Citation
Internal curing of pervious concrete

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Title:
Internal curing of pervious concrete
Creator:
Majdoub, Driss
Publication Date:
Language:
English
Physical Description:
xii, 145 leaves : illustrations ; 28 cm

Subjects

Subjects / Keywords:
Lightweight concrete -- Curing ( lcsh )
Genre:
bibliography ( marcgt )
theses ( marcgt )
non-fiction ( marcgt )

Notes

Bibliography:
Includes bibliographical references (leaves 143-145).
General Note:
Department of Civil Engineering
Statement of Responsibility:
by Driss Majdoub.

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Source Institution:
|University of Colorado Denver
Holding Location:
|Auraria Library
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All applicable rights reserved by the source institution and holding location.
Resource Identifier:
747713641 ( OCLC )
ocn747713641
Classification:
LD1193.E53 2011m M34 ( lcc )

Full Text
INTERNAL CURING OF PERVIOUS CONCRETE
By
Driss Majdoub, E.I.
B.S., University of Colorado Denver, 2008
A thesis submitted to the
University of Colorado Denver
in partial fulfillment
of the requirements for the degree of
Masters of Science
Civil Engineering
2011


This thesis for the Masters of Science
Degree by
Driss Majdoub, E.I.
has been Approved
by
Stephan A. Durham
Chengyu Li
Date


Majdoub, Driss (Master of Science, Civil Engineering)
Internal Curing of Pervious Concrete
Thesis directed by Asst. Professor Stephan A. Durham
ABSTRACT
Pervious concrete pavements have gained national recognition, especially
in warm climate regions due to its use as a Best Management Practice (BMP) to
improve stormwater runoff, improve the quality of water that flows through it,
and decreasing the heat island effect.
In Colorado, the unique arid environment mixed with the severe winter
weather can greatly affect the durability of pervious concrete pavements. The low
humidity and high wind velocities significantly affect the early age hydration and
strength development of the pervious concrete. As a result, the long durability of
the pavement can be jeopardized. Early applications of pervious concrete
pavements in Colorado failed as a result of improper mixture design, placement
and curing of the pervious concrete.
Due to the hydrological criterion, pervious concrete contains a large
volume of voids which produces lower compressive strength and freeze-thaw
durability when compared to conventional concrete. Improving the strength and


the freeze-thaw durability while maintaining a high porosity of pervious concrete
is essential to its use in Colorado.
This research examined the phenomenon of internal curing pervious
concrete with Lightweight Aggregate (LWA) to increase structural and durability
performance. Different concrete mixtures were developed to test the effect of the
LWA. These mixtures were compared to those containing normal weight sand
(NWA) at varying percentages of fine aggregate on three concrete properties:
compressive strength, porosity, and freeze-thaw durability.
Test results showed that the inclusion of LWA increased compressive
strength up to 200 psi (1379 KPa) at 56-days of age and increased freeze-thaw
resistance by 85 cycles when compared to that of mixtures with NWA. Porosity
values were similar between mixtures using LWA and NWA. The optimum fine
aggregate content was found to range between 5% and 7.5% by total weight of
aggregate.
This abstract accurately represents the content of the candidates thesis, I
recommend its publication.
Signed
Stephan A. Durham


DEDICATION
I dedicate my thesis to my Moroccan, and American Family.


ACKNOW LEDGEMENT
I would like to acknowledge the many individuals and organizations that
have contributed to the success of this research study. These individuals include
professors at the University of Colorado Denver, material suppliers, classmates,
friends, and members of my family.
I would like to thank .Dr. Stephan A. Durham, my thesis advisor, for his
advice and knowledge in the concrete industry that helped shape this research
from its infant stage to the mixing, testing, and formulation of this thesis
document. In addition, I would like to thank my thesis committee members Dr.
Kevin Rens and Dr. Chengyu Li.
I would like to acknowledge TXI, Inc for their generous donation of
Lightweight Aggregate used in this study. Furthermore, I would like to thank
Bestway Concrete for their donation of the coarse and fine aggregate used for the
pervious concrete.
Advice and support on pervious concrete and assistance during the
laboratory phase of this research study was provided by Dr. Angela S. Hager, Dr.
Rui Lui, Patrick L Maier, Adam Kardos, and Ryan Alsyum ...
I would like to thank my grandfather-in-law Marvin Mansfield for his help
providing the place and the tools to construct the concrete blocks (9 total), and the
freeze-thaw molds (9 total).


Lastly, I would like to thank my wife Christine A. Majdoub; this thesis
would not exist if it were not for her support (socially, emotionally, and
economically).


TABLE OF CONTENTS
Figures.............................................................ix
Tables..............................................................xi
Chapter
1. Introduction.....................................................1
1.1 General........................................................1
1.2 Objective...................................................3
1.3 Scope.........................................................3
2. Literature Review..................................................5
2.1 History and Uses of Pervious Concrete.........................5
2.2 Pervious Concrete Materials...................................6
2.2.1 Aggregates...............................................6
2.2.2 Cement...................................................7
2.2.3 Water....................................................8
2.2.4 Mineral Admixtures.....................................9
2.2.5 Chemical Admixtures.....................................10
2.3 Current Practices and Recommendations....................... 11
2.3.1 American Concrete Institute.............................12
2.3.2 Portland Cement Association.............................12
2.3.3 National Ready Mix Concrete Association.................13
2.3.4 Colorado Ready Mix Concrete Association.................13
2.4 Internal Curing..............................................14
2.5 History of Pervious Concrete in Colorado.....................19
2.5.1 2004 Colorado Hardscapes................................21
2.5.2 2005 Safeway Grocery Store..............................23
2.5.3 2005 City of Lakewood Maintenance Facility..............24
2.5.4 2006 Wal-Mart Super Center..............................26
2.5.5 2006 Bestway Aggregates.................................28
2.5.6 2007 Vitamin Cottage....................................29
2.5.7 2007 Red Lobster........................................32
2.5.8 2008 University of Colorado Denver Parking Lot K......33
2.5.9 2008 UDFCD Moratorium...................................35
3. Problem Statement.................................................36
4. Experimental Plan.................................................38
4.1 Introduction.................................................38
4.2 Mixture Design (SSD).........................................38
4.3 Mixture Proportioning........................................40
4.3.1 Water to Cement Ratio...................................41
4.3.2 Cement Content..........................................41
4.3.3 Aggregates Content......................................41
4.3.4 Hydration Stabilizer....................................45
4.4 Testing......................................................46
vii


4.4.1 Compressive Testing.....................................47
4.4.2 Porosity Testing........................................49
4.4.3 Freeze-thaw Testing.....................................50
5. Laboratory Results................................................57
5.1 Phase I Normal weight Aggregate............................59
5.1.1 Compressive Strength Testing Results....................59
5.1.1.1 28-Day...........................................59
5.1.1.2 56-Day...........................................60
5.1.2 Porosity Testing Results................................62
5.1.2.1 28-Day...........................................62
5.1.2.2 56-Day...........................................64
5.1.3 Freeze-Thaw Testing Results.............................67
5.1.4 Conclusion..............................................69
5.2 Phase II Lightweight Aggregate & Comparison................69
5.2.1 Compressive Strength Testing Results....................69
5.2.1.1 28-Day...........................................69
5.2.1.2 56-Day...........................................71
5.2.2 Porosity Testing Results...............................74
5.2.2.1 28-Day...........................................74
5.2.2.2 56-Day...........................................77
5.2.3 Freeze-Thaw Testing Results.............................80
5.2.4 Conclusion..............................................82
6. Statistical Analysis..............................................84
6.1 Introduction.................................................84
6.1.1 Compressive Strength Analysis...........................85
6.1.2 Porosity Analysis.......................................85
6.1.3 Freeze-Thaw Analysis....................................86
7. Conclusion and Recommendations....................................88
7.1 Pervious Concrete Recommendations............................88
7.2.1 LWA and Fine Inclusion Recommendations..................88
7.2.2 Recommendations for Future Research.....................89
Appendix
A. Pictures of Pervious Concrete Project in Denver Metro Area.....91
B. UDFCD Moratorium Letter.......................................115
C. Pervious Concrete Mixture Design Spreadsheets.................116
D. Pictures of Laboratory Testing................................125
E. Freeze-thaw Record Data.......................................138
F. Aggregates Data Reports.......................................140
viii
References
143


FIGURES
2.1 Internal Curing at the Contact Zone [P. Lura 2003]...................15
2.2 X-ray microtomograph................................................15
2.3 Process flow manufacturing of LWA (EPA 2009)........................18
2.4 Timeline of Previous Concrete Projects in the Denver Metro Area.....20
2.5 Pervious Concrete at Colorado Hardscapes (3/4 inch).................21
2.6 Pervious Concrete at Colorado Hardscapes (3/8 inch).................22
2.7 Pervious Concrete at Colorado Hardscapes (3/4 inch)-(Typical condition)...22
2.8 Pervious Concrete at Colorado Hardscapes (3/4 inch)-(Typical condition)...23
2.9 Lakewood City Maintenance Facility Parking Lot......................24
2.10 Pervious Concrete at Lakewood Maintenance facility (3/4 inch)......25
2.11 Pervious Concrete at Lakewood Maintenance facility (3/8 inch)......25
2.12 Lakewood Maintenance Facility Potholes............................26
2.13 Lakewood Maintenance Facility Scaling.............................26
2.14 Typical section of Pervious Concrete at Wal-Mart (Wheel Path)......27
2.15 Pervious Concrete at Wal-Mart (Joints)...........,.................28
2.16 Pervious Concrete at Wal-Mart (Not subject to loading).............28
2.17 Parking Lot at Vitamin Cottage (North Side)........................30
2.18 Typical Section of Vitamin Cottage Parking Lot (North side)........30
2.19 Parking Lot at Vitamin Cottage (South Side)........................31
IX


2.20 Typical Section of Vitamin Cottage Parking Lot (South side)......31
2.21 Red Lobster at 810 S Wadsworth Blvd..............................32
2.22 Red lobster Typical Section....................................33
2.23 Parking Lot K at University of Colorado Denver...................33
2.24 Typical Section of Parking Lot K at UCD..........................34
2.25 Pervious concrete at Parking Lot K (Joint).......................34
4.1 Rock Gradation ....................................................44
4.2 NWA Gradation ....................................................44
4.2 LWA Gradation ....................................................45
4.4 Impervious zone ..................................................46
4.5 Test Block Core Drill Mounting Platform...........................48
5.1 28-Day Compressive Strength Results Phase 1......................60
5.2 56-Day Compressive Strength Results Phase 1.....................61
5.3 (%) Increase in Compressive Strength Compared to the Control.....62
5.4 28-Day Porosity Results Phase 1................................63
5.5 Porosity Vs Compressive Strength at 28-Day Phase 1.............64
5.6 56-Day Porosity Results Phase 1................................65
5.7. (%) Increase in Compressive Strength Compared to the Control.....,66
5.8 Porosity Vs Compressive Strength at 56-Day Phase 1..............67
5.9 Freeze-thaw Testing Results Phase 1............................68
5.10 28-Day Compressive Strength Results Phase II...................70
5.11 28-Day Compressive Strength Results Phase I & II...............71
5.12 56-Day Compressive Strength Results Phase 1....................72
x


5.13 56-Day Compressive Strength Results Phase I & II...............73
5.14 (%) Increase in Compressive Strength Compared to the Control.....74
5.15 28-Day Porosity Results - Phase II...............................75
5.16 28-Day Porosity Results - Phase I & II...........................75
5.17 Porosity Vs Compressive Strength at 28-Day Phase I & II........76
5.18 56-Day Porosity Results - Phase II...............................77
5.19 56-Day Porosity Results - Phase I & II...........................78
5.20 (%) Decrease in Porosity Compared to the Control.................79
5.21 Porosity Vs Compressive Strength at 56-Day Phase I & II........80
5.22 Freeze-thaw Testing Results Phase I & II.......................67
xi


TABLES
Table 2.1 Pervious Concrete Proportion Recommendations by ACI.....12
Table 2.2 Pervious Concrete Proportion Recommendations by PCA.....13
Table 2.3 Pervious Concrete Proportion Recommendations by NRMCA... 13
Table 2.4 Pervious Concrete Proportion Recommendations by CRMCA... 13
Table 4.1 SSD Weights.............................................39
Table 4.2 Physical Properties of Cement...........................42
Table 4.3 Physical Properties of Aggregates.......................43
Table 5.1 28-Day Compressive Strength Results - Phase 1......... 59
Table 5.2 56-Day Compressive Strength Results - Phase 1......... 61
Table 5.3 28-Day Porosity Results - Phase I..................... 63
Table 5.4 56-Day Porosity Results - Phase I..................... 65
Table 5.5 Freeze-thaw Testing Results Phase I................... 68
Table 5.6 28-Day Compressive Strength Results - Phase II.........70
Table 5.7 56-Day Compressive Strength Results - Phase II.........72
Table 5.8 28-Day Porosity Results - Phase II.....................74
Table 5.9 56-Day Porosity Results - Phase II.....................77
Table 5.10 Freeze-thaw Testing Results Phase II.................81
Table 6.1 Compressive Strength Paired t-test Results..............85
Table 6.2 Porosity Paired t-test Results..........................87
Table 6.1 Freeze-thaw Paired t-test Results.......................87
xii


1. Introduction
1.1 General
Water from rain and melting snow usually run off over road pavement
surfaces, sidewalks to curbs & gutters instead of permeating through the ground.
A report by the United States National Research Council identified urban
stormwater as a leading source of water quality problems in the U.S [EPA, 2008].
As urbanization and land development increase the surface runoff increases by
creating more impervious surfaces such as roadway, sidewalk, curb & gutter and
parking lots, which prevent movement of the water through the soil.
This runoff usually travels as a result of the roadway grades, and curb &
gutter to a stormwater inlet. During this process debris, harmful contaminants and
pollutants will have negative impact on the water resources, and wild life.
Once the runoff water collects pollutants, finds its way to a stormwater
inlet. The change start by transporting pollutants to our water bodies which
require expensive treatments to make the water potable. In addition, there is the
potential for flooding when stormwater inlets are undersized or obstructed with
debris during large storm events. .
The Environmental Protection Agency (EPA) and other governmental
authorities have been enforcing strict environmental regulations to reduce and
control the negative impact from pollutants due to runoff. However, the need
1


urbanization the issue is getting more persistent at a much higher rate than
what the agencies can regulate.
Similar to conventional concrete, pervious concrete consists mostly of
Portland cement, water and aggregate. Pervious concrete is achieved by reducing
or eliminating the amount of fine aggregate from the mixture. This reduction in
fine aggregate creates air voids throughout the concrete. Water is therefore able to
pass directly through the pervious concrete pavement (PCP).
Once the pervious concrete is placed and cured, the benefits may include
but are not limited to [EPA, 2008]:
Reduction in untreated runoff discharging into stormsewer systems.
. Recharge groundwater to maintain aquifer levels.
. Channel more water and air to tree roots and landscaping in urban areas
(less need for irrigation).
. Eliminate hydrocarbon pollution.
Pollutants are absorbed into the concrete along with rainwater that allows
soil chemistry and biological processes to treat the toxins naturally and
effectively.
. Eliminate the need for retention ponds providing for more efficient land
use.
. Lower cost installing underground piping and storm drains.
. Elimination for the need to increase inlet sizes to accommodate new
residential development.
2


. Stormwater management practice.
. Reduction in heat island effect.
The benefits listed above are limited to warm climate regions such as
Florida where PCPs have seen a great deal of success. In Colorado, limited
success of PCPs have been observed primarily due to (1) arid environment (low
humidity, high winds, and high summer temperatures) provide for increased
evaporation of water from the mixture during placement leading to decreased
compressive strength and durability, and (2) severe winter weather that results in
decreased durability as a result of freeze/thaw durability..
1.2 Objective
The purpose of this research is to improve the performance of pervious
concrete with special attention given to strength and freeze-thaw properties. In
addition, it is goal of this research to maintain sufficient porosity for proper use of
the PCP as a stormwater management practice (must be able to drain water at an
accelerated rate). The effect of internal curing on pervious concretes properties
was examined by testing concrete mixtures containing LWA for compressive
strength, porosity, and freeze-thaw resistance and comparing them to mixtures
containing NWA. These properties were tested, assessed, and summarized in this
thesis.
1.3 Scope
A history and uses of pervious concrete, timeline of previous concrete
projects and it is current condition in Colorado is provided in the literature review
in Chapter 2. In addition, the current practices, rules, and standards for pervious
3


concrete as well as the 2008 Urban Drainage and Flood Control District
(UDFCD) moratorium are discussed.
Pervious concrete materials (cement, coarse, fines, chemical & mineral
admixtures, and water), mixture proportioning recommendations from the
American Concrete Institute (ACI), National Ready Mix Concrete Association
(NRMCA), and Portland Cement Association (PCA) is discussed in Chapter 2.
Furthermore, the concept of internal curing is discussed.
The significance of this research is discussed in the problem statement
located in Chapter 3.
The experimental plan is presented in Chapter 4, which consists of two
different phases: Phase I investigated the optimum range of fine aggregate (sand)
to increase structural and durability performance while maintaining a certain level
of porosity.. Phase II examined the beneficial use of LWA to internally cure the
pervious concrete, thereby increasing the structural and durability performance.
Methodologies and procedures of the three tests: compressive strength, porosity,
and freeze-thaw tests performed are included in Chapter 4.
Chapter 5 provides the results of the experimental study. A Statistical
analysis was conducted to determine whether LWA produced a significant
difference in improving compressive strength, porosity, and freeze/thaw durability
when compared to the NWA. The results of this investigation are included in
Chapter 6.
The study conclusions, recommendations, and future work are provided in
Chapter 7.
4


2. Literature Review
2.1 History and Used of Pervious Concrete
The first time pervious concrete was documented as a building material was in
1852 in the United Kingdom, where two houses were built using pervious concrete
which was achieved by combining concrete and gravel to increase its volume of voids
within, due to the limited amount of cement available at the time [Ann 2005]. Five
years after World War I, in 1923, pervious concrete was used in the construction of
fifty 2-story homes in Scotland [Ann 2005], Between 1930 and 1942 the number of
homes constructed using pervious concrete increased to 900.
Shortly after the end of World War II, the need for newer cost effective homes
made pervious concrete use spread throughout Europe [Ann 2005], This was a result
of pervious concrete using less cement than traditional concrete, thus reducing
construction costs. From here, pervious concrete spread to area such as Latin
America, Far East Europe, Middle East, Australia, and South Africa.
In the 1960s, pervious concrete made its debut in Eastern Canada, and
eventually in the Eastern United States [Ann 2005. Unlike Europe, the United States
had and consumes plenty of cement, so the need for pervious concrete and its
existence in the eastern part of the U.S. was due to high stormwater runoff in newly
developed areas.
5


Throughout the evolution of pervious concrete, it has been used as bearing walls,
parking lots, driveways, sidewalks, curb and gutters, roadways, pedestrian plazas,
swale and ditches, erosion control, slope protection, etc [EPA 2008]
2.2 Pervious Concrete Materials
The main components of pervious concrete include: cement, water, and
aggregates. In addition, chemical, and mineral admixtures may be added to the
mixture to enhance one or more properties of the concrete mixture. Standards for
pervious concrete mixtures differ from one entity to another; however, the differences
in these standards are not significant.
2.2.1 Aggregates
The aggregates usually account for approximately 60 % of the pervious
concrete volume. Aggregates can vary starting with the raw material, which can be
sand, gravel, crushed stone, slag, recycled concrete and more. The aggregates are
categorized according to shape, from smooth and rounded that can be found in
riverbeds, to rough and angular that is obtained through mechanical crushing. The
gradation of the aggregate is essential in pervious concrete as it can greatly affect the
compressive strength and porosity of the mixture
Applications that require fairly high strength and hydraulic properties can use
a blended gradation consisting of higher proportions of the % in. and Vi in. aggregate
sizes. Such requirements can be met with aggregate gradations. [Neptune 2008],
Best Management Practices (BMP) stated that open-graded aggregate are used to
create void space in porous concrete is in the 15%-22% range. [BMP 2007]
6


All these variation in the characteristics of the aggregates calls for trial
mixtures to determine the most suitable combination for the intended use of the
concrete.
The size of aggregate used in PCPC commonly ranges from No. 4 to % inch
sieves with 1 inch aggregate being used in some instances [Tennis et al. 2004],
Rounded and crushed aggregate, both normal and lightweight, have been used in
pervious concrete. The effective air voids, compressive strength, and permeability are
greatly affected by the size of the aggregates [Crouch 2007]. The size of the
aggregates is directly a factor in the compressive strength, the air voids depend on the
gradation [Ghafoori 1995], The smaller size of aggregates creates a bigger contact
area which increases the compressive strength. The aggregate used in the mixture
should meet ASTM D 448 and ASTM C33 [2008].
2.2.2 Cement
Portland cement is the glue that holds the concrete together. In addition, it is
the most expensive component that goes into making concrete excluding some
mineral admixtures. The cement contains four major compounds: tricalcium silicate,
dicalcium silicate, tricalcium aluminate, and tetracalcium alumnoferrite with each
affecting the strength and setting characteristics of concrete. The quantities of each of
these chemical compounds leads to a wide variety of different cement types that
ASTM C 150 [2008] categorizes into eight major types:
Type I For use when the special properties specified for any other type are
not required.
7


Type IA Air-entraining cement for the same uses as Type I, where air
entrainment is desired.
Type II For general use, especially when moderate sulfate resistance or
moderate heat of hydration is desired.
Type IIA Air-entraining cement for the same uses as Type II, where air
entrainment is desired.
Type III For use when high early strength is desired.
. Type IIIA Air-entraining cement for the same use as Type III, where air
entrainment is desired.
Type IV For use when a low heat of hydration is desired.
Type V For use when high sulfate resistance is desired.
The most commonly used cement in pervious concrete is Type I-II. The
cement is the major contributor to the strength of the pervious concrete. Unlike
traditional concrete where the cement paste fills the pores, in the pervious concrete
the cement is only used to coat the aggregates and form a bound between them.
2.2.3 Water
Water is the most influential component in the producing concrete. Water is
added for two main reasons; one is to hydrate the cement, and the other is to provide a
certain level of workability. The strength of the concrete is mainly determined by how
much water is added to the mixture.
The amount of water added into the concrete mixture is determined by the
cement content and the water to cement ratio (w/cm). The higher the w/cm (0.4 to
0.65) the more workable and less strength the concrete will have. Making this ratio
8


smaller (0.2 to 0.4), the concrete will exhibit higher compressive strength and have
workability. Too much water may cause segregation and too little water may produce
a mixture that is not workable. Water to cement ratio ranges from 0.25 to 0.43 with
water reducers causing typical pervious concrete mixes to have a slump less than one
inch as measured by ASTM C143 [Tennis et al. 2004]
The laboratory testing phases of research established the mixture
characteristic of an optimal mixture design that contained 525 lbs (238 kg) of cement
and had a w/cm of 0.30[Hager 2009],
Low values of the water to cement ratio is needed to increase the compressive
strength of the paste that hold the pervious concrete together. Usually pervious
concrete fails at the cement binder, improving strength of the paste is critical to the
success of the pervious concrete.
Potable is adequate for use in concrete mixtures. Impurities in the mixing
water will affect the setting time, concrete strength, volume stability, and
efflorescence or corrosion of reinforcement [PCA 2008].
2.2.4 Mineral Admixtures
For the purpose of enhancing short or long term strength, increase the
workability of the mixture, and to design a more sustainable pervious concrete
mixture, a percentage of cement can be replaced with fly ash, blast furnace slag, or
silica fume [PCA 2008] These supplementary cementitious materials (SCMs) should
meet the requirements of ASTM C 618, ASTM C 989, and ASTM C 1240 [2008]
respectively.
9


Mineral Admixtures improve the workability and the strength of the pervious
concrete. It does not hydrate like cement as it does not posses cementitious material;
instead it reacts with the CH to produce more CSH, as results the strength increases.
Also they help improve the workability due to the spherical shape the it particles.
The most commonly used mineral admixture is fly-ash, laboratory testing
determined that up to 20% of the cement could be replaced with either Class C or
Class F fly ash. The use of fly ash in the mixture decreased the porosity and
compressive strength at 28 and 56 days of age [Angela 2009],
2.2.5 Chemical admixtures
Chemical admixtures are used to enhance one or multiple properties of
concrete during both fresh and harden states such as workability, set time, strength...
The admixtures should meet the requirements of ASTM C 494 [2008], These
admixtures are used to alter one or multiple properties of fresh and harden concrete.
There are seven types of chemical admixtures [ASTM 2008]:
. Type AWater-reducing admixtures,
Type BRetarding admixtures,
Type CAccelerating admixtures,
Type DWater-reducing and retarding admixtures,
. Type EWater-reducing and accelerating admixtures,
Type FWater-reducing, high range admixtures, and
Type GWater-reducing, high range, and retarding
Admixtures are used to improve pervious concrete properties. The National
Ready Mixed Concrete Association (NRMCA) suggests using 4-8% of air
10


entrainment with a spacing factor of 0.01 inches to provide satisfactory freeze-thaw
resistance [NRMCA 2004], As for the Hydration stabilizer it is almost not
recommended the making of pervious concrete without its use.
High range water reducers (HRWR) may be used to improve paste appearance
(sheen) and workability. Special consideration must be provided in obtaining dosage
quantities, since paste could become very fluid, with a tendency to segregate at the
bottom of the sample [Flores et al. 2006].
Hydration controlling admixtures (HCA) slow the rate of hydration and extend the
life of fresh pervious concrete. At ambient temperature conditions, a dosage of 5 fl
oz/cwt of the HCA provides between 60 and 90 minutes of extra working time. [Bury
et al. 2006],
Along with the HCA, VMA or viscosity modifying admixtures may be beneficial to
the performance of pervious concrete. The use of VMAs results in better flow,
quicker discharge time from a truck, and easier placement and compaction.
Furthermore, VMAs prevent drain down, and may increase both compressive and
flexural strength of pervious concrete [Bury et al. 2006],
2.3 Current Practices and Recommendations
Recommendations concerning the mixture proportioning of pervious concrete
differ from one agency to another. These differences are due to the different types of
applications intended for the mixture, and the environment surrounding it. Mixture
proportions for a PCP parking lot in Colorado will vary greatly a PCP in Florida, as to
the what the pervious concrete will have to withstand. The loading is the same in both
area but the concrete in Colorado has to be more durable to freeze-thaw cycles than a
11


pervious concrete in Florida. This report provides recommendations from the
American Concrete Institute (ACI), Portland Cement Association (PCA), and the
National Ready-Mixed Concrete Association (NRMCA).
2.3.1 American Concrete Institute
ACI provides technical information on pervious concretes application, design
methods, material properties, mixture proportions, construction methods, testing, and,
inspection [ACI 2009], This information is provided in ACI 522R-10. In addition,
ACI provides information on selecting proportions of the mixture under ACI 211.3R
Appendix 6. Table 2.1 shows typical mixture proportion recommendations by ACI.
Table 2,1 Pervious Concrete Proportion Recommendations by ACI
Material Amount
Cement Depends on the volume of the paste and w/c
Coarse Aggregate Depends on the dry-rodded density of the aggregates, and size (No. 8 or No 67)
Fine Aggregate 0%, and 10% of total aggregates by volume
Water to Cement Ratio 0.35 to 0.45
2.3.2 Portland Cement Association
PCA has published a guide to pervious concrete pavement, where it includes
discussion on: construction techniques, environmental benefits, structural and
hydraulic properties [PCA 2009]. Table 2.2 provides material quantities
recommended by PCA.
12


Table 2.2 Pervious Concrete Proportion Recommendations by PCA
Material Amount
Cement 450 (267) to 700(415) Ib/cy (kg/m3)
Coarse Aggregate 2000 (1186) to 2700 (1602) Ib/cy (kg/m3)
Fine Aggregate Maximum of 6% of total aggregates by volume
Water to Cement Ratio 0.20 to 0.45
2.3.3 National Ready Mix Concrete Association
NRMCA published Text Reference: Pervious Concrete Contractor
Certification that provides technical data on: pervious concrete material, mixture
proportioning, production, design principles, construction, and proper tools and
equipment used in the placement of pervious concrete [NRMCA 2008]. Table 2.3
provides material quantities recommended by NRMCA.
Table 2.3 Pervious Concrete Proportion Recommendations by NRMCA
Material Amount
Cement 450 (267) to 700 (415) lb/cy (kg/m3)
Coarse Aggregate 4 to 4.5 : 1 by mass ASTM C33
Fine Aggregate 0 to 1 : 1 by mass
Water to Cement Ratio 0.27 to 0.34
2.3.4 Colorado Ready Mix Concrete Association
CRMCA published Specifiers Guide for Pervious Concrete Pavement
Design to assist designers specifying the pervious concrete component of a
stromwater management system [CRMCA 2008]. Table 2.4 provides material
quantities recommended by CRMCA.
13


Table 2.4 Pervious Concrete Proportion Recommendations by CRMCA
Material Amount
Cement No less than 600 (415) lb/cy (kg/m3)
Coarse Aggregate Shall meet ASTM C33
Fine Aggregate 6% +- 2% of total aggregates
Water to Cement Ratio 0.26 to 0.35
2.4 Internal Curing
Internal curing is the process by which the cement hydration continues due to
the availability of additional water that is not part of the mixture water [ESCSI 2006].
It is known as a time-dependent improvement to the strength of the concrete due to
the water released from the aggregates.
According to John Reis, executive director of the Expanded Shale, Clay &
Slate Institute, improvement to long term strength due to saturated aggregates was
first documented in 1957, by Paul Klieger [ESCSI 2006]. Eight years later, the
National Ready Mixed Concrete Association confirmed the strength improvement
through research on lightweight aggregates. The concept of internal curing is widely
used to increase the strength of concrete mixtures and control cracking.
The main objective of this thesis is to research the effects of internal curing on
pervious concrete. Saturated lightweight fine aggregates can act as internal reservoirs,
thereby supplying water throughout the hydration process. The internal curing
process takes place at the contact zone that ASTM D169 refers to as two different
phenomena [P. Laura 2003]. The first is the mechanical adhesion of the cementitious
matrix to the surface of the aggregate and second is the variation of physical and
chemical characteristics of the transition layer of the cementitious matrix close to the
aggregate particle.
14


Figure 2.1 shows the internal curing at the contact zone for both normal and
lightweight aggregates before and after concrete sets.
Figure 2.2 shows X-ray microtomograph (left) shows pores in blue that remain within
lightweight aggregates (LWAs) after water has migrated from the pre-wetted
materials during the first day of hydration. In the two-dimensional image (right), the
emptied pores are superimposed over the original microstructure (hydrating cement
paste is white, sand is light grey, and LWA is dark grey), illustrating the detailed pore
structure of LWA particles. [NIST 2010]
Internal Curing at the Contact Zone
LWA NWA
Interface between two porous 4 f Interface between Hydrating Cement
materials [LWA pores and V Paste (HCP) and the non-absorbing
Hydrating Cementitious Paste (HCP)] dense normalweight aggregate "wall"
lu
t
LLI
x
o
z
o
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in
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Two-way moisture movement
between porous LWA and
porous HOP
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hygral
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Higher water content
may develop at
dense aggregate
"wall" Interface
Empty pores
WtS
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qs Si Water
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o
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contact surface
is pozzolonic.
Integrity of Transition Zone
improves at the LWA interface
Transition Zone:
W/Cm tends to increase in
transition zone at approach to dense
normalweight aggregate "wall."
Figure 2.1 Internal Curing at the Contact Zone [P. Lura 2003]
15


Figure 2.2 [NIST 2010]
Clay, shale, or slate are the primary materials that are used in the production
of LWA. During the production process of the lightweight aggregates raw material
expands it size to roughly twice its original.
Raw material that goes in the production of lightweight aggregate comes from
mining or quarrying. With the help of cone crushers, jaw crushers, hammer mills, or
pug mills the material is crushed and screened for size. Oversized material is returned
to the crushers, and the material that passes through the screens is transferred to
hoppers. From the hoppers, the material is fed to a rotary kiln, which is fired with
coal, natural gas, or fuel oil, to temperatures of approximately 1200C (2200F) [EPA
2009]. As the material is heated, it liquefies and carbonaceous compounds in the
material form gas bubbles, which expand the material. During the process, volatile
organic compounds (VOC) are released. From the kiln, the expanded product
(clinker) is transferred by conveyor into the clinker cooler where it is cooled by air,
forming a porous material. After cooling, the LWA is screened for size, crushed if
necessary, stockpiled, and shipped. Figure 2.3 illustrates the LWA manufacturing
process [EPA 2009].
16


Although the majority (approximately 90 percent) of plants uses rotary kilns,
traveling grates are also used to heat the raw materials. In addition, a few plants
process naturally occurring LWA such as pumice.
Substituting saturated LWA as fines in the concrete mixture will give the
mixture the opportunity to internally cure and ensure prolonged cement hydration.
17


Figure 2.3 Process flow manufacturing of LWA [EPA 2009]
18


2.5 History of Pervious Concrete in Colorado
Pervious concrete has been in existence in Colorado since 2004. There are
about a dozen of projects in the Denver metro area of pervious concrete; the majority
of the pervious concrete projects are parking lot. Different methods of placement,
subbases, and aggregate sizes that ranges from 3/8 inch (1cm) to 1 inch (2.5 cm) have
been used. Some of these parking lots have already been replaced with a more
durable material, the rest of the projects are not showing promising results as time
and freeze-thaw cycles go by. Figure 2.4 summaries these pervious concrete parking
lots in a chronological order.
Sections 2.5.1 through 2.5.9 provide summaries of PCPs within the Denver
Metropolitan area since 2004. A description of the PCP and its current condition is
discussed. This summary provides an updated condition assessment of PCP site
locations to the Hager dissertation [Hager, 2009].
2.5.1 2004 Colorado Hardscapes
In December 2004, Colorado Hardscapes placed two sections of PCP. The
two sections of the parking lot are shown in Figures 2.5 and 2.6 and typical
conditions are shown in Figures 2.7 and 2.8. The first section has a 3/4 inch sized
coarse aggregates, and shows no signs of structural deterioration. The pavement along
the curb and gutter where snow is pushed during plowing accumulates more fine
particles on the surface than the rest of the pavement.
19


Pervious Concrete in Colorado
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Figure 2.4 Timeline of Previous Concrete Projects in the Denver Metro Area
20
v>a


Figure 2.5 Pervious Concrete at Colorado Hardscapes (3/4 inch)
Figure 2.6 Pervious Concrete at Colorado Hardscapes (3/8 inch)
21


Figure 2.7 Pervious Concrete at Colorado Hardscapes (3/4 inch)-
(Typical condition)
The second section is the larger of the two; this section has 3/8 inch sized
coarse aggregates, and consists of 6 parking stalls. Each stall has a different mixture
design and different method of placement. Some of the stalls surfaces were sealed due
to the use of a vibrating compactor.
Figure 2.8 Pervious Concrete at Colorado Hardscapes (3/8 inch)-
(Typical condition)
22


2.5.2 2005 Safeway Grocery Store
In 2005, the Safeway Store on the northeast corner of 13th Avenue and
Krameria Street in Denver, Colorado placed pervious concrete on the entire parking
lot. The pavement consisted of 3/8 inch sized coarse aggregates in its mixture design.
Three years into service the pervious concrete in the parking lot was replaced by
asphalt due to surface raveling which impaired the usability of the pavement. In
addition, there were visible cracks at the widely spaced joints [Delatte, et al.2007].
The cause of failure was blamed on the harsh weather condition at the time of
placement. The pervious concrete was placed with snow on the ground. Additionally,
the thermal blankets blew off during curing the night following placement, and it is
believed that the concrete did not hydrate properly. Additionally, it is suspected that
the concrete froze during the curing process [Angela, et al.2009]. Furthermore, steel
tipped snow plows were used to clear snow from the parking lot [Rottman 2008].
2.5.3 2005 City of Lakewood Maintenance Facility
In 2005 UDFCD placed pervious concrete on the parking lot of the Lakewood
City Maintenance facility shown in Figure 2.9.
23


Figure 2.9 Lakewood City Maintenance Facility Parking lot
Figures 2.10 and 2.11 show that two different design mixtures were place on
the north side of the parking lot on two different types of base coarse. The coarse
aggregate used in the pervious concrete mixtures consisted of. 3/8 and 3/4 inch sized
crushed stone
The pervious concrete is raveling at the joints, potholes exist at random
locations on the surface, see Figure 2.12. In addition, the pervious concrete is scaling
at the surface, see Figure 2.13. During a site visit, it seemed as thought the snow was
melting with the exception of the snow on top of the PCP portion.
24


Figure 2.10 Pervious Concrete at Lakewood Maintenance facility (3/4 inch)
25


Figure 2.12 Lakewood Maintenance Facility Potholes
2.5.4 2006 Wal-Mart Super Center
In 2006 a section in the parking lot of the Wal-Mart Supercenter on the
northwest corner of Tower Road and Interstate 70 was constructed using a 3/8 inch
26


sized coarse aggregate pervious concrete mixture. The pervious concrete section is
located at the entrance of the parking lot, the most travelled section. The condition of
this pavement has worsened since the last inspection of this pavement by Dr. Angela
Hager in 2008. There are numerous potholes in the wheel path within the middle
portion of the section. Figure 2.14 shows the typical condition of the pavement where
it is subjected to wheel loading. The pavement surface is severely damaged due to
reveling on the surface especially at the joints, see Figure 2.15. In addition, there is
a significant accumulation of fines on the surface of the PCP. The pavement away
from the heavily travelled path was intact and in great condition, see Figure 2.16.
Figure 2.14 Typical section of Pervious Concrete at Wal-Mart (Wheel Path)
27


Figure 2.16 Pervious Concrete at Wal-Mart (Not subject to loading)
2.5.5 2006 Bestway Aggregate
In 2006, Bestway Concrete constructed a test slab at their Milliken, Colorado,
plant location. A 3/8-inch rock was used as the coarse aggregate for this test slab.
28


This PCP is not subjected to vehicular loadings and does not show any signs of
deterioration at this time.
The Bestway Concrete ready mixed plant in Denver, Colorado has two strips
of pervious concrete. These pervious concrete sections each provide for parking and
are separated by a standard concrete aisle. The first section, colored green, is located
near the plant office. The other section is at the edge of the parking lot and consists of
eight parking spaces. A 3/8 inch (1cm) rock was used as the coarse aggregate for both
pervious concrete sections. This parking lot is subjected to a daily vehicular loading
and the occasional heavy loadings of concrete trucks. Currently, this parking lot does
not show any structural deterioration. However, it is visually apparent that this
location is severely clogged [Angela, et a!.2008]
2.5.5 2007 Vitamin Cottage
In 2007, pervious concrete was placed on the parking lot of the Vitamin
Cottage located on the northwest corner of Colorado Boulevard and Evans Avenue in
Denver, Colorado. A 3/8 inch coarse aggregate was used in the pervious concrete
mixture. The condition of the pavement varies throughout. As shown in Figures 2.17
and 2.18, the north side of the section, the least travelled section of the parking lot, is
in good condition..
29


Figure 2.17 Parking Lot at Vitamin Cottage (North Side)
Figure 2.18 Typical Section of Vitamin Cottage Parking Lot (North side)
The south side of the section, the busiest section in the parking lot, shows
deterioration, raveling, and surface sealing. Figure 2.19 shows the extent of the
30


deterioration for this side of the parking lot, and its typical condition is shown in
Figure 2.20.
Figure 2.19 Parking Lot at Vitamin Cottage (South Side)
Figure 2.20 Typical Section of Vitamin Cottage Parking Lot (South side)
31



2.5.7 2007 Red Lobster
In 2007, pervious concrete was placed in the parking lot of the Red Lobster
restaurant located at 810 S Wadsworth Boulevard, see Figure 2.21 for typical section.
'I
The pervious concrete was placed on the north and the south side of the restaurant.
Figure 2.21 Red lobster at 810 S Wadsworth Blvd. (Typical Section)
Both north and south sides of the parking lot have pervious concrete with 3/8
inch (1cm) coarse aggregate. Figure 2.22 shows the typical condition of the
pavement. The PCP is deteriorating, raveling and its surface sealed due to fines
accumulation.
32


. jurw* y
i
t
Figure 2.22 Red Lobster Typical Section
2.5.8 University of Colorado Denver Parking Lot K
In July 2008, as part of Angele Hagers PhD dissertation, a pervious concrete
section was constructed in Parking Lot K on the Auraria Campus of the University of
Colorado Denver see Figure 2.23 [Hager, 2009].
m* > vw
^ - *''
Figure 2.23 Parking Lot K at University of Colorado Denver [google.maps 2011]
Overall the section is in good condition. The typical condition of the pervious
concrete is shown in Figure 2.24; however, surface raveling is taking place around
33


some joints where the pervious concrete meets the asphalt, see Figure 2.25. In
addition, some deterioration is shown along the wheel path.
Figure 2.24 Typical Section of Parking Lot K at UCD
Figure 2.25 Pervious concrete at Parking Lot K (Joint)
34


2.5.9 2008 UDFCD Moratorium
During the time that Angela Hager was placing her PCP test section on the
Auraria Campus, the Urban Drainage and Flood Control District (UDFCD) issued a
temporary moratorium on PCP in the Denver Metropolitan area due to the condition
of the existing PCP placed between 2004-2007. This moratorium is included in
Appendix B.
UDFCD noted the conditions on the Safeway Store, Vitamin Cottage, and
Wal-Mart Supercenter as deteriorating to the point that usability was impaired.
The research conducted by Dr. Angela Hager helped to lift the moratorium on
PCP in the Denver Metropolitan Area in 2009. A document was subsequently
published by the Colorado Ready-Mixed Concrete Association (CRMCA) titled
Specifiers Guide for Pervious Concrete Pavement Design in which many of the
findings from Hager, 2009, were incorporated into the document.
35


3. Problem Statement
Over the past 30 years, pervious concrete has seen a great deal of success,
especially in the southeast area of the U.S., where weather conditions are suitable
for the durability and the strength development of the pervious concrete.
Cold and arid climate areas such as Denver, Colorado, produce difficulties
in constructing durable PCP. The arid environment (low humidity, high winds,
and high summer temperatures) causes water to evaporate out of the freshly
placed PCP. Subsequently, this evaporation of water results in less water
available for cement hydration causing decreased strength development. This is
even more severe if proper placement and curing procedures are not followed.
The many freeze/thaw events that occur provide for a severe environment for PCP
to be located in if the PCP is not properly designed and placed. Theoretically, the
water should never be allowed to freeze within the pervious concrete layer of a
PCP. Adequate storage and drainage of the subsequent layers of the system (i.e.
free draining rock and sand) should prevent water from freezing in the pervious
concrete. However, there may be residual water on the surface of the cement
paste of the pervious concrete. This water may freeze resulting in the potential
for durability issues.
Pervious concrete was introduced to Colorado in the early 21st century.
Most of the early pervious concrete projects deteriorated due to hostile winter
36


weather conditions Based on the observations of projects mentioned in the
literature review of pervious concrete in Colorado, these signs of deterioration
start to show roughly after two or three years of service. Usually by the fifth years
of service the pervious concrete is seriously deteriorated or has already been
replaced with a different material.
The intent of this research is to determine the optimum range of fine
aggregate content and evaluate the performance of pervious concrete containing
LWA used for internal curing. The performance of the pervious concrete will be
evaluated based on compressive strength, porosity, and freeze-thaw durability.
This study consists of two phases. Several design mixtures were
developed in Phase I varying contents of NWA (0.0%, 2.5%, 5.0%, 7.5%, and
10%) to optimize the quantity of fine aggregate needed to produce a pervious
concrete that is both porous, durable with adequate strength. Phase II introduced
pre-soaked LWA in order to internally cure the pervious concrete. Once the
concrete hardens, the LWA will release the water within its pores. This water will
be used for continued cement hydration, thus increased compressive strength and
durability is expected.
37


4. Experiment Plan
4.1 Introduction
The purpose of this research is to verify the optimum fine aggregate
content from past studies [Hager, 2009] for pervious concrete when using NWA
and determine the optimum fine aggregate content and the subsequent effects of
internal curing on pervious concrete when using LWA by determining the
compressive strength, porosity and freeze-thaw properties of the pervious
concrete containing each. In addition, this research accounts for the air void
structure (typically 15-25%) within the pervious concrete during the design phase
of the mixtures. This research follows the laboratory testing methodologies
discussed/developed in the PhD dissertation of Dr. Angela Hager. These methods
are used to avoid variation and provide same conditions for the concrete mixtures
to be mixed, cured, tested and compared.
4.2 Mixture Design (SSD)
After an initial trail mixture phase a total of nine mixtures were designed
to optimize the fine aggregate content and study the effects of internal curing.
Table 4.1 presents the saturated surface dry weight of the materials used in the
mixtures. A detailed mixture spreadsheet for each mixture design is provided in
Appendix C.
38


Table 4.1 SSD Weights
Mixtures Cement Ib/cy (Kg/m3) Coarse Agg. lb/cy (Kg/m3) Fine Agg. lb/cy (Kg/m3) Water lb/cy (Kg/m3) Hydration Stabilizer (oz/cwt)
Phase I & II Mix 1 0.0% Fines 525 (311) 2649 (1571) 0 (0) 157.5 (93) 20
Phase I Mix 2 525 2583 66 157.5 20
2.5% NWA (311) (1532) (39) (93)
Phase I Mix 3 525 2517 132 157.5 20
5.0% NWA (311) (1493) (78) (93)
Phase I Mix 4 525 2452 199 157.5 20
7.5% NWA (311) (1454) (118) (93)
Phase I Mix 5 525 2386 265 157.5 20
10% NWA (311) (1415) (157) (93)
Phase II Mix 2 525 2555 65 157.5 20
2.5% LWA (311) (1515) (38) (93)
Phase II Mix 3 525 2463 130 157.5 20
5.0% LWA (311) (1461) (77) (93)
Phase II Mix 4 525 2373 192 157.5 20
7.5% LWA (311) (1407) (113) (93)
Phase II Mix 5 525 2297 255 157.5 20
10% LWA (311) (1362) (151) (93)
All mixtures were design with a 20% air void content. This air void
content was an initial estimate based on literature. It was later found through this
research that the air void content decreases as the fine aggregate content increases
regardless of whether NWA or LWA is used as the fine aggregate.
During the trial phase, it was determined to add the mixing proportions
into the mixing drum in a certain way. Due to the limiting amount of water, the
addition of water and cement were the most curtail. Failure to follow the these
step ended up in a mixing that consist of aggregates that are coated with the
wetted cement and made look like small golf size balls which was very hard to
work with.
39


Add all the coarse, fine aggregates, and half of the cement into the mixing
drum to ensure and even distribution of all the materials. This is especially critical
for the fines aggregates due to its minimal amount. Once the three materials are
evenly distributed, half of the water was pored slowly into the mixing drum, this
is a very important step since the water to cement ration was 0.3. The rest of the
cement is then added gradually once the mixture is starting to show a good
consistency, followed by the rest of the water. Again the rest of the water is to be
added at the edge of the drum slowly. The Hydration Stabilizer was added last 2
min before removing the pervious concrete from the mixing drum.
After the mixing and prior to the placement of the pervious concrete, two
fresh properties were taken: Concrete Temperature which ranges from 58F and
61F, and unit weight and its results are presented with the rest of the results in
Chapter 5.
4.3 Mixture Proportioning
All the mixture designs in this researched assumed an air void of 20%,
which is considerably higher than the air void used by Dr. Angela Hager during
the design phase. A 20% air void will give the pervious concrete a lower unit
weight to that of conventional concrete. A 20% air void content was used in this
research due to the fact that pervious concrete has between 15-25% void structure.
To account for this void structure in the mixture design phase, a 20% air void was
assumed and used in the volumetric design process.
Air-entraining admixtures were not used in this study such that the effects
of the internal curing could be isolated, specifically the contribution of the LWA
40


for freeze/thaw durability. Hager reported that entraining air into the cement paste
will improve the freeze-thaw durability; however, it is difficult to quantify the
amount of air entrainment using the current ASTM standards on pervious
concrete.
4.3.1 Water-to-cement ratio
The cement needs water to hydrate. Once the hydration takes place, a
bond is formed between the cement paste and aggregates. This bond plays a major
role in the strength development of concrete.
It takes 0.00776 oz (0.22 grams) of water to hydrate 0.0353 oz (1 gram) of
cement. In order to fully hydrate the cement particles included in a mixture, a
minimum w/cm of 0.42 is required. However; at w/cm above 0.42, the space
occupied by the additional water will remain as pore space filled with air once the
concrete dries.
It is necessary to lower the w/cm to ensure a certain level of compressive
strength is reached. In this research a w/cm was established at 0.30 similar to that
in Dr. Angela S. Hagers Dissertation. At this ratio, the average compressive
strength surpassed 2000 (psi) and provided acceptable workability.
4.3.2 Cement Content
A cement Type I/II was used in all concrete mixture. The more cement
paste in the mixture typically the higher strength obtained. Yet the paste will fill
the pores within the concrete and therefore the concrete is not as pervious.
The cement content was chosen at 525 (lb/cy) which provides an
aggregate to cement ratio by volume of 6.0, which is within the recommended
41


values of 0.4 to 0.7 [Ann, 2003], At this content the concrete mixtures surpassed
the 2000 (psi) (13789 (kPa))in compressive strength. An increase in the cement
content would make the concrete less porous, and a decrease would result in a
weaker mixture.
Table 4.2 presents the physical and chemical properties of the cement used
in this research.
Table 4.2 Physical Properties of Cement
Fineness-Blaine 1,878 ffVlbs (90 (kPa)
C/2 CL, o Specific gravity 3.15
Vicat setting time 90 min.
u. Cu
15 o 55 Compressive strength 7-day 4,460 psi (30750 (kPa))
.c eu Compressive strength 28-day 6,300 psi (43437 (kPa))
Autoclave expansion 0.02 %
4.3.3 Aggregates Content
The aggregates used in the mixtures conformed to ASTM C 33. The
rounded shape of the aggregates used in this study will help improve the
workability of the mixtures since the w/cm is lower that recommended for
workable mixtures. The 3A inch size aggregates, gradation is shown in Figure 4.1.
In addition, due the limited amount of cement paste, it will be much easier to coat
rounded shaped aggregates than angular ones due the low surface to volume ratio
of rounded aggregates.
42


The fine aggregates are separated into two different phase studies. Phase I
where NWA was used and Phase II where LWA was introduced to the mixtures.
The fine contents for both NWA and LWA were based on percentages of the total
weight of aggregate and varied from 0% to 10% in 2.5 % increments. Gradation
for NWA is shown in Figure 4.2, and LWAs gradation is shown in Figure 4.3.
The strength and the durability of the concrete will be strongly linked to
the cement paste. Any improvements on the properties from between the two
pastes will be directly related to the fines.
Table 4.3 illustrates the physical properties of the coarse and fine
aggregates used in this research. More information on the aggregates is provided
in appendix F.
Table 4.3 Physical Properties of Aggregates
Physical Properties Rock NWA LWA
Bulk Specific gravity 2.59 2.61 1.88
Bulk Specific gravity (SSD) 2.61 2.63 1.91
Apparent Specific gravity 2.64 2.66 1.93
Absorption Capacity 0.8% 0.7% 19.56
43


120
100
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Seive Size (mm)
Figure 4.1 Rock Gradation
Figure 4.2 NWA Gradation
44


Figure 4.3 LWA Gradation
4.3,4 Hydration Stabilizer
During the trail phase it' was noticed that a layer of impervious concrete
was present toward the bottom of the concrete cylinders. Due to the high amount
of voids in the mixtures, the cement paste tends to consolidate and find its way to
the bottom of the molded concrete. This process will decrease the cement
particles on the top layer of the concrete; therefore the sample will have lower
compressive strength, and freeze-thaw durability. In addition, the impervious zone
created by the settling of cement paste will prevent adequate drainage of water
and prevent the pervious concrete from performing as its intended use. The
dosage of 20 oz/cwt of hydration stabilizer was necessary to prevent this process,
the amount was determined during trial phase. The cement particles are physically
coated by the hydration stabilizer, preventing water from contacting the cement,
thereby inhibiting hydration. In time, this physical coating breaks down, and
45


hydration occurs normally [Delvo 2001]. Similar findings were observed by
Hager [Hager, 2009],
Figure 4.4 shows on of the mixture with an impervious zone that was
obtained from one of the trail mixtures.
4.4 Testing
The testing part of this research consists of three tests, compressing
strength, porosity, and freeze-thaw testing. At 28 days of age 2 cored cylinders
will be tested for porosity, then tested for compressive strength. The same process
is repeated at 56 day of age. At 28 days of age one freeze thaw from each mixture
will be placed in the freeze-thaw chamber, the weight loss was recorded until the
complete deterioration of the beam.
46


4.4.1 Compression Testing
Compression testing requirements and procedures are addressed under
ASTM C39 [2005] for conventional concrete. Though this test procedure was not
necessarily intended for pervious concrete, currently, there is no standardized test
procedure for pervious concrete. During this test an axial load is applied to the
concrete cores samples at a rate of 35 +/- 7 psi/s [0.25 +/- 0.05 MPa/s] until
failure.
The compressive strength of the pervious concrete sample is obtained by
dividing the cross sectional area of the sample by the maximum axial load the
sample resisted prior to failure.
Unit weights of pervious concrete mixtures arc approximately 70% of
traditional concrete mixtures (100 125 pcf, 1602 2002 kg/m3) [Tennis, et al.
2004],
In order to conduct compression testing in the laboratory, 10-inch x 10-
inch x 7-inch (25.4 cm x 25.4 cm x 17.78 cm) wood molds, were was constructed
for the pervious concrete mixtures (9 total). A core drill mounting platform,
shown in Figure 4.5, was designed and constructed by Dr. Angela Hager and used
to core four 4 (in) diameter concrete samples out of each concrete block.
47


%
Figure 4.5 Test Block Core Drill Mounting Platform
Procedure:
Construct 10-inch x 10-inch x 7-inch (25.4 cm x 25.4 cm x 17.78 cm)
wood molds for concrete block.
1. Use 6 mil thick (0.006 in, 0.1524 mm) to cover the insides of the
wooden molds, spray with WD-40, then place the concrete in the
mold in four equal lifts by volume. After each lift of concrete should
be rodded 50 times, and the sides of the molds be tapped 25 times
using a rubber hammer to ensure proper compaction.
2. Use 6 mil thick (0.006 in, 0.1524 mm) plastic sheathing to cover the
top of the concrete block.
3. Label the concrete block on the top.
4. Immediately store the concrete block in the curing room.
5. Remove the plastic cover and take the concrete block out of the mold
at 10 days of age, and leave the pervious concrete block in the curing
48


room, which keep the concrete in a 50% relative humidity
environment, and 73F +- 3F.
6. At 28 days of age, core all four concrete samples from the concrete
block
7. Measure the diameter and the height of each specimen.
8. Perform porosity testing.
9. Saw cut the top and bottom of the cylinders to create a plane surface.
10. Place the concrete sample with the caps on into the compressive
testing machine.
11. Zero the compressive testing machine.
12. Since pervious concrete is weaker than conventional concrete, the
loading rate used for testing was half prescribed by ASTM C 39
[2005] ( 17.5 +/- 7 psi/s [0.125 +/- 0.05 MPa/s]).
13. Compressive strength is calculated in accordance with ASTM C 39
[2005],
4.4.2 Porosity Testing
The porosity testing utilized in this study was based on the volume
displacement method developed by Dr. Angela Hager during her testing. The
volume displacement accounts only for the porous voids in the sample and not on
the porous air pockets. In addition this method is fast and easy to follow.
Procedure:
1. Measure the diameter and the height of a plastic cylinder mold.
2. Measure the diameter and height of the pervious concrete sample.
49


3. Insert the pervious concrete sample into the plastic cylinder mold.
4. Fill the cylinder with the pervious concrete sample with water over a
period of one minute. Once water overflows from the top, keep
pouring water slowly for an additional 15 seconds.
5. Pour the water from the plastic cylinder mold into a measuring cup,
and measure the amount of water. Let the water drain for 30 seconds.
Note: When the plastic cylinder mold is flipped to drain the water,
the pervious sample should be secure and avoid shaking the
sample to force the water to exit the pervious concretes voids. In
addition, protect the sample from falling and breaking during the
test.
6. Calculate the percent porous void space as:
% Porous Void Space = (Volume of Water)/(Volume of Concrete
Specimen) (Equation 4.1)
4.4.3 Freeze-Thaw Testing
ASTM C 666 [2005] discusses the freeze-thaw testing of concrete. This
method calls for two different procedures. The first is called Procedure A, it
involves the rapid freezing and thawing in water and Procedure B involves the
rapidly freezing of the sample in air and thawing in water. Both procedures under
ASTM C666 [2005] evaluate the transverse frequency of the freeze-thaw beams
by sending a current through the beam and calculating the Relative Dynamic
Modulus of Elasticity of the beam before, during, and after the freeze-thaw
testing. However, the pervious concrete sample contains approximately 20%
50


voids, which make the frequency testing unfit for the pervious concrete samples.
Thus another more appropriate method for determining freeze/thaw durability
must be utilized. Dr. Angela Hager evaluated the freeze/thaw durability of
pervious concrete using mass loss measurements during the freezing and thawing
testing. Samples that were more durable exhibited increased numbers of cycles
with less mass loss. Procedure A was used for this study. Though this procedure
is not realistic to the conditions of the pervious concrete in the field (ie. the
pervious concrete should never be submerged), the test does provide an indication
of freeze/thaw durability when compared to other samples subjected to the same
testing.
A total of nine freeze-thaw beam molds were constructed out of wood for
the freeze-thaw testing.
Procedure:
1. Use 6 mil thick (0.006 in, 0.1524 mm) to cover the insides of the wood
molds, spray with WD-40, then pour concrete in the mold in three
equal lifts by volume. After each lift, the concrete was rodded 30
times, and tapped 15 times on the sides using a rubber hammer to
ensure proper compaction.
2. Use 6 mil thick (0.006 in, 0.1524 mm) plastic sheathing to cover the
top of the concrete block.
3. Label the concrete freeze-thaw beams on the top.
4. Store the concrete freeze-thaw beams in the curing room.
51


5. Remove the plastic cover and take the concrete block out of the mold
at 10 days of age, and leave in the curing room until testing.
6. At 28 days of age, the freeze-thaw beams were prepared for testing in
the Freeze-Thaw Chamber. The preparation included:
a. Measure the dry weight of the concrete sample.
b. Submerge the concrete sample in water, dry the surface, then
measure the saturated surface dry weight of the concrete
sample.
c. Place a z shaped spacer bar into the bottom of the freeze-
thaw tray to keep the beams from touching the bottom of the
tray.
d. Place the concrete sample into the tray.
e. Place a z shaped spacer on top of the beam, it will be a guide
for the water placed on top of the beam.
f. Place the tray into the freeze-thaw chamber.
g. Attach adjacent trays using 2 clips per side to ensure the
distribution of heat during the thaw process.
h. Fill the tray with water until the top z shaped spacer is
submerged.
i. As water migrates to the inner pores inside the concrete
sample, the water level will go down, make sure to add water.
7. Record the date and time.
52


8. The tray with the beams in it to be removed from the freeze-thaw
chamber three times a week during the thawing phase.
9. Clean the surfaces of the freeze-thaw beam to remove any loose
aggregate. Then, dry the beam and measure the saturated surface dry-
weight.
10. Repeat steps c through i of the beam preparation included in step 6
of this procedure.
11. Remain measuring the mass of the freeze-thaw beam until the beam
has disintegrated.
The type of freeze thaw testing that pervious concrete mixtures were
exposed to was severe and not realistic of field-site conditions. The fact that the
freeze-thaw beams were submerge in water throughout the cycles is a condition
the pervious concrete may never see. Pervious concrete relies on its pore structure
to drain water, in addition to a free draining gravel that ranges from 6 in (2.4 cm)
to 12 in (4.7 cm) in thickness below the pervious concrete in addition to a sand
layer beneath that. Thus, pervious concrete is designed to avoid going through
these submerge freeze-thaw conditions by allowing water to drain at an
accelerated rate through the pervious concrete layer of the system.
There is much more realistic approach to test the freeze-thaw durability of
pervious concrete such as depending on the climate. NRMCA recommends three
different types of freeze:
Dry Freeze and Hard Dry Freeze (Typical Metro Denver Area
Environment)
53


Dry freeze areas are those parts of the country that undergo a
number of freeze-thaw cycles (15+) annually in which there is little
precipitation during the winter. If the ground stays frozen as a result of a
long continuous period of average daily temperatures below freezing, the
area is referred to as hard dry freeze area. Since pervious concrete is
unlikely to be fully saturated in this environment, no special precaution is
necessary for successful performance of pervious concrete. However, a
100- to 200mm (4- to 8-in.) thick layer of clean aggregate base below the
pervious concrete is recommended as an additional storage for the water.
Many parts of the western United States at higher elevations fall under this
category. [NRMCA 2009]
Wet Freeze
This includes areas of the country that undergo a number of freeze-
thaw cycles annually (15+) and there is precipitation during the winter.
Since the ground does not stay frozen for long periods, it is unlikely that
the pervious concrete will be fully saturated. No special precaution is
necessary for successful performance of pervious concrete, but a 100- to
200mm (4- to 8-in.) thick layer of clean aggregate base below the pervious
concrete is recommended. The middle part of the eastern United States
falls under this category. [NRMCA 2009]
Hard Wet Freeze
Certain wet freeze areas where the ground stays frozen as a result
of a long continuous period of average daily temperatures below freezing
54


are referred to as hard wet freeze areas. These areas may have situations
where the pervious concrete becomes fully saturated because frozen soil
will have very low water permeability. The frost penetration depth (depth
at which the temperature is at 0 C [32 F]) varies throughout the country.
To design the pervious concrete pavement for freeze-thaw resistance the
following is suggested by NRMCA. [NRMCA 2009]
1. Calculate the frost penetration depth in your area. Calculate 65%
of that. The Federal Aviation Administration (FAA) says that the
top 65% should contain non-frost-susceptible materials and the
bottom 35% may be in frost susceptible subgrade. It should be
noted that the FAA uses the 65% limitation to prevent frost heave.
In this case, the key factor is water infiltration. This is about 50 cm
(19.5 in.) for the 75 cm (30 in.) frost penetration depth. [NRMCA
2009]
2. Provide pervious concrete pavement plus aggregate base equal to
the number calculated. For a 50-cm (19.5-in.) calculation, a 15-cm
(6-in.) thick pervious concrete pavement over a 35-cm (13.5-in.)
thick aggregate base would be sufficient. The aggregate base must
consist of clean well draining open graded aggregate base with less
than 1.5% finer than 0.02 mm (0.5 mm). [NRMCA 2009]
During Phase I, compressive strength, and porosity results behavior as the
NWA content increases was recorded and plotted at both at 28 and 56 day of age.
55


During the freeze-thaw testing the beams durability was quantified by measuring
their mass loss, the beams that show less mass loss over time compared to the rest
was the most durable. The effect of the voids on strength was obtained by plotting
the void measured from the porosity testing and the compressive strength. Also,
the NWA content was determined based on the compressive strength,
hydrological, and durability criteria.
The results from Phase II was used in the same way as in Phase I, in
addition a comparison of all three testing results to establish the changes that
happened to the Phase #11 mixtures due to the inclusion of LWA.
56


5. Laboratory Results
Sand inclusion up to 10% enhances the durability of the pervious concrete,
and any increase in fine content beyond the 10% will compromise the hydraulic
requirement of the mixture [Hager 2009].
Phase I of this research study was conducted to verify the optimum fine
aggregate content that provides increased freeze/thaw durability and acceptable
compressive strength while meeting the hydrologic requirements. Typically, as
the fine aggregate content increases, the air void content decreases resuiting in
decreased porosity.
To stay consistent with [Hager, 2009], five different mixture designs, with
varying amount of NWA were utilized for Phase I. The five mixtures varied by
sand content from 0% to 10% in 2.5% increments.
1. Phase I and II Mixture 1 0% fine aggregate
2. Phase I Mixture 2 - 2.5% fine aggregate (NWA)
3. Phase I Mixture 3 - 5.0% fine aggregate (NWA)
4. Phase I Mixture 4 - 7.5% fine aggregate (NWA)
5. Phase I Mixture 5 - 10% fine aggregate (NWA)
The primary difference between this study and [Hager, 2009] is the air
void content accounted for during the design phase of the study. The design of
each pervious concrete mixture was achieved using the absolute volume method.
Thus, the total volume of all constituents for each mixture equaled one cubic yard.
57


In Hager, 2009, the air void content was assumed to be 2%; whereas, in
this study a 20% air void content was used. The 20% is more realistic of the
pervious concrete stmeture as pervious concrete mixtures typically contain
between 15-25% voids. The increased void content assumed in this study
ultimately results in less volume of aggregate in the mixture. Subsequently this
results in an increased amount of paste availabl e to cover and bind the aggregate
particles.
In Phase II, LWA was used to determine the effects of internal curing on
the compressive strength, porosity, and freeze/thaw durability of pervious
concrete. In addition, the performance of the mixtures containing LWA will be
compared to those of Phase I with the N W A to determine whether the internal
curing significantly enhances the performance of the pervious concrete. The
design mixtures in Phase II are similar to that of Phase I except for the fine
aggregate type; Phase II contained LWA as the fine aggregate. At 0% fine
aggregate content, Mixture #1 is the same for both phases of the study. Mixtures
for Phase II are shown below:
1. Phase I and II Mixture 1 0% fine aggregate
2. Phase II Mixture 2 - 2.5% fine aggregate (LWA)
3. Phase II Mixture 3 - 5.0% fine aggregate (LWA)
4. Phase II Mixture 4 - 7.5% fine aggregate (LWA)
5. Phase II Mixture 5 - 10% fine aggregate (LWA)
58


A summary of the SSD proportions for all the mixtures are presented in
Chapter 4, Section 4.2, and the complete mixture design spreadsheet is presented
in Appendix C.
Four cored cylinders and one freeze-thaw beam were fabricated for all
mixture designs. The cored cylinders were used for porosity and compressive
strength at 28 and 56 days of age and the beam used for freeze/thaw durability
testing beginning at 28 days of age. The cylinders were first tested for porosity
and then compressive strength thereafter. There was no apparent difference
between the two studies; however, within each Phase, as the fine aggregate
content increased, the workability of the mixture decreased.
5.1 Phase I Normal Weight Sand
5.1.1 Compressive Strength Testing Results
5.1.1.1 28 Days of Age
The compressive strength of two cored cylinders from each design mixture
was tested at 28 days of age. The results of these tests are shown in Table 5.1 and
illustrated in Figure 5.1.
Table 5,1 28-Day Compressive Strength Results Phase I
%Sand Compressive Strength (psi) Compressive Strength (kPa)
0.0% 1,443 9,949
2.5% 2,145 14,789
5.0% 2,254 15,541
7.5% 2,589 17,851
10.0% 2,708 18,671
59


Figure 5.1 28-Day Compressive Strength Results Phase I
These results correlate well with [Hager, 2009] results. As predicted, the
compressive strength increases as the fine aggregate content increases. All the
samples that contain fines in the design mixture surpassed the structural criteria of
2000 (psi) 13789 (kPa) of compressive strength.
5.1.1.2 56 Day of Age
The compressive strength of two cylinders from each mixture were tested
at 56 days of age. The results of the testing are shown in Table 5.2 and graphically
in Figure 5.2.
60


Table 5.2 56-Day Compressive Strength Results Phase I
%Sand Compressive Strength (psi) Compressive Strength (kPa)
0.0% 1,590 10,963
2.5% 2,247 15,493
5.0% 2,385 16,444
7.5% 2,703 18,637
10.0% 2,966 20,450
3500 25000
3QQQ ,
*w5 & 2500 - < 20000
u> c 9nnn 1 sz O) 15000
**
to 0) k. Q_ - mnn _ - 10000 Q> Q. E
o O f;nn _ o 5000
n - 0
0.( )% 2.5% 5.0% 7.5% 10 0%
Sand %
Figure 5.2 56-Day Compressive Strength Results Phase I
The trend of increasing compressive strength with increasing fine
aggregate content holds true at 56 days of age. These results confirm those found
by Hager, 2009. All the samples that contained fines in the design mixture
surpassed the structural criteria of 2000 (psi) of compressive strength.
The percent increase in the compressive strength of the mixtures
containing fine aggregate compared to the control without fine aggregate is
61


illustrated in Figure 5.3. This graph shows that a substantial increase in
compressive strength is observed between 0.0% and 2.5% and continued increase
in compressive strength with increasing contents of fine aggregate content. A
greater increase in compressive strength compared to the control was observed at
28 days of age than 56 days of age.
Figure 5.3. (%) Increase in Compressive Strength Compared to
the Control
5.1.2 Porosity Testing Results
5.1.2.1 28 Days of age
The results for porosity testing are shown in Table 5.3 and presented as a
graph in Figure 5.4.
62


Table 5.3 28-Day Porosity Results Phase I
%Sand Average % Porous Void Space
0.0% 18.80%
2.5% 14.82%
5.0% 12.95%
7.5% 10.84%
10.0% 8.18%
20%
%Sand inclusion
Figure 5.4 28-Day Porosity Results Phase I
As predicted, the porosity of the concrete mixtures decreases as the fine
content increases. The hydrologic requirement of 10% porosity is met by all
mixtures in Phase I except for Mixture 5 10% NWA. Again, there results
confirm that of Hager, 2009. Ash shown in Figure 5.4, the relationship between
porosity and fine aggregate content is approximately linear. Thus, the percent
porosity can be estimated based on this linear relationship.
63


Figure 5.5 shows the compressive strength with respect to porosity at 28
days of age. In order to meet the hydrologic criterion of 10% porosity, a
maximum sand inclusion that could be used in a pervious design mixture is 7.5%.
Figure 5.5 Porosity Vs Compressive Strength at 28-Day Phase I
5.1.2.2 56 Days of Age
The results for porosity testing at 56 days of age are shown in Table 5.4
and illustrated in Figure 5.6
64


Table 5.4 56-Day Porosity Results Phase I
%Sand Average % Porous Void Space
0.0% 18.48%
2.5% 14.80%
5.0% 13.17%
7.5% 10.62%
10.0% 7.98%
% Sand Inclusion
Figure 5.6 56-Day Porosity Results Phase I
As predicted, the porosity of the concrete mixtures decreased as the NWA
increased; however, there is no variation from the porosity measured at 28 days of
age. The hydrologic requirement of 10% porosity is met by all mixtures in Phase I
except for Mixture #5 10% NWA. These results confirm that of Hager, 2009.
65


The percent decrease in porosity of the mixtures containing fine aggregate
compared to the control without fine aggregate is illustrated in Figure 5.7. This
graph shows that a substantial decrease in porosity that is almost linear is
observed throughout the mixtures with increasing contents of fine aggregate
content for both 28 and 56 days of age. A greater increase in compressive
strength compared to the control was observed at 28 days of age than 56 days of
age.
Figure 5.7 (%) Decrease in Porosity Compared to the Control
- Phase I
Figure 5.8 shows the compressive strength with respect to porosity at the
56 days of age. In order to meet the hydrologic criterion of 10% porosity, a
maximum NWA inclusion that could be used in a pervious design mixture is
7.5%.
66


Figure 5.8 Porosity Vs Compressive Strength at 56-Day -
Phase I
5.1.3 Freeze-thaw Testing Results
Freeze-thaw testing took place when the concrete reached 28 days of age.
The concrete went through five freeze-thaw cycles per day until the beam
completely deteriorated. The temperature was recorded using a probe into an
electric device. The recorded data was downloaded and stored as pdf files.
Appendix E contains a week of recorded temperature that pervious concrete went
through. Table 5.5 and Figure 5.9 provide freeze-thaw results for Phase I. It took
between 95 and 145 cycles for the concrete beams to be completely deteriorated.
67


Table $.5 Freeze-thaw Testing Results Phase 1
# FT Cycles 0.0% Sand 2.5% Sand 5.0% Sand 7.5% Sand 10% Sand
START 100% 100% 100% 100% 100%
20 87.6% 83.4% 95.0% 95.9% 98.5%
45 84.3% 65.5% 92.7% 80.3% 88.3%
70 0.0% 63.1% 86.4% 72.1% 54.4%
95 0.0% 60.2% 37.9% 0.0%
120 39.1% 0.0%
145 0.0%
Freeze-Thaw T esting
120.0 -
D 20 40 50 BO K'D 120 140 160
OFT Cycles
| 0.0%Fines 2.5'%3AND a 7.5%SAND 10.0%SAND 5.0% SAND
Figure 5.9 Freeze-thaw Testing Results Phase I
The 5.0% sand inclusion mixture showed the highest durability against
freeze-thaw. Hager found the 7.5% sand inclusion mixture to be the most durable
68


mixture. These results confirm the findings of Jones (2008) from Iowa State
University who recommended 5% to 7% sand inclusion.
5.1.4 Conclusion
From the compressive strength testing, all mixtures satisfied the structural
requirement; except Mixture #1 0% NWA which has an average compressive
strength of 1,443 (psi) 9949 (kPa), more than 500 (psi) 3447 (kPa) lower than
strength desired.
Porosity showed that all mixtures satisfied the hydrological requirement
except Mixture #5 10% NWA; which was lower than 10% porosity.
Freeze-thaw testing of the mixtures found that mixtures Mixture #3-5%
NWA, and Mixture #4 7.5% NWA to be the most durable mixtures.
Therefore, to produce a mixture that satisfies a 10% porous void as a
hydrological requirement for water drain properly, withstand at least 2000 (psi)
13789 (kPa) of compressive force. In order to provide an acceptable level of
freeze-thaw resistance, mixtures should have a maximum sand inclusion of 7.5%.
Based on the 28 and 56 days of age test results for Phase I testing the NWA
content should range between 5 7.5% by total weight of aggregate to provide
increased compressive strength and durability while meeting minimum porosity
requirements.. These results confirm those published by Hager, 2009. .
5.2 Phase II Lightweight Aggregate and Comparison
5.2.1 Compression Strength Testing Results
5.2.1.1 28 Days of Age
69


The compressive strength of two cored cylinders from each mixture were
tested at 28 days of age. The results of the testing are listed in Table 5.6and
graphed in Figure 5.10. .A comparison of the NWA and LWA pervious concrete
mixtures is presented in Figure 5.11.
Table 5.6 28-Day Compressive Strength Results Phase II_____________
% LWA Compressive Strength (psi) Compressive Strength (kPa)
0.0% 1,443 9,949
2.5% 2,256 15,555
5.0% 2,355 16,237
7.5% 2,677 18,457
10.0% 2,756 19,002
Figure 5.10 28-Day Compressive Strength Results Phase II
70


3000
Figure 5.11 28-Day Compressive Strength Results Phases I and II
These results show that the compressive strengths of Phase II mixtures
containing LWA are slightly higher than Phase I mixtures with NWA. An average
compressive strength increase of approximately 100 (psi) 689 (kPa) is noticeable
among all mixtures.
5.2.1.2 56 Days of Age
The compressive strength of two cored cylinders from each mixture were
tested at 56 days of age. The results of the compressive strength tests are shown in
Table 5.7 and presented as a graph in Figure 5.12. In addition, a comparison
between the Phase I and II mixtures are shown in Figure 5.13.
71


Table 5.7 56-Day Compressive Strength Results Phase LI
% LWA Compressive Strength (psi) Compressive Strength (kPa)
0.0% . 1,590 10,963
2.5% 2,431 16,761
5.0% 2,535 17,478
7.5% 2,891 19,933
10.0% 3,102 21,388
Figure 5.12 56-Day Compressive Strength Results Phase II
72


Figure 5.13 56-Day Compressive Strength Results Phase 1 and II
These results show that the compressive strengths of Phase II mixtures
with LWA are slightly higher than Phase I mixtures with NWA. An average
compressive strength increase of 170 (psi) is noticeable among all mixtures at 56
days of age.
The percent increase in the compressive strength of the mixtures
containing fine aggregate compared to the control without fine aggregate is
illustrated in Figure 5.14. This graph shows that a substantial increase in
compressive strength is observed between 0.0% and 2.5% and continued increase
in compressive strength with increasing contents of fine aggregate content. A
greater increase in compressive strength compared to the control was observed at
28 days of age than 56 days of age.
73


Figure 5.14. (%) Increase in Compressive Strength Compared
to the Control Phase II
5.2.2 Porosity Testing Results
5.2.2.1 28-Day
The results for porosity testing are shown in Table 5.8 and presented as a
graph in Figure 5.15. In addition a comparison of the mixtures containing LWA
and NWA are presented in Figure 5.16.
Table 5.8 28-Day Porosity Results Phase II____
% LWA Average % Porous Void Space
0.0% 18.80%
2.5% 14.40%
5.0% 13.76%
7.5% 8.24%
10.0% 7.31%
74


% LWA Inclusion
Figure 5.15 28-Day Porosity Results Phase II
Figure 5.16 28-Day Porosity Results Phases I and II
75


The porosity of the concrete mixtures decreased as the fine aggregate
content increased for both NWA and LWA. The hydrologic requirement of 10%
porosity is met by all mixtures in Phase II except for Mixture #5 10% LWA,
and for Mixture 4 7.5% LWA. Overall, the porosity remains similar between
Phases I and II. The internal curing with LWA for the mixtures in Phase II had
little effect on the hydrological property of the pervious concrete when compared
to mixtures of Phase I.
Figure 5.17 shows the compressive strength with respect to porosity at 28
days of age for the Phase I and II mixtures. In order to meet the hydrologic
criterion of 10% porosity, a maximum sand inclusion that could be used in a
pervious design mixture is 7.5%.
Figure 5.17 Porosity Vs Compressive Strength at 28 Days-
Phase I and II
76


5.22.2 56 Days of Age
The results for porosity testing are shown in Table 5.9 and presented as a
graph in Figure 5.18. A comparison of LWA ang NWA mixtures is shown in
Figure 5.19.
Table 5.9 56-Day Porosity Results Phase II______
% LWA Average % Porous Void Space
0.0% 18.48%
2.5% 15.15%
5.0% 13.80%
7.5% 8.4%
10.0% 7.39%
Figure 5. 18 56-Day Porosity Results Phase II
77


Figure 5.19 56-Day Porosity Results Phases I and II
The percent decrease in porosity of the mixtures containing fine aggregate
compared to the control without fine aggregate is illustrated in Figure 5.20. This
graph shows a decrease in porosity is observed throughout the mixtures with
increasing contents of fine aggregate content for both 28 and 56 days of age. A
greater increase in compressive strength compared to the control was observed at
28 days of age than 56 days of age.
78


Figure 5.20 (%) Decrease in Porosity Compared to the Control
- Phase II
The results are almost unchanged in comparison to those at 28 days of age.
Figure 5.21 shows the compressive strength with respect to porosity at the 56 days
of age. In order to meet the hydrologic criterion of 10% porosity, a maximum
sand inclusion that could be used in a pervious design mixture is 7.5%.
79


3500
3000
= 2500
2000
i 1500
£
a
E
o
o
1000
500
0.00
2.00 4.00 6.00
8.00 10.00 12.00
% Porous Void Space
14.00 16.00 18.00 20.00
I NWA
LWA
Figure 5.21 Porosity Vs Compressive Strength at 56-Day Phase I
and II
5.2.3 Freeze-Thaw Durability
Freeze-thaw testing took place when the concrete reached 28 days of age.
The concrete went through five freeze-thaw cycles per day until the beam has
deteriorated. The temperature was recorded using a probe the records data into an
electric device from which the data is downloaded into pdf files. Appendix E
contains a week of recorded temperature that pervious concrete went through.
Table 5. lOand Figure 5.22 present summary of the freeze-thaw results for phase
II. It took between 125 and 200 cycles for the concrete beams to be completely
deteriorated. Phase II mixtures are more durable to freeze-thaw than mixtures
from Phase I. It took on average of 80 more cycles for Phase II mixtures to
deteriorate.
80


These results were expected, due to the large void structure of the
lightweight aggregates, more water finds its way to these pore and freezes. Unlike
the normal weight aggregates where the pores are very limited, as a result water
freeze-thaw damage comes quicker than the LWA mixtures.
Table 5.10 Freeze-thaw Testing Results Phase II
# FT Cycles 0.0% LWA 2.5% LWA 5.0% LWA 7.5% LWA 10% LWA
START 100% 100% 100% 100% 100%
20 87.6% 94.9% 97.3% 95.2% 98.0%
45 84.3% 80.9% 96.0% 92.5% 90.5%
70 0.0% 75.6% 92.0% 84.0% 88.0%
95 37.1% 76.6% 69.8% 76.0%
120 0.0% 68.9% 64.0% 28.5%
145 59.5% 42.3% 0.0%
170 46.2% 37.0%
195 34.2% 0.0%
220 26.8%
245 0.0%
81


Figure 5.22 Freeze-thaw Testing Results Phase I & II
The 7.5% sand inclusion mixture showed the highest durability against
freeze-thaw.
5.2.4 Conclusion
At 28 days of age, Phase II mixtures surpassed Phase I mixtures in
compressive strength by an average of 100 (psi) 689 (kPa). The difference
between the LWA and NWA mixtures increases to 170 (psi) 1172 (kPa) at 56
days of age.
The porosity results of Phase II were similar to that of Phase I. The
internal curing showed little to no effect on the hydrological properties of the
pervious concrete at 28 and 56 days of age.
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Phase II freeze-thaw testing showed more durable mixtures than Phase I
mixtures. On average, Phase II mixtures withstood an additional 80 more freeze-
thaw cycles that those of Phase I. Mixture #3 5% showed to be the most durable
mixture to freeze-thaw cycles, whereas in Phase I Mixture #4 7.5% was the
most durable.
When examining the results of Phase I and II, it is important to notice that
the voids within the pervious concrete are not the same as entrained air. Thus, the
fact that the compressive strength and freeze-thaw durability was improved in
Phase II is in fact related to fine aggregate. The results of this experimental study
demonstrate that the use of saturated LWA improves the structural and durability
performance of pervious concrete. Due to interna! curing, the migrating water
from the LWA pores to the paste helps continue the hydration of the cement. As
the cement kept hydrating, more cement hydration products were formed, thereby
producing a stronger paste. In addition, the use of the LWA helped to improve
the freeze/thaw durability of the pervious concrete. The increased freeze/thaw
performance is believed to be the result of additional voids within the LWA.
LWA contains approximately 18% voids, thereby providing room for water to
freeze and thaw.
Internal curing using LWA improves the compressive strength of pervious
concrete, and improves its durability against freeze-thaw cycles.
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6. Statistical Analysis
6.1 Introduction
A paired t-test is used to compare means on the same or related subject over time
or in differing circumstances. The observed data are from the same subject or
from a matched subject and are drawn from a population with a normal
distribution. Subjects are often tested in a before-after situation, or subjects are
paired such as with twins, or with subject as alike as possible. The paired t-test is
actually a test that the difference between the two observations is 0. So, if D
represents the difference between observations, the hypotheses are: Ho: D = 0 (the
difference between the two observations is 0), and Ha: D 0 (the difference is not
0). The test statistic is t with n-1 degrees of freedom. If the p-value associated
with t is low (< 0.05), there is evidence to reject the null hypothesis. Thus, you
would have evidence that there is a difference in means across the paired
observations.
Excel spreadsheet were used to determine the probability p-value,
If the p-value is less that the 5% confidence level that means the probability of the
hypothesis difference between the two data is zero is to be rejected. The closer
the p-value to zero the more significant the difference between the data.
The results of the paired t-test are summarized in the tables below. These
results confirm that the internal curing does in fact improve the compressive
strength and the freeze-thaw durability of the pervious concrete. Statistically, the
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internal curing with the LWA does not have an significant effect on the porosity
of the pervious concrete.
6.1.1 Compressive Strength Analysis
As shown in the Laboratory Results Chapter, the difference between
compressive strength between the NWA and the LWA ranges from 48 (psi) to
111 (psi) at 28 Days of age, and 136 (psi) (937 (kPa)) to 188(psi) (1296 (kPa)).
So, normally 200 (psi) (1379 (kPa)) plus or minus in concrete compressive
strength is a small number to be considered a major difference. However, this
difference is consistent throughout the samples the paired t test confirmed that the
difference is significant.
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Table 6.1 Compressive Strength Paired t-test Results
Mixture NWA psi (kPa) LWA psi (kPa) Difference t (Stat.) t(Crit.) P Value
2.5% 2,145 (14,789) 2,256 (15,555) 111
es Q 5.0% 2,254 (15,541) 2,355 (16,237) 101 6.29 3.182 0.0081
00 10.0% 2,708 (18,671) 2,756 (19,002) 48
2.5% 2,247 (15,493) 2,431 (16,761) 184
c Q 5.0% 2,385 (16,444) 2,535 (17,478) 150 12.9 3.182 0.0010
VO 7.5% 2,703 (18,637) 2,891 (19,933) 188
10.0% 2,966 (20,450) 3,102 (21,388) 136
6.1.2 Porosity Analysis
The porosity values from NWA to LWA did not follow any specific
trends. In some cases the NWA was more porous than the LWA and vice versa,
and they difference was not large enough to tell if there is an effect of LWA on
porosity or not. The t-test confirmed that the results between the two phases were
not significant.
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Table 6.2 Porosity Paired t-test Results
Mixture NWA LWA Difference t (Stat.) t(Crit.) P Value
28 Day 2.5% 14.82 14.4 -0.42 1.09 3.182 0.3551
5.0% 12.95 13.76 0.81
7.5% 10.84 8.24 -2.6
10.0% 8.18 7.31 -0.87
56 Day 2.5% 14.8 15.15 0.35 0.712 3.182 0.5280
5.0% 13.17 13.8 0.63
7.5% 10.62 8.4 -2.22
10.0% 7.98 7.39 -0.59
6.1.3 Freeze-Thaw Analysis
The freeze-thaw statistical analysis results showed that the difference
between the two different phase studies were significant, but it was not as
significant as the compressive strength. This is due to the fact the freeze-thaw
measure during the laboratory testing was done every 4 to 5 days, as a results the
data was in increments of 25 cycles, as to the compressive strength where the
compressive strength was measured on increments of 1 (psi). If the freeze thaw
beams were to be measures every 2 day, the results would have been more
significant.
Table 6.3 Compressive Strength Paired t-test Results
Mixture NWA LWA Difference t (Stat.) t(Crit.) P Value
2.5% 95 120 75 3.87 3.182 0.0352
5.0% 145 245 100
7.5% 120 195 75
10.0% 95 145 50
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