Mechanical and deformational properties, and shrinkage cracking behaviour of lightweight concretes

MECHANICAL AND DEFORMATIONAL PROPERTIES,
AND SHRINKAGE CRACKING BEHAVIOUR OF
LIGHTWEIGHT CONCRETES








DANETI SARADHI BABU










NATIONAL UNIVERSITY OF SINGAPORE
2008



MECHANICAL AND DEFORMATIONAL PROPERTIES,

AND SHRINKAGE CRACKING BEHAVIOUR OF
LIGHTWEIGHT CONCRETES








DANETI SARADHI BABU
(B.Tech., JNTU; M.S. (by Research), IITM)







THESIS SUBMITTED

FOR THE DEGREE OF DOCTOR OF PHILOSOPHY

DEPARTMENT OF CIVIL ENGINEERING

NATIONAL UNIVERSITY OF SINGAPORE

2008

i

ACKNOWLEDGEMENTS


I would like to express my gratitude and sincere appreciations to my supervisor
Associate Professor Wee Tiong Huan for his inspiring, invaluable and untiring guidance and
help in all the matters. I also wish to thank Dr. Tamilselvan S/O Thangayah for his comments
and kind advises in finalising my thesis. I gratefully acknowledge and admire the generosity
and infinite patience shown by them in all matters.

My gratitude is also extended to my examiners Associate Professor Tan Kiang Hwee
and former Associate Professor Mohamed Maalej for their support and helpful
recommendations to improve the research work during the PhD qualifying examination
presentation. I would also like to thank Associate Professor Tam Chat Tim and Professor
Balendra, T for serving on my committee. The valuable suggestions and encouragement given
by them has helped me immensely.

The research reported in this thesis was part of the more comprehensive R&D program
entitled “Development of high strength lightweight concretes with and without aggregates”
jointly funded by Building and Construction Authority of Singapore (BCA) and National
University of Singapore (NUS). The research scholarship and support from NUS is gratefully
acknowledged.

I am highly thankful to my colleagues Dr. Lim, Kum, Dr. Kannan, Dr. Rafique, Mathi,
Lim Sun Nee, Kong Ruiwen, and friends Dr. Nagi Reddy, Dr. Pavan Kumar, Dr. Chava, Dr.
Rajan, Niranjan, Vijay, Uma, PineGrove group and others for their valuable help,
encouragement and suggestion during my research work. I wish to express my thanks to the
staff of the Structural and Concrete Laboratory, namely, Mr. Lim, Sit, Ang, Choo, Koh, Ow,
Yip, Kamsan, Ong and Mdm. Tan Annie are greatly appreciated.

Last but not least, the work is devoted to my loving parents - Ramaswamy and

Varahalamma, Wife – Madhuri, Brother – Kesava Rao, sisters – Eswaramma and Venkatamma,
In-Laws and their family and relatives for their patience, abundant love and affection towards
my education.


Daneti Saradhi Babu
2008


ii
















Dedicated

To my Loving

Parents

&

Wife

iii
TABLE OF CONTENTS

ACKNOWLEDGEMENTS i
TABLE OF CONTENTS iii
SUMMARY viii
NOMENCLATURE xi
LIST OF TABLES xiv
LIST OF FIGURES xv

CHAPTER 1: INTRODUCTION 1
1.1 Background 1
1.2 Need for the research 2
1.3 Objectives and Scope 5
1.4 Organization of the thesis 6

CHAPTER 2: LITERATURE REVIEW 11
2.1 Introduction 11
2.2 Cracking in concrete 11
2.3 Mechanism of shrinkage cracking 13
2.4 Mechanical properties of LWC 14
2.4.1 Foamed concrete 14
2.4.1.1 Air-void system 16
2.4.2 Lightweight aggregate concrete (LWAC) 18

2.5 Fracture parameters 20
2.6 Shrinkage of concrete 22
2.6.1 Autogenous shrinkage 23
2.6.2 Drying shrinkage 25

iv
2.6.3 Shrinkage of foamed concrete 28
2.6.4 Shrinkage of lightweight aggregate concrete 29
2.7 Creep of concrete 31
2.8 Shrinkage cracking 32
2.8.1 Methods to control shrinkage cracking and shrinkage effects 33
2.8.2 Methods to assess shrinkage cracking 34
2.9 Restrained ring test 37
2.10 Shrinkage cracking of LWC 37
2.11 Summary 39

CHAPTER 3: MECHANICAL PROPERTIES OF LIGHTWEIGHT
CONCRETES 51

3.1 Introduction 51
3.2 Experimental investigation 53
3.2.1 Materials 53
3.2.2 Mix proportions 54
3.2.3 Test program 55
3.2.3.1 Air-void system 55
3.2.3.2 Rheology test 57
3.2.3.3 Fracture toughness 57
3.2.3.4 Compressive strength 60
3.2.3.5 Splitting and flexural tensile strength 60
3.2.3.6 Modulus of elasticity and stress-strain test 60

3.3 Results and discussion 61
3.3.1 Air-void system of foamed concrete 61
3.3.1.1 Experimental study: Effect of air-void system on mechanical
properties 66



v
3.3.1.2 Numerical study: Effect of air-void system on mechanical properties68

3.3.1.3 Relationship between air content, w/c ratio, density on strength and
modulus 71

3.3.2 Fracture toughness 74
3.3.2.1 LWC without fibers 74
3.3.2.2 Fiber reinforced LWC 76
3.3.3 Mechanical properties of LWCs and their comparison with NWC 79
3.3.3.1 Compressive strength 79
3.3.3.2 Tensile strength 82
3.3.3.3 Fracture toughness 85
3.3.3.4 Modulus of elasticity of aggregates and concretes 87
3.3.3.5 Stress-strain behaviour 90
3.3.3.6 Poisson’s ratio 91
3.4 Summary 92

CHAPTER 4: DEFORMATIONAL PROPERTIES OF LIGHTWEIGHT
CONCRETES 122

4.1 Introduction 122
4.2 Experimental investigation 124

4.2.1 Test program 124
4.2.1.1 Shrinkage test 124
4.2.1.2 Creep test 125

4.2.1.3 Microstructure test 125
4.3 Results and discussions 126
4.3.1 Autogenous shrinkage 126
4.3.2 Drying shrinkage 129
4.3.2.1 Effect of air content 129
4.3.2.2 Effect of aggregate density/type and aggregate volume 131

vi
4.3.2.3 Effect of w/c ratio, curing, mineral admixtures, fibers and aggregate
soaking 138

4.3.2.4 Relationship between shrinkage of foamed concrete vs LWAC and
NWC 142

4.3.3 Creep 144

4.3.3.1 Effect of air content 145
4.3.3.2 Effect of aggregate density/type and aggregate volume 146
4.3.3.3 Effect of w/c ratio and mineral admixtures 151
4.3.4 Comparison of shrinkage and creep prediction models for LWCs 152
4.4 Summary 154

CHAPTER 5: SHRINKAGE CRACKING BEHAVIOUR OF LIGHTWEIGHT
CONCRETES 181

5.1 Introduction 181

5.2 Experimental program 183
5.2.1 Specimen details and test program 183
5.2.2 Theoretical restrained shrinkage analysis 186
5.3 Results and discussion 188
5.3.1 Effect of filler (air or aggregate) volume and filler type/density 188
5.3.1.1 Stress development and age of cracking: Experimental study 188
5.3.1.2 Stress development and age of cracking: Theoretical study 196
5.3.2 Effect of fibers 204
5.3.3 Effect of mineral admixtures 207
5.3.4 Effect of curing and soaking condition of aggregate 209
5.3.5 Parameters influencing the potential for shrinkage cracking of LWCs 211
5.4 Summary 214

CHAPTER 6: CONCLUSIONS AND RECOMMENDATIONS 239
6.1 Review of the investigation 239

vii
6.2 Conclusions 242
6.3 Recommendations for further research 244

REFERENCES 245
ANNEX 1 256
ANNEX 2 258
ANNEX 3 259
PUBLICATIONS 267


viii
SUMMARY
Title:

Mechanical and deformational properties, and shrinkage cracking
behaviour of lightweight concretes.

The study reported in this thesis addresses the role of constituent materials of different
lightweight concrete (LWC) – foamed concrete without aggregate (FC), foamed concrete with
aggregate (FCA) and lightweight aggregate concrete (LWAC) – on mechanical and
deformational properties, and shrinkage cracking behaviour both theoretically and
experimentally. The present investigation was divided in to three parts for a systematic
approach to the study. The main constituent materials of LWC considered in the study include
filler volume (air and aggregate), filler type or density, fibers, and mineral admixtures.
The first part of the work focused on understanding the role of constituents on
mechanical properties such as compressive strength, tensile strength, modulus of elasticity,
fracture toughness and stress-strain behaviour. Particular emphasis has been given to study the
effect of w/c ratio on air-void system of FC and their effect on mechanical properties through
experimental and numerical analysis. The effects of filler volume, filler type and fiber on
fracture toughness, strength, and modulus of elasticity of FC, FCA and LWAC were tested.
The results indicate that the air-void system with a spacing factor of about 0.05 mm, average
air-void size of lower than 0.15 mm and air content of 40%, were collectively found to be
optimal for different w/c ratios at which foamed concrete with high strength to weight ratio can
be achieved. The air-void system and w/c ratio control the mechanical properties of FC. Use
of higher volume of lightweight aggregate (LWA) is not beneficial in improving the fracture
toughness of LWAC, due to its porous nature. The performance of fibers in improving the
toughness of FC is found to be as good as that in LWAC. The modulus of elasticity of LWA
with different density is observed to be 60 to 90% lower than the modulus of elasticity of
normal weight aggregate (NWA). The adequacy of some of the familiar relationships for

ix
predicting the tensile strength, modulus of elasticity and fracture toughness has been critically
examined and suitable expressions are suggested, to cover FC strength ranging from 2 to 60
MPa, in comparison with LWAC and normal weight concrete (NWC).

The second part of the work focused on understanding the role of constituents on
deformational properties such as drying shrinkage and creep of concrete. Since FC of higher
strengths are relatively new; the autogenous shrinkage of FC in comparison to LWAC and
NWC was also briefly studied. The results indicate that for the equivalent mixture proportions
but for the change of filler type (air, LWA and NWA), FC shows highest autogenous shrinkage
followed by NWC and LWAC. Air content was found not to affect the autogenous shrinkage
of FC much, but it significantly affects the drying shrinkage and creep of FC and FCA. The
drying shrinkage and creep of FC can be controlled by adding aggregates. The drying
shrinkage and creep of LWAC decrease with increase in aggregate density and volume. For
equivalent mixture proportions but for the change of filler type, long term drying shrinkage and
creep of LWAC is higher than NWC. FC shows higher creep followed by FCA and LWAC of
comparable modulus of elasticity of concrete. The dying shrinkage and creep of LWC can be
controlled with use of low w/c ratios and mineral admixtures. Different shrinkage and creep
prediction models found in literatures were verified against the FC, FCA and LWAC.
Finally, shrinkage cracking behaviour of LWCs were evaluated though experimental
and theoretical analysis. The restrained ring test was adopted to evaluate the cracking potential
of LWC with and without aggregates. The results of these tests are presented and discussed,
and the implications on the selection of constituent materials, and their influence on potential
risk of shrinkage cracking have been addressed. The results indicate that use of lower air
contents and higher aggregate volumes in FC are favorable in lowering the potential of
shrinkage cracking. It was found that the use of LWA as filler in FC is more effective in
controlling the shrinkage cracking of FC than sand. The use of higher volumes of aggregate,
higher density aggregates (stronger aggregate) and low w/c ratio helps to mitigate the potential

x
risk of shrinkage cracking in LWAC. The tensile strain at cracking of LWAC (~213 µε) is
twice that of NWC (~100 µε) and it is independent of the age of cracking. The shrinkage
cracking potential of foamed concrete with and without aggregate is higher than both LWAC
and NWC. Both experimental and theoretical analysis collectively shows that it is essential to
control the shrinkage rates of concrete to control the shrinkage cracking problem. The use of

fibers, mineral admixtures and prolonged age of curing are also effective in controlling
potential risk of shrinkage cracking in LWC. The shrinkage cracking behaviour of FC and
FCA in comparison with LWAC has been evaluated. The key parameters and constituents
needed to control or mitigate the shrinkage cracking of LWC for given geometry have been
discussed and possible guidelines have been suggested.
Key words: foamed concrete, lightweight aggregate concrete, air-void system, fracture
toughness, tensile strength, modulus of elasticity, shrinkage, creep, tensile stress and shrinkage
cracking.


xi
NOMENCLATURE



f
t
tensile strength

f
c
’
cylinder compressive strength

f
cu
cube compressive strength

E
p

, E
m,
E
a
, E
c,
E
s
modulus of elasticity of paste, mortar, aggregate, concrete and steel

K
ic
s
fracture toughness

ε
sh
shrinkage strain

ε
elastic
elastic tensile strain

w/c water to cement ratio

a/c air to cement ratio

σ
elastic
elastic tensile stress

a
e
effective crack length

a
c
critical crack length

a
o
initial crack length

C
i
, C
u
intial, unloading compliance

cap
σ
pressure in capillary pore water

φ
c
creep coefficient

γ
surface tension of water

b, d breadth, depth of beam

W
h0
self-weight of beam

S, L span and length of beam

W density of concrete

L
spacing factor

p paste content

A Air content


xii
α specific surface area

V volume of the specimen

N average number of air-voids

x
mean of air content or average air-void size

x
i

air content or average air-void size of each line length traverse

n total number of lines traversed

s standard deviation

COV coefficient of variation

r actual radius of air-void

R maximum possible radius of air-void

σ compressive strength of porous material

σ
o
compressive strength of matrix

σ
p
compressive strength of cement paste

P porosity

y constant (strength - porosity)

f
cu,p
cube comp. strength of paste

K
icC,
K
icM
concrete, mortar fracture toughness

f
r
, f
ct
flexural, splitting tensile strength

a
ρ
particle density of aggregate

s/b sand to binder ratio

α
max
maximum degree of hydration

CS chemical shrinkage during hydration

S
c
, S
m
, S
a

, S
p
shrinkage of concrete, mortar, aggregate and paste

V
c
, V
m
, V
a
, V
p
volume of concrete, mortar, aggregate and paste

c
ν
,
m
ν
,
a
ν
,
p
ν

s
ν
poisson’s ratio of concrete, mortar, aggregate, paste and steel

m modular ratio

C
m
, C
c
specific creep of matrix, concrete

xiii

p
residual
residual stress

ε
steel
strain in steel

R
IC
inner radius of concrete ring

R
OC
outer radius of concrete ring

R
IS
inner radius of steel ring

R
OS
outer radius of steel ring

σ
Actual-Max
actual tensile stress in concrete ring

),(
0
ttR relaxation function

σ
Relaxation
relaxation stress









xiv
LIST OF TABLES



Table 2.1 Summary of restrained shrinkage cracking methods and assessing techniques for

different concretes 41



Table 3.1 Physical properties and chemical compositions of cementitious materials 94

Table 3.2 Physical properties of LWA 94

Table 3.3 Physical properties of fibers 94

Table 3.4 (a) Mix details of FC to study air-void system 94

Table 3.4 (b) Mix proportions and parameters considered for FC and FCA 95

Table 3.5 Mix proportions and parameters considered for LWAC 96

Table 3.6 Statistical analysis of air content and air-void size of FC for different w/c ratios and
air contents 98

Table 3.7 Air-void system, density, compressive strength and modulus of elasticity of FC with
different w/c ratios and air contents 99

Table 3.8 Numerical modeling results 100

Table 3.9 Mechanical properties of FC and FCA 101

Table 3.10 Mechanical properties of LWAC 102

Table 3.11 Effect of fiber on toughness performance of LWAC and FC 103

Table 3.12 Estimated modulus of elasticity of aggregates using different models 103



Table 4.1 Shrinkage and creep models limitations and required parameters 157

Table 4.2 Statistical parameters for drying shrinkage of different models 158

Table 4.3 Statistical parameters for specific creep of different models 158

Table 4.4 Ratios of Predicted deformation to Measured deformation 159


Table 5.1 Restrained shrinkage cracking results of fiber reinforced LWC 216




xv
LIST OF FIGURES




Fig. 1.1 Classification of different lightweight concretes, Wee (2005) 8

Fig. 1.2 Factors affecting shrinkage cracking of concrete 9

Fig. 1.3 Flowchart of PhD work 10

Fig. 2.1 Influence of strength, shrinkage and creep on shrinkage cracking of concrete
(Neville 1997) 45

Fig. 2.2 Creep deformation definitions: (a) original length, (b) elastic deformation, (c) creep
loading, and (d) permanent creep after loading (Mehta and Monteiro1997) 45

Fig. 2.3 (a) Fresh concrete density versus cube compressive strengths of foamed concrete
(FC) with and without aggregates (Wee 2005) 46

Fig. 2.3 (b) Fresh concrete density versus cube compressive strengths of lightweight
aggregate concrete (Wee 2005) 46

Fig. 2.4 Failure modes for concrete with (a) normal weight aggregate (b) lightweight
aggregate (FIP manual 1983) 47

Fig. 2.5 Summarized possible toughening mechanisms 47

Fig. 2.6 Typical load and CMOD curve for a notched concrete beam 48

Fig. 2.7 Causes of drying shrinkage of cement paste (a) Capillary stress; (b) Disjoining
pressure; (c) Surface tension (Mindess et al. 2003) 48

Fig. 2.8 Plate test for restrained shrinkage cracking study (Kraai 1985) 49

Fig. 2.9 Longitudinal restraining ring test developed by Banthia et al. (1993) 49

Fig. 2.10 Schematic description of the closed loop instrumented restraining system developed
by Kovler (1994) 49

Fig. 2.11 Geometry of ring specimen and drying directions (Weiss et al. 2001) 50



Fig. 3.1 Typical prepared specimen used to measure air-void system 104

Fig. 3.2 Microscope and the typical image from specimen for air-void analysis 104

Fig. 3.3 (a) Coaxial-cylinder rheometer; (b) Schematic diagram of the coaxial-cylinders
containing paste sample 105

Fig. 3.4 Testing configuration and geometry of specimen with clip gauge 105

xvi

Fig. 3.5 Testing configuration and geometry of specimen with LVDTs 105

Fig. 3.6 Air-void system of FC for different w/c ratios 106

Fig. 3.7 (a) variation of shear stress with shear rate for different w/c ratios; (b) variation of
yield stress and plastic viscosity with w/c ratio; (c) relationship between yield stress
and plastic viscosity 107

Fig. 3.8 Relationship between (a) compressive strength to density ratio, (b) modulus of
Elasticity to density ratio and spacing factor for different w/c ratios 108

Fig. 3.9 Relationship dry density versus compressive strength and spacing factor for different
w/c ratios 109

Fig. 3.10 Relationship between compressive strength to density ratio and air-void size for
different w/c ratios 109

Fig. 3.11 (a) Single size void arranged in hexagonal packing; (b) Model meshed with 20-node
brick element 110

Fig. 3.12 Comparison of numerical analysis with experimental results for (a)compressive
strength and (b) modulus of elasticity for different w/c ratios 110

Fig. 3.13 Relationship between air content and spacing factor 111

Fig. 3.14 Relationship between compressive strength to density ratio and w/c ratio for different
air contents 111

Fig. 3.15 Relationship between compressive strength and air content for different w/c ratios 112

Fig. 3.16 Relationship between compressive strength and modulus of elasticity in relation to
density for different w/c ratios 112

Fig. 3.17 Effect of air or aggregate volume and aggregate type on fracture toughness 113

Fig. 3.18 Effect of fiber percent and fiber type on load-deflection curves and toughness of
LWAC (L9 LWA) 114

Fig. 3.19 Effect of polypropylene fiber percent on load-deflection curves and toughness of
FC (FC30-0.3) 115

Fig. 3.20 Effect of air or aggregate volume and type on compressive strength 116

Fig. 3.21 Correlation between cube and cylinder compressive strength 116

Fig. 3.22 Effect of air or aggregate volume and type on splitting tensile strength 117

Fig. 3.23 Effect of fiber on tensile strength of LWAC and FC 117

Fig. 3.24 Relationship between splitting tensile strength and compressive strength 118

Fig. 3.25 Relationship between flexural tensile strength and compressive strength 118

Fig. 3.26 Relationship between fracture toughness and flexural tensile strength 119

xvii

Fig. 3.27 Relationship between particle density and modulus of elasticity of aggregate 119

Fig. 3.28 Effect of air or aggregate volume and type on modulus of elasticity 120

Fig. 3.29 Relationship between modulus of elasticity and compressive strength 120

Fig. 3.30 Stress-strain behaviour of FC and FCA 121



Fig. 4.1 Digital Strain demec gauge (Demountable Mechanical Gauge) 160
Fig. 4.2 Typical photo graph of hydraulically creep test rigs with specimens 160

Fig. 4.3 Mercury intrusion porosimeter (Carlo Erba 4000) 160

Fig. 4.4 Effect of air content and w/c ratio on autogenous shrinkage of FC 161

Fig. 4.5 Autogenous shrinkage of different concretes for equivalent mixture proportions 161

Fig. 4.6 Effect of sand and LWA volume on autogenous shrinkage of FC 162

Fig.4.7 Effect of air content on drying shrinkage of FC and FC with sand 163

Fig. 4.8 Effect of air content on pore size distribution of FC 163

Fig. 4.9 Effect of aggregate type on drying shrinkage of FC 164

Fig. 4.10 Effect of sand and LWA volume on drying shrinkage of FC 164

Fig. 4.11 Shrinkage ratio (S
fca
/S
fc
) in terms of modulus ratio (E
fca
/E
fc
) for FC with different
volumes of sand and LWA 165

Fig. 4.12 Effect of L9 aggregate volume of draying shrinkage of LWAC 165

Fig. 4.13 Effect of aggregate volume on shrinkage (S
c
/S
m
) ratio of concrete at 90 days of

drying 166

Fig. 4.14 Effect of aggregate type on drying shrinkage with age of drying for equivalent
mixture proportions of concrete 166

Fig. 4.15 Normalized drying shrinkage of concretes with different aggregates at 150 days 167

Fig. 4.16 Shrinkage ratio (S
c
/S
m
) in terms of modulus ratio (E
c
/E
m
) at 90-days of drying 167

Fig. 4.17 Effect of w/c ratio on drying shrinkage of FC and LWAC 168

Fig. 4.18 Effect of age of curing on drying shrinkage of FC and LWAC 169

Fig. 4.19 Effect of mineral admixtures on drying shrinkage of FC and LWAC 170

Fig. 4.20 Effect of fiber on drying shrinkage of FC and LWAC 171

Fig. 4.21 Effect of aggregate soaking on drying shrinkage of LWAC 171

xviii

Fig. 4.22 Correlation between drying shrinkage and modulus of elasticity of different concretes

at 90 days 172

Fig. 4.23 Long term drying shrinkage behaviour of different concretes 172

Fig. 4.24 Relationship between observed shrinkage at 1 year and at 28 days for different
concretes 173

Fig. 4.25 Relationship between observed shrinkage at 1 year and at 90 days for different
Concretes 173

Fig.4.26 Effect of air content on creep of FC 174

Fig.4.27 Effect of aggregate volume on creep of FC 175

Fig. 4.28 Effect of L9 aggregate volume on creep of LWAC 176

Fig. 4.29 Effect of aggregate volume on creep (C
c
/C
m
) ratio of concrete at 90 days of drying
176

Fig. 4.30 Effect of aggregate type on specific creep with age of loading for equivalent mixture
proportions of concrete 177

Fig. 4.31 Normalized creep of concretes with different aggregates at 150 days 177

Fig. 4.32 Correlation between specific creep and modulus of elasticity of concretes at 90 days
178

Fig. 4.33 Effect of (a) w/c ratio (b) mineral admixtures on specific creep of LWAC (L9 LWA)
178

Fig. 4.34 Comparison between measured and predicted drying shrinkage with various models
for different concretes (FC, FCA, LWAC and NWC) 179

Fig. 4.35 Comparison between measured and predicted specific creep with various models for
different concretes (FC, FCA, LWAC and NWC) 180



Fig. 5.1 Restrained ring specimen geometry 217

Fig. 5.2 Typical restrained ring specimens exposed to drying (T – 30
o
C, RH – 65%) 217

Fig. 5.3 Typical picture of crack in a restrained concrete ring specimen 218

Fig. 5.4 Microscope for crack width measurements (1 division = 0.002 mm) 218

Fig. 5.5 The typical variations of (a) strain in steel ring, (b) interface pressure and (c) residual
tensile stress for the mortar (w/c - 0.40) 219

Fig. 5.6 Effect of air content on strain in steel ring, stress development in concrete ring and age
of racking for FC 219

xix
Fig. 5.7 Effect of sand volume on strain in steel ring, stress development in concrete ring and
age of cracking for the FC with 30% air content 220

Fig. 5.8 Effect of sand volume on strain in steel ring, stress development in concrete ring and
age of cracking for the FC with 45% air content 220

Fig. 5.9 Effect of LWA volume on strain in steel ring, stress development in concrete ring and
age of cracking for the FC with 30% air content 220

Fig. 5.10 Effect of LWA volume on strain in steel ring, stress development in concrete ring
and age of cracking for the FC with 45% air content 221

Fig. 5.11 Effect of sand and LWA volume on age of cracking for the FC with 30 and 45%
air content 221

Fig. 5.12 Effect of sand and LWA volume on stress at cracking for the FC with 30 and 45%
air content 221

Fig. 5.13 Relationship between shrinkage rate at cracking and age of cracking for FC and FCA
222

Fig. 5.14 Restrained shrinkage cracking results (actual stress in concrete ring vs age of drying)
for LWAC: (a) Effect of aggregate volume; (b) Aggregate type/density for av-0.20;
(c) Aggregate type/density for av-0.40; and (d) Effect of w/c ratio 222

Fig. 5.15 Effect of aggregate volume on (a) Age of cracking; (b) Stress in concrete @
cracking; and (c) Shrinkage rate @ cracking of LWAC with different aggregate
type/density 224

Fig. 5.16 Relationship between shrinkage rate @ cracking and age of cracking for LWAC 225

Fig. 5.17 Relationship between shrinkage rate at cracking and age of cracking: Comparion of
FC, FCA and LWAC 225

Fig. 5.18 Influence of strength, shrinkage and creep on shrinkage cracking of concrete
(Neville 1997) 226

Fig. 5.19 Effect of LWA volume on restrained shrinkage cracking of FC with 30% air content
(L6 LWA) 226

Fig. 5.20 Effect of aggregate volume on restrained shrinkage cracking of LWAC (L9 LWA)227

Fig. 5.21 Effect of aggregate density on restrained shrinkage cracking of concrete 228

Fig. 5.22 Effect of w/c ratio on restrained shrinkage cracking of LWAC (L9 LWA) 229

Fig. 5.23 Comparison of experimental and predicted (a) age cracking; (b) actual stress and
stress after creep relaxation at cracking for the FC and FC with LWA 230

Fig. 5.24 Comparison of experimental and predicted (a) age cracking; (b) actual stress and
stress after creep relaxation at cracking for the FC and FC with sand 230

Fig. 5.26 Comparison of experimental and predicted (a) age cracking; (b) actual stress and
stress after creep relaxation at cracking for the effect of aggregate volume 231


xx
Fig. 5.27 Comparison of experimental and predicted (a) age cracking; (b) actual stress and
stress after creep relaxation at cracking for the effect of aggregate density 231

Fig. 5.28 Comparison of experimental and predicted (a) age cracking; (b) actual stress and
stress after creep relaxation at cracking for the effect of w/c ratio 231


Fig. 5.29 Comparison of experimental and predicted age cracking for LWCs with and without
aggregates 232

Fig. 5.30 Stress distribution along the depth (Z-) direction 232

Fig. 5.31 Comparison of experimental and predicted stress at cracking for LWCs with and
without aggregates 233

Fig. 5.32 Correlation between the splitting tensile strength and actual tensile stress in concrete
ring at cracking 233

Fig. 5.33 Effect of polypropylene fiber percent on stress and age of cracking of (30%
air content) 234

Fig. 5.34 Effect of (a) fiber percent and (b) fiber type on stress and age of cracking of LWAC
(L9 LWA) 234

Fig. 5.35 Effect of fiber percent and fiber type on age of cracking of different concretes (FC,
LWAC and NWC) 235

Fig. 5.36 Effect of fiber percent and fiber type on crack widths of different concretes
(FC, LWAC and NWC) 235

Fig. 5.37 Effect of mineral admixtures on restrained shrinkage cracking of LWAC (L9 LWA)
236

Fig. 5.38 Effect of curing age and soaking condition on restrained shrinkage cracking of
LWAC with 0.30 and 0.56 w/c ratios (L9 LWA) 237

Fig. 5.39 Schematic diagram for controlling the potential risk of shrinkage cracking by
controlling amount and rate of shrinkage 238

Fig. 5.40 Relationship between shrinkage rate at cracking and age of cracking: comparison of
FCA and LWAC 238
CHAPTER 1
INTRODUCTION
1.1 Background

Today, concrete is the most widely used construction material worldwide in various
applications. In spite of its ancient origin in 9000 years ago, the real development of concrete
technology came only in early 1960’s when superplasticizer was first introduced in concrete as
admixture in Japan and West Germany. Since then, a great variety of chemical and mineral
admixtures have emerged which are now commercially available and they have brought
significant changes in fresh and hardened concrete properties and resulted in taller, massive and
more cost-effective structures in concrete construction. Cementitious concrete composites are
construction materials that can be used even for the structures that are required to perform
under very severe environmental conditions such as marine, freeze and thaw, etc. The adverse
nature of such an environment leads to the deterioration of the concrete which limits the
structural performance. To improve the long term durability and to do repairs effectively,
engineers and researchers must know the fundamentals of how concrete behaves in its
surrounding environment and researchers must develop new materials that are capable of
withstanding both the mechanical and environmental loadings. Accurate testing and evaluation
procedures must also be developed, based on a fundamental understanding of the material
behavior, to assess how these materials will perform in service.
Lightweight concrete (LWC) is a versatile material that has created great interest and

large industrial demand in recent years in wide range of construction projects, despite its known
use dates back over 2000 years. LWC is a concrete which by one means or another has been
made lighter than conventional (normal weight aggregate) concrete. LWC encompasses two
main categories of concrete, one in which air and the other in which lightweight aggregate

1
(LWA) is introduced into concrete to reduce its density. LWC has not only been further
classified into sub-categories based on compressive strength and density but method of
production have also been used to differentiate the LWC, as summarized by Wee (2005),
presented in Fig. 1.1.
The most obvious advantage of LWC is its lower density that results in reduction of
dead load, faster construction rates and lower handling costs. The weight of a structure in
terms of loads transmitted to the foundations is an important factor in design particularly in the
case of tall buildings or heavy structures where the bearing capacity of the soil is very weak.
Moreover, the higher strength to weight ratio is very advantages particularly in floating and
offshore structural applications. The other important characteristic of LWC is its relatively low
thermal conductivity, a property which enhances with decreasing density. Due to increasing
cost and scarcity of energy resources, in recent years, more attention has been given to thermal
conductivity to improve the efficiency of equipments, safety and comfort for humans.
Due to the inherent advantages of LWC, various LWC structures, ranging from low-
rise bungalow to multi-storey buildings (One Shell Plaza Building, Houston, USA; BMW
Central Administrative Building, Germany), bridges (Stolmen Bridge, Norway) and flyovers to
marine and offshore structures (Heidrum Tension Leg Plat from at Heidrum field of the North
sea) can now be found in many parts of the world. ACI Committee 213 has given a
comprehensive summary of the major structural applications of lightweight aggregate concrete
(LWAC) and its future application potentials. As discussed, many applications of LWC have
already been reported. Further growth on a much wider scale is anticipated in the near future
because it offers cost effective solutions in a variety of structural applications.
1.2 Need for the research
Unfortunately, the South East Asian region where we belong is yet to experience large-

scale structural applications of LWC with and without aggregates. There are two main reasons
Chapter 1: Introduction


2
for LWC not being so popular here. First, there is a general lack of understanding on the
production technique of this material, which requires greater skills and technology back up than
ordinary normal weight concrete (NWC). Secondly, lack of understanding on the role of
constituent materials (such as filler type and volume, density, fibers, mineral admixtures, etc)
and its structural and serviceable performance information available locally on this material to
provide adequate guidance and confidence to the designers.
A recent addition to the scope of structural LWC is the development of foamed
concrete with high compressive strength of 40 MPa and fresh density of 1600 kg/m
3
and above.
This new LWC is basically produced using low water to cement or cementitious materials ratio
and air in the form of preformed foam. Foamed concrete is lighter, simple to use, economic yet
more environmentally sustainable (Jones and McCarthy 2005) and it has the ability and greater
flexibility to achieve a wide range of concrete densities (300 to 2000 kg/m
3
). The commercial
demand for this special LWC has been increasing worldwide in a variety of non- and semi-
structural applications in recent years and its potential use and performance as a structural
material are being investigated by many research groups lately.
The mechanical properties of concrete are important since these are inextricably
connected with the design and long-term performance of concrete structures. The development
of shrinkage cracks also depends on many mechanical properties in addition to deformational
properties. The deformational properties such as shrinkage and creep of concrete has great
influence on the development of cracks in concrete members which are restrained and also
causes loss of pre-stress in pre-stressed concrete members. On the practical side, designers

require more accurate relationships and improved methods of predicting structural
deformations. The interaction between the mix constituents such as fillers (aggregates, air, etc.)
and matrix is also a continuing field of study, with implications for concrete deformability.
Moreover, shrinkage cracking can be a serious problem in concrete structures. It has
become evident that cracks can be problematic because they accelerate the penetration of
aggressive agents into concrete, thereby accelerating the corrosion of reinforcing steel (Wang et
Chapter 1: Introduction