Low Heat High Performance Concrete for Glass Fiber Reinforced Polymer Reinforcement by Alien Jawara A Thesis Submitted to the Faculty of Graduate Studies of the University of Manitoba in Partial Fulfillment of the Requirements of the Degree of Master of Science Structural Engineering Division Department of Civil Engineering University of Manitoba Wmnipeg, Manitoba
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Low Heat High Performance Concrete for Glass Fiber Reinforced Polymer Reinforcement
by
Alien Jawara
A Thesis Submitted to the Faculty of Graduate Studies of
the University of Manitoba in Partial Fulfillment of the Requirements of the Degree of
Master of Science
Structural Engineering Division Department of Civil Engineering
University of Manitoba Wmnipeg, Manitoba
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LOW HEAT mGH PERFORMANCE CONCRETE FOR GLASS FIBER REINFORCED POLYMERREllWORCEMrnNT
BY
ALIEU JAWARA
A ThesislPracticum submitted to the Faculty of Graduate Studies of The University
of Manitoba in partial fulfillment of the requirements of the degree
Permission has been granted to the Library of The University of Manitoba to lend or sen copies of this thesislpracticnm, to the National Library of Canada to microfilm this thesis and to lend or sen copies of the ~ and to Dissertations Abstracts International to publish an abstract of this thesis/practicum.
The author reserves other publication rights, and neither this thesis/practicum nor extensive extracts from it may be printed or otherwise reproduced without the author's written permission.
----------------------ACKNOWLEDGMENTS
The author would like to acknowledge the following people who were vital to the research performed for this testing program.
• Dr. Sami Rizkalla for his guidance and continuous support throughout the research work;
• Atomic Energy of Canada Limited for providing the financial support for this research;
• Messrs. Moray McVey of ISIS Canada, Scott Sparrow and Roy Hartle of University of Manitoba and Nazeer Khan of AECL for their assistance in fabricating and testing the specimens;
• ISIS Canada staff for their support and cooperation;
• Professor John Glanville for reviewing the final draft of this thesis.
---------------------------------ABSTRACT
Low heat high performance concrete (LHHPC) is concrete with low cement
content, a consequent low heat of hydration and a relatively low alkalinity. The research
program described in this thesis was designed to study Lffi-lPC in terms of mechanical
properties, structural behaviour and durability under freezing and thawing. The
durability of reinforcement (steel and GFRP) in the low alkaline environment of LHHPC
is also investigated.
Use of glass fiber reinforced polymer (GFRP) as a replacement for conventional
steel reinforcement has increased rapidly for the last ten years. The non-corrosive
characteristics and high strength-to-weight ratio of GFRP might significantly increase the
service life of structures. However, the chemical composition of glass is known to be
unstable in the high alkaline environment of concrete pore water. The low alkalinity of
LHHPC might have beneficial effects in the use of GFRP as reinforcement for this new
concrete. The low alkalinity might, on the other hand accelerate corrosion of steel
reinforcement.
Over sixty standard size cylinders were cast and tested to study the mechanical
properties of LIll-IPC and the results indicate compressive strengths of over 70 ~a at 28
days for LHHPC.
Abstract
Eight beams of rectangular section were cast and tested to study the behaviour of
the reinforced LHHPC. The results indicate a higher strength and ductility for LHHPC
than the control normal conventional concrete (Nee) beams.
The results from the air-entrained concrete indicate that LHHPC has an excellent
durability factor against freezing and thawing while maintaining high compressive
strengths for an air content of 4.6 percent.
The tensile strength ofGFRP bars embedded in both LHHPC and NCe, at 60°C,
are identical after one month.
iii
TABLE OF CONTENTS
Acknowledgements
Abstract
Table of Contents
List of Tables
List of Figu res
1. Introduction
1.1 General
1.2 Objectives
1.3 Scope and Contents
2. Literature Review
2.1 General
2.2 Constituents ofLHHPC
2.2.1 Sulfate-Resistant Portland Cement (Type 50)
2.2.2 Silica Fume
2.2.3 Silica Flour
2.2.4 Liquid Superplasticizer (Disal)
1
ii
iv
vii
ix
1-1
1-2
1-2
2-1
2-1
2-1
2-1
2-2
2-2
2-3
2.2.S Mix Water
2.2.6 LSL Sand
2.2.7 Granite Gravel
2.2.8 Pea Stone Gravel
2.3 Properties ofLHHPC
2.4 Freeze-Thaw Durability of Concrete
2.S Glass Fiber Reinforced Polymer Reinforcements
2.S.1 Mechanical Properties of GFRP
2.S.2 Durability ofGFRP in Concrete
3. Experimental Program
3.1 Phase I: Material Properties
3.1.1 Materials
3.1.2 Instrumentation and Test Procedure
3.2 Phase II: Structural Behaviour
3.2.1 Materials
3.2.2 Instrumentation
3.3 Phase III: Durability Aspects
3.3.1 Freeze-Thaw Cycles
3.3.1.1 ~erials
3.3.1.1 Methodology
3.3.2 DurabilityofGFRP inLHHPC
3.3.2 Durability of Steel in LHHPC
v
Table of Contents
2-3
2-3
2-4
2-4
2-S
2-7
2-8
2-9
2-10
3-1
3-1
3-2
3-3
3-4
3-4
3-S
3-6
3-6
3-6
3-7
3-8
3-10
4. Test Results and Discussions
4.1 Phase I: Material Properties
4.2 Phase II: Structural Behaviour
4.2.1 Load-Deflection Behaviour
4.2.2 Crack Patterns and Failure Modes
4.2.3 Strain Distribution
4.2.4 Ductility
4.2.5 Analytical Model
4.3 Phase m: Durability Aspects
4.3.1 Freeze-Thaw Cycles
4.3.2 Compressive Strength
4.3.2 Durability of Reinforcements in LHHPC
5. Summary and Conclusions
5.1 Phase I: Material Properties
5.2 Phase II: Structural Behaviour
5.3 Phase ill: Behaviour under Cycles of Freezing and Thawing
5.4 Durability of Reinforcements
5.5 Recommendations for Future Research
6. References
vi
Table of Contents
4-1
4-1
4-7
4-7
4-10
4-12
4-13
4-14
4-15
4-15
4-17
4-17
5-1
5-1
5-2
5-3
5-4
5-4
6-1
-------------- LIST OF TABLES
Table
2.1 Resuhs of the 28-day LHHPC from CANMET 2-14
2.2 Results of the 90-day LHHPC from CANMET 2-15
3.1 Mix Design for LIllIPC and SHPC 3-12
3.2 Details of Beams Reinforced by Steel 3-13
3.3 Details of Beams Reinforced by GFRP 3-13
3.4 Mix Design and Properties for Different Batches of the Freeze-Thaw Samples 3-14
3.5 Test Dates for Durability Specimens for Steel and GFRP Reinforcements 3-15
4.1 14 Day Test for Batch 1 4-19
4.2 28 Day Test for Batch 1 4-19
4.3 90 Day Test for Batch 1 4-20
4.4 28 Day Test for Batch 2 ofLIllIPC 4-21
4.5 14 Day Test for Batch 3 ofLHHPC 4-22
4.6 28 Day Test for Batch 3 ofLIDIPC 4-22
4.7 90 Day Test for Batch 3 ofLHHPC 4-23
4.8 180 Day Test for Batch 3 ofLHHPC 4-23
4.9 28 Day Test for Batch 4 ofLHHPC 4-24
4.10 90 Day Test for Batch 4 ofLHHPC 4-24
List of Tables
4.11 180 Day Test for Batch 4 ofLIllIPC 4-25
4.12 Average Strength at Different Ages for 100 rom Diameter Cylinders 4-26
4.13 Average Strength and Elastic Moduli at Different Ages for 150 mm Diameter
Cylinders 4-26
4.14 Summary of Test Results for all Tested Beams in Phase II 4-27
4.15 Durability Factor for the Specimens with Different Air Contents 4-28
4.16 28 Day Compressive Strength Results for Cylinders with Different Air
Contents 4-29
4.17 Tension Test Results ofGFRP Bars after 36 days of Embedding in Concrete 4-29
viii
LIST OF FIGURES
Figure
2.1 Particle Size Distribution of the Components ofLHHPC 2-16
2.2 Strength Development in LHHPC and SHPC 2-17
2.3 Tensile Strength ofLHHPC and SHPC 2-18
2.4 Shrinkage ofLHHPC and SHPC with Varying Duration of Water Curing 2-19
2.5 pH ofLHHPC and SHPC as a Function of Time After Casting 2-20
2.6 Temperature Rise in LHHPC and SHPC 2-21
3.1 Picture and Schematic of Cylinder Testing System 3-16
3.2 Design and Instrumentation for Beams Reinforced by Steel and GFRP 3-17
3.3 Stress-Strain Diagram for 15M Steel Reinforcing Bar 3-18
3.3 Stress-Strain Diagram for 12M C-Bar Reinforcing Rod 3-19
3.5 Picture and Schematic of Beam Test Set-Up 3-20
3.6 Testing of Fundamental Transverse Frequency 3-21
3.7 Tension Specimen to Investigate the Durability ofGFRP in Concrete 3-22
4.1 28 Day Stress-Strain in Compression from Batch 1 4-30
4.2 Comparison of Different End-Preparations 4-31
4.3 Strength vs. Age ofLIllIPC, SHPC and NCC 4-32
4.4 Changes in Stress-Strain Behaviour with Age ofLHHPC 4-33
List of Figures
4.5 Load-Deflection Behaviour ofLHHPC and NeC Reinforced by Steel 4-34
4.6 Load-Deflection Behaviour ofLHHPC and Nee Reinforced by GFRP 4-35
4.7 Load-Deflection Behaviour ofNCC Reinforced by Steel and GFRP 4-36
4.9 Crack Pattern at Failure for Beams Reinforced by Steel 4-38
4.9 Crack Pattern at Failure for Beams Reinforced by Steel 4-38
4.10 Crack Pattern at Failure for Beams Reinforced by GFRP 4-39
4.11 Load vs. Reinforcement Strain for Beams Reinforced by GFRP 4-40
4.12 Strain Distribution at Ultimate for Beams Reinforced by Steel 4-41
4.13 Strain Distnoution at Ultimate for Beams Reinforced by GFRP 4-42
4.14 Analytical vs. Experimental for NCC Beam Reinforced by Steel 4-43
4.15 Analytical vs. Experimental for LHHPC Beam. Reinforced by Steel 4-44
4.16 Average Fundamental Transverse Frequency for LHHPC Prisms 4-45
4.17 Freeze-Thaw Cycling Specimens after 300 Cycles 4-46
4.18 Stress-Strain Diagrams for Cylinders with Different Air Contents 4-47
4.19 Compressive Strength and Durability Factor for Freeze-Thaw Samples 4-48
4.20 Picture of Durability Tension Specimen (with GFRP) at Failure 4-49
x
1. INTRODUCTION
1.1 General
Low heat high performance concrete (LHHPC) mix design was patented by
Atomic Energy of Canada Limited (AECL) in July 1996 [United States Patent #
5,531,823]. The purpose of the research conducted by AECL was to investigate the
suitability of using LmIPC in the construction of waste disposal facilities and massive
concrete plugs. The use of LHHPC would substantially reduce the heat of hydration of
mass concrete structures and therefore reduce the potential for thermal cracking.
LHHPC has the characteristic of low heat of hydration of 15°C compared to 45
°C in standard high perfonnance concrete (SHPC). The low heat of hydration is of great
advantage for massive concrete structures where thermal cracking is considered to be a
serious problem. LHHPC also has a relatively low alkalinity level of pH 9, which may be
advantageous for concrete structures reinforced with glass tiber reinforced polymer
(GFRP) reinforcements where high pH might cause deterioration of the glass fibers.
The research topic of this thesis includes an extensive experimental program
conducted at the University of Manitoba to evaluate the suitability of using LHHPC for
concrete structures including structures reinforced by GFRP reinforcements. The short
term behaviour was studied while the long tenn behaviour is currently being investigated.
Chapter I. lntroduction
1.2 Objectives
The various specific objectives of this research program are:
1. to detennine the fundamental characteristics of LffilPC. The characteristics
include properties such as compressive strength. elastic modulus and strain at
ultimate load. Maturity of the concrete with time was also investigated.
2. to evaluate the performance of LHHPC as concrete for structural members.
reinforced by steel as well as GFRP reinforcement. subjected to flexure.
3. to detennine the durability of LHHPC using accelerated freezing and thawing
tests. The effect of air content on the durability and compressive strength was
also investigated in this phase.
4. to detennine the effect of the low pH of LflliPC on the durability of GFRP
reinforcement.
1.3 Scope and Contents
In order to have an efficient experimental program and to achieve the desired
objectives, the research is divided into three phases:
Phase I: Material Properties:
This phase was designed to study the fundamental characteristics of LfllIPC. The
characteristics studied include axial compressive strength. modulus of elasticity 9 stress
strain characteristics and maturity. Sixty standard cylinders were cast and tested in
1-2
Chapter I. Introduction
compression using an MTS closed-loop cyclic loading testing machine. The variables
included the size of cylinders (100 mm or 150 nun diameter) and the type of end
preparation (either capped or ground). The cylinders were tested at ages 14, 28, 90 and
180 days. Standard high perfonnance concrete (SHPC) and nonna! conventional concrete
(NCe) were used for comparison with LIDIPC.
Phase U: Structural Behaviour
This phase was designed to study the structural behaviour of LffiIPC. The
program included eight singly-reinforced LHHPC beams tested in flexure up to failure.
The various parameters considered in this phase were the reinforcement ratio and the type
of reinforcement. An additional four beams fabricated with NeC were also tested and
used as control specimens.
Phase ill: Durability Aspects
This phase was designed to study the durability aspects of LHHPC. Phase III is
subdivided into two parts. The first part includes investigation of the durability of the
LmIPC subjected to freezing and thawing cycles. Three different batches of LIfl-IPC
were manufactured with different air contents. The effect of the amount of air entrained
in the concrete on the freeze-thaw durability and the compressive strength is studied.
The second part of Phase III was designed to study the effect of the low alkaliniry
of LHHPC on the tensile strength of GFRP reinforcements and the corrosion of steel in
comparison to NCC. It has been reported that glass fibre deteriorates in alkaline solution
and the degree of deterioration increases with increasing pH and temperature of the
1-3
Chapter 1. lntroduction
solution [Katsuki and Uomoto; prediction of deterioration of glass fibres due to alkali
attack]. It is anticipated that the low pH value of LHHPC is beneficial to the use of
GFRP but will accelerate the corrosion of steel reinforcement. Generally, steel
reinforcement is protected against corrosion by the highly alkaline concrete-pore solution
(PH in excess of 12.5). Such alkaline environments cause the passivation of the steel.
This research is focussed on evaluating the long-term structural behaviour of
LHHPC with GFRP and steel reinforcements in comparison with Nee. Due to the time
constraints of the study, this thesis includes the initial results of the research. Other
researchers at the University of Manitoba will present the long-tenn results in the future.
The following is a brief description of the contents of each chapter in the thesis:
Chapter 2: Literature Review
This chapter reviews the work available in the literature related to low heat high
performance concrete. The properties of GFRP and their durability in concrete are also
presented. Due to the lack of any literature or work conducted on the durability of
LHHPC, the durability standard for high performance concrete in tenns of freezing and
thawing are reviewed to provide data base for the new work presented in this thesis.
Chapter 3: Experimental Program
This chapter describes the experimental program of the research including the
three phases conducted at the University of Manitoba. Detailed description of the
material used and the instrumentation are discussed. The experimental program is
divided into the three phases described above.
1-4
Chapter I. Introduction
Chapter 4: Results and discussions
This chapter presents the results of the three phases of the experimental program.
Analyses of the test results in terms of load-deflection behavior, member ductility, crack
pattern and failure modes are described. The results for the different phases are presented
separately.
Chapter S: Summary and Conclusions
A Summary of the different phases of the investigation is presented. The main
conclusion for the short-tenn structural behaviour is discussed.
1-5
2. Literature Review
2.1 General
This chapter presents an overview of the work reported in the literature in the field
of low heat high performance concrete (LIrnPC). The majority of the research on
LHHPC has been carried out by the Canada Centre fur Min{;r~l and Energy Technology
(CANMET) under contract with Atomic Energy of Canada Limited (AECL). The
chapter also includes a brief review of the durability of concrete under the effect of
freezing and thawing cycles. The properties of glass fiber reinforced polymer
reinforcements (GFRP) and their durability in concrete is also reviewed.
2.2 Constituents of LHHPC
This section describes the various constituents of LfllIPC and their unique
characteristics that give the concrete its outstanding qualities.
2.2.1 Sulfate-Resistant Portland Cement (Type 50)
Sulfate-Resistant Portland Cement (type 50) used in this project was supplied by
LaFarge. Type 50 Portland cement is generally used in conditions where the concrete is
subject to sulfate action.
Chapter 2. Literature Review
2.2.2 Silica Fume
The silica fume used was obtained from SKW Canada Incorporated. This
material contains 96.5 percent silicon dioxide (Si02) with a specific surface area of 18 to
20 m2/g. The average particle diameter is 0.1 to 0.2 J.lm with a generally spherical shape.
The bulk density of this material is 250 to 300 kglm3 and the specific gravity is 2.2. This
material is chemically reactive and is considered to be part of the cementitious
component of the mixes for LHHPC. Silica fume acts like a filler and as a pozzolan. A
pozzolanic material reacts with calcium hydroxide produced during the hydration of the
cement to form a cementitious product, which helps to block the pores and provide a
dense and impermeable concrete. The use of silica fume as a replacement for a part of
the cement has been shown to result in a considerable increase in compressive strength.
The use of silica fume is therefore of particular interest in high perfonnance concrete.
There have been several independent studies on the use of silica fume as a cement
replacement over the last decade. R. D. Hooton, 1993, summarized the influence of silica
fume in imparting higher resistance to sulfate attack, alkali reactive aggregates, and
freezing and thawing. Carette et aI, 1989 found out that the addition of silica fume causes
a small increase in the rate of strength gain up to 28 days. However, at later ages the
plain concrete continued to gain strength while the silica fume concrete appeared to have
reached a threshold.
2.2.3 Silica Flour
Silica flour is made from mined quartzite and contains approximately 100 percent
silicon dioxide (Si02). The specific surface area of this material is 0.350 m2/g. The bulk
2-2
Chapter 2~ Literature Review
density is 850 kglmJ and the pH is 6.8. This material is non-reactive and is used as a
filler. The particle size distribution ranges from 0.50 to 75 f.lm.
2.2.4 Liquid Superplasticizer (Disal)
The liquid superplasticizer (Disal) was manufactured by Handy Chemicals
Limited. The use of superplasticisers is beneficial in the production of high strength
concrete. They disperse cement particles and increase the fluidity of the concrete.
Therefore they are used to increase the workability of the concrete at a constant water
cement ratio or to reduce the amount of water in the mix and maintain the required
workability.
2.2.5 Mix Water
The mix water used in this project was obtained from the City of Winnipeg water
system.
2.2.6 LSL Sand
LaFarge supplied the LSL sand. It was used as a substitute for the LHHPC sand
normally used by AECL. The particle size distribution reveals that the two sands are
very similar but the LSL sand is slightly finer (Figure 2.1). In this application the particle
size difference is considered to be insignificant. The LSL sand was used because of its
availability on site at the concrete plant.
2-3
Chapter 2. Literature Review
2.2.7 Granite Gravel
The granite gravel was obtained by AI Meisner Limited from a quarry operated by
the Province of Manitoba, located 10 Ian east of the town of Seven Sisters, Manitoba.
This material was crushed and washed by AI Meisner Limited. After crushing of the
material, the particle size distribution was between 5 and 13 nun (Figure 2.1). This
material contains micro-fractures as a result of the blasting and crushing processes.
2.2.8 Pea Stone Gravel
LaFarge supplied the pea stone gravel. This is a sub-rounded material consisting
of approximately 95 percent limestone and 5 percent granite. The particle sizes of the
material ranges from one to ten rom and had a moisture content of 4.4 percent. The
particle size analysis information can be seen in Figure 2.1.
The properties of aggregates that are of importance in the production of high
strength concrete are shape, grading, strength, and chemical and physical interaction with
the cement paste, which affect the bond between the aggregates and the mortar. Shape
and grading of the aggregate influence the water requirement of the concrete. The level
of strength achieved in high strength concrete is often limited by the mechanical
properties of the aggregate and the bond with the cement paste. Gjorv et aI, 1987
reported that for concrete strengths of up to 70-90 MPa the concrete fracture is mostly
characterised by bond failure between aggregate particles and the cement paste. For
concrete strengths greater than 90 :MPa, the fracture is mainly controlled by the strength
of the aggregates. A compressive strength of 165 MPa at 28 days was achieved using
Jasper aggregate (Gjorv et ai, 1987). Strength levels of 260 rvlPa were obtained using
2-4
Chapter 2. Literature Review
special aggregates such as calcined bauxite (Hose, 1990). Generally, the strength of the
coarse aggregate has a greater effect on the strength of the concrete than that of the fine
aggregate (Meininger, 1978).
2.3 Properties of Low Heat High Performance Concretes
The Canada Center for Mineral and Energy Technology (CA.N}dET), under
contract with AEeL, has conducted laboratory-scale studies of concrete samples,
including LHHPC. The studies provided data on the thermo-mechanical properties of the
concretes. The purpose of their study was to establish the basic mechanical properties of
low heat and standard high perfonnance concretes (SHPC) in uniaxial and triaxial
compression at ambient and elevated test temperatures.
In a presentation in 1996, Dr. Malcolm Grey of AECL reported that the
unconfined compressive strengths of LIllIPC are very well stabilized around 20, 40 and
70 MPa for 3-, 7- and 28-day old concretes, respectively, as shown in Figure 2.2. Figure
2.2 also shows the relationship of the unconfined compressive strength with curing time
and water-cementitious (W/CM) ratio of LffiIPC compared with SHPC. The tensile
strength of LIDIPC is virtually zero until three days of nonnal curing, and it increases to
6 MPa at 28 days. Figure 2.3 shows a comparison of the split cylinder tensile strengths
between LHHPC and SHPC. Unlike LHHPC, SHPC has a tensile strength of about 5
MPa after only one day of curing. The tensile strengths of LffilPC and SHPC are
identical after 28 days of curing.
2-5
Chapter 2., Literature Review
The report from AECL also discussed the shrinkage characteristics of LHHPC.
The shrinkage of LHHPC is shown to be very sensitive to the duration of water curing.
Shrinkage of LID-IPC decreased dramatically with the duration of water curing. After
one day of curing under water, the 1 OO-day shrinkage of LHHPC was 850 J.1£,
significantly higher than the 550 J,l£ of SHPC. With 7 days of water curin& the 100-day
shrinkage of LHHPC dropped to 400 J,l£, which was lower than the shrinkage of SHPC.
Figures 2.4 (a) to Cd) show the shrinkage ofLHHPC compared with SHPC with different
duration of water curing.
SOOg of granulated mortars each of LHHPC and SHPC were cured under water
for 28 days after casting and measured for pH using a Becham pH meter equipped with
an Ag-AgCl electrode, [United States Patent # 5,531,823]. The results for LHHPC and
SHPC are presented in Figure 2.5 and show that after six months, the pH of LHHPC and
the SHPC mixtures are stable at 9.65 and 12.30, respectively.
To detennine the temperature rise during hydratio~ AECL researchers measured
the temperatures with time at the center of cubical specimens poured into an insulated
box with a specimen volume of 0.027 m3, [United States Patent # 5,531,823]. The
temperature rise of the LHHPC and SHPC specimens is shown in Figure 2.6. The
temperature rise of LIDIPC was only 15°C, which is far lower than the 43 °C
temperature rise of SHPC.
In June 1995, researchers at CANMET conducted compressive tests on 102 nun
diameter LHHPC and SHPC specimens at confining pressures of 0, 4.5, 9, 18 and 36
l\1Pa and at temperatures of 23°, 50° and 90°C. Both the 28-day and 90-day old
specimens were tested under each condition to study the thenno-mechanical properties of
2-6
Chapter 2~ Literature Review
the two types of concrete. It was observed that at confining pressures below 9 MP~ both
concretes exhibited elastic behaviour. At and above 9 MP~ the concretes exhibited
pseudo-plastic behaviour. The results of CANMET show that SHPC has a higher
compressive strength than LHHPC. The 90-day old specimens displayed higher strength
than the 28-day specimens~ and the increase in strength was found to be more pronounced
in the LHHPC. Heating up to 90°C reduced the strengths of both concretes but it was
noted that the reductions were larger for SHPC than for LfiliPC. Tangent Young's
modulus and Poisson's ratio seemed to be unaffected by the confining pressure and
temperature. The 90-day SHPC and LIflIPC had slightly higher tangent Young's moduli
than the concretes that were cured for 28-day. Tables 2.1 and 2.2 summarize the results
of the thermo-mechanical properties of LffilPC at 28 days and 90 days, respectively.
2.4 Freeze-Thaw Durability of Concrete
One of the major problems of concrete is its susceptibility to damage during
freezing and thawing cycles when it is in a saturated or near saturated condition. There
has been much research in the field of high performance concrete to study behaviour
under cycles of freezing and thawing. No research was conducted to study the behaviour
of LffiIPC under cycles of freezing and thawing; therefore, literature in the field of high
performance concrete is presented.
Cohen et aI, 1992~ subjected non-air-entrained high-strength concrete specimens
with 0.35 water-cementitious materials ratio and 10 percent silica fume by mass of
Portland cement to freeze-thaw cycles. The specimens were cured in saturated lime-
2-7
Chapter 2~ Literature Review
water for periods of7, 14,21, and 56 days to evaluate the effects of the duration of curing
on their frost resistance properties. The use of frost resistant aggregates in their research
implies that the failure of non-air- entrained concrete could be attributed only to the
cracking of the paste and not the aggregate. It was found that silica fume improved the
frost resistance mechanism of the paste in the concrete. All specimens failed when tested
in accordance with ASTM C 666 Standard Tests, Procedure A, using 60 percent relative
modulus as the failure criterion. Cohen et al found out that after 300 cycles the modulus
of elasticity dropped to 4.6 percent of its original value while the compressive strength
only dropped to 72.7 percent of its original value.
There have been several criticisms of the testing conditions of ASTM C 666 as
being too harsh and not representative of actual environmental exposure. Ghaffoori et ai,
1997, made a comparison of the perfonnance of concrete pavers tested under ASTM C
67 to that of ASTM C 666. The test results revealed significant variation in the amount
and rate of deterioration, and the mode of failure. In view of the diverse results obtained
by Ghafoori et ai, development of a new freezing and thawing procedure, representative
of cement-based materials and the field exposure conditions appears to be warranted.
2.5 Glass Fiber Reinforced Polymer Reinforcements
The use of glass fiber reinforced polymer (GFRP) is a promising solution for the
corrosion problems of steel reinforcement in concrete structures. In addition to its non
corrosive characteristics and magnetic neutrality, its light weight leads to lower costs of
transportation, handling on the job site, and installation, compared to steel reinforcement.
2-8
Chapter 2, Literature Review
The use of GFRP bars as replacement of tensile steel bars can also reduce the overall cost
of construction if one takes into account the cost associated with maintenance and
prolonged durability [Al-Salloum et ai, 1996].
2.5.1 Mechanical Properties of GFRP
The GFRP reinforcement used in Phase II of this study is 12 m.m diameter "C
BAR TM" produced by Marshall Industries Composites, Inc. of the United States, with E
glass as fiber type. C-BAR reinforcing rods with E-glass as fiber type are designated as
Type G C-BAR reinforcing rods. The ultimate tensile strengths of E-glass reinforcing
rods range from 550 l\APa to 1000 MPa, depending on the test methodology, fiber type,
fiber volume fraction and size of bars [Marshall industries composites inc.]. The typical
stress-strain diagram of the bars is a straight line up to the point of failure. The modulus
of elasticity is a function of the fiber type and the fiber volume fraction. A reference
value is 42 GPa. The nominal weight of C-BAR reinforcing rod is 0.25 kglm for 12 mm
diameter bars [Marshall industries composites inc.]. The 12 nun C-BAR deformed bars
have a nominal cross-section barrel diameter and cross-sectional area of 12 mm and 113
mm2, respectively. The surface of the bar is deformed to improve the bond between the
bar and concrete. The defonnations spacing and height of 12 M C-BAR rods are 6.1 and
1.0 mm, respectively.
S.H. Rizkalla et ai, 1997, tested 12M C-BAR reinforcing rods for their material
characteristics. The results of the tension tests they performed indicate that failure
occurred within the anchorage zone with a recorded ultimate stress, ultimate strain and
Poisson's ratio of640 MPa, 1.58 percent and 40.6 GPa, respectively_ Rizkalla et aI also
2-9
Chapter 2. Literature Review
performed pull-out tests on the 12 M C-BAR rods and found out that their bond strengths
in confined concrete is in the order of 21 MPa provided that the compressive strength of
the concrete is at least 44 ~a. The unfactored development length of the 12 M C-BAR
can be conservatively estimated as 180 mm (12 times the diameter).
2.5.2 Durability of GFRP in Concrete
Over the last decade~ fiber reinforced plastic (FRP) such as glass~ have emerged as
one of the most exciting solutions to the deterioration problems caused by the corrosion
of steel reinforcement in structural concrete [Katawaki et al~ 1992]. However, the high
pH value (12.5-13.0) of the concrete pore water creates a potentially damaging
environment for the GFRP reinforcements. It is known that all commercial glass fibers
are based on fused silica. The chemical, physical and mechanical integrity of glass fiber
is provided by a continuous 3-dimensional network of silica-oxygen-silica bonds [Warren
et ai, 1936]. It so happens that this bond is particularly susceptible to hydroxyl attack as
explained by the following chemical equation:
-Si-O-Si- + OR Si-OH + SiO (in solution)
Therefore the drastic strength loss of all commercial glass fibers that are exposed
to strong alkali solutions can be due to the occurrence of the above chemical reaction [B.
A. Proctor, 1985].
The high pH value (12.5-13.0) of normal concrete may cause the corrosion of
fiberglass and thus the degradation of the FRP rebars containing fiberglass. As
2-10
Chapter 2, Literature Review
concluded by Bank et ai, 1995, the main disadvantage of using GFRP arises from the
high alkalinity of the surrounding concrete.
L. C. Bank et al examined the deteriorated E-glass GFRP bars when embedded in
concrete and subjected to environmental conditions. Observations of surfaces and cross
sections of the bars by optical microscopy and SEM revealed a variety of degradation
phenomena. Smooth bars developed surface blisters and showed significant deterioration
of the polymeric matrices in layers close to the surface of the bar to a depth of
approximately 15 fiber diameters. Helically wrapped bars showed degradation of both
the resin and the fiber in the helical wraps and degradation at the interface between the
core and the wraps. Sand-coated bars were found to have developed a dense network of
surface layer cracks surrounding the sand particles which lead to flaking of this layer, as
well as degradation of the interfaces between the three layers in the bar.
Katsuki et al, 1995 used acrylic cases of 10 x 10 x 20 cm capable of
accommodating twenty FRP rods in each case. The cases were kept airtight by filling the
holes for pouring alkali solution and inserting FRP rods with silicone. The part (20cm
long) of the FRP rods (40cm long) which were immersed in alkali solution was the
portion subjected to tensile test. The anchoring parts of the FRP rods were not affected by
alkali. The test medium was 1.0 molll aqueous NaOH at 40°C for GFRP and the
deterioration was detected by tensile test and microscope observation after 7 days of
immersion.
Accelerated aging tests in continuously hot wet conditions had been proven to be
well correlated with real weathering [Aindowet aI, 1984]. A typical accelerated aging
test was proposed by K.. L. Litherland et ai, 1981. In this test, a small block of cement
2-11
Chapter 2. Literature Review
paste or mortar was cast around a glass fiber strand with proper protection to prevent
damage of the fiber at the edge of the block. After 24 hours of curing at 100 percent RH9
specimens were transferred to a suitable storage environmen~ most commonly at 50°C,
for the required period and then tested in direct tension. A linear fonnula was derived to
predict the time required in real environment for the fiber to reach the strength value
obtained in the accelerated test. In a more recent study, Max L. Porter et ai, 1997,
exposed GFRP rebars to accelerated aging in a tank containing alkaline solution with pH
value of 12.5 to 13 at 60°C for 2 to 3 months. This condition, they suggested, was
simulating approximately 50 years of real weather aging. Their results show that the
accelerated aging and the stress corrosion severely reduced the ultimate tensile strength
and the maximum strain capacity of the GFRP rebars.
Nanni, 1992, proposed two procedures for testing prestressed FRP in alkaline
environment. In the first procedure, the prestressed FRP rods were anchored in a test cell
with the central segments of the rods exposed to the alkaline solution, which was
composed of 0.2 percent Ca (OHh, 1.0 percent NaOH and 1.4 percent KOH by weight.
The prestressing forces were at the values of 0.6, 0.7 and 0.8 of the rated capacity of the
rods. The time of stress-rupture failure was recorded or the residual strengths were
obtained through tensile test. In the other procedure, a pretentioned rod was embedded
along the centroidal axis of a concrete prism, 360 mm long and 100 X 100 mm in cross
section. The concrete was maintained wet and at constant temperatures of 20°C and 60
°e. The initial prestressing forces were 0.5, 0.6 and 0.8 of the rated capacity. After 1, 3
and 12 months from construction, the tendons were pulled to failure.
2-12
Chapter 2. Literature Review
The above literature offers a background to the study of the durability of GFRP in
LHHPC. The present experimental program., which is described in detail in chapter 3, is
composed of embedding 500 mm long GFRP bars in a concrete prism. The specimens
are immersed in a water bath maintained at 60°C and tested in tension after the required
curing period of 1, 3, 6, 9, 12 and 24 months. The degree of deterioration is detennined
by the loss of tensile strength in the GFRP bar.
2-13
Chapter 2, Literature Review
Table 2.1, Results of the 28-day LHHPC from CANMET
Temp (OC) Confining Modulus of Poisson's Ratio Ultimate
pressure (MPa) Elasticity (GPa) Stress (~a)
23 0.0 36.26 0.114 74.90
4.S 36.65 0.147 94.03
9.0 35.66 0.110 108.22
18.0 35.06 0.112 122.01
36.0 33.65 0.072 144.S0
50 0.0 34.85 0.188 67.27
4.S 34.89 0.129 90.73
9.0 34.43 0.114 10S.S6
18.0 34.S7 0.126 109.43
36.0 35.38 0.120 122.87
90 0.0 31.30 0.145 66.95
4.5 32.63 0.069 88.18
9.0 32.32 0.131 103.11
18.0 33.90 0.081 108.15
36.0 38.02 0.068 111.00
2-14
Chapter 2., Literature Review
Table 2.2~ Results of the 90-day LHHPC from CANMET
Temp (OC) Confining Modulus of Poisson's Ratio Ultimate
pressure (MPa) Elasticity (GPa) Stress (rvtPa)
23 0.0 38.18 0.144 89.19
4.5 38.84 0.119 110.45
9.0 39.61 0.106 124.76
18.0 39.83 0.200 133.85
36.0 41.25 0.194 148.05
50 0.0 36.92 0.109 81.65
4.5 37.46 0.158 103.65
9.0 38.15 0.128 117.92
18.0 38.19 0.155 125.51
36.0 39.02 0.161 131.86
90 0.0 34.00 0.157 74.93
4.5 34.85 0.126 97.46
9.0 35.21 0.107 113.27
18.0 36.28 0.108 113.99
36.0 37.85 0.102 117.36
2-15
Q)
.~ CIl ~
~ §
I o [) ~
100 ~ -. ::At;:a.w6
1--~------4---~----~~~~~~-tt7'L-------~IIr---------l I • 75 I
50
25
o
Silica flour
0.001 0.01 0.1
Figure 2.1, Particle Size Distribution of the Components of LHHPC (from AECL)
Design Concrete mm mm (MPa) (GPa) (MPa) (GPa) (mm!) (%) Concrete at
Testing ation·
(days)
LS1.8-1 LHHPC 150 300 80 39.5 450 177 800 1.8 33
LS1.8-2 3S
LS2.7-1 1200 2.7 39
LS2.7-2 42
NS1.8-1 NCC 150 300 40 33.6 450 177 800 1.8 28
NS2.7-1 1200 2.7 32
Table 3.3, Details of Beams Reinforced by GFRP
Beam Type of b, d. rc Ec fu Es As p Age of
Design Concrete mm mm (MPa) (GPa) (MPa) (GPa) (mm2) (%) Concrete at
Testing ation
(days)
LOO.S-l LHHPC ISO 300 82 33.4 532 34 226 0.5 53
LOO.S-2 60
LGI.S-l 678 1.5 48
LGl.S-2 50
NOO.S-I NCC 150 300 38 36 532 34 226 0.5 34
NG1.5-1 678 1.5 36
• The first two letters In the beam desIgnation refers to the type of concrete and the type of remforcement: L refers to low heat high performance concrete (LHHPC) and N refers to nonnal conventional concrete (NCe). S refers to steel reinforcement and G refers to glass fibre reinforced polymer (GFRP) reinforcement.
3-13
Chapter 39 Experimental Program
Table 3.4; Mix Design and the Properties of the Different Batches of the Freeze .. Thaw
Samples
Constituents Quantity in kglm.) for different batches
Batch 1 Batch 2 Batch 3
Cement 97.02 97.02 97.02
Silica fume 97.02 97.02 97.02
Silica flour 193.85 193.85 193.85
Fine aggregates 894.74 894.74 894.74
Coarse aggregates 1039.59 1039.59 1039.59
Superplasticizer 10.32 10.32 10.32
Water 108.60 108.60 108.60
AEA (ml/kg of concrete) 0.000 0.310 0.571
Slump(mm) 220 230 240
Unit weight (lqifm") 2474 2396 2229
Air Content (%) 1.6 4.6 10.0
3-14
Chapter 3. Experimental Program
Table 3.5, Test Dates for Durability Specimens for Steel and GFRP Reinforcement
Date Activity
Thursday, December 10, 1998 Cast specimens made from NeC
Thursday, December 17, 1998 Cast specimens made from LHHPC
Friday, January 15, 1999 Tension test for GFRP embedded in Nee for 36 days
Friday, January 22, 1999 Tension test for GFRP embedded in LHHPC for 36 days
Thursday, March 4, 1999 Tension test for GFRP embedded in NCC for 3 months
Thursday, March 11, 1999 Tension test for GFRP embedded in LHHPC for 3 months
Thursday, June 10, 1999 Tension test for GFRP embedded in NCe for 6 months
Qualitative study of corrosion of steel embedded in NeC for 6 months
Thursday, June 17,1999 Tension test for GFRP embedded in LHHPC for 6 months
Qualitative study of corrosion of steel embedded in LHHPC for 6 months
Thursday, September 9, 1999 Tension test for GFRP embedded in NCC for 9 months
Thursday, September 16, 1999 Tension test for GFRP embedded in LHHPC for 9 months
Thursday, December 9, 1999 Tension test for GFRP embedded in NCe for 12 months
Qualitative study of corrosion of steel embedded in Nee for 12 months
Thursday, December 16, 1999 Tension test for GFRP embedded in LHHPC for 12 months
Qualitative study of corrosion of steel embedded in LHHPC for 12 months
Thursday, December 7, 2000 Tension test for GFRP embedded in Nee for 24 months
Qualitative study of corrosion of steel embedded in Nee for 24 months
Thursday, December 14,2000 Tension test for GFRP embedded in LID-IPC for 24 months
Qualitative study of corrosion of steel embedded in LHHPC for 24 months
3-15
Figure 3.1 (a), Picture of Cylinder in a Compression Testing Machine
o ~~~--------------------~--------------~-----------------~-------------------~--------------------~-----------------~-------------------------~--------------------~--------------------~ o 5 10
Figure 4.14 Analytical vs. Experimental for NCC Reinforced by Steel