strength and durability properties of lightweight …
TRANSCRIPT
STRENGTH AND DURABILITY PROPERTIES
OF LIGHTWEIGHT FOAMED CONCRETE
FOR HOUSING CONSTRUCTION
by
FAHRIZAL ZULKARNAIN
Thesis submitted in fulfilment of the requirements
For the degree of
Doctor of Philosophy
2011
i
DEDICATION
In Memory of my Father
ii
ACKNOWLEDGEMENT
My profound thanks and deepest appreciation to my supervisor Professor Ir. Dr.
Mahyuddin Ramli, P.J.K., for his encouragement, inspirational ideas, academic input
and beneficial guidance, that he has been providing me from the beginning of this
study until the end. A special appreciation is dedicated to the Institute of
Postgraduate Studies (IPS) Universiti Sains Malaysia, for the provision of
scholarship and financial assistance throughout the author’s PhD Candidate. My
appreciation also extends to the kind assistance of the technical staff at the building
technology laboratory, School of Housing, Building, Planning particularly Mr.
Khalid Ahmad and Mr. Hj. Idris Shaari.
Next, I would like to convey my gratitude to the academic staff of School of
Housing, Building and Planning in Universiti Sains Malaysia for their warm, special
friendship and for never failing to support me during my research in any way, not
forgetting the Housing, Building and Planning Resource Centre and the USM
Library.
Also, I wish to thank Dr. Mohd. Zailan Sulieman and Dr. Norizal Mohammed
Noordin, also my colleagues for their tireless support during the preparation of my
studies, and my sincere thanks to all my friends in the School of Housing, Building
and Planning, Universiti Sains Malaysia for their hospitality and which contributes to
making my stay here enjoyable and comfortable.
iii
Finally, I express my sincere gratitude to my mother for her prayers, patience and
never-ending support in every way during my long absence from them. For all my
family members and my relatives, I appreciate and honour your prayers, assistance
and encouragement. I also would love to capture my gratitude to my beloved wife,
my brother and sisters, for their motivation and continuous encouragement
throughout the duration of my studies.
FAHRIZAL ZULKARNAIN.
iv
TABLE OF CONTENTS
Dedication i
Acknowledgement ii
Table of Contents iv
List of Tables x
List of Figures xii
Abstrak xvi
Abstract xviii
CHAPTER 1 INTRODUCTION 1
1.1 Introduction 1
1.2 Problem Statement 6
1.3 Research Aim and Objectives 7
1.4 Scope of this Research 8
1.5 Research Methodology 10
1.6 Layout of Thesis 11
CHAPTER 2 LITERATURE REVIEW 15
2.1 Introduction 15
2.2 History of lightweight foam concrete 16
2.2.1 Lightweight foam concrete in construction 19
v
2.2.2 Application of lightweight foam concrete in construction 23
2.3 Classification of lightweight concrete 26
2.3.1 No-fines concrete 32
2.3.2 Lightweight aggregate concrete 36
2.3.2.1 Types of lightweight aggregate 41
2.3.2.2 Density 44
2.3.2.3 Water absorption 45
2.3.2.4 Workability and water content 48
2.3.2.5 Durability of lightweight aggregate concrete 51
2.3.2.6 Application of lightweight aggregate 52
2.3.2.7 Requirement aggregate for structure concrete 53
2.3.3 Aerated concrete 56
2.3.3.1 Chemical/foaming agent 61
2.3.3.2 Foam types 64
2.3.3.3 Constituent material of foam concrete 66
2.3.3.4 Proportioning and preparation of foam concrete 67
2.3.3.5 Properties of foam concrete 68
2.3.3.6 Density 69
2.3.3.7 Compressive strength 70
2.3.3.8 Flexural and tensile strength 73
2.3.3.9 Stability 73
2.3.3.10 Drying shrinkage 74
2.3.3.11 Modulus of elasticity 75
2.3.3.12 Resistance to aggressive environment 76
2.3.3.13 Thermal insulation 76
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2.3.3.14 Fire resistance 78
2.4 Lightweight sandwich panels 80
2.4.1 Rigid plastic foam materials 81
2.4.2 Polyurethane/polyisocyanurate (PUR/PIR) 82
2.4.3 Polystyrene (EPS and XPS) 83
2.4.4 Syntactic foam and phenolic resin foam (PF) 84
2.5 Honeycomb cores 89
2.6 Adhesive and other components 90
2.7 Application of foam concrete in housing 91
2.8 Critical summary 92
CHAPTER 3 MATERIALS AND EXPERIMENTAL WORK 88
3.1 Introduction 96
3.2 Testing of materials 96
3.2.1 Cement 97
3.2.1.1 Compound composition of Portland cement 97
3.2.1.2 Method of testing cement 102
3.2.2 Aggregate 104
3.2.2.1 Sieve test for aggregate 106
3.2.2.2 Sieve analysis for fine aggregate 110
3.2.3 Water 112
3.2.4. Foam generator equipment 113
3.2.4.1 Filling and operation 117
3.2.4.2 Operation 118
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3.2.4.3 Quality of foam 120
3.2.4.4 Test of lightweight foam concrete 121
3.2.5 Preparing of admixture 123
3.3 Test of strength lightweight foam concrete 124
3.3.1 Introduction 124
3.3.2 Slump test 124
3.3.3 Compressive strength test 126
3.3.4 Flexural strength test 127
3.3.5 PUNDIT test 129
3.3.6 Modulus of elasticity test 131
3.3.7 Tensile splitting strength 132
3.3.7.1 The tensile splitting strength test 133
3.3.7.2 Components of apparatus B 135
3.4 Test of durability lightweight foam concrete 136
3.4.1 Introduction 136
3.4.2 Carbonation test 136
3.4.3 Water absorption test 137
3.4.4 Permeability test 139
3.4.5 Loss of weight test 141
3.4.6 Shrinkage limit test 141
3.4.7 Block specimen 142
3.5 Quality control and procedure 142
3.6 Preparation of specimen 143
3.7 Curing of lightweight foam concrete 147
3.8 Concrete mixed design 148
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CHAPTER 4 STRENGTH OF LIGHTWEIGHT FOAM 150
CONCRETE
4.1 Introduction 150
4.2 Method for determination of density of hardened concrete 151
4.3 Effect of different foam density with target density 154
4.4 Compressive strength test 155
4.5 Flexural strength test 159
4.6 Correlation between compressive strength and flexure strength 162
4.7 PUNDIT test 164
4.8 Correlation between PUNDIT with compressive strength 166
4.9 Modulus of elasticity test 167
4.10 Correlation between the modulus of elasticity with compressive 170
strength
4.11 Tensile splitting strength test 171
4.12 Correlation between tensile splitting strength with compressive 174
strength
4.13 Summary 175
CHAPTER 5 DURABILITY OF LIGHTWEIGHT FOAM 177
CONCRETE
5.1 Introduction 177
5.2 Carbonation test 177
5.3 Correlation between carbonation effects with compressive 181
ix
strength
5.4 Water absorption test 182
5.5 Correlation between water absorption with compressive strength 185
5.6 Permeability test 187
5.7 Loss of weight test 187
5.8 Shrinkage limit test 189
5.9 Block specimen 196
5.9.1 Preparing of mould specimen 197
5.9.2 Mixed design and testing of lightweight cellular concrete 199
block
5.9.3 Correlation between lightweight cellular concrete block 200
with compressive strength
5.10 Summary 202
CHAPTER 6 CONCLUSIONS AND SUGGESTIONS FOR 204
RESEARCH IN THE FUTURE
6.1 Summary of conclusion 204
6.2 Detailed conclusions 204
6.3 Suggestions for research in the future 209
REFERENCES 211
APPENDIX A 224
APPENDIX B 235
x
LIST OF TABLES Page
Table 2.1 Typical properties of no-fines concrete with 9.5-19 mm 35
aggregate
Table 2.2 Grading requirement of lightweight coarse aggregate 54
according to ASTM C 330-89
Table 2.3 Grading requirement of lightweight coarse aggregate 54
according to BS 3797:1990
Table 2.4 Grading requirements of lightweight fine aggregate 54
according to BS 3797:1990 and ASTM C 330-89
Table 2.5 History of foam extrusion 62
Table 2.6 Typical markets for high density foam 65
Table 2.7 Typical markets for low density foam 65
Table 2.8 Salient literature on lightweight foam concrete 95
Table 3.1 Main compounds of Portland cement 98
Table 3.2 Usual composition limits of Portland cement 99
Table 3.3 Oxide and compound compositions of a typical Portland 99
cement of the 1960s
Table 3.4 Chemical properties of cement 101
Table 3.5 Final results testing of cement 104
Table 3.6 Calculation of sieve test for aggregate 106
Table 3.7 Relative density and water absorption 108
Table 3.8 Percentage moisture content of aggregate 110
Table 3.9 Percentage of sieve analysis for fine aggregate 111
Table 3.10 Foam density 122
Table 3.11 Quality of concrete based on pulse velocity 131
xi
Table 3.12 Mixed design foam concrete in 0.05 m3 149
Table 4.1 The variation of density with age and curing 152
condition (kg/m3)
Table 4.2 Mixed lightweight foamed concrete in 0.05 m3 155
Table 4.3 Compressive strength result foam concrete (N/mm2) 157
Table 4.4 Flexural strength result of foam concrete (N/mm2) 159
Table 4.5 Result in pulse velocity of foam concrete (km/s) 164
Table 4.6 Modulus of elasticity of foam concrete (N/mm2) 168
Table 4.7 Tensile splitting strength result (N/mm2) 172
Table 5.1 Carbonation result in lightweight foamed concrete (mm) 179
Table 5.2 Water absorption in lightweight foamed concrete (%) 183
Table 5.3 Loss of weight of the foam concrete 188
Table 5.4 Shrinkage limit test (1050 kg/m3) 191
Table 5.5 Shrinkage limit test (1150 kg/m3) 192
Table 5.6 Shrinkage limit test (1250 kg/m3) 193
Table 5.7 Shrinkage limit test (1350 kg/m3) 194
Table 5.8 Shrinkage limit test (1450 kg/m3) 195
Table 5.9 Lightweight cellular concrete block (N/mm2) 199
xii
LIST OF FIGURES Page
Figure 2.1 The three basic types of lightweight concrete 27
Figure 2.2 Morphology of foam with different densities 28
in a 2-d array
Figure 2.3 Formation of foam morphology in 2D 28
Figure 2.4 Polyhedral model of foam cell in 3D space 31
Figure 2.5 Relation between 28-day compressive strength 50
(measured on cubes) and cement content for
various lightweight aggregates with a slump of
50 mm (2 in.) (A) sintered fly ash and normal
weight fine aggregates; (B) pelletized
blastfurnace slag and normal weight fine
aggregates; (C) sintered fly ash; (D) sintered
colliery shale; (E) expanded slate; (F) expanded
clay and sand; (G) expanded slag
Figure 2.6 Hexagonal honeycomb core 89
Figure 3.1 Ordinary Portland cement ‘Blue Lion’ 102
Figure 3.2 Vicat apparatus for method of testing of cement 103
Figure 3.3 Fine aggregate after sieving 105
Figure 3.4 Cumulative undersize of fine aggregete 112
Figure 3.5 Layout of front panel of Portafoam 114
Figure 3.6 Pressure tank/holding tank details 115
Figure 3.7 Details of foam nozzle or lance unit 116
Figure 3.8 Details of hose connection to holding tank 118
Figure 3.9 Portafoam TM-1 in laboratories 119
Figure 3.10 Preparing Portafoam TM-1 before mixed with 121
NORAITE TM-1
xiii
Figure 3.11 Foam concrete from Portafoam TM-1 123
Figure 3.12 Slump test 125
Figure 3.13 Specimen with compressive strength machine 127
Figure 3.14 Test of flexural strength with Gotech Universal 128
Testing Machine
Figure 3.15 Specimen with PUNDIT 130
Figure 3.16 a, b Suitable jigs for the tensile splitting strength test 134
Figure 3.17 Plane of loading 135
Figure 3.18 Fracture concrete without carbonation 137
Figure 3.19 Mould in size cube and prism before used 143
Figure 3.20 Foam concrete mixed design before used 145
Figure 3.21 Mortar density in slump test 146
Figure 3.22 Specimen wrapped in polythene wrapping 147
Figure 4.1 Target density with curing time 154
Figure 4.2 Compressive strength with curing time 158
Figure 4.3 Variation of compressive strength increase 159
with curing time
Figure 4.4 Flexural strength with curing time 161
Figure 4.5 Variation between flexural strength with 161
curing time
Figure 4.6 Correlation between compressive strength with 163
the flexural strength in target density 1050 kg/m3,
1150 kg/m3, 1250 kg/m
3, 1350 kg/m
3,
and 1450 kg/m3
Figure 4.7 Pulse velocity with duration of curing time (km/s) 165
Figure 4.8 Variation of pulse velocity increasing with 166
curing time
Figure 4.9 Correlation between Pundit with compressive 167
strength in target density 1050 kg/m3, 1150 kg/m
3,
xiv
1250 kg/m3, 1350 kg/m
3, and 1450 kg/m
3
Figure 4.10 Modulus of elasticity with curing time 168
Figure 4.11 Variation of compressive strength increase 169
with curing time
Figure 4.12 Correlation between the modulus of elasticity 170
compressive strength in target density 1050 kg/m3,
1150 kg/m3, 1250 kg/m
3, 1350 kg/m
3,
and 1450 kg/m3
Figure 4.13 Tensile splitting strength 171
Figure 4.14 Results of tensile splitting strength 173
Figure 4.15 Variation of tensile splitting strength increase 173
with curing time
Figure 4.16. Correlation between tensile splitting strength with 174
compressive strength in target density 1050 kg/m3,
1150 kg/m3, 1250 kg/m
3, 1350 kg/m
3,
and 1450 kg/m3
Figure 5.1 Carbonation test with phenolphthalein 178
Figure 5.2 Carbonation effects in lightweight foamed 180
concrete (mm)
Figure 5.3 Carbonation increases with curing time 180
Figure 5.4 Correlation between carbonation effects with 181
compressive strength in target density 1050 kg/m3,
1150 kg/m3, 1250 kg/m
3, 1350 kg/m
3,
and 1450 kg/m3
Figure 5.5 Water absorption in curing time 184
Figure 5.6 Water absorption decrease with curing time 185
Figure 5.7 Correlation between water absorption with 186
compressive strength in target density 1050 kg/m3,
1150 kg/m3, 1250 kg/m
3, 1350 kg/m
3
and 1450 kg/m3
Figure 5.8 Loss of weight with curing time 188
Figure 5.9 Loss of weight decreases with curing time 189
xv
Figure 5.10 Expansion with curing time 196
Figure 5.11 Lightweight cellular concrete block mould 198
Figure 5.12 Lighweight cellular concrete block with 199
curing time
Figure 5.13 Test of lightweight cellular concrete block 200
Figure 5.14 Correlation between lightweight cellular concrete 201
block with compressive strength in target density
1050 kg/m3, 1150 kg/m
3, 1250 kg/m
3, 1350 kg/m
3,
and 1450 kg/m3
xvi
CIRI-CIRI KEKUATAN DAN KETAHANAN
KONKRIT RINGAN BERBUSA UNTUK PEMBINAAN PERUMAHAN
ABSTRAK
Konkrit berbusa adalah sama ada pasta simen yang diklasifikasikan sebagai simen
ringan, di mana rongga-rongga udara terperangkap dalam mortar oleh agen
pembusaan yang sesuai. Ia mempunyai keboleh aliran yang tinggi, berat yang
rendah, penggunaan aggregat yang rendah, kekuatan rendah yang terkawal, dan sifat
penebatan haba yang sangat baik. Ketumpatan-ketumpatan konkrit berbusa dalam
julat yang luas di antara (1600-400 kg/m3), melalui kawalan dos yang sesuai, boleh
diperolehi untuk applikasi kepada struktur, dinding sekat, atau gred pengisian. Dalam
penyelidikan ini, konkrit berbusa menggunakan aggregat halus yang melepasi tapisan
5 mm atau 3/16 inci, dan 10% Norizal Hardener Powder Code: 4 (NHP4)
berdasarkan berat simen, untuk meningkatkan kekuatan dan ketahanan konkrit ringan
berbusa. Nisbah bagi rekabentuk campuran ini adalah 1:1.5:0.45 dengan ketumpatan
sasaran dari 1050 kg/m3, 1150 kg/m
3, 1250 kg/m
3, 1350 kg/m
3 dan 1450 kg/m
3.
Rekabentuk campuran dalam penyelidikan ini mempunyai isipadu 0.05 m3 dan ujian
penurunan sekitar 18 cm hingga 20 cm. Ketumpatan mortar sekitar 2150 kg/m3 bagi
kesemua ketumpatan sasaran dan berat busa dalam rekabentuk campuran sekitar 75-
80 g/liter. Konkrit ringan berbusa dijalankan dengan pengawetan selama 3, 7, 28, 60,
90, 180, dan 365 hari. Ujian bagi semua spesimen dalam penyelidikan meliputi
kekuatan mampat, kekuatan lentur, kekuatan tegangan pecah dan blok konkrit selular
ringan dalam jangkamasa pengawetan didapati berbeza. Kekuatan mampatan bagi
konkrit berbusa telah ditentukan daripada kiub berukuran 100 mm x 100 mm,
xvii
kekuatan lentur diuji dengan ukuran 100 mm x 100 mm x 500 mm, kekuatan
tegangan pecah diuji dengan ukuran diameter 150 mm x 300 mm panjang bagi
silinder dan blok konkrit selular ringan diuji dengan ukuran 200 mm x 100 mm x 500
mm. Kiub-kiub tersebut telah dituang dalam acuan-acuan keluli, dikeluarkan
daripada acuan setelah 24 jam, dibalut dalam pembalut politena, dan disimpan dalam
sebuah bilik dengan suhu malar ± 28°C sehinggalah ke hari ia diuji. Setiap satu kiub
telah dibuka pembalutnya dan ditimbang sebelum ujian. Kajian ini telah
menghasilkan ketumpatan sasaran berbeza dan juga jenis ujian yang berbeza.
Kekuatan mampatan minimum untuk kekuatan mampatan dalam ACI 532.2R-96
adalah 300 psi (2.07 MPa), bagi unit-unit lantai konkrit seluar bertetulang pratuang,
bumbung dan dinding. Berdasarkan piawaian British (BS) 5628: Part 1: 1978,
kekuatan mampatan adalah 2.8 N/mm2. Bagi sampel 28 hari, kesemua data
mempunyai nilai melebihi nilai minimum daripada ACI atau BS, dan kesimpulan
daripada kajian ini juga, secara umumnya boleh digunakan untuk pembinaan
bangunan.
xviii
STRENGTH AND DURABILITY PROPERTIES OF
LIGHTWEIGHT FOAMED CONCRETE FOR HOUSING CONSTRUCTION
ABSTRACT
Foamed concrete is either cement paste classified as lightweight concrete, where air-
voids are entrapped in mortar by a suitable foaming agent. It possesses high-flow
ability, low self-weight, minimal consumption of aggregate, controlled low strength,
and excellent thermal insulation properties. A wide range of densities of the foam
concrete between (1600-400 kg/m3), with proper control in the dosage of the foam,
can be obtained for the structural, partition, insulation application and the filling
grades. In this research, foam concrete uses fine aggregate passing a 5 mm or 3/16
inch sieve, and 10% of Norizal Hardener Powder Code: 4 (NHP4) based on the
weight of cement, for increasing the strength and durability of lightweight foamed
concrete. The ratio for this mix design is 1:1.5:0.45 with target density from 1050
kg/m3, 1150 kg/m
3, 1250 kg/m
3, 1350 kg/m
3 to 1450 kg/m
3. The mix design adopted
for this research has the volume of 0.05 m3 and slump test around 18 cm to 20 cm.
Mortar density around 2150 kg/m3 for all target densities and foam weights in mix
design is around 75-80 g/litre. Lightweight foamed concrete with curing time took
place for 3, 7, 28, 60, 90, 180, and 365 days. Tests for all specimens in this research
such as the compressive strength, flexural strength, splitting tensile strength and
lightweight cellular concrete block had been performed in different durations of the
curing time. The compressive strength of the foamed concrete was determined from
100 mm x 100 mm cubes, flexural strength with 100 mm x 100 mm x 500 mm,
tensile splitting strength with 150 mm diameter x 300 mm long for cylinders and
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lightweight cellular concrete block with 200 mm x 100 mm x 500 mm. The cubes
were cast in steel moulds, demoulded after 24 hours, wrapped in polythene wrapping,
and stored in a room with a constant room temperature of ± 28°C up to the day of
testing. Each cube was unwrapped and weighed before testing. This research has
resulted in different target densities and also different types of testing. The minimum
compressive strength for that in American Concrete Institute (ACI) 532.2R-96 is 300
psi (2.07 MPa), where this is used for precast reinforced cellular concrete floor, roof,
and wall units. From the British Standard (BS) 5628: Part 1: 1978, the compressive
strength is 2.8 N/mm2. This research also ensures that the material and foam for this
research are suitable in the non-loadbearing lightweight block foam. The strength
and durability of these specimens also include the tests for the compressive strength,
flexural strength and tensile splitting strength. All specimens with the mixed design
of the lightweight foamed concrete are tested in different target densities, which were
1050 kg/m3, 1150 kg/m
3, 1250 kg/m
3, 1350 kg/m
3 and 1450 kg/m
3. The target
density of 1050 kg/m3 has the maximum compressive strength of 15.27 N/mm
2 in
365 days of curing time. The maximum compressive strength for the target density
1150 kg/m3 would be 21.15 N/mm
2 in 365 days of curing time. The maximum
compressive strength for the target density 1250 kg/m3 is 24.06 N/mm
2 in 365 days
of curing time. The maximum compressive strength for the target density of 1350
kg/m3 is 25.43 N/mm
2 in 365 days of curing time. Next, the maximum compressive
strength for the target density 1450 kg/m3 is 29.52 N/mm
2 in 365 days of curing time.
For 28 days, the results concerning compressive strength from either the ACI or BS
have been minimal, and the conclusion deduced from this research can also be used
for the housing construction in general.
1
CHAPTER 1
INTRODUCTION
1.1 Introduction
In the last four decades, lightweight concrete has been employed in both residential
housing and tall building construction. Precast lightweight concrete panels have
become widely used materials in construction. Considerable attention is being paid to
reducing the dead load and thermal conductivity of concrete panels and improving
their fire resistance. In addition the earthquake resistance and seismic of concrete
structure are becoming more important issues (Kim, 2004).
According to Kearsley (1999), foam concrete is perceived to be weak, non-durable
with high shrinkage characteristics and untreated aerated concrete should not be
exposed to an aggressive atmosphere and that unprotected reinforcement in aerated
concrete would be vulnerable to corrosion even when the external attack is not very
severe. Low density concrete is normally defined as concrete having an air-dry
density of below 2000 kg/m3 as opposed to normal concrete with a density in the
region of 2350 kg/m3. Low density concrete has practical and economical advantages
as the reduced weight of the superstructure can lead to savings in the cost of super
and substructures and components can be handled and erected relatively easily. Fire
resistance and thermal insulation of low density concrete are superior to those of
normal density concrete.
2
Low density concrete can be manufactured with a density of between 300 and 1850
kg/m3. The strength of low density concrete is a function of density and therefore
density can be used to classify low density concrete according to the purpose for
which it is to be used. Low density concrete can be used to classify as one of the
following:
Structural low density concrete has a density between 1350 kg/m3 and 1850
kg/m3 and minimum compressive cylinder strength of 17 MPa.
Low density concrete has a density between 300 kg/m3 and 800 kg/m
3 and is
used for non-structural applications, mainly for thermal insulation purposes.
A third category between the previous two used for masonry units.
Since the introduction of cellular concrete systems to the construction industry more
than 50 years ago, the use of foamed concrete has been almost exclusively limited to
the following applications: non structural void filling, thermal insulation, acoustic
damping, trench filling reinstatement of roads and building blocks. In the
Netherlands foamed concrete has been used not only for level correction in housing
developments, but also for fill-material where ground subsidence has taken place and
ask founding layer for road works on very weak soils (Kearsley, 1999).
Structural lightweight concrete is a structural concrete made with lightweight
aggregate, the air-dried unit weighed at 28 days is usually in the range of 1440 kg/m³
to 1850 kg/m³ and the compressive strength is more than or 17.2 MPa. (213R-87,
1999).
3
Lightweight concrete maintains its large voids and not forming laitance layers or
cement films when placed on the wall. In this research, is based on the performance
of aerated lightweight concrete. However, sufficient water cement ratio is vital to
produce adequate cohesion between cement and water. Likewise, too much water can
cause cement run off aggregates to form laitance layers, subsequently weakening in
strength.
Foamed concrete or type of lightweight concrete is either cement paste or mortar
classified as lightweight concrete, where air-voids are entrapped in the mortar by a
suitable foaming agent. It possesses high flow ability, low self-weight, minimal
consumption of aggregate, controlled low strength, and excellent thermal insulation
properties. A wide range of densities (1600-400 kg/m3) of foamed concrete, with
proper control in the dosage of the foam, can be obtained to be applied to the
structural, partition, insulation, and filling grades (Ramamurthy et al., 2009).
Foamed concrete is a lightweight material consisting of the Portland cement paste or
cement filler matrix (mortar), with a homogeneous void or pore structure created by
introducing air in the form of small bubbles (Nambiar and Ramamurthy, 2007a).
Pre-formed foam concrete is manufactured by adding foam, prepared by aerating a
foaming agent solution, to cement paste or cement mortar. The composition, physical
properties and uses of foam concrete have been discussed in detail by (Nambiar and
Ramamurthy, 2006).
4
The properties of its components-the cement paste and the voids-have a measurable
effect on the properties of the combined materials (Nambiar and Ramamurthy,
2007b).
The method of production in aerated concrete (either through gas release or foaming)
can influence the microstructure and, consequently, its properties. The material
structure of aerated concrete is characterized by its solid microporous matrix and
macropores (Narayanan and Ramamurthy, 2000). The macropores are formed due to
the expansion of the mass caused by aeration. Micropores also appear in the walls
between the macropores (Alexanderson, 1979). Macropores have usually been
defined as pores with a diameter of more than 60 μm (Petrov and Schlegel, 1994).
Aerated lightweight aggregate concrete is formulated by the minimum matrix
methods, which seeks to achieve volume ratio of comentitious matrix to hard
aggregate. The optimal value yields the closest possible contact of each particle of
aggregate. When the matrix is completely without voids, it is in the minimum matrix
condition. For concrete density between 75 and 90 pcf, this conditions produces the
best possible values of compressive and tensile strengths, elasticity, and other
properties. It requires, only the minimum amount of cement necessary to produce
adequate strength, so that the shrinkage is less than in ordinary lightweight concrete.
In this manner, cost may also be reducing since cement is most expensive ingredient
of concrete (Kim, 2004).
In 1963, Short and Kinniburgh presented the first comprehensive review on cellular
concrete, summarizing the composition, properties, and uses of cellular concrete,
5
irrespective of the method of formation of the cell structure. Subsequently, Jones and
McCarthy recently reviewed the history of the uses of foamed concrete and its
constituent material, properties, and construction application, including for some
projects carried out worldwide. These reviews included an evaluation of its
functional properties such as fire resistance, thermal conductivity, and acoustics.
However, data on fresh state properties, durability, and air-void systems of foamed
concrete are found to be limited (Short and Kinniburgh, 1978).
The production of stable foamed concrete mix depends on many factors, such as the
selection of foaming agent, method of foam preparation and addition of uniform air-
voids distribution, material section and mixture design strategies, and production of
foamed concrete (Ramamurthy et al., 2009).
The applications of lightweight concrete for composite structures are ostensible in
the building industry. Glass reinforced plastic (GRP) components have been used in
this sector for over three decades. As building materials, composites are suitable for
numerous applications, such as in pipes, sills, slabs, formwork, linings, pillars,
foundations, tanks, housings, containers, doors, covers, bricks, walls, frames, steps,
and gutters. The possibilities are virtually unlimited. Composites innovations
continue to find usefulness in building sites (Reichl, 2007).
This growing popularity has led to the development of scaffolding boards made of
GRP. The idea is to replace the heavy timber boards, relieving the stress on high
scaffolding as well as enabling higher transport and erection performance by
scaffolders. This objective is achieved. Savings of over 20% (in weight) has been
6
achieved over the conventional timber scaffolding boards after successful load and
weathering tests (Reichl, 2007).
Most of the residential houses offered in the market today from a “low cost house”,
and the developers cannot lower the cost because the current available construction
technology entails too much manpower and material wastage (Lejano, 1997).
Kearsley (1999) reported, unstable foams have in the past resulted in foamed
concrete having properties unsuitable for reinforced, structural applications. The
development of protein-hydrolisation based foaming agents and specialized foam
generating equipment have improved the stability of the foam, making it possible to
manufacture foamed concrete for structural applications. In recent years foamed
concrete has been used as a structural material in schools, apartment and housing
developments in countries such as Brazil, Singapore, Kuwait, Nigeria, Botswana,
Mexico, Indonesia, Libya, Saudi Arabia, Algeria, Iraq and Egypt.
1.2 Problem Statement
The production of stable foam concrete’s mix design depends on many factors such
as the selection of foaming agent, method of foam preparation and addition for
uniform air-voids distribution, material section and mixture design strategies,
production of foam concrete, and performance with respect to fresh and hardened
state are of greater significance (Ramamurthy et al., 2009). Many researchers have
paid attention to this area and produced foam with durability and high-performance.
All aspects should be considered and produced for sustainable, durable and
environmental-friendly housing construction.
7
The prominent advantage of aerated concrete is its lightweight, which economises
the design of the supporting structures including the foundation and walls of lower
floors. It provides a high degree of thermal insulation and considerable savings in
material due to the porous structure. By adopting an appropriate method of
production, aerated concrete with a wide range of densities (300 ± 1800 kg/m3) can
be obtained thereby offering flexibility in manufacturing products for specific
applications of structural, partition and insulation grades (Narayanan and
Ramamurthy, 2000).
The first element to obtain the durability and strength lightweight foamed concrete is
a selection of ratio foam agent with water, and the design of mixture of the current
foam concrete, also producing the foam for sustainably low cost in the housing
construction.
1.3 Research Aim and Objectives
In general, the main purpose of this research is to examine the lightweight foamed
concrete in detail, based on its strength and durability in housing constructions. In the
literature review, it is established that lightweight foamed concrete can generally be
used in the constructions, especially where the housing industry is concerned.
Otherwise, in this particular context, lightweight foamed concrete necessitates further
research and practical tests in laboratories to obtain a result with decreased density,
increased compressibility and is suitable for use in a housing construction. Also, the
quality of the materials would be ensured from the selection stage until the
mix design stage.
8
We now come to the objective of this research:
1. To design and determine a mixed design of lightweight foamed
concrete and percentage of foam in lightweight foamed
concrete for housing construction.
2. To define and test the structure of the lightweight block foam
concrete based on the strength and durability.
3. To evaluate the strength and durability of lightweight foamed
concrete for housing construction.
Our pursuit is to design and determine a mixed design of strong and durable
lightweight foamed concrete and establish the suitable percentage of foam concrete
for the housing construction. Furthermore, a mixed design of lightweight foamed
concrete is to be defined and tested in target densities from 1050 kg/m3 until 1450
kg/m3, and also in different curing times from 3 days until 365 days.
This study is an attempt to find any method that can work towards improving of
building materials. It focuses on the properties and the performance of the stabilized
lightweight foamed concrete. One of these studies is to propose and summarize the
information, pertaining to the basic characteristics attributable to lightweight foamed
concrete and on the stabilization and compaction.
9
1.4 Scope of this Research
This research will be focusing on lightweight foamed concrete, which offers better
quality structure and faster building construction solution other than being
economical in the housing construction. Many aspects have been clarified through
the literature regarding building material properties and lightweight foamed concrete
for building construction. Quite differently, this research focuses on the design and
selection of material properties in building construction, and has put forth a
technique of processing lightweight foamed concrete.
The scope of this research lingers around the lightweight foamed concrete, where
some theoretical principles on the lightweight foamed concrete in correlation to
strength and durability for housing construction have been provided. The target
densities used in the range of 1050 kg/m3 to 1450 kg/m
3 in different curing times
from 3 days until 365 days were decided. In general term, the lightweight foamed
concrete maximum target density is 1850 kg/m3 approximately, and it comes with
different admixtures in the concrete itself. In this research, the maximum target
density is chosen to be 1450 kg/m3 because for 3 days, the compressive strength
would be 7.04 N/mm2, to compare with the Malaysian Standard (MS) 27: 1996
which establishes 2.8 N/mm2 as the minimum compressive strength for the block.
Based on these criteria, target density results are suitable for the lightweight foamed
concrete block. On the other hand, basic constituents such as cement, sand, water,
with Norizal Hardener Powder Code: 4 (NHP4), and silica fume serve as the
contributors for the increase of strength and durability of lightweight foamed
concrete.
10
This research also evaluates strength, durability and performance structure of this
lightweight foamed concrete based on the selected materials such as foam, fine
aggregate, and cement. Also, we went on to examine the relationship between the
control mixture with foam, Ordinary Portland Cement (OPC), fine aggregate, and
water, respectively. This relationship scrutinises the fine aggregate and silica fume
such as their increased strength and performance, and stabilized lightweight foamed
concrete such as fresh density and slump for new mix design of the foam concrete.
1.5 Research Methodology
In this study, elaborated studies equipped with laboratories experiments, their results
and the inevitable conclusions. For literature review, the entire source is based on the
historical background of lightweight foamed concrete and its contributions to the
building construction and the housing construction. The focus of this research
therefore is to estimate the strength and durability of a lightweight foamed concrete
for constructions, applicable to both building and housing constructions.
In the laboratories, the experimental procedure is divided into six chapters, with
research activities already determined. This research such as the test of all materials,
test of fresh air void (bubble) foam, test of density a lightweight foamed concrete,
test of compressive strength and test of flexural and tensile strengths. In the first
research a material is selected for the mix design of the lightweight foamed concrete.
There is a test for air void, test for hardened cement paste, test of particle size
distribution, test of water absorption, and test of fresh density of concrete.
11
In this research, a trial and error mix design of lightweight foamed concrete to get a
quality and the quantity of mix design is required. The first of this mix design is a
fresh density of the lightweight foamed concrete, meaning lightweight foamed
concrete must obtain a standard fresh density around 1000 kg/m3 to 1850 kg/m
3.
Before this, a test is performed, with the degradation of cement (slump test) known
as the combination of cement and water with a circle diameter of 18.0 cm to 20.0 cm.
After the test has produced good results, we then move on to the compressive and
flexural strength test. Compressive strength of the foamed concrete is determined
from 100 mm cubes. The cubes were cast in steel moulds, demoulded after 24 hours,
wrapped in polythene wrapping, and stored in a room with a constant room
temperature of ± 28°C up to the day of testing. Each cube was unwrapped and
weighed before testing. All of the specimens were kept in storage for the maximum
365 days. Estimation in this research for all specimens, such as the cube and prism is
a test of methods of testing cement, determination of relative density and water
absorption, methods for determination of particle size distribution, fresh density,
slump test, test of quality foam, compressive strength, flexural strength, Portable
Ultrasonic Non-Destructive Digital Indicating Tester (PUNDIT), carbonation, tensile
splitting strength, modulus of elasticity, and the drying shrinkage.
At the end of this research, the lightweight foam’s concrete panel with a high ratio
compressive strength are selected and ready to be used. This current research also
recommends credible performance and high achievement of the lightweight foamed
concrete, such as in air condition. All of this research has been carried out, based on
the Malaysian Standard (MS), British Standard (BS) and American Standard
(ASTM).
12
1.6 Layout of Thesis
This chapter is divided into six chapters including detailed discussions regarding the
research done in the laboratories. This thesis is designed in such a way as for the
objectives in this research to be able to be fulfilled, by thorough discussions that are
present chapter by chapter. Generally, the substance of every chapter is given below:
For chapter 1, this chapter includes the general introduction between studies that
have been done previously, research objectives, scope of this research, problem
statement, and research methodology, and the layout of the thesis.
In chapter 2, researcher will be presented with ample literature review, which
highlights the discussions that surround the subject matter, which is based on the
classification of lightweight concrete, technology of lightweight foamed concrete and
historical background of the lightweight concrete, lightweight foamed concrete for
housing construction, honeycomb cores, adhesive and other components, chemical
aspect of lightweight concrete, and manufacture of foam agent. This chapter also
focuses on a process of preparing the material and lightweight foamed concrete in
general. In specific, a material and mixed design of lightweight foamed concrete are
prepared, such as a material concrete for structural lightweight foamed concrete for
housing construction.
Chapter 3, highlights the research methodology performed in laboratories, with
respect to the lightweight foamed concrete, where this research starts from selecting
and testing natural materials or basic materials for use until preparing the lightweight
foamed concrete. Another discussion concerns a design and preparation of the mix
13
design of the lightweight foamed concrete and testing of a specimen. Discussion of
the final research of this specimen includes a mix design of the lightweight foamed
concrete, type of conservation and duration of conservation. Details of these include
also the engineering research with basic standard materials being studied, such as the
testing of materials, testing of strength of lightweight foamed concrete, testing of
durability of lightweight foamed concrete, process and installing mould concrete,
processing mixed design concrete, processing preservation lightweight foamed
concrete, mixed design concrete, and mixed design in this research.
Chapter 4, sheds light on the strength of lightweight foamed concrete. The discussion
brings into the picture the strength of lightweight foamed concrete based on results
and the processing of all specimens in the laboratories. Some tests have also been
covered such as the slump test, density of lightweight foamed concrete test, effect of
different foam density with target density, test of compressive strength, test of
flexural strength, test of PUNDIT, modulus of elasticity test, tensile splitting strength
test. This research also covers an analysis of results and comparison analysis, where
the tests are being compared to another testing in the laboratories.
Chapter 5, sees the durability behaviour of lightweight foamed concrete being
discussed. These tests also include the carbonation test, water absorption test, oxygen
permeability test, lost of weight test, shrinkage limit test, and structural test. Another
evaluation and the impending conclusion are also presented, regarding the durability
of lightweight foamed concrete in the housing construction. The test results
pertaining to all specimens being tested have also taken place in some paragraphs in
14
this chapter, and what follow are the analysis results of each testing and the
comparison with another testing done previously.
Chapter 6 presents the conclusion and suggestion for future research. This chapter
also deals with all testing done in laboratories. In overall, the mixed design of the
lightweight foamed concrete is in the density of 1450 kg/m3 with high compressive
strength lasting in 365 days. This ratio can be used for the non-load bearing
structures. Flexural strength in all tests also increases in different days, where the
density of 1450 kg/m3 produces good results compared with other target densities.
The result in 365 days is not very significant but we can notice an increase from the
beginning, such as in 3 days. In the structural test there is also noticeably an increase
from 3 days to 365 days. Suggestions for similar future research would include the
fact that the mixed design lightweight foamed concrete can use different density
levels, ratio and curing time. Researcher is also suggested to be more open and
flexible to use other materials for the mixed design of the lightweight foamed
concrete.
15
CHAPTER 2
LITERATURE REVIEW
2.1 Introduction
Concrete is a construction material that consists of cement, aggregate (fine and
coarse), water, and admixtures such as fly ash, silica fume, and other chemical
agents. After the mixing process, concrete is hardened by a chemical process called
hydration. Concrete can be used for several applications such as pavements,
buildings, foundations, pipes, dams, and other civil infrastructural structures.
Concrete is one of the most popular construction materials. According to the ASCE
(2005), every year approximately six billion cubic meters of concrete is produced. In
addition, more than 55,000 miles of roads and highways in America are built by
using concrete. Usually, concrete has an outstanding compressive strength but very
low tensile strength. Therefore, steel reinforcement is applied in concrete structures
to handle the tensile strength of structures (Piyamaikongdech, 2007).
The idea of using lightweight materials in concrete construction has become popular
due to economical reasons. If the production of lightweight concrete with adequate
strength and ductility is achieved, the construction cost will be significantly reduced.
The most important advantages of using concrete are to reduce dead load of a
structure. Besides reduction of dead load, faster construction, lower transportation
and handling costs and reduction of labour become dominant factors to use
lightweight concrete. Besides being lightweight, low thermal conductivity is another
characteristic of lightweight concrete. As reducing energy of fuel consumption
16
during operation of buildings become necessary, demands for lightweight concrete
increase (Arisoy, 2002).
Lightweight concretes can be produced with a density range of approximately 300-
2000 kg/m3, corresponding cube strength from approximately 1 to over 60 N/mm
2
and thermal conductivities of 0.2 to 1.0 W/m K. These values can be compared with
those for formal weight concrete of approximately 2100-2500 kg/m3, 15 to greater
than 100 N/mm2 and 1.6-1.9 W/m K (Clarke, 1993).
According to Neville and Brooks (1987), the density (unit weight) of such concrete
(determined in the dry state) should not exceed 1840 kg/m3, and usually between
1400 and 1800 kg/m3. The Draft International Standard Model Code for Concrete
Construction classifies lightweight concrete as having densities between 1200 and
2000 kg/m3.
2.2 History of lightweight foam concrete
Whereas the use of air entrained and foamed concrete has grown rapidly in recent
years it is by no means a new product. Two thousand years ago the Romans were
making a primitive concrete mix consisting of small gravel and coarse sands mixed
together with hot lime and water. They soon discovered that by adding animal blood
into the mix and agitating it, small air bubbles were created making the mix more
workable and durable; they were even adding horse hair into mixes to reduce
shrinkage, much like we use fibres today. There is also evidence of this type of
technology being used by the Egyptians over 5000 years ago, with similar results
(Aldridge, 2005).
17
Foamed concrete was used nearly a century ago in the special precast application of
autoclaved aerated concrete, with the first reported applications being two apparently
independent initiative in 1923, one in Denmark the other in Sweden (Beningfield et
al., 2005).
According to Short and Kinniburgh (1978) and Ismail (2010), lightweight concrete
has been used since the eighteen centuries by the Romans. The application on the
‘The Pantheon’ where it uses pumice aggregate in the construction of cast in-situ
concrete is the proof of its usage. In United State of America (USA) and England in
the late nineteenth century, clinker was used in their construction for example the
‘British Museum’ and other low cost housing. The lightweight concrete was also
used in construction during the First World War. The United States used mainly for
shipbuilding and concrete blocks. The foamed blast furnace-slag and pumice
aggregate for block making were introduced in England and Sweden around 1930s.
According to Beningfield et al., (2005) foamed concretes based on this concept
began to be adopted in the early 1980’s and at that time take up began to accelerate
in much of Europe with Germany in particular leading the way. Portable foam
generators were developed by Ready Mixed Concrete (RMC) that could be used to
add foam directly into the back of a ready-mix truck, via a so-called ‘elephants
trunk’. Within the United Kingdom (UK), specifications began to appear in the early
1990’s and the market has continued to grow rapidly, with current estimates of
perhaps 300,000 to 350,000 m3 per annual used in the United Kingdom. Typical
applications are for general backfilling, filling of redundant sewers, ducts, tunnels,
underground tanks and similar with probably the largest being the backfilling of
18
utility trenches. Other United Kingdom applications include use below bituminous
finishes for roofs, multi storey car parks and similar where the light weight is
beneficial and the material may be conveniently placed by pump.
One of the earliest, significant research and development of foamed concrete was
carried out in the Netherland by the CUR (Dutch Concrete Society) in the late 1980s
and 1990s. This helped establish foamed concrete as an accepted building material.
In addition to considering a range of constituent materials and different production
methods, the extensive test programme aimed at obtaining a database of foamed
concrete properties as a function of its density. Some of the properties considered
were compressive and bending tensile strength, modulus of elasticity, heat
conductivity, freeze/thaw resistance and water absorption (Jones & McCarthy 2005,
Van Dijk 1991, & British Cement Association 1991).
Obviously these very early air entrained concretes were extremely basic with no
control over air content, etc. It was not until the early 1900’s that the manufacture of
highly air entrained materials began to be commercially explored, with perhaps
surprisingly Sweden being the pioneers behind it, based on the working of Axel
Eriksson. Doubtless the extreme weather experienced by this country gave impetus
to the development of an extremely thermally efficient building material but this
foresight remains today with Sweden still being one of the biggest users of
lightweight foamed concrete’s (Aldridge, 2005).
The promotion of foamed concrete in the United Kingdom, in term of research into
and development of the material, was initiated by the British Cement Association
19
(BCA). The findings of the work were included in six publications between 1990 and
1994 (Jones & McCarthy 2005, British Cement Association 1990, 1991, 1993, &
1994). This provided an overview of the material (properties, advantages, application
and was particularly aimed at the trench reinstatement market (British Cement
Association 1990 & 1991).
2.2.1 Lightweight foam concrete in construction
According to Lee and Hung (2005), the first major application of Lightweight
Concrete Method (LCM) foamed concrete in Malaysia is at the SMART tunnel
project in Kuala Lumpur. The foamed concrete specified was of density 1800 kg/m3
which achieved compressive strength of 3 N/mm2 at the age of 28 days. Foam
concrete block of size 17 m x 17 m x 6 m was cast in three stages in order to allow a
maximum height of 2 m per cast. The completed foamed concrete block serves to
protect the diaphragm wall when the tunnelling machine is coming out into the
junction box.
Other lightweight, inert, finely divided materials such as powdered waste plastics,
rice husk and other locally available biomass are also being experimented. The
composition is proposed to be injected at prescribed locations with innovative precast
lightweight hollow-core concrete pile to effect replacement of portions of the soil.
The system is expected to provide cost-effective geotechnical solution as the
surrounding soft ground becomes compacted while foamed concrete solidifies in situ.
Foundation system with the utilisation of used tyres is being experimented in some
housing project in Malaysia. Successful development of the system is expected to
provide a fast-track method for affordable quality-assured housing. The system is
20
applicable for the homeless people who urgently need a decent shelter (Lee and
Hung, 2005).
According to Boughrarou and Cale (2005), foamed concrete has been selected as a
novel solution for the large scale infilling of old mine working as part of an ongoing
project for stabilisation of the historical stone mines in Combe Down. The historical
Combe Down mines are located in the centre of the Combe Down area, situated
some three kilometres south of the city of Bath. The mines comprise a significant
complex of shallow underground workings, mined predominantly during the 18th
century to provide dimension stone for buildings and structures in Bath and other
cities both in the United Kingdom and around the world. It is planned for over
400,000 m3 of foamed concrete to be placed in the shallow underground mines,
which potentially cover more than 25 hectares.
Problems with surface stability of the area were first formally identified in 1986
when the underground mine workings were exposed by a contractor during
excavation of a shallow trench. Initial underground investigation revealed to
condition of the mines, including ongoing collapse and progressive deterioration of
rock pillars and the mine roof (Hawkins, 1994). Subsequent detailed investigation
involved mapping and classification of the majority of the accessible areas, which
indicated that the mine workings posed a hazard to life and property. Weight
restrictions and other safety measures were imposed on the highways overlying a
number of areas identified as posing a high hazard. Given the significant impact that
any mine collapse could have on the safety of the life and property in the Combe
Down area, an Emergency Works programme was initiated in 2001 by the local
21
authority, Bath and North East Somerset Council. The works have focussed on the
reduction of immediate health and safety risks within selected high hazard areas
beneath public highways, including a section of major route (A3602) known locally
as North Road. The works have also involved the construction of over 4,000 metres
of enabling and investigation roadways within accessible parts of the mines
(Boughrarou and Cale, 2005).
Boughrarou and Cale, (2005), reported a number of methods are available for the
stabilisation of old mines workings. In general, stabilisation entails infilling the mine
voids, with selected bulk materials, to provide effective support to the overlying
ground. These materials include pulverised fuel ash (pfa), lean mix concretes/grouts,
aggregates materials, tailing paste, etc.
Foam concrete has been selected as the principal technique for stabilisation of the
Combe Down mine for following reasons:
It is environmentally acceptable, lightweight and requires less consumption
of primary materials that are available locally.
It can be delivered underground more easily than other materials.
It can be manufactured to variable mechanical characteristics (strength and
density) which can be modified to suit the ground conditions encountered
within the mines.
It is free flowing and therefore has the ability to penetrate and consolidate
loose discards and collapsed zones. Variation of its flow characteristics
allows control, as required, of the degree of penetration into discards and in
situ fractured rock.
22
It is self levelling, self compacting and is characteristic by volume stability.
It satisfies the project design criteria.
Other void filling project worldwide include an undermined road in Poland, which
was threatened by collapse when the ground below was washed away by heavy rain,
and a geotechnical rehabilitation following an earthquake in San Francisco (Anon,
1997). Old sewer pipes and inspections chambers in Poland were also filled with
foamed concrete, before a new system was built above. In addition, 19,500 m3
density foamed concrete were used in 1986 in the Netherlands, on a large-scale
harbour fill, where the maximum permissible settlement in the first year was
restricted to 0.08 m (Basiurski, 2000).
The first project in United Kingdom to take a lightweight foam concrete or CLC was
Canary Wharf in the London Docklands in the East End of London. The project
consisted of 930,000 square meter of total net office space, recreational facilities
covering a net surface area of some 46500 square metres. The project houses the
largest business centre in London total cast was some £4 billion pounds. Several
office buildings and railways station have been constructed; among the buildings was
the Tower which is the eye catcher of the project with its 50 floors reaching some
240 metres into the air (Cox, 2005).
According to Cox (2005), foam concrete also use for sub-base for roads in Boston,
USA (2001-2002). This project I-90/Route 1A Interchange – Boston, USA, is a part
of the Central Artery Project and concerns the interchange of two roads, the I-90 and
route 1A. Fly-overs are being constructed, but the ramps leading up to these fly-overs
23
lie on soft soil layers. For that reason, a low settlement solution was obtained by
excavating some of the top soils and replacing these soils with low density foam
concrete. A Mechanically Stabilised Earth (MSE) panel system was used, serving as
formwork and erosion protection at the same time. Panels are anchored in foam
concrete with rebar. Foam concrete used has a 450 kg/m3 density and 0.5 MPa
compressive strength.
Cox (2005), reported as part of the Central Artery/Tunnel Project, the I-90 and Route
1A connector roads at Logan Airport were being reconstructed over the existing
compressible fill soils. To reduce construction cost and vertical loading, designers
chose MSE wall panels with a foam concrete backfill to build 5 bridge abutment
ramps and one raised grade structures over soft soils without the need of extensive
piling, cantilever walls or surcharging. A levelling pad is place for the MSE panels to
sit on; the foam concrete is placed in lifts as the wall panels are erected, anchoring
the horizontal strapping in place. The wall panels serve as forms and erosion
protection, providing a settlement free construction.
2.2.2 Application of lightweight foam concrete in construction
According to Jones and McCarthy (2005), foamed concrete is widely used in void
filling, as an alternative to granular fill, as foamed concrete has the ability to flow
easily under its own weight. Some such applications include filling of old sewerage
pipes, wells, cellars and basements of old buildings, storage tanks, tunnels and
subways (British Cement Association, 1994). Two of the largest foamed concrete
void filling projects in United Kingdom is the Heathrow railway tunnel and Combe
Down mines. For the former, 14,500 m3 of foamed concrete of 1400 kg/m
3 density
24
were pumped into the ground over a period of 14 days to stabilise it, following the
collapse of the railway express tunnel at Heathrow airport in 1994 (Heathrow tunnel
collapse, 2005). Similarly, 500 to 600 kg/m3 density foamed concrete is currently
being used to stabilise a redundant, 200 year old stone mine site of 400,000 m3 void
volume in Combe Down, near Bath (Dolecki, 2003). This project is expected to take
around 5 years to complete.
Foamed concrete has also often been used in bridge construction. Bridge abutments
have, on several occasions, been built with foamed concrete, as both low density
(usually between 1200 to 1400 kg/m3) and relatively high strength (around 5 N/mm
2)
are typically required. In addition, the lateral load imposed on the structure is
significantly lower with foamed concrete than with other materials. Furthermore, its
light weight minimises the risk of ground settlement and allows a reductions in the
size of the bridge foundations, with concomitant savings in steel reinforcement
(Pickford 1996, Kessler 1998, & Aldridge 2000). Foamed concrete is also often used
to fill the bridge arches until the final road surface. In most cases, a higher density
and strength mix (examples 1400 kg/m3 and 7 N/mm
2 respectively) is used in the
layers near the road surface, whilst lower density mixes (example 600 kg/m3) are
usually employed at greater depths (Aldridge, 2005).
The lightweight and excellent thermal properties of foamed concrete have been
advantageous in housing applications. Indeed, in the Middle East and South Africa,
foamed concrete has been used as roofing insulations material while its low density
and resulting high thixotropicity enables the creation of roof slopes (Eabassoc 1996,
Wimpey Laboratories Ltd 2004, De Rose and Morris 1999, Dransfield 2000, & Cox