Structural behavior of fiber reinforced mortar related to material fracture resistance

158 Pages·2016·8.96 MB·English

STRUCTURAL BEHAVIOR OF FIBER REINFORCED
MORTAR RELATED 'IO MATERIAL FRACTURE RESISTANCE
by
ROBERT JAMES WARD
B.E. University College Galway, Ireland
(1986)
SUBMITTED IN PARTIAL FULFILLMENT OF
THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF SCIENCE IN CIVIL ENGINEERING
at the
MASSACHUSETTS INSTITUTE OF TECHNOLOGY
June 1989
0
Massachusetts Institute of Technology 1989
All rights reserved
Signature redacted
Signature of Author
Department of Civil Engineering
Signature redacted
Certified by
Victor C. Li
Associate Professor of Civil Engineering
Thesis Supervisor
Signature redacted
Accepted by -------
J
Ole S. Madsen
Chairman, Departmental Committee on Graduate Students
Department of Civil Engineering
NSS. JIST. TECd
JU 1 '89
ARCHIVES
U C)
STRUCTURAL BEHAVIOR OF FIBER REINFORCED MORTAR
RELATED TO MATERIAL FRACTURE RESISTANCE
by
ROBERT JAMES WARD
Submitted to the Department of Civil Engineering
on May 11, 1989, in partial fulfillment of the
requirements for the Degree of Master of Science
in Civil Engineering
ABSTRACT
An indirect J-integral technique for measuring the tension softening
curve of non-yielding materials like concrete is presented and is applied
to mortars reinforced with various short fiber types (steel and
synthetic). The tension softening curve serves to characterize and
measure material fracture resistance. The dependence of structural
behavior on material fracture resistance is investigated through
third-point loading tests on unreinforced fiber mortar beams which fail
in flexure and through center-point loading tests on longitudinally
reinforced fiber mortar beams without shear stirrups which fail in shear.
Conclusive evidence, relating improved structural performance directly to
improvements in material fracture resistance due to fiber reinforcement,
is presented.
Semi-empirical formulae are proposed which relate flexural toughness
indices directly to parameters involving just the flexural strength, the
splitting tensile strength and the fiber length. Also, semi-empirical
design formulae are proposed which relate the ultimate shear strength of
longitudinally reinforced beams with fibers as shear reinforcement, to
the material fracture resistance (represented by a combination of
flexural and splitting tensile strengths), the shear span/effective depth
ratio, the longitudinal reinforcement ratio and the beam depth. All
proposed formulae are suitable for the purposes of design and quality
control.
Thesis Supervisor: Dr. Victor C. Li
Title: Associate Professor of Civil Engineering
2
A I'DGD ENT
I wish to thank the following people:
Professor Victor Li for introducing me to the subjects of fracture
mechanics and fiber reinforced concrete, and for overseeing my entire
research program. He provided me with invaluable guidance, support and
encouragement and above all I thank him for making my stay at M.I.T. a
truly enjoyable experience.
My fellow graduate students who so often offered their advice and help,
especially in the laboratory.
Professor Stanley Backer who always ensured that I had a large and varied
supply of synthetic fibers with which to work.
Mr. Rick Smith of Ribbon Technology Corporation, Ohio, who provided me
with all the steel fibers.
Mr. Kevin Grogan of W. R. Grace and Co., Cambridge, Mass., who provided
me with the superplasticiser.
The U.S. National Science Foundation and the Shimizu Corporation of Japan
who both provided vital funding which made this research program
possible.
Miss Irene Uesato, who took time out of her very busy schedule, to type
this thesis.
3
TABLE OF CONTENTS
Title Page 1
Abstract 2
Acknowledgements 3
Table of Contents 4
List of Figures 6
List of Tables 10
Chapter 1: INTRODUCTION 11
Chapter 2: TENSION SOFTENING CURVE BY J-INTEGRAL TECHNIQUE 17
2.1 Introduction 17
2.2 Theoretical Basis of J-Integral Technique 18
2.3 Numerical Verification of Test Technique 21
2.4 Experimental Procedure 22
2.4.1 Specimen preparation 22
2.4.2 Testing procedure 24
2.5 Results and Data Analysis 25
2.6 Calculation of GF 27
2.7 Discussion and Recommendations for the J-Integral Test. 28
2.8 Current Status of J-Integral Test Technique 30
Chapter 3: FLEXURAL BEHAVIOR OF FIBER REINFORCED MORTAR 40
3.1 Introduction 40
3.2 General Behavior of Fiber Concrete in Flexure 42
3.3 Experimental Program 46
3.3.1 Specimen preparation 46
3.3.2 Testing procedure 47
3.4 Compressive Strength 48
3.5 Splitting Tensile Strength 49
3.6 Flexural Strength 50
3.6.1 Size dependence of flexural strength 51
3.6.2 Flexural strength related to fracture resistance 52
57
3.7 Flexural Load-Deflection Curves
4
3.7.1 Effect of fiber type and volume fraction on the
flexural load-deflection curve 57
3.7.2 Effect of beam size on the flexural load-deflection
curve 60
3.8 Flexural Toughness Indices 62
3.8.1 15' 10' 3 and 150 indices 62
3.8.2 Tmaxp T and T indices 65
50 10
3.9 Simple Flexural Toughness Estimates 68
Appendix 3.1 Comparison of Size-Effect Predicted by the Weibull and
Fictitious Crack Models 73
Chapter 4: FIBERS AS SHEAR REINFORCEMENT IN LONGITUDINALLY REINFORCED
BEAMS 102
4.1 Introduction 102
4.2 Advantages of Fibers as Shear Reinforcement 104
4.3 Experimental Program 107
4.3.1 Specimen preparation 107
4.3.2 Testing procedure 110
4.4 Observed Failure Modes 111
4.4.1 Beam-action (a/d > 2.5) 111
4.4.2 Arch-action (a/d < 2.5) 113
4.5 Test Results and Discussion 115
4.5.1 First crack strength 115
4.5.2 Shear span/effective depth ratio 118
4.5.3 Reinforcement ratio 121
4.5.4 Beam depth 122
4.6 Simple Design Formulae for the Shear Strength of
Reinforced Mortar Beams with Fibers 124
Chapter 5: CONCLUSION 144
Chapter 6: RECOMMENDED FUTURE RESEARCH 147
References
154
5
List of Figures
Fig. 2.1 Cohesive Zone Ahead of the Crack Tip
Fig. 2.2 Specimen Configurations used with J-Integral Test
Fig. 2.3 Inside of Omni-mixer
Fig. 2.4 Specimens covered in Plastic just after Casting
Fig. 2.5 Notched Beam ready for Testing
Fig. 2.6 Loading Machine Used for J-Integral Test Program
Fig. 2.7 Average Load versus Load Point Displacement Curves
Fig. 2.8 Average Load Point Displacement versus Crack Opening Curves
Fig. 2.9 J-Integral versus Crack Opening Curve
Fig. 2.10 Deduced Tension Softening Curve
Fig. 2.11 Comparison Between Deduced and Directly Measured Tension
Softening Curves
Fig. 2.12 Flexural Load Deflection Curve Corrected to Account for
Energy Supplied by Beam Self-Weight
Fig. 2.13 Tension Softening Curves Deduced by Indirect J-Integral
Technique
Fig. 3.1 Specimen Geometry and Loading Configuration for Flexural
Test
Fig. 3.2 Wooden Mold for 228 mm Deep Beam
Fig. 3.3 Beams Covered with Plastic Just After Casting
Fig. 3.4 Cylinders in Plastic Molds and Covered with Plastic Just
After Casting
Fig. 3.5 228 mm Deep Beam ready for Testing Under Third Point Loading
Fig. 3.6 Cylinder with LVDTs on either side ready for Compression
Test
Fig. 3.7 Cylinder ready for Splitting Tension Test
Fig. 3.8 Effect of Fiber Reinforcement on Compressive Strength
Fig. 3.9 Effect of Fiber Reinforcement on the First Crack Splitting
Tensile Strength
Fig. 3.10 Influence of Beam Size on Flexural Strength
Fig. 3.11 Average Normalized Flexural Strength Values as a Function of
Beam Depth
Fig. 3.12 Theoretical Curves Relating the ff/ft Ratio to the d/lch
Ratio Calculated Using the Fictitious Crack Model [101
6
Fig. 3.13 Empirical Relationship Between the Flexural/Tensile Strength
Ratio and the Compressive Strength for Plain Concrete [401
Fig. 3.14 Empirical Relationship Between the Flexural/Tensile Strength
Ratio and the Material Characteristic Length for Plain
Concrete [10]
Fig. 3.15 Effect of Fiber Reinforcement on the Ratio Between Flexural
and Splitting Tensile Strengths
Fig. 3.16 Typical Tension Softening Curves of Mortars Reinforced with
various Fibers
Fig. 3.17 Flexural Load-Deflection Curves for Mortars Reinforced with
various Fiber Types
Fig. 3.18 Flexural Load-Deflection Curves for Kevlar Fiber Reinforced
Mortar Beams
Fig. 3.19 Flexural Load-Deflection Curves for Steel Fiber (25 mm)
Reinforced Mortar Beams
Fig. 3.20 Flexural Stress versus Normalized Deflection for Different
Beam Sizes of Kevlar Fiber Reinforced Mortar
Fig. 3.21 Flexural Stress versus Normalized Deflection for Different
Beam Sizes of Steel Fiber Reinforced Mortar
Fig. 3.22 Calculation of Flexural Toughness Indices from Flexural
Load-Deflection Diagram
Fig. 3.23 Influence of Beam Size on Flexural Toughness Indices 5
I10' 130 and 150
Fig. 3.24 Influence of Beam size on Flexural Toughness Index Tmax
Fig. 3.25 Influence of Beam Size on Flexural Toughness Index T 5m
Fig. 3.26 Influence of Beam Size on Flexural Toughness Index T10
Fig. 3.27 Various Flexural Toughness Indices for Mortars Reinforced
with each Fiber Type
Fig. 3.28 Semi-Empirical Relationship Between the f /ft Ratio and the
Flexural Toughness Index Tmax
Fig. 3.29 Semi-Empirical Relationship Between the Flexural Toughness
Index T and a Parameter involving the Flexural and Tensile
10
Strengths and the Fiber Length
Fig. 3.30 Theoretical Curves Relating the f /ft Ratio to the d/lch
Ratio Calculated Using the Fictitious Crack Model [38]
Fig. 3.31 Comparison of Size Dependence of Flexural Strength Predicted
by the Weibull and Fictitious Crack Models
7
Fig. 4.1 Specimen Geometry and Loading Configuration for Shear Beam
Test
Fig. 4.2 Rebars Fixed at Proper Spacing Using Short Steel Bars
Fig. 4.3 Rebars Fixed in Mold Ready for Casting
Fig. 4.4 Shear Beam Ready for Center Point Loading
Fig. 4.5 Loading System for Large Shear Beams.
Bottom Beam is just a Support
Fig. 4.6 (a) Typical Crack Shape in Plain Mortar Beam with a/d > 2.5
(b) Typical Critical Crack Shape in Fiber Reinforced Beam
with a/d > 2.5
Fig. 4.7 Force System in Reinforced Concrete Beam at a Diagonal Shear
Crack
Fig. 4.8 Failure Patterns for Shear Beams with a/d = 3.0 and d = 204
mm
(a) = Plain Mortar (c) Kevlar 2%
(b) = 25 mm Steel 1% (d) 25 mm Steel 2%
Fig. 4.9 Shear Failure Patterns in Beams with a/d = 3.0, d = 204 mm
and 25 mm Steel Fiber Reinforcement 2%
Fig. 4.10 Typical Shear Failure Patterns in Beams with a/d < 2.5
(a) Splitting Failure
(b) Shear Compression Failure
(c) Flexural Tension Failure Under Eccentric Compression
Fig. 4.11 Typical Splitting Tension Like Failures of Plain Mortar
Beams with a Reinforcement Ratio of 2.2% and Loaded with a/d
= 1.0 [18]
Fig. 4.12 Typical Shear Compression Like Failures of Beams Reinforced
with 2% Acrylic Fibers. The Reinforcement Ratio is 2.2% and
a/d = 1.0 [18].
Fig. 4.13 Cracking and Ultimate Shear Strengths of various Fiber
Reinforced Mortar Beams
Fig. 4.14 Influence of the Shear Span/Effective Depth Ratio on
Ultimate Shear Strength of Fiber Reinforced Mortar Beams
Fig. 4.15 Influence of the Shear Span/Effective Depth Ratio on the
Maximum Bending Moment in Fiber Reinforced Mortar Beams with
Longitudinal Steel
Fig. 4.16 Influence of the Longitudinal Reinforcement Ratio on the
Ultimate Shear Strength of Fiber Reinforced Mortar Beams
8
Fig. 4.17 Influence of Beam Depth on the Ultimate Shear Strength of
Fiber Reinforced Mortar Beams
Fig. 4.18 Semi-Empirical Relationship Between Ultimate Shear Strength
and the Material and Geometrical Properties for a/d > 2.5
Fig. 4.19 Semi-Empirical Relationship Between Ultimate Shear Strength
and the Material and Geometrical Properties for a/d < 2.5
9
List of Tables
Table 2.1 Summary of J-Integral Test Results
Table 3.1 Fiber Properties
Table 3.2 Flexural, Splitting Tensile and Compressive Strengths of
Mortars Reinforced with various Fiber Types
Table 3.3 Flexural Toughness Indices of Mortars Reinforced with various
Fiber Types
Table 3.4 Size Dependence of Flexural Strength Predicted by the Weibull
and Fictitious Crack Models
Table 4.1 First Crack and Ultimate Shear Strengths
Table 4.2 Flexural, Splitting Tensile and Compressive Strengths
10