fresh Concrete Properties..............................................101
xi


8.2.1.2 Slump.........................................................101
8.2.1.3 Concrete Temperature..........................................101
8.2.1.3 Air Content...................................................102
8.2.1.4 Unit Weight...................................................102
8.2.2 Hardened Concrete Properties....................................102
8.2.2.1 Compressive Strength..........................................102
8.2.2.2 Permeability..................................................103
8.2.2.3 Shrinkage.....................................................103
8.3 Summary of Results............................................103
8.4 Recommendations...................................................104
APPENDIX A............................................................106
BIBLIOGRAPHY..........................................................118
xii


LIST OF FIGURES
Figure
3.1 Microscopic View of UFFA..........................................13
3.2 Microscopic View of Silica Fume...................................18
5.1 RCIP Test.........................................................44
5.2 Freeze/Thaw Chamber...............................................46
5.3 Specimen being tested for the Fundamental Transverse Frequency....47
5.4 Photograph of Restrained Shrinkage Ring...........................48
6.1 Measures Slump and Required HRWRA.................................51
6.2 Phase 1 Concrete Temperature......................................53
6.3 Measure Air Content...............................................55
6.4 Example of a Concrete Cylinder being Tested.......................58
6.5 Compressive Strength vs. Time.....................................60
6.6 Percentage of 56 Day Compressive Strength.........................62
6.7 UFFA Compressive Strength Percent Difference Compared to Silica Fume at
56 days................................................................63
xm


6.8 Permeability Results...................................................65
6.9 Silica Fume Permeability Values as a Percentage of UFFA Permeability
Values.................................................................67
6.10 Relative Dynamic Modulus of Elasticity vs. Cycles......................76
6.11 Durability Factor......................................................79
6.12 Percentage Increase in Silica Fume Durability Compared to UFFA
Durability.............................................................80
7.1 Measure Slump..........................................................82
7.2 Concrete Temperature and Ambient Temperature...........................83
7.3 Measured Air Content...................................................84
7.4 Compressive Strength vs. Time..........................................87
7.5 Percentage of 56 Day Compressive Strength..............................89
7.6 Phase II Permeability Results..........................................91
7.7 Micro-Strain vs. Time..................................................93
7.8 Percent of Final Strain................................................95
7.9 UFFA Strain as a Percent of Silica Fume Strain.........................96
xiv


LIST OF TABLES
Table
3.1 UFFA Properties Compared to AASHTO M 321-04 Requirements..............14
5.1 Coarse Aggregate Sieve Analysis Compared to ASTM C33 Size 57 & 67....30
5.2 Fine Aggregate Sieve Analysis Compared to ASTM C33.......................31
5.3 Physical and Chemical Properties of Portland Cement.....................32
5.4 Physical and Chemical Properties of Fly Ash.............................33
5.5 Physical and Chemical Properties of UFFA................................34
5.6 Physical and Chemical Properties of Silica Fume.........................35
5.7 Phase 1 Mixture Proportions..............................................37
5.8 CDOT Class H Mixture Proportion Limits and Ranges....................38
5.9 CDOT Class H Mixture Property Limits and Ranges.......................38
5.10 Phase II Mixture Proportions.............................................40
5.11 Fresh Concrete Properties and Methods....................................41
5.12 Hardened Concrete Properties and Methods.................................41
5.13 Chloride Ion Penetrability Based on Charge Passed........................45
xv


6.1 Phase 1 Fresh Concrete Properties......................................50
6.2 Measured Unit Weight Compared to Predicted Unit Weight.................56
6.3 Average Ultimate Compressive Load......................................58
6.4 Average Ultimate Compressive Stress....................................59
6.5 Permeability Results...................................................64
6.6 0.34 UFFA Average Freeze/Thaw Results..................................68
6.7 0.34 SF Average Freeze/Thaw Results....................................69
6.8 0.29 UFFA Average Freeze/Thaw Results..................................69
6.9 0.29 SF Average Freeze/Thaw Results....................................70
6.10 0.27 UFFA Average Freeze/Thaw Results..................................70
6.11 0.27 SF Average Freeze/Thaw Results....................................71
6.12 0.34 UFFA Relative Dynamic Modulus of Elasticity.......................72
6.13 0.34 SF Relative Dynamic Modulus of Elasticity.........................73
6.14 0.29 UFFA Relative Dynamic Modulus of Elasticity.......................73
6.15 0.29 SF Relative Dynamic Modulus of Elasticity.........................74
6.16 0.27 UFFA Relative Dynamic Modulus of Elasticity.......................74
xvi


6.17 0.27 SF Relative Dynamic Modulus of Elasticity..........................75
6.18 Phase I Durability Factors..............................................77
7.1 Phase II Fresh Concrete Properties......................................81
7.2 Predicted Unit Weights Compared to Measured Unit Weights................85
7.3 Average Ultimate Compressive Load.......................................86
7.4 Average Compressive Stress..............................................86
7.5 Phase II Permeability Results Coulombs Passed...........................90
7.6 Average Strain Reading..................................................94
XVII


1. Introduction
This thesis examines and compares the effects of ultra-fine fly ash (UFFA) and
silica fume as partial replacements of portland cement at low water-to- cementitious
ratios (w/cm). Research had been completed comparing the effect of these two
supplemental cementitious materials on concrete, though much of the research was
completed at higher w/cm. Findings have mostly shown that an increase in the amount
of UFFA or lowering the w/cm ratio was needed to find comparable results of
compressive strength, permeability and durability. Lowering the w/cm of concrete
containing UFFA is not difficult because UFFA has a significant affect on the water
demand of concrete. UFFA has shown to reduce the water demand and increase the
workability of concrete not only when compared to concrete containing silica fume
but with concrete containing only portland cement.
A recent study by the Bureau of Reclamation (BOR) has shown that mixtures
containing UFFA show similar compressive strength to mixtures containing silica
fume at low w/cm with all other materials the same.
This research was completed in two phases. Phase I of this research examined
the concrete properties on mixtures with w/cm of 0.34, 0.29, and 0.27 and equal
amounts of 50 lbs/yd3 (29.7 kg/m3) either UFFA or silica fume. The fresh and
hardened concrete properties examined in this phase included slump, air content, unit
1


weight, concrete temperature, compressive strength, permeability and freeze/thaw
durability. The objective of Phase I was to determine if the trends that are shown at
higher w/cm continue at lower w/cm or if the use of UFFA in concrete mixtures is
more beneficial and similar to concrete mixtures containing silica fume. Compressive
strength results from this study were compared with the findings from the BOR. The
BOR did not perform permeability and freeze/thaw durability tests on concrete
mixtures containing UFFA and silica fume..
Phase II of this thesis compared the effects of UFFA and silica fume on
concrete restrained shrinkage. Two concrete mixtures meeting the Colorado
Department of Transportation (CDOT) Class H concrete specification for bridge deck
concrete mixtures were examined for restrained shrinkage. The 2009 Class H mixture
recommendations established by the University of Colorado were included in the
design [Cavaliero, 2009]. The two mixtures included a cement replacement of either
5% UFFA or silica fume. In addition to restrained shrinkage other testing was
performed on the mixtures, concrete slump, air content, unit weight, concrete
temperature, compressive strength, and permeability were examined for each mixture.
1.1 Research Objective
The primary objective of this thesis was to evaluate the beneficial use of UFFA
and silica fume for concrete strength, durability, and restrained shrinkage. The
2


results of this thesis will provide the concrete industry with the necessary information
to take advantage of UFFA in concrete construction with the benefit of producing
stronger and more durable concrete mixtures.
This thesis compares the effect of UFFA and silica fume on concrete with low
w/cm. The objective is to examine whether trends shown in past research will continue
at the lower w/cm or will new trends be shown as suggested in the BOR study. In
addition, this research examined a comparison of UFFA and silica fume on
compressive strength, permeability and restrained shrinkage for the CDOT Class H
mixture. The mixtures were designed using the newly recommended values for w/cm
and allowable fly ash replacement [Cavaliero, 2009]. The main focus of this phase of
the research is to examine the effects of UFFA and silica fume on restrained
shrinkage.
3


2. Background
2.1 Research Interest
2.2 Bureau of Reclamation High Strength Mix Design Summary
Currently, the BOR is conducting a study for a high strength concrete design
that will be used for spillways for their dams. The specification for the high strength
concrete was to obtain 8000 psi (31Mpa) compressive strength at 28 days and have a
slump of 6 inches. The BOR is examining concrete mixtures with w/cm of 0.34, 0.29,
and 0.27 and comparing the effects of silica fume and UFFA on the concrete
compressive strength. The amount of silica fume and UFFA was held constant at 50
j i
lb/yd (29.7 kg/m ) regardless of the cement content. They also examined two
different maximum size aggregates; they examined 3A and 1 VF maximum coarse
aggregate size.
In a draft report by the BOR their studies have shown that the compressive
strength of the UFFA mixtures out performed mixtures containing silica fume. This is
contrary to most other research that has shown a greater amount of UFFA is needed to
obtain similar compressive strengths than concrete mixtures containing silica fume.
2.3 Comparison of Ultra-Fine Fly Ash and Silica Fume in Concrete Mixtures
In the thesis Comparison of Ultra-Fine Fly Ash and Silica Fume in Concrete
Mixtures, Ruybal compared concrete properties for mixtures containing UFFA and
4


silica fume. Ruybal examined concrete compressive strength, permeability, and
freeze/thaw resistance.
This research examined six concrete mixtures containing partial replacements
of either UFFA or silica fume. The UFFA mixtures that were examined were produced
with a w/cm of 0.38 with both 5% and 10% replacement of UFFA, w/cm of 0.42 with
both 5% and 10% replacement of UFFA, and two mixtures containing 4% silica fume
with w/cm of both 0.38 and 0.42.
The 0.42 w/cm silica fume mixture showed higher compressive strength than
both of the 0.42 UFFA mixtures. The UFFA mixtures had approximately 75% of the
compressive strength of the silica fume mixture. In addition, the amount of UFFA
didnt seem to have a great affect on the compressive strength. However, on the 0.38
mixtures the UFFA mixtures compared more favorably to the silica fume mixture in
compressive strength. The 10% replacement of UFFA showed the greatest 56 day
compressive strength, it was 113% of the silica fume mixtures compressive strength.
The 5% UFFA mixture showed very similar compressive strengths to the silica fume
mixture.
The rapid chloride ion permeability was tested on these mixtures. The
permeability was tested at 28 and 56 days of age. Silica fume showed to be more
5


effective in reducing the permeability of the concrete at 56 days. However, the
permeability at 28 days after batching seemed to be comparable.
Freeze/Thaw durability was also tested on these mixtures. The results showed
that the silica fume mixtures out performed the UFFA mixtures. The silica fume
mixture showed to better resist freezing and thawing cycles. There was no air
entraining admixture used in the mixture designs. In addition, concrete shrinkage was
not tested as part of this research.
The major findings from this research were that for concrete mixtures with
w/cm between 0.38 and 0.42, cement replacement rates with UFFA should be twice
the replacement rate with silica fume in order to obtain the same level of performance.
2.4 Evaluation of Crack Resistant Concrete for Colorado Bridge Decks
The objective of the thesis Evaluation of Crack Resistant Concrete for
Colorado Bridge Decks by Mr. Robert Cavaliero was to develop a concrete mixture
that is more resistant to cracking than the current CDOT Class H and HT mixtures.
This research examined 11 different concrete mixtures. These included two
mixtures that were currently within the CDOT specification and nine other mixtures to
examine the effects of higher w/cm, different types of cement, lower cement contents,
higher replacements SCMs and chemical admixtures. The concrete fresh properties
that were tested on these mixtures were slump, air content, unit weight and concrete
6


temperature. The hardened concrete properties that were tested were compressive
strength, permeability, freeze/thaw durability, and restrained shrinkage.
Two different types of portland cement were examined in the research type II
and type G. The cement content in the mixtures ranged from 6.0 to 6.8 sacks which
equates to 564 lbs/yd3 to 640 lbs/yd3 (335 kg/m2to 380 kg/m2). The cement
replacement with class F fly ash ranged from 16% to 30%. A mixture with a cement
replacement with 50% of blast furnace slag was examined. The cement replacement
with silica fume ranged from 3.5% to 5%. Shrinkage reducing and set retarding
chemical admixtures were also examined in this research.
Increasing the w/cm to 0.44, increasing replacement of fly ash to 30% and
lowering the cement content was beneficial in decreasing the strain in the concrete
mixtures. Lowering the cement content in the mixture without any SCMs also
appeared to be beneficial. A high dosage of the shrinkage reducing admixture showed
to greatly decrease and rate and over all shrinkage of the mixture, while maintaining
the compressive strength and permeability properties of the mixture.
7


3. Literature Review
3.1 Concrete Properties
3.1.1 Fresh Concrete Properties
3.1.1.1 Workability
The ease of placing, consolidation, and finishing freshly mixed concrete and
the degree to which it resists segregation is called workability (PCA, 2002). The
amount of workability has a major affect on the labor cost of placing concrete and the
effectiveness of the concrete properties. If the concrete is to thick the concrete may
be difficult to transport, place, consolidate, or finish causing the cost of these to
increase due to the increased labor that would be involved. Where as if the concrete is
to soupy the concrete may segregate, causing the materials within the concrete to
separate. Segregation may cause the concrete not to perform as expected. One method
to measure workability is the slump test. The slump test consists of filling a cone
shaped mold with fresh concrete, then slowly lifting the mold and measuring the
vertical displacement of the concrete. The amount of displacement is the slump.
3.1.1.2 Air Content
The air content is the amount of air that is either entrapped or entrained within
the concrete as a percentage of volume. Air content has a great effect on both fresh
and hardened properties. The most notable effect of air content in concrete is its effect
8


on compressive strength. The greater the air content the less compressive strength.
Approximately every 1% increase in air content equates to a reduction of 5% in
compressive strength (Mindess, et. al., 2003).
3.1.2 Hardened Concrete Properties
3.1.2.1 Compressive Strength
Compressive strength is the amount of compressive load or compressive stress
that a concrete sample can be subjected to prior to failure. The concrete compressive
strength was determined per the standard ASTM C 39.
Many factors can affect the compressive strength of concrete. Water-to-cement
ratio, cement content, age, or SCMs are a few that can affect concrete compressive
strength.
The w/cm has the greatest effect on the concrete compressive strength. There is
an inverse relationship between the w/cm and compressive strength. As the w/cm
decreases the concrete compressive strength increases. The increase in compressive
strength is cause by the decreasing volume of capillary pores in the hardened concrete
as the w/cm decreases (Mindess, et. al., 2003). The reduced amount of capillary pores
in a cement paste causes the paste to be denser and a more solid structure.
The cement content of a concrete mixture has an effect on the compressive
strength of a concrete mixture. The compressive strength increases as the cement
9


content increases. However, the increasing cement content has a point of diminishing
returns. The increased surface area obtain at high cement contents ultimately requires
a higher water content (Mindess, et. ah, 2003).
SCMs affect the compressive strength of concrete in many different ways. Fly
ash, UFFA and silica fume all increase the compressive strength of concrete. These
SCM react with calcium hydroxide (CH) to create calcium silicate hydrate (C-S-H)
that leads to a more homogenous microstructure (Mindess, et. ah, 2003). The C-S-H
has a lower specific gravity than CH, hence a decrease in the porosity and pore size of
the concrete paste (Mindess, et. ah, 2003). Some of the finer SCMs can also pack into
the voids between the other larger particles within the cement paste.
3.1.2.2 Permeability
Permeability is the ability of concrete to resist penetration by water or other
substances (liquid, gas, or ions) (PCA, 2002). The permeability is affected by the
w/cm, SCMs, degree of cement hydration, length of moist curing, and the permeability
of the aggregate. The w/c has a great affect on the permeability of the concrete. As the
w/c ratio decreases, the porosity of the paste decreases and the concrete becomes more
impermeable (Mindess et. al, 2003). The amount and type of SCM has a large affect
on the permeability of the concrete mixture. This is due to the reduction in both total
10


porosity and pore size. In addition, the amount of calcium hydroxide present in the
paste is decreased as a result of the pozolanic reaction.
3.1.2.3 Durability
The durability of concrete is the ability of concrete to resist weathering action,
chemical attack, and abrasion while maintaining its desired engineering properties
(PCA, 2002). Durability can be affected by w/c, air content, concrete ingredients, and
mixture proportions.
Concrete permeability and air content both have an affect on the durability of
the concrete mixture. As the permeability of a mixture decreases the durability
increases. The reason for the increase in durability as the permeability decreases is
because if the water cannot enter the concrete the effects of freezing and thawing are
reduced. In addition, the decrease in permeability reduces the rate at which aggressive
chemicals can enter the concrete (Mindess et. al, 2003). The increase in the concrete
air content up to approximately 9% will increase the durability of the concrete.
Beyond 9% air content, the concrete becomes too weak as a result of the decrease in
compressive strength. The air content provides empty space within the paste to which
the excess water can move and freeze without damage.
11


3.1.2.4 Shrinkage
Shrinkage is a paste property in concrete and the aggregate has a restraining
influence in the volume changes that take place within the cement paste (Mindess et.
al, 2003). There are two major types of concrete shrinkage; plastic and drying
shrinkage. Plastic shrinkage is the volume change of the fresh concrete as a result of
rapid evaporation of the bleedwater from the concrete surface. Drying shrinkage is the
volume change in hardened concrete as a result of water loss over time.
Plastic shrinkage occurs in fresh concrete after the concrete has been placed
and appears mostly on horizontal surfaces (PCA, 2002). Plastic shrinkage is caused
by the loss of water on the surface of fresh concrete. The loss of water if not prevented
plastic shrinkage can cause cracking in the concrete.
Drying shrinkage represents the strain caused by the loss of water from the
hardened concrete (Mindess et. al, 2003). The water content has the biggest impact on
the amount of drying shrinkage. The greater the water content, the greater amount of
drying shrinkage (PCA, 2002). High fresh concrete temperatures, high amounts of fine
aggregate, small sized coarse aggregate, and high cement contents will increase
shrinkage (PCA, 2002).
12


3.2 Supplementary Cementitious Materials
3.2.1 Ultra-Fine Fly Ash
UFFA is a product that is produced from the smallest particles in fly ash.
UFFA is much finer than standard fly ash It has an average particle diameter of
approximately 3.0pm (micro meters) where standard fly ash has an average particle
size of 25pm. 90% of the UFFA particles have a diameter of less than 7pm (Obla,
2003).. According to ACI 232.2R-03 Use of Fly Ash in Concrete, the fineness within a
particular source is a relatively consistent indicator of fly ash performance in concrete
and that performance improves with increased fineness. Figure 3.1 show microscopic
view of UFFA.
13


UFFA is considered a high-reactivity pozzolan based on the requirements in
AASHTO Designation M 321-04. The chemical and physical requirements for high-
reactivity pozzolans are compared to the UFFA properties in Table 3.1. The chemical
and physical properties of the UFFA are from Research Summary Phase 1 March
1999 published by Boral Material Technologies.
Table 3.1: UFFA Properties Compared to AASHTO M 321-04 Requirements
Chemical Properties AASHTO Requirement UFFA
Reactive Oxides (Si02+A1203+Fe203) % > 75.0 79.31
Sulfur Trioxide (S03) % <3.0 0.89
Loss in Ignition % <6.0 0.14
Moisture Content % <3.0 0.10
Physical Properties
Strength Activity at 7 Days % > 85.0 100.81
Percent Retained on the No 325 Sieve (45pm) < 10.0 *
* 90% of the U
'FA particles have a diameter less than 7pm. Hence UFFA meets the
requirement
14


UFFA has been approved for use by the department of transportations of
Alabama, Florida, Georgia, Illinois, Nevada, Ohio and the City of Los Angeles.
3.2.1.1 Fresh Concrete Properties
3.2.1.1.1 Slump
Concrete containing UFFA has shown an increase in concrete workability.
Concrete containing 8%, 12%, or 16% replacements of UFFA progressively needed
less High Range Water Reducing Admixture (HRWRA) to produce comparable
slumps to a mixture using 100% portland cement (Obla, 2003). The decrease in water
demand is caused by the spherical shape acting like micro-ball bearings to reduce
friction (Boral Material Technologies, 2001).
3.2.1.2 Hardened Concrete Properties
3.2.1.2.1 Compressive Strength
Research has shown that UFFA increases the concrete compressive strength.
The increased compressive strength is due to the ability of UFFA to fill in the voids
within the mixture; the smaller particle size increases the pozzolanic reaction in the
concrete, and the ability of UFFA to reduce the water content because of the increased
workability (Boral Material Technologies, 2001). The combined effects of these
provide the ability to increase the compressive strength to comparable strengths of
concrete containing silica fume. However, most research has shown that greater
15


replacement of UFFA or a lower w/cm was required to show comparable strengths to
silica fume mixtures (Obla, 2003).
3.2.1.2.2 Permeability
It is known that the addition of fly ash into concrete mixtures will reduce the
permeability of the mixture. Fly ash is especially effective at reducing permeability at
high volume replacements. This was shown in a study completed by the Federal
Highway Administration where a concrete mixture containing greater than 50%
replacement of fly ash had rapid chloride permeability values of 500-2000 coulombs
(low to very low permeability) at 28 days of age and 200-700 coulombs (very low) at
90 days.
The smaller particles in UFFA appear to dramatically decrease the
permeability of the concrete mixtures without the need of high volume replacements.
The same study by the Federal Highway Administration examined the rapid chloride
permeability of mixtures containing 8% and 12% UFFA. The 8% mixture had
permeability values of 857 coulombs (very low) at 28 days and 418 coulombs (very
low) at 90 days of age. The 12% mixture had permeability values of 707 coulombs
(very low) at 28 days and 314 coulombs (very low) at 90 days of age.
The mixtures containing UFFA did not require the volume of the SCM as the
standard fly ash mixtures did to obtain similar permeability results.
16


3.2.1.2.3 Shrinkage and Restrained Shrinkage
It has been shown that concrete containing UFFA has less shrinkage than
concrete containing only portland cement or concrete containing silica fume.
Restrained shrinkage testing by Obla in Properties of Concrete Containing Ultra-Fine
Fly Ash reported that cracking didnt occur in the UFFA mixture until an average of
12.3 days where as the control (portland cement) and the silica fume mixtures cracked
on an average of 10 and 5.3 days respectively.
3.2.2 Silica Fume
Silica fume is a very fine noncrystalline silica produced in electric arc furnaces
as a by-product of the production of elemental silicon or alloys containing silicon
(ACI 116R-06). The particle size of silica fume is much smaller than other
supplementary cementitious materials. The average particle diameter is 0.1pm to
0.2pm with a surface area of 20,000 m2/kg. Figure 3.2 shows a microscopic view of
silica fume.
17


Figure 3.2: Microscopic View of Silica Fume
3.2.2.1 Fresh Concrete Properties
3.2.2.1.1 Workability
Silica fume has a negative effect on the workability of a concrete mixture.
Concrete containing silica fume has increased water demand. This is due to the large
surface area of the silica fume (ACI 234R-06). The increased water demand can be
overcome with the use of a water reducing admixture.
According to ACI 234R-06 concrete containing silica fume is more cohesive
than concrete without silica fume. This causes the concrete to become sticky and
difficult to finish. The stickiness increases as the amount of silica fume increases. It
has been shown that an increase in the initial slump of 2 inches is needed to maintain
the same apparent workability (ACI 234R-06)
18


3.2.2.2 Hardened Concrete Properties
3.2.2.2.1 Compressive Strength
Silica fume has been used for many years to make high strength concrete.
Silica fume is a very reactive pozzolan that along with its very small particle size
makes it a very effective admixture to use when making high strength concrete. Silica
fume increases the concrete compressive strength by decreasing the large pores,
packing within the paste-aggregate transition zone, and chemical composition. Silica
fume decreases the amount of large pores creating a more homogeneous pore
structure. Silica fumes small particle size gives it the ability to pack into voids around
the aggregate that are left behind by the aggregate, portland cement and other SCM. In
addition, silica fume consumes much of the calcium hydroxide to form calcium-
silicate hydrate through the pozolanic reaction (ACI 234R-06)
3.2.2.2.2 Permeability
Silica fume is very effective in reducing the permeability of concrete mixtures.
Using a 5% cement replacement with silica fume was more effective than reducing the
w/c from 0.50 to 0.40 (ACI 116R-06). In addition, this study showed that as the
amount of silica fume increased the permeability decreased. ASTM 1202 C (Rapid
Chloride ion Permeability) was used in determining the results above. The reduction
19


of permeability in concrete containing silica fume is accredited to the reduction of the
pore structure that is provided with the addition of silica fume.
3.2.2.4 Restrained Shrinkage
The amount of silica fume replacement has shown to have a proportional effect
on the amount of restrained shrinkage. Shrinkage Cracking of High-Strength Concrete
by Wiegrink showed that as the amount of silica fume was increased the earlier the
specimen cracked and the greater width the crack had at 90 days of shrinkage. The
cracks on the mixtures with the higher replacements of silica fume seemed to increase
the width much faster than the mixtures with less or no silica fume.
3.3 CDOT Class H Mixture
The CDOT Standard Specification for Road and Bridge Construction was
revised in 2003 to include two new concrete mixture designs Class H and Class HT.
The CDOT Class H mixture is a concrete mixture that is used for bare concrete bridge
decks that will not receive a waterproofing membrane (Xi et. al, 2003). CDOT Class H
concrete was developed to be resistant to concrete shrinkage. The specification for a
CDOT class H mixture is:
w/cm must be between 0.38 and 0.42
The field compressive strength at 56 days must exceed 4500 psi (31 Mpa)
20


The laboratory compressive strength at 56 days must exceed 5175 psi
(35.7Mpa)
Air content must be between 5 and 8%
Rapid Chloride Ion Permeability must be below 2000 Coulombs at 56 days
The concrete mixture must not crack before 14 days when use the AASHTO
PP 34 Restrained Shrinkage Test.
3.3.1 History
Data collected in 2002 on newly construction bridges in Colorado by CDOT
showed that 82% of the bridges show various degrees of cracking (Xi et. al, 2003).
These cracks ranged in size 0.01 inches to 0.1 inches (0.25 mm to 2.5 mm). This
problem prompted research to develop new concrete mixture specifications that would
be resistant to cracking. Assessment of the Cracking Problem in Newly Constructed
Bridge Decks in Colorado made several recommendations for new classes of concrete
mixtures. The recommendation that were implemented resulted in the CDOT Class H
and Class HT mixtures.
However, CDOT has noticed cracking in bridge decks using the Class H and
HT specification (Cavaliero, 2009). It is suspected that the high rate of strength gain
may be contributing to the cracking of these mixtures (Cavaliero, 2009). Due to the
21


ongoing problem with concrete cracking UCD conducted research into improving the
current CDOT Class H and HT concrete mixtures.
3.3.2 UCD Finding/Recommendations
The thesis Evaluation of Crack Resistant Concrete for Colorado Bridge Decks
by Mr. Robert Cavaliero examined the current Class H and Class HT concrete
specifications and made recommendations to CDOT for improving these
specifications.
The research found that increasing the w/cm to 0.44, cement replacements of
up to 30% of Class F fly ash, and lowering the cement content showed to be very
beneficial. The use a high dosage of shrinkage reducing admixture, also showed to be
beneficial in reducing concrete cracking.
Evaluation of Crack Resistant Concrete for Colorado Bridge Decks
recommended adjustments to CDOT Class H and HT bridge deck mixture. The
recommended adjustments were:
Increase maximum allowable w/cm from 0.42 to 0.44;
Increase maximum allowable cement replacement with Class F fly ash
from 20-30%;
Incorporate the use of cement replacement with ground-granulated blast
furnace slag up to 50%;
22


Incorporate the use of a shrinkage reducing admixture at high dosage
rates;
Incorporate the use of a set retarder admixture at average dosage rates;
Decrease cement content to 564 lb/cy (335 kg/m ) when supplementary
cementitious materials are not used.
3.4 Summary
Both UFFA and silica fume have shown to affect fresh and hardened concrete
properties. UFFA has shown to increase the workability of fresh concrete due to its
spherical shape acting like micro-ball bearings. Silica fume decreases the workability
of fresh concrete, this due to the high surface area of the SCM, this cause a higher
water demand. Concrete containing UFFA or silica fume has shown an increase in
compressive strength, a decrease in permeability. The increase in compressive strength
is partly due in part because the SCMs are high-reactive pozzolans. The permeability
is decrease in concrete containing both SCMs because the pozzolanic reaction and the
particle size decreases the porosity and the average pore size. UFFA shows to decrease
concrete shrinkage, whereas silica fume has shown to increase concrete shrinkage.
Ultra-Fine Fly Ash
Increases Workability
Increases Compressive Strength
23


Decreases Permeability
Decreases Shrinkage
Silica Fume
Decrease Workability
Increases Compressive Strength
Decreases Permeability
Increases Shrinkage
24


4. Problem Statement
4.1 Statement
Silica Fume has been used as a SCM in concrete for many years. The addition
of silica fume to a concrete mixture provides many desirable properties of hardened
concrete. It increases both the compressive strength and durability, along with
decreasing the permeability of the concrete mixture. Lowering the w/cm with the
addition of adding silica fume to a concrete mixture compounds the desirable
properties of compressive strength, durability and permeability.
An increase in concrete compressive strength is beneficial because it allows for
more effective and efficient structural sections. Being able to consistently reproduce
high strength concrete allows for lighter beams that can span further and smaller
columns that can carry larger building loads, which allows for the construction of
taller concrete buildings. It allows for concrete to be used in many applications that
that would otherwise not include concrete as the structural material.
Decreased permeability improves concretes resistance to freezing and
thawing, resaturation, sulfate, and chloride-ion penetration, and other chemical attacks
(PCA, 2002). Concrete that has a high resistance to the above attacks results in
concrete that has an increased life span and lower required maintenance.
25


The addition of silica fume to concrete mixtures has many undesirable
properties as well. The water demand is increased with the addition of silica fume; this
is due to the fineness of the admixture. Water reducing admixtures are needed to
maintain the same w/c and slump. The concrete becomes more difficult to finish in
concrete containing silica fume. The concrete becomes sticky and increases
difficultly to finish. Shrinkage is also increased in concrete containing silica fume. The
increase in shrinkage may cause the concrete to crack allowing chemicals, water, or
sulfate to penetrate the concrete and degrade the concrete or reinforcement. The cost
of silica fume is much greater than the cost of portland cement or other SCMs.
According to Boral Material Technologies the manufacture of Mircon3 (their
UFFA product), many of the desirable concrete properties provided by silica fume can
be achieved using UFFA without the undesirable effects of silica fume.
Mircon has an average partial size diameter 3.0pm which is approximately ten
times the size of the average silica fume partial and approximately one-eighth the size
of the average standard fly ash partial. According to Boral Material Technologies this
particle size has been optimized to increase compressive strength, decrease
permeability, decrease shrinkage, and increase durability.
Past research comparing the properties of concrete mixtures including UFFA
and silica fume was completed with w/cm values of 0.35 or higher. This research has
26


shown that UFFA does increase compressive strength, decrease permeability and
increase durability. However, may not be as effective as silica fume at higher w/cm
values.
According to Properties of Concrete Containing Ultra-Fine Fly Ash by Obla
research has shown that more UFFA is needed in a mixture to get comparable
compressive strengths of a mixtures containing silica fume. In addition, a reduction in
the water content was required in the UFFA mixture to acquire comparable early
compressive strengths. Oblas research has shown that adding UFFA to a concrete
mixture does indeed greatly improve the properties of permeability and durability.
Ruybals research at the University of Colorado Denver confirmed these findings.
Currently, a high strength concrete mixture design study is being completed by
the BOR. The w/cm that the BOR are testing are 0.34, 0.29, and 0.27. The only
hardened concrete property tested was compressive strength. The BORs results show
that low w/cm mixtures containing UFFA performed as well as or out performed
mixtures containing silica fume. This is contrary to research that has been completed
on higher w/c that showed greater amounts of UFFA were required to produce
comparable compressive strengths of mixtures containing silica fume.
The objective of this research is to examine the concrete properties of concrete
containing UFFA at low w/c in comparison to mixtures containing silica fume. The
27


concrete properties tested in this experimental program include: slump, air content,
unit weight, concrete temperature, compressive strength, permeability, and durability.
In addition, restrained shrinkage testing was conducted on a CDOT Class H concrete
mixture to examine the benefits of using UFFA for reduced drying shrinkage and
increased concrete performance. The findings from this thesis will be used to
recommend potential cement replacement rates with UFFA to develop concrete
mixtures with equal or better strength, durability, and shrinkage properties of mixtures
containing silica fume.
28


5. Research Plan
5.1 Preface
This research focused on the comparison of concrete properties containing
UFFA and silica fume at low w/cm. It was completed in two phases. Phase I compared
the properties of slump, air content, unit weight, concrete temperature, compressive
strength, permeability, and freeze-thaw durability between mixtures with varying
w/cm and cement replacements with either UFFA or silica fume. To complete this
three comparison mixtures were examined. The w/cm of the concrete mixtures were
0.34, 0.29 and 0.27.
Phase II examined the properties of slump, air content, unit weight, concrete
temperature, compressive strength, permeability and restrained shrinkage for a CDOT
Class H concrete mixture. The two comparison mixtures consisted of a w/cm of 0.44,
30% class F fly ash and 5% of either silica fume or UFFA.
5.2 Materials Used
5.2.1 Coarse Aggregate
The coarse aggregate used for this research was from the UCD stock at the
Civil Engineering laboratory. The coarse aggregate test reports are listed in Appendix
A. The nominal maximum aggregate size (NMAS) of the stock coarse aggregate was
V". The NMAS is the smallest sieve opening through which the entire sample is
29


permitted to pass, but not needed to do so. A percentage of the sample weight may be
retained in this sieve (Mindess et. al, 2003). This matched the NMAS for the BOR
concrete mixtures.
In addition, the coarse aggregate met the specifications for size 57 and size 67
of the ASTM C33 specification. The specifications for size 57 and size 67 are listed
and compared to the sieve analysis of the coarse aggregate in Table 5.1. Meeting the
specification for size 67 of ASTM C33 is required for a CDOT Class H mixture.
Table 5.1: Coarse Aggregate Sieve Analysis Compared to
ASTM C33 Size 57 & 67
Sieve Sample % Passing No. 57 No. 67
Size Spec. Spec.
2"
1 1/2" 100 100
1" 100 90-100 100
3/4" 92 90-100
1/2" 60 25-60
3/8" 40 20-55
#4 7 0-10 0-10
#8 3 0-5 0-5
#16 2
#30 2
#50 1
#100 1
#200 0.9
30


5.2.2 Fine Aggregate
The fine aggregate used in this research was from the UCD stock at the Civil
Engineering laboratory. The fine aggregate test reports are listed in Appendix A. The
fine aggregate meets the ASTM C33 specification for fine aggregates. The sieve
analysis compared to the ASTM C33 specification is shown in Table 5.2.
Table 5.2: Fine Aggregate Sieve Analysis Compared to ASTM C33
Sieve Sample % Passing Fine
Size Aggregate
3/8" 100
#4 100 95-100
#8 99 80-100
#16 71 50-85
#30 38 25-60
#50 14 5-30
#100 4 0-10
#200 1.4 0-2
Fineness Modulus 2.74 2.3-3.1
5.2.3 Portland Cement
The portland cement used throughout this study was a Holcim Type I/II
cement. Holcim Type I/II portland cement meets or exceeds the requirements stated by
ASTM C-150. (See Appendix A for Product Data Sheet) Table 5.3 shows some typical
physical properties of portland cement. The physical properties are typical values from
31


Concrete by Mindess. The chemical properties are values stated in the product data
sheet in Appendix A.
Table 5.3: Physical and Chemical Properties of Portland Cement
Physical Properties
Shape Angular
Specific Gravity 3.2
Mean Particle Size (pm) 10-15
Chemical Properties
Silicon Dioxide (Si02) % 19.6
Aluminum Oxide (Al203) % 4.7
Iron Oxide (Fe203) % 3.2
Calcium Oxide (CaO) % 63.4
Magnesium Oxide (MgO) % 1.5
5.2.4 Fly Ash
The fly ash used in this research was a Boral Material Technologies Class F
Fly Ash. According to Boral Material Technologies product data sheets the fly ash
meets or exceeds the requirements for ASTM C 618. (See Appendix A for Product
Data Sheet) Table 5.4 shows some typical physical and chemical properties of Class F
fly ash. The values shown in table 5.4 are from Concrete by Mindess.
32


Table 5.4: Physical and Chemical Properties of Fly Ash
Physical Properties
Shape Mostly Spherical
Specific Gravity 22-2.4
Mean Particle Size (pm) 10-15
Chemical Properties
Silicon Dioxide (Si02) % >50
Aluminum Oxide (Al203) % 20-30
Iron Oxide (Fe203) % <10
Calcium Oxide (CaO) %
Magnesium Oxide (MgO) %
5.2.5 Ultra-Fine Fly Ash
The UFFA used for this research is manufactured by Boral Material
2
Technologies under the commercial name Micron (See Appendix A for Product Data
Sheet) This UFFA is manufactured from fly ash that meets the requirements for class
F fly ash. Table 5.5 shows some typical physical and chemical properties of UFFA.
The values in table 5.5 are from Research Summary Phase 1 March 1999 published by
Boral Material Technologies.
33


Table 5.5: Physical and Chemical Properties of UFFA
Physical Properties
Shape Spherical
Specific Gravity 2.53
Mean Particle Size (pm) 3.0
Chemical Properties
Silicon Dioxide (Si02) % 49.5
Aluminum Oxide (Al203) % 26.19
Iron Oxide (Fe203) % 3.64
Calcium Oxide (CaO) % 13.34
Magnesium Oxide (MgO) % 2.44
5.2.6 Silica Fume
The silica fiime used in this research was Rheomac SF 100. (See Appendix A
for Product Data Sheet). The silica fume meets all the requirements stated by ASTM C
1240. Table 5.6 shows some typical physical and chemical properties of silica fume.
The values shown in table 5.6 are from for Concrete by Mindess.
34


Table 5.6: Physical and Chemical Properties of Silica Fume
Physical Properties
Shape Spherical
Specific Gravity 2.2
Mean Partcal Size (pm) 0.1-0.3
Chemical Properties
Silicon Dioxide (Si02) % 85-98
Aluminum Oxide (Al203) % <2
Iron Oxide (Fe203) % <10
Calcium Oxide (CaO) % ...
Magnesium Oxide (MgO) % ...
5.2.7 Chemical Admixtures
5.2.7.1 High Range Water Reducing Admixture
HRWRA was used in the batching process of the phase 1 mixtures. Due to the
low w/c the HRWRA was needed to provide the necessary workability to properly
consolidate the mixtures into the forms.
5.2.7.2 Air-Entraining Admixture
An air-entraining admixture was required for the Phase II mixtures to provide
the air content require by the CDOT specification. The AEA that was used was MB-
AE 90 by Master Builders. The product data sheet is in Appendix A. One fluid ounce
per cwt (lOOlbs of cement) was added to the mixtures.
35


5.3 Mixture Designs
5.3.1 Phase I
For phase I of this research it was chosen to design the mixtures to be very
similar to the mixtures examined by the Bureau of Reclamations high strength mix
design study. The BORs study examined only the compressive strength of the
concrete mixtures. In this study the permeability and freeze/thaw durability were
examined in addition to the compressive strength. The w/cm that were examined,
were 0.34, 0.29, and 0.27. The total cement contents were 837, 940, and 1010 pounds
per cubic yard (497, 558, and 599 kg/m ) respectively with a 20% replacement of
class F fly ash when only taking the portland cement and fly ash into account. The
UFFA or Silica Fume was added at 50 pounds per cubic yard regardless of the cement
content. The mixture designs are listed in Table 5.7.
36


Table 5.7: Phase I Mixture Proportions
Mixture ID 0.34UFFA 0.29UFFA 0.27UFFA 0.34SF 0.29SF 0.27SF
w/cm 0.34 0.29 0.27 0.34 0.29 0.27
Cement Content (lb/yd3) 837 940 1010 837 837 1010
Portland Cement (lb/yd3) 630 712 768 630 712 768
Class F Fly Ash (lb/yd3) 157 178 192 157 178 192
UFFA (lbs/yd3) 50 50 50 0 0 0
Silica Fume (lbs/yd3) 0 0 0 50 50 50
Coarse Agg. (lbs/yd3) 1662 1642 1622 1662 1642 1622
Fine Agg. (lbs/yd3) 1167 1117 1098 1159 1109 1090
Water (lbs/yd3) 285 276 268 285 276 268
HRWRA (fl oz/cwt) 3.1 9.1 11.3 6.8 12.1 19.8
5.3.2 Phase II
Phase II of the research compared the compressive strength, permeability, and
restrained shrinkage for two CDOT Class H mixture containing either silica fume or
UFFA as a substitute for cement.
37


A CDOT Class H mixture is a concrete mixture that is used for bare concrete
bridge decks that will not receive a waterproofing membrane (CDOT Specification,
2008). There are a number of requirements for a concrete mixture to be considered a
CDOT Class H mixture. The mixture proportion requirements for a CDOT Class H
mix are listed in Table 5.8. The hardened concrete mixture properties minimums are
listed in Table 5.9.
Table 5.8: CDOT Class H Mixture Proportion Limits and Ranges
w/c Cementitious Content (lbs/yd3) Portland Cement (lbs/yd3) Fly Ash (lbs/yd3) Silica Fume (lbs/yd3) Percent of Coarse Agg.
Class H Mix 0.38- 0.42 580 to 640 450 to 500 90 to 125 20 to 30 > 55%
Table 5.9: CDOT Class H Mixture Property Limits and Range
w/c Compressive Strength (psi) Air Content (%) Rapid Chloride Test (Coulombs) Must Not Crack before per AASHTO P 334
Class H Mix 0.38- 0.42 4500 at 56 days* 5 to 8 <2000 14 Days
*A Field Compressive strength of 4500 psi is required; the laboratory results must
show a compressive of 5175 psi
The mixture design for Phase II consisted of w/c of 0.44 and a cementitious
content of 611 lbs/yd3 (362.5 kg/m3) 30% replacement of class F fly ash, and 5%
38


replacement of either silica fume or UFFA. This mixture design is currently outside of
the CDOT Class H specification. This mixture design is based on 2009
recommendations to the CDOT from the UCD (Cavaliero, 2009). The
recommendations that were used in the phase II mixtures were:
Increase the maximum allowable w/cm from 0.42 to 0.44
Increase the maximum allowable cement replacement with Class F fly ash
from 20% to 30%
The absolute volume method of mixture proportioning was used to determine the
mixture proportions. The mixture designs for both the silica fume and UFFA mixtures
are listed in Table 5.10.
39


Table 5.10: Phase II Mixture Proportions
UFFA Class H SF Class H
w/cm 0.44 0.44
Cement Content (lb/yd3) 611 611
Portland Cement (lb/yd3) 397 397
Class F Fly Ash (lb/yd3) 183 183
UFFA (lbs/yd3) 30 0
Silica Fume (lbs/yd3) 0 30
Coarse Agg. (lbs/yd3) 1755 1755
Fine Agq. (lbs/yd5) 1167 1167
Water (lbs/yd3) 269 269
Air Entraining Admixture (fl oz/cwt) 1.0 1.0
5.4 Method for Testing Concrete Properties
5.4.1 Fresh Concrete Properties
Immediately after batching, the fresh concrete properties were tested. The fresh
concrete properties tested were slump (ASTM C 143), concrete temperature (ASTM
40


Cl064), unit weight (ASTM 138), and air content (ASTM C 231). The test methods
and time of testing are listed in Table 5.11.
Table 5.11: Fresh Concrete Properties and Methods
Fresh Concrete Tests Standard Time of Test
Slump ASTM C143 At Batching
Unit Weight ASTM C138 At Batching
Air Content ASTM C 231 At Batching
Temperature ASTM C 1064 At Batching
5.4.2 Hardened Concrete Properties
The hardened concrete properties performed on the Phase I concrete mixtures
included compressive strength, permeability, and freeze/thaw durability. Compressive
strength, permeability, and restrained shrinkage were tested on the Phase II concrete
mixtures. The properties and the methods of the hardened concrete properties tests are
listed in Table 5.12.
Table 5.12: Hardened Concrete Properties and Methods
Fresh Concrete Tests Standard Time of Test
Compressive Strength ASTM C 39 1, 7, 28, 56 Days
Permeability ASTM C 1202 28, 56 Days
Durability* ASTM C 666 28+ Days
Shrinkage** ASSHTO PP 34 Until Cracking
* Durability was only tested on Phase I Mixtures
** Shrinkage was only tested on Phase II Mixtures
41


5.4.2.1 Compressive Strength
Compressive strength was examined using the ASTM C 39 (Standard Test
Method for Compressive Strength of Cylindrical Concrete Specimens). The
compressive strength was tested and reported on all mixtures at 1, 7, 28, and 56 days
of age. Three concrete cylinders were tested for each mixture and each testing day.
5.4.2.2 Rapid Chloride Ion Permeability
The rapid chloride ion permeability (RCIP) test was used to determine the
concrete permeability. This test was completed per ASTM C 1202 (Standard Test
Method for Electrical Indication of Concrete Ability to Resist Chloride Ion
Penetration) and examined at 28 and 56 days of age on both the Phase I and Phase II
mixtures.
The test was completed by testing two samples from each mixture. The test
consists of measuring the amount of electrical current passing though a two inch thick
sample over six hours. Four inch diameter by eight inch tall cylinders were cast during
batching to provide the test sample. The samples are then cut using a wet saw to
provide the (2)-two inch thick (51 mm) samples. These samples are then placed in a
desiccator and place under a vacuum for three hours. Once this is completed the
samples are submerged in water and a vacuum is again pulled for an additional hour.
42


After that hour is completed the vacuum is released and the samples are left
submerged for at least 18 hours.
The samples are then placed between two testing cells. The testing cells
consist of metal screen that is placed against the concrete sample and a small reservoir
on each side. The reservoirs are then filled with a NaCl (sodium chloride) solution on
one side and a NaOH (sodium hydroxide) solution on the other.
A 60V dc charge is maintained over the sample for three hours. The amount of
charge passed through the samples is measure in coulombs. ASTM C 1202 states that
the test must be ran for six hours. However, studies have shown that the results are
linear after three hours and the results can be doubled to provide the six hour results.
Figure 5.1 shows the rapid chloride ion penetrability test setup and running.
43


Figure 5.1 RCIP Test
After the tests are completed the six hour measured coulombs are compared to
values in Table 5.13 to determine the chloride ion penetrability. Table 5.13 is a replica
of Table 1 in ASTMC 1202.
44


Table 5.13: Chloride Ion Penetrability Based on Charge Passed
Coulombs Chloride Ion Penetrability
>4000 High
2000-4000 Moderate
1000-2000 Low
100-1000 Very Low
<100 Negligible
5.4.2.3 Freeze-Thaw Durability
The freeze-thaw durability was examined per ASTM C 666 (Standard Test
Method for Resistance of Concrete to Rapid Freezing and Thawing). This test was
started 28 days after batching. This is 14 days later than stated by ASTM C 666. The
freeze/thaw test was delayed to allow for the pozzalanic reaction to develop as a result
of the addition of the SCMs. The freeze/thaw durability test was only completed on
the Phase I mixtures.
Two concrete beams were made and tested for each concrete mixture. The
concrete beams were submerged in water and cured for 28 days. After curing for 28
days the initial fundamental transverse frequency was measured and the beams were
placed in the freeze/thaw chamber. A photograph of the freeze/thaw chamber is shown
in Figure 5.2.
45


Figure 5.2: Freeze/Thaw Chamber
The concrete beams were placed in the freeze/thaw chamber and were
submerged in water. The chamber freezes and thaws the concrete sample over several
cycles a day. The freeze/thaw cycle consist of lowering the temperature of the sample
to 0 F (-17.8 C) and than raising it to 40 F (4.4 C) before lowering the temperature
again.
After several freeze/thaw cycles are completed the fundamental transverse
frequency was again measured. Then the samples were again placed in the freeze/thaw
chamber and allowed to run for approximately 36 more cycles. As the concrete beams
degrade the fundamental transverse frequency decreased due to cracks and voids
46


within the beam. Figure 5.3 shows a specimen being tested for the fundamental
transverse frequency.
Figure 5.3: Specimen being tested for the Fundamental Transverse Frequency
Once the fundamental transverse frequency fall below 60% of its initial value
the durability factor for the mixture can be calculated.
5.4.2.4 Restrained Shrinkage
Shrinkage was examined only during Phase II of the study. This test began
immediately after batching and ran until cracking. The AASHTO PP 34 test was used
to measure the restrained shrinkage in this research. This test consists of curing
concrete around a steel ring and measuring the amount of strain in the rings as the
concrete cures. The steel ring is 12 inches (305mm) in diameter by 6 inches
47


(152.4mm) tall. There are four strain gauges placed 90 degrees apart at the mid-height.
The outside form consists of an 18in (457.2 mm) diameter concrete forming tube. The
strain gauges are connected to a data collecting device that reads and records the strain
in each gauge every 30 minutes until the test is terminated. Figure 5.4 is a photograph
of a concrete ring during testing.
Figure 5.4: Photograph of Restrained Shrinkage Ring
Two concrete rings were cast for each mixture. The rings were cast and
immediately placed in the curing room. They were allowed to set for 24 hours. After
the 24 hours the outer forms were removed and the top edges were ground to a
48


rounded smooth comer. The edges are rounded to eliminate any stress concentrations
at the comers.
5.5 Curing
Once the concrete specimens for compressive strength, permeability, and
freeze/thaw durability were fabricated, they were immediately placed in the curing
room and submerged in water tanks at the UCD laboratory. The samples remained in
the water tank for moist curing until time of testing. The shrinkage rings were
fabricated and immediately place in the curing room. Wet burlap was placed over the
rings to wet cure the top of the rings. After 24 hour the wet burlap is removed and the
ring are allowed to cure in the humidity controlled room until cracking.
49


6. Phase I Experimental Results
6.1 Fresh Concrete Properties
The fresh concrete properties tested for Phase I were slump, air content, unit
weight, and concrete temperature. The fresh concrete properties were tested
immediately after batching and are listed in Table 6.1.
Table 6.1: Phase 1 Fresh Concrete Properties
Mixture ID Slump (in) Air Content (%) Unit Weight (lbs/ft3) Ambient Temp (F) Concrete Temp (F) HRWRA (fl oz/cwt)
0.34UFFA 4.5 2.2 147 72 72 3.1
0.29UFFA 8 1.5 149.2 75 78 9.1
0.27UFFA 10.25 1.4 150.4 75 76 11.3
0.34SF 2.5 2.1 147.2 75 79 6.8
0.29SF 2.75 1.8 149.6 75 80 12.1
0.27SF 8.5 1.5 150.4 75 80 19.8
6.1.1.1 Slump
HRWRA was needed to provide that necessary workability to properly
consolidate and work with the Phase I mixtures. As shown in Table 6.1 the slump
increases with the reduction of w/cm. Although this seems a little counterintuitive, the
HRWRA was greatly increased as the w/cm was decreased. This provided the increase
in concrete slump as the w/cm decreased.
50


The type of supplementary cementations material also had an effect on the
slump of the mixtures. The UFFA mixtures consistently needed less HRWRA and
provided a greater slump per w/cm. The 0.34 w/cm mixtures the UFFA required 3.1 fl
oz/cwt of HRWRA to result in a slump of 4.5 inches (114.3 mm), whereas the
companion silica fume mixture required more than double the HRWRA it required 6.8
fl oz/cwt to result in a slump of 2.5 inches (63.5 mm). The silica fume mixtures
continuously required more HRWRA and show less slump than the UFFA mixtures.
This is shown in Figure 6.1.
Mixture ID
25
20
f
15 "g i 1 Slump
(in)
HRWRA
10 | (fl oz/cwt)
X X
5
0
Figure 6.1: Measured Slump and Required HRWRA
51


From Figure 6.1 it is clear that UFFA has a positive influence on workability.
This is consistent with previous research that stated UFFA reduces water demand.
During batching the mixtures using the UFFA mixture did not have a stickiness like
the silica fume mixtures. As the w/cm decreased the silica fume mixtures became
stickier. The silica fume mixtures became very difficult to finish and work with
although the slumps were within acceptable ranges.
As the w/cm decreased the cementations content increased. This could have
contributed to the increase in water demand and the increase in required F1RWRA. As
the cementations content was increased the UFFA and silica fume content remained
constant. The percentage of UFFA decreased as the cementations content increased,
which reduced the effectiveness of the water reducing properties of UFFA.
6.1.1.2 Concrete Temperature
The desired concrete temperature for placement is between 50 to 60 F (10-
15.5C) and should not exceed 85 to 90F (29.4 to 32C) (Mindess, et. al., 2003).
High concrete temperatures may cause many problems such as loss of moisture,
decreased setting times, increased plastic shrinkage, and lower ultimate strength. The
Phase I concrete temperatures are shown in Figure 6.2.
52


82
80 80
Mixture ID
Figure 6.2: Phase 1 Concrete Temperature
The concrete temperatures ranged from 72 to 80 F (22.2 to 26.6C). The
temperatures are higher than the ideal temperature range, but still remained lower than
the 85 F (29.4C) maximum. However, the higher concrete temperature may need to
be considered if these mixtures were to be used in a large mass pour.
The silica fume mixtures had a slightly higher temperature than the UFFA
mixtures. According to the PCA Manual, fly ash has a lower heat of hydration when
compared to portland cement, hence lowering the concrete temperature, where as
53


silica fume may or may not lower the heat of hydration. Thus, these results showing
the silica fume mixtures having higher temperatures are not out of the ordinary. In
addition, the cement content contributes to higher concrete temperatures. The greater
the cement content, the higher the fresh concrete temperature. This may have
increased concrete temperatures.
6.1.1.3 Air Content
Air-entraining admixture (AEA) was not used in the Phase I mixtures. The
reason for not using AEA is due to the objective of this research being to focus on the
comparison of UFFA and silica fume. If the air contents were to range dramatically it
would greatly affect the other concrete properties. The amount of air content can affect
workability, compressive strength, permeability, and durability.
When the mixtures were designed, it was assumed that the air content would
be 2%. The actual air contents were measured at the time of batching of each mixture.
The air content was measured using the ASTM C 231 (Air Content of Freshly Mixed
Concrete by the Pressure Method). The measured air contents are shown in Figure 6.3.
54


2.5 -
22
<
2.1
Mixture ID
Figure 6.3: Measure Air Content
The air content of the concrete mixture appears to decrease with the decrease
in w/cm. Cement content will affect the amount of air content in concrete. As the
cement content increases the amount of entrapped air will decrease. Both fly ash and
silica fume reduces the amount of entrapped air in a concrete mixture (PCA, 2002).
Since the amount of portland cement and fly ash both increase as the w/cm decreased,
it was expected to measure decreased air contents for the UFFA and silica fume
mixtures.
6.1.1.4 Unit Weight
The unit weight of the concrete was measured at the time of batching. The
measurement was completed per ASTM 138. The measured unit weight was compared
to the predicted unit weights which are shown in Table 6.2.
55


Table 6.2: Measured Unit Weight Compared to Predicted Unit Weight
Mixture ID 0.34UFFA 0.29UFFA 0.27UFFA 0.34SF 0.29SF 0.27SF
Measured Unit Weight (lbs/ft3) 147.0 149.2 150.4 147.2 149.6 150.4
Predicted Unit Weight (lbs/ft3) 146.3 147.2 148.1 146.0 146.9 147.8
The measured unit weights are consistently higher than the predicted unit
weights. This could be caused by a number of reasons. One explanation for the higher
than expected unit weight would be the lower than assumed air contents. As the air
contributes to the volume of concrete but does not contribute to the weight of the
concrete. Hence, a lower than excepted air content explains a higher than predicted
unit weight. Though it would not explain the difference in predicted and measured unit
weight of the 0.34 UFFA and 0.34 SF mixtures, as the air content is greater than
expected. It is assumed that human error may have resulted in this difference.
6.1.2 Hardened Concrete Properties
The hardened concrete properties that were tested as part of the Phase I study
included compressive strength, rapid chloride ion permeability, and freeze/thaw
durability.
56


6.1.2.1 Compressive Strength
Compressive strength is the most important property of a concrete mixture.
The compressive strength is a property that needs to be reproducible as a structural
engineer may be requiring and counting on a specific compressive strength. The
compressive strengths of the mixtures for Phase I were examined at 1, 7, 28, and 56
days of age. Three cylinders were tested on each day to provide an average
compressive strength. The compressive cylinders that were used in this research were
four inches in diameter by eight inches tall. Equation 6.1 shows the calculation of
determining compressive stress. Figure 6.4 is a photograph of the type of cylinder
being tested.
Load (lbs)
Area (in2)
Area of Concrete Cylinders = n r2
Equation 6.1
Load = The measure load at failure
57


Figure 6.4: Example of Concrete Cylinder being Tested
The compressive strength of each cylinder was tested in accordance with
ASTM C39 (Standard Test Method for Compressive Strength of Cylindrical Concrete
Specimens). Each cylinder was loaded until failure and the average ultimate load
values are listed in Table 6.3.
Table 6.3: Average Ultimate Compressive Load
Mixture 0.34UFFA 0.29UFFA 0.27UFFA 0.34SF 0.29SF 0.27SF
ID (lbs) (lbs) (lbs) (lbs) (lbs) (lbs)
1 Day 34,237 49,138 72,945 35,693 62,308 69,882
7 Day 63,282 75,330 100,368 63,537 93,770 108,187
28 Day 88,163 93,097 119,673 71,997 103,455 126,022
56 Day 96,993 103,303 134,580 84,928 110,278 130,278
58


The average compressive load was than divided by the area of the concrete
cylinder to determine ultimate concrete compressive stress. The values are listed in
Table 6.4.
Table 6.4: Average Ultimate Compressive Stress
Mixture ID 0.34UFFA (psi) 0.29UFFA (psi) 0.27UFFA (psi) 0.34SF (psi) 0.29SF (psi) 0.27SF (psi)
1 Day 2,724 3,910 5,805 2,840 4,958 5,561
7 Day 5,036 5,995 7,987 5,056 7,462 8,609
28 Day 7,016 7,408 9,523 5,729 8,233 10,028
56 Day 7,718 8,221 10,710 6,758 8,776 10,367
The values of compressive stress are plotted versus time and shown in Figure 6.5.
59


12000
k0.34UFFA
0.29UFFA
A0.27UFFA
0.34SF
X-0.29SF
0.27SF
I BOR Req'd Strength
Figure 6.5: Compressive Strength vs. Time
Figure 6.5 shows that the 0.27 UFFA mixture had the greatest 56 day strength
at 10,710psi (73.8 Mpa). Though the 0.27 SF mixture was quite comparable with a 56
day strength of 10,367psi (71.5 Mpa). The silica fume out performed the UFFA for the
0.29 w/cm mixtures with a 56 day strength of 8776psi (56.7 Mpa) versus the UFFA
mixture of 8221psi (56.7 Mpa) though the results again are very similar. In fact the 56
day strengths for all the UFFA and SF mixtures at each w/cm are quite comparable. It
is reasonable to believe the reason that the strengths of the UFFA mixtures are more
comparable to the silica fume mixture as the w/cm decreases is due to more material
60


being use for packing. The low w/cm would cause the concrete to self-desiccate
resulting in less of the UFFA hydrating and more used for packing in the voids
between the cement paste and the aggregates.
The only mixtures that meet the BOR requirement of 8000 psi (55.2 Mpa) at
28 days of age were the both 0.27 UFFA and silica fume mixtures and the 0.29 silica
fume mixture. However, the 0.29 UFFA mixture had a strength of 8221 psi (56.7
Mpa) at 56 days. The UFFA and silica fume mixtures with a w/cm of 0.34 didnt meet
the BOR strength requirement at 28 or 56 days.
The silica fume mixtures seem to generally out perform the UFFA mixtures in
early strength. The fact that the silica fume mixtures gain higher early strength is not
surprising as silica fume is a highly reactive pozzolan and contribute to early strength
(Mindess, et. al., 2003). Figure 6.6 shows the percentage of the 56 day strength at each
testing day for each mixture.
61


0.34UFFA
0.29UFFA 0.27UFFA 0.34SF 0.29SF
i
r.
r
Li
r
f *
v
Li
0.27SF
Mixture ID
1 Day
7 Day
D 28 Day
56 Day
Figure 6.6: Percentage of 56 Day Compressive Strength
As previously stated the silica fume mixtures gain strength earlier than the
UFFA mixture. The silica fume on average gained 81% of its 56 day strength by its 7
days of age and 92% by the 28 days of age. Where the UFFA mixtures on average
gained 71% of its 56 day strength by its 7 days of age and 90% by the 28 days of age
Though, the silica fume mixture may gain strength at a quicker rate, the UFFA
mixture shows very comparable results at 56 days. This is not surprising because fly
ash, particularly Class F fly ash, shows increased later strength gain when compared to
other SCMs. Figure 6.7 shows the percentage difference in compressive strength of
the UFFA mixture over the SF mixtures at each w/cm.
62


20.00%
15.00%
10.00%
5.00%
0.00%
-5.00%
-10.00%
14.21%
0.34UFFA

0.29UFFA '
t '
r ' vt''
-6.32%
w/cm
3.30%
0.27UFFA
Figure 6.7: UFFA Compressive Strength Percent Difference Compared to Silica
Fume at 56 Days
The figure shows that the 0.27 UFFA mixture had 3.3% more compressive
strength than the same silica fume mixture and the UFFA mixture had 14.2% more
compressive strength at a w/cm of 0.34. Though, the UFFA mixture had 6.32% less
strength than the comparable silica fume mixture.
6.1.2.2 Permeability
Permeability is a measurement of the concretes ability to resist penetration of
water and any aggressive chemicals. The permeability of the concrete mixtures was
63


measured using the method stated in ASTM C 1202. The test was performed at 28 and
56 days after batching. The results from running the RCIP test on the phase 1 mixtures
are listed in Table 6.5.
Table 6.5: Permeability Results
Mixture ID 28 Day Coulombs Chloride Ion Penetrability 56 Day Coulombs Chloride Ion Penetrability
0.34UFFA 1423 Low 648 Very Low
0.29UFFA 1067 Low 650 Very Low
0.27UFFA 563** Very Low 573 Very Low
0.34SF 933 Very Low 557* Very Low
0.29SF 657 Very Low 453 Very Low
0.27SF 252** Very Low 225 Very Low
* Tested 78 days after batching, only moist curec for 56 days
**Tested 42 days after batching, only moist cured for 28 days
The vacuum pump that was used to provide the vacuum for the desiccator quit
working during the very beginning of the permeability test of the 0.27 w/cm mixtures.
The civil engineering lab wasnt able to acquire a replacement right away. The testing
of some of the mixtures was delayed while a replacement vacuum pump was acquired.
Though the testing wasnt able to take place on time, the concrete samples were
removed from the curing tank to stop concrete hydration on the desired testing date.
The results in Table 6.6 show the permeability levels for the UFFA and silica fume
mixtures. The silica fume mixtures clearly out perform the UFFA mixtures for all
w/cm. The 0.27 SF mixture had the best permeability levels for both the 28 day and 56
64


day values. The chloride ion penetrability was 252 coulombs (very low) at 28 days and
225 coulombs (very low) at 56 days. All of the silica fume mixtures showed
permeability levels of very low with the highest silica fume permeability level of
933 coulombs (very low), which was on the 0.34 SF mixture at 28 days. The 0.27
UFFA mixture showed chloride ion penetrability levels of very low for both 28 day
and 56 day testing times. The 0.29 UFFA showed 1067 coulombs at 28 day which is
consider low chloride ion penetrability. Then at 56 days the 0.29 UFFA mixture had
a very low chloride ion penetrability at 650 coulombs. Figure 6.8 shows the
measured coulombs at both 28 and 56 days for each mixture.
0.27SF
0.29SF
Very Low
- Permeabilty
Limit
Low
Permeability
Limit
0 0.34SF
1
3
K
E 0.27UFFA
28 Day
Coulombs
56 Day
Coulombs
0.29UFFA
0.34UFFA
0 200 400 600 800 1000 1200 1400 1600 1800 2000
Permeability (Coulombs)
Figure 6.8: Permeability Results
65


Figure 6.9 shows that for most of the mixtures, the additional curing time
increases the concrete ability to resist chloride ion penetration. The benefit seemed to
decrease with the decrease of w/cm. The 56 day value for the 0.34 SF mixture was
about 60% of the 28 day value. With the 0.29 UFFA mixture the 56 day value was
about 61% of the 28 day value. With the 0.27SF mixture the 56 day permeability value
was about 90% of the 28 day permeability value and for the 0.27 UFFA mixture the 56
day value was actually slightly higher than the 28 day value.
It appears that UFFA doesnt provide the same level of resistance to chloride
ion penetration as silica fume. Figure 6.9 show the silica fume permeability value as a
percentage of the UFFA values.
66


100.0%
0.34 0.29 0.27
Mixture ID
Figure 6.9: Silica Fume Permeability Values as a Percentage of UFFA
Permeability Values
Figure 6.9 shows that as the w/cm decreases the more beneficial the silica
fume becomes. The 56 day permeability value for the 0.27 SF mixture was about 40%
of the 56 day 0.27 UFFA value and 56 day permeability value for the 0.29 SF mixture
was about 70% of the 56 day 0.29 UFFA value.
6.1.2.3 Durability
Freezing and thawing of moisture that has penetrated the concrete causes
internal stresses that degrade the concrete over continuous freezing and thawing
cycles. This is caused by water entering the voids within the concrete. When the water
inside the concrete freezes, it expands pressing against the void walls causing internal
67


stresses that crack the concrete. As the cycles continue the cracks grow larger and
larger, degrading the concrete over time.
Since, the Phase I mixtures did not include any AEA and the air content of the
mixtures was low. It was expected that the durability factors would be low. The results
from testing the fundamental transverse frequency on the concrete beams are listed in
Tables 6.6 thru 6.11.
Table 6.6: 0.34 UFFA Average Freeze/Thaw Results
Specimen A Specimen B
Cycles Fundamental Transverse Frequency (Hz) Fundamental Transverse Frequency (Hz)
0 2187.5 2180.99
36 2115.9 2070.3
102 1536.6 1328.1
138 1152.3 722.7
68


Table 6.7: 0.34 SF Average Freeze/Thaw Results
Specimen A Specimen B
Cycles Fundamental Transverse Frequency (Hz) Fundamental Transverse Frequency (Hz)
0 2063.8 2063.8
48 2011.7 2031.25
104 1790.4 1529.9
155 1210.9 1464.51
197 709.6 1152.3
233 338.5 924.5
269 71.6 403.6
Table 6.8: 0.29 UFFA Average Freeze/Thaw Results
Specimen A Specimen B
Cycles Fundamental T ransverse Frequency (Hz) Fundamental Transverse Frequency (Hz)
0 2187.5 2187.5
56 2115.9 2128.9
109 1992.2 1953.1
151 1595.1 1354.2
187 706.5 996.1
223 429.7 683.6
250 240.9 501.3
286 78.2 260.4
69


Table 6.9: 0.29 SF Average Freeze/Thaw Results
Specimen A Specimen B
Cycles Fundamental Transverse Frequency (Hz) Fundamental Transverse Frequency (Hz)
0 2109.4 2109.4
56 2063.8 2070.3
109 1933.6 1894.5
151 1601.6 1419.3
187 950.5 983.1
223 196.3 488.3
250 58.6 58.6
Table 6.10: 0.27 UFFA Average Freeze/Thaw Results
Specimen A Specimen B
Cycles Fundamental Transverse Frequency (Hz) Fundamental Transverse Frequency (Hz)
0 2148.4 2207.0
53 2044.2 2109.4
95 2044.3 2128.9
131 2070.3 2128.9
167 1953.1 2135.4
194 1894.5 2135.4
230 1757.8 2148.4
266 1757.8 2181.0
301 1679.69 2141.93
70


Table 6.11: 0.27 SF Average Freeze/Thaw Results
Specimen A Specimen B
Cycles Fundamental T ransverse Frequency (Hz) Fundamental Transverse Frequency (Hz)
0 2187.5 2187.5
53 2122.4 2089.8
95 2129.0 2102.7
131 2109.4 2128.9
167 2122.4 2115.9
194 2128.9 2128.9
230 2135.4 2122.4
266 2161.5 2148.4
301 2128.9 2063.8
The specimens were required to run in the freeze/thaw chamber for either 300
cycles or until the relative dynamic modulus of elasticity reached 60% of it initial
value. The concrete samples in this study were allowed to run past 60% of their initial
relative dynamic modulus of elasticity. The relative dynamic modulus of elasticity is
calculated using Equation 6.2.
71


Pc =(12/2)xl00
Equation 6.2
Where:
Pc = relative dynamic modulus of elasticity, after c cycles of freezing and thawing,
percent
n = fundamental transverse frequency at 0 cycles of freezing and thawing
ni = fundamental transverse frequency at c cycles of freezing and thawing
The calculated relative dynamic modulus of elasticity for each mixture is listed
in Tables 6.12 thru 6.17. The highlighted values in the below tables are the values
when the dynamic modulus of elasticity falls below 60% of its initial value.
Table 6.12: 0.34 UFFA Relative Dynamic Modulus of Elasticity
Cycles Average Fundamental Transverse Frequency (Hz) Relative Dynamic Modulus of Elasticity
0 2184.2 100.0
36 2093.1 91.8
102 1432.4 43.0
138 937.5 18.4
72


Table 6.13: 0.34 SF Relative Dynamic Modulus of Elasticity
Cycles Average Fundamental Transverse Frequency (Hz) Relative Dynamic Modulus of Elasticity
0 2063.8 100.0
48 2021.475 95.9
104 1660.15 64.7
155 1337.705 42.0
197 930.95 20.3
233 631.5 9.4
269 237.6 1.3
Table 6.14: 0.29 UFFA Relative Dynamic Modulus of Elasticity
Cycles Average Fundamental T ransverse Frequency (Hz) Relative Dynamic Modulus of Elasticity
0 2187.50 100.0
56 2122.40 94.1
109 1972.65 81.3
151 1474.65 45.4
187 851.30 15.1
223 556.65 6.5
250 371.10 2.9
286 169.31 0.6
73


Table 6.15: 0.29 SF Relative Dynamic Modulus of Elasticity
Cycles Average Fundamental Transverse Frequency (Hz) Relative Dynamic Modulus of Elasticity
0 2109.38 100.0
56 2067.06 96.0
109 1914.06 82.3
151 1510.42 51.3
187 966.80 21.0
223 342.30 2.6
250 58.59 0.1
Table 6.16: 0.27 UFFA Relative Dynamic Modulus of Elasticity
Cycles Average Fundamental T ransverse Frequency (Hz) Relative Dynamic Modulus of Elasticity
0 2177.74 100.0
53 2076.80 90.9
95 2086.59 91.8
131 2099.61 93.0
167 2044.28 88.1
194 2014.98 85.6
230 1953.13 80.4
266 1969.40 81.8
301 1910.81 77.0
74


Table 6.17: 0.27 SF Relative Dynamic Modulus of Elasticity
Cycles Average Fundamental T ransverse Frequency (Hz) Relative Dynamic Modulus of Elasticity
0 2187.50 100.0
53 2106.12 93.5
95 2115.86 94.4
131 2119.14 94.7
167 2119.14 94.7
194 2128.91 95.6
230 2128.92 95.6
266 2154.95 97.9
301 2096.36 92.7
Figure 6.10 show the calculated value relative dynamic modulus of elasticity vs.
cycles.
75


120.0 n
*0.34 UFFA
0.34 SF
-alr-0.29 UFFA
-X- 0.29 SF
0.27 UFFA
e0.27 SF
(60%
Figure 6.10: Relative Dynamic Modulus of Elasticity vs. Cycles
Figure 6.10 shows that the higher the w/cm, the sooner the relative dynamic
modulus of elasticity fell below 60% of its initial value. The difference between the
0.34 mixtures and the 0.29 mixture is slight. However the 0.27 w/cm mixtures never
fell below the 60% mark.
The durability factor of the concrete mixture is calculated using Equation 6.3.
The durability factor is calculated when the relative dynamic modulus of elasticity
falls below 60% of is initial value or the specimen has been subjected to 300 cycles.
76


DF = PN / M
Equation 6.3
Where:
DF = durability factor of the test specimen
P = relative dynamic modulus of elasticity at N cycles, %
N = number of cycles at which P reaches the specified minimum value for
discontinuing and test or the specified number of cycles at which the exposure is to be
terminated, which ever is less.
M = specified number of cycles at which the exposure is to be terminated.
The highlighted values in the above Tables 6.13 thru 6.18 are the values that
were used to calculate the durability factors. The calculated durability factors are listed
in Table 6.18
Table 6.18: Phase 1 Durability Factors
Mixture ID Number of Cycle Relative Dynamic Modulus of Elasticity Durability Factor
0.34 UFFA 104 48.2 16.71
0.29 UFFA 151 45.4 22.87
0.27 UFFA 301 77.0 77.24
0.34 SF 155 42.0 21.71
0.29 SF 151 51.3 25.81
0.27 SF 301 92.7 92.97
77


According to Concrete by Midness there is no defined value for acceptance or
rejection for concrete durability factor. However, the book does state that when using
Procedure A in ASTM C 666 (which was the procedure used in this research) values
lower than 40 the concrete may be unsatisfactory and values greater than 60 the
concrete may perform well. The only mixtures that showed durability factors greater
the 60 were both the 0.27 w/cm mixture, where as all the other mixtures had durability
factors of lower than 40. This indicates that the 0.34 and 0.29 w/cm mixture are
unsatisfactory and both 0.27 mixtures will perform well when exposed to severe
freezing and thawing. In fact there was a dramatic increase in the durability factor
between the w/cm of 0.29 and 0.27. The 0.27 mixture showed an average increase of
327% in the durability factor. This is explained by the very low permeability
measured for the 0.27 w/cm UFFA and silica fume mixtures. Since there was no air-
entraining admixture used and there was little difference in air content. The air-content
would have little effect on the durability of these mixtures. However, the permeability
of these mixtures did range greatly. The permeability dramatically decreased as the
w/cm ratio decreased. From examining the results from section 6.1.2.2 permeability
and the durability results, there is a direct inverse relationship between permeability
and durability.
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The silica fume and UFFA seemed to perform comparably in their effect on the
durability factor. However the silica fume mixtures did slightly outperform the UFFA
mixtures. Figure 6.15 compares the durability factors of the silica fume and UFFA
mixtures.
100.0 ,
90.0 !
80.0 :
2 70.0 :
i LL 60.0 j
!> 50.0
!3 E 3 40.0 -
8 30.0 }
20.0 i
10.0 -
0.0 -
0.34 0.29 0.27
w/cm
UFFA
a Silica Fume
Figure 6.11: Durability Factor
The 0.27 silica fume mixture shows a durability factor of approximately 20%
greater than the UFFA mixture, where as the 0.29 mixture the silica fume mixture is
only 13% greater. This is shown in Figure 6.12.
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35%
30%
0.34 0.29 0.27
w/cm
Figure 6.12: Percentage Increase in Silica Fume Durability Compared to UFFA
Durability
It is apparent that silica fume is more effective at increasing the durability
factor for low w/cm mixtures. This is due to the fact that the silica fume mixtures
outperformed the UFFA mixtures in concrete permeability.
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7. Phase II Experimental Results
7.1 Fresh Concrete Properties
The fresh concrete properties that were tested in Phase II were slump,
temperature, air content and unit weight. The fresh properties were tested immediately
after batching and are listed in Table 7.1
Table 7.1: Phase II Fresh Concrete Properties
Mixture ID Slump (in) Air Content (%) Unit Weight (lbs/ft3) Ambient Temp (F) Concrete Temp (F) AEA (fl oz/cwt)
UFFA Class H 6.5 5.5 141.4 70 70 1.0
SF Class H 2.75 6.0 141.2 70 72 1.0
7.1.1 Slump
HRWRA was not needed in the Phase II mixtures. The higher w/cm provided
enough workability to properly consolidate and finish the mixtures. Figure 7.1 shows
the measured slump for the both mixtures.
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7
0
Mixture ID
Figure 7.1: Measured Slump
Both UFFA and silica fume had effect on the workability of the mixtures. The
UFFA had a much greater slump than the silica fume mixture. This follows the same
trend that was shown in the Phase I testing where the UFFA mixture did not require as
much HRWRA. In addition, the UFFA did not show the stickiness the silica fume
mixtures exhibited. This made it much easier to finish the concrete for the UFFA
mixtures.
7.1.2 Concrete Temperature
The measured concrete temperatures and the ambient temperatures are shown
in Figure 7.2.
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75
74 f
73 )
72
UFFA Class H SF Class H
Mixture ID
Figure 7.2: Concrete Temperature and Ambient Temperature
The UFFA showed a lower concrete temperature than the silica fume mixtures.
According to the PC A manual due to fly ashs low heat of hydration it can lower the
concrete temperature. This likely explains the difference in the concrete temperature.
Both mixtures show temperatures greater than the ideal placing temperature
range which is 50 to 60 F (10-15.5C) (Mindess, et. ah, 2003). However, the concrete
temperature should not exceed 85 F (29C). The concrete temperatures were less than
the maximum but greater than the ideal temperature.
83