MECHANICAL AND DEFORMATIONAL PROPERTIES,
AND SHRINKAGE CRACKING BEHAVIOUR OF
LIGHTWEIGHT CONCRETES DANETI SARADHI BABU

NATIONAL UNIVERSITY OF SINGAPORE
2008
MECHANICAL AND DEFORMATIONAL PROPERTIES,

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

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

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

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:

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

, 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

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

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

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


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

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. 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. 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

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

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. 5.28 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

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-

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