PSZ 19:16
UNIVERSITI TEKNOLOGI MALAYSIA BORANG PENGESAHAN STATUS TESIS ♦ JUDUL: APPLICATION OF MORTAR AND SLAG CEMENT BASED AERATED LIGHTWEIGHT CONCRETE IN NON-LOAD BEARING WALLPANELS SESI PENGAJIAN: 2004/05 -II ____________________ LEONARD MARK AROKIAM_____________ (HURUF BESAR)
Saya :
mengaku membenarkan tesis (PSM/Sarjana/Doktor Falsafah)* ini disimpan di Perpustakaan Universiti Teknologi Malaysia dengan syarat-syarat kegunaan seperti berikut : 1. 2. 3. 4.
Tesis adalah hakmilik Universiti Teknologi Malaysia Perpustakaan Universiti Teknologi Malaysia dibenarkan membuat salinan untuk tujuan pengajian sahaja. Perpustakaan dibenarkan membuat salinan tesis ini sebagai bahan pertukaran antara institusi pengajian tinggi. **Sila tandakan ( / )
SULIT TERHAD
(Mengandungi maklumat yang berdarjah keselamatan atau kepentingan Malaysia seperti yang termaktub di dalam AKTA RAHSIA RASMI 1972) (Mengandungi maklumat TERHAD yang telah ditentukan oleh organisasi/badan di mana penyelidikan dijalankan)
TIDAK TERHAD Disahkan oleh
(TANDATANGAN PENULIS)
(TANDATANGAN PENYELIA)
Alamat Tetap : 465 JALAN B-11, TAMAN MELAWATI, 53100, KUALA LUMPUR
PROF. DR. SALIHUDDIN RADIN SUMADI Nama Penyelia
Tarikh
Tarikh : 18 MAC 2005
CATATAN :
: 18 MAC 2005
* **
♦
Potong yang tidak berkenaan Jika Tesis ini SULIT atau TERHAD, sila lampirkan surat daripada pihak berkuasa/ organisasi berkenaan dengan menyatakan sekali sebab dan tempoh tesis ini perlu dikelaskan sebagai SULIT atau TERHAD. Tesis dimaksudkan sebagai tesis bagi Ijazah Doktor Falsafah dan Sarjana secara penyelidikan, atau disertai bagi pengajian secara kerja kursus dan penyelidikan atau Laporan Projek Sarjana Muda (PSM).
I hereby declare that I have read this thesis and in my opinion this thesis is sufficient in terms of scope and quality for the award of the degree of Bachelor of Civil Engineering
Signature Name of supervisor Date
APPLICATION OF MORTAR AND SLAG CEMENT BASED AERATED LIGHTWEIGHT CONCRETE IN NON-LOAD BEARING WALL PANELS
LEONARD MARK AROKIAM
A report submitted in partial fulfilment of the requirements for the award of the degree of Bachelor of Civil Engineering
Faculty of Civil Engineering Universiti Teknologi Malaysia
MARCH, 2005
I declare that this thesis entitled “Application o f Mortar and Slag Cement Based Aerated Lightweight Concrete in Non-Load Bearing Wall Panels ” is the result of my own research except as cited in the references. The thesis has not been accepted for any degree and is not concurrently submitted in candidature of any other degree.
Signature
: ......................................................
Name
: LEONARD MARK AROKIAM
Date
: 18 MARCH 2005
iii
Especially for my parents, brother, sister, friends and my love one
iv
ACKNOWLEDGEMENTS
I would like to take this opportunity to thank and acknowledge certain people, whom if not for their contributions and help, the completion of this study would not be possible. First and foremost, dully gratitude and praises goes to GOD, in whom I have put my faith and trust in. During the entire course of this study, my faith has been tested countless times and with the help of the Almighty, I have been able to go pass the obstacles that stood in my way. Secondly, I would like to thank my parents, brother and sister who has over the years looked out for me and stood by me in my good and bad times. As the saying goes, blood is thicker than water, and in my case, true to every word. I would also like to extend my gratitude to my supervisor, Professor Dr. Salihuddin Radin Sumadi for giving me the chance to complete my study under his supervision. His abundant knowledge in the civil and construction field is a benefit especially for an undergraduate like I. A word of thanks also to my co-supervisor, Miss Lenny for her help and guidance during my course of study. Special thanks and gratitude goes out to my friends, especially Arnold, Fabian, Harold, Kugan, Indrani and Mei Choo. A big part of this study would not have been completed without the participation of this kind and generous people. A special thank you is reserved to the staff of the Materials Laboratory for taking time off their busy schedule to assist me especially in the testing of the wall panels. Last but not least, my gratitude and thanks goes out to the love of my life, Jill, who is the pillar of strength and a place of comfort. Your patience and support during this period can never be fully repaid. I would like to end by saying that the people mentioned above will forever hold dear in my heart and will never be forgotten. Thank you all.
v
ABSTRACT
This study is mainly focused on the production of non-load bearing wall panels. The wall panels are made of two layers which are slag cement based aerated lightweight concrete and mortar. This study also looks into the mix proportions used in the production of the slag cement based aerated lightweight concrete and also of the mortar. The materials needed to produce the wall panels were also discuss in this study. The initial mix proportions were obtained from previous research done and altered to obtain the desired strength and density. The mix proportions were tested and the desired mix was taken based on the strength and density of the cubes produce. The results were then used to produce the non-load bearing wall panels. The procedures of making the wall panels are also discussed in this study. Subsequently, the wall panels were then subjected to various tests to ensure that it was durable. The tests perform on the wall panels were, compressive strength, drying shrinkage and non-destructive test in the form of Schmidt rebound hammer method. Based on the results obtained, it can be concluded that the study has met its objectives which was to produce non-load bearing wall panels that were light and durable.
vi
ABSTRAK
Penyelidikan yang dijalankan, memberikan fokus utama kepada penghasilan dinding tanpa galas beban. Dinding galas tanpa beban yang dihasilkan terdiri daripada dua bahan yang berlainan iaitu konkrit ringan berudara yang sebahagianya digantikan dengan “slag” dan bahan yang keduanya ialah mortar. Penyelidikan ini juga memberikan fokus kepada bancuhan yang digunakan untuk menghasilkan konkrit ringan berudara yang digantikan dengan “slag” dan juga bancuhan untuk mortar. Bahan-bahan yang digunakan dalam penyelidikan ini juga diberi keutamaan dan dibincangkan dengan terperinci. Bancuhan untuk penyelidikan ini dipilih daripada keputusan dari ujian kekuataan dan juga ketumpatan yang diambil. Selepas bancuhan dipilih, ia akan digunakan dalam penghasilan dinding tanpa galas beban tersebut. Seterusnya, panel-panel yang dihasilkan diuji untuk memastikan panel yang kuat dan berkualiti dihasilkan. Langkah-langkah untuk menghasilkan panel-panel tersebut juga diperkatakan dalam penyelidikan ini. Ujian-ujian yang dijalankan ke atas panel-panel tersebut adalah seperti ujian kekuatan mampatan, ujian “drying shrinkage” dan juga ujian tanpa musnah seperti tukul pantulan Schmidt. Daripada keputusan ujian-ujian yang dijalankan, boleh dikatakan bahawa objektif penyelidikan iaitu untuk menghasilkan dinding tanpa galas beban yang kuat dan ringan telah dicapai.
vii
CONTENT
CHAPTER
SUBJECT
PAGE
CERTIFICATION OF THESIS CERTIFICATION BY SUPERVISOR TITLE PAGE
CHAPTER 1
AUTHOR’S DECLARATION
ii
DEDICATION
iii
ACKNOWLEDGEMENTS
iv
ABSTRACT
v
ABSTRAK
vi
CONTENTS
vii
LIST OF TABLES
xii
LIST OF FIGURES
xiv
LIST OF PLATES
xv
LIST OF ABBREVIATIONS
xvii
INTRODUCTION
1
1.1
Introduction
1
1.2
Research Problem
2
1.3
Objectives
3
1.4
Scope
3
viii
CHAPTER 2
LITERATURE REVIEW
4
2.1
Introduction
4
2.2
Aerated Concrete
5
2.2.1
Gas Concrete
5
2.2.2
Foamed Concrete
6
2.3
2.4
Properties of Aerated Concrete
6
2.3.1
Density
7
2.3.2
Compressive Strength
7
2.3.3
Tensile Strength
8
2.3.4
Drying Shrinkage
9
2.3.5
Water Absorption
10
2.3.6
Fire Resistance
10
2.3.7
Thermal Conductivity
11
2.3.8
Workability
11
Ground Granulated Blast Furnace Slag
12
(GGBFS) 2.5
Chemical Characteristics
12
2.6
Hydraulic Reactivity of Slag
13
2.7
Properties of Ground Granulated Blast
14
Furnace Slag
2.8
2.9
2.7.1
Fineness
14
2.7.2
Glass Content
15
2.7.3
Workability
16
2.7.4
Setting Time
17
2.7.5
Strength of Hardened Concrete
18
2.7.6
Durability
18
Water Reducing Agent (Superplasticizer)
20
2.8.1
Mechanism of Action
21
2.8.2
Effects
22
2.8.2.1 Fresh State
22
2.8.2.2 Setting State
23
2.8.2.3 Hardened State
24
Mortar
25
ix
2.9.2
Properties of Mortar
25
2.9.2.1 Workability
26
2.9.2.2 Water Retentivity
26
And Flow
2.10
2.9.2.3 Bond Strength
28
2.9.2.4 Compressive Strength
29
Pulverised Fuel Ash (PFA)
30
2.10.1 Properties of Pulverised
30
Fuel Ash (PFA) 2.10.2 Role of Pulverised Fuel Ash
31
2.10.3 Benefits of Pulverised Fuel
32
Ash (PFA) in Concrete
CHAPTER 3
RESEARCH METHODOLOGY
37
3.1
Introduction
37
3.2
Materials
38
3.2.1
Aerated Concrete
38
3.2.1.1 Sand (300|im)
38
3.2.1.2 Cement
38
3. 2. 1. 3 Ground Granul ated
39
Blast Furnace Slag (GGBFS)
3.2.2
3.2.1.4 Aluminium Powder
39
3.2.1.5 Superplasticizer
40
3.2.1.6 Water
40
Mortar
40
3.2.2.1 Palm Oil Fuel Ash (POFA)
41
3.2.2.2 Pulverised Fuel Ash (PFA)
41
3.2.2.3 Rice Husk Ash (RHA)
41
3.2.2.4 Sand (600|im)
41
x
3.3
Mix Proportions
42
3.3.1
42
Mix Proportion for Aerated Lightweight Concrete
3.3.2 3.4
Mix Proportion for Mortar
43
Mixing Procedure
43
3.4.1
44
Procedure for Mixing Aerated Lightweight Concrete
3.4.2 3.5
3.6
Procedure for Mixing Mortar
44
Producing Samples
45
3.5.1
Cubes
45
3.5.2
Wall Panels
45
Testing Done on Cubes and Wall Panels
47
3.6.1
Compressive Strength
47
3.6.1.1 Compressive Strength
47
For Cubes
3.6.1.2 Compressive Strength
48
For wall panels
3.7
CHAPTER 4
3.6.2
Drying Shrinkage
49
3.6.3
Non-destructive Test
50
Summary
50
RESULTS AND DISCUSSION
69
4.1
Introduction
69
4.2
Comparison of Strength and Density
69
Of Cubes 4.3
Compressive Strength of Wall Panels
70
4.4
Density of Wall Panels
72
4.5
Non-Destructive Test
72
4.6
Dimension Stability
73
xi
4.7
CHAPTER 5
Summary
74
CONCLUSIONS AND RECOMMENDATIONS 87
Conclusion
87
5.1.1
Mix Proportions
87
5.1.2
Compressive Strength and
88
Density of Wall Panel 5.1.3
Dimension Stability and
89
Uniformity Tests 5.2
REFERENCE
Recommendations for Future Research
89
xii
LIST OF TABLES
TABLE NO.
TITLE
PA
2.1
Chemical composition of GGBFS
33
2.2
Physical properties of PFA
33
2.3
Chemical properties of PFA
33
3.1
Chemical compositions and properties of Ordinary Portland
52
Cement and Granulated blast furnace slag 3.2
Chemical composition of aluminium powder
52
3.3
Physical properties of PFA
53
3.4
Chemical properties of PFA
53
3.5
Sieve analysis for sand
53
3.6
Mix proportion of slag cement based aerated lightweight concrete
54
3.7
Materials used for 1m3 of slag cement based lightweight concrete
54
3.8
Ultimate strength of mortar at 3 days
54
3.9
Ultimate strength of mortar at 7 days
55
3.10
Weight of mortar at 3 days
55
3.11
Weight of mortar at 7 days
55
3.12
Water ratio for each sand-binder ratio of mortar
55
3.13
Types of pozzolans and the percentage replacement
56
3.14
Material used to produce 1m3 of mortar
56
3.15
Dimension of wall panels
56
4.1
Compressive strength comparison between controlled samples
75
and slag cement aerated concrete 4.2
Density comparison between controlled samples and slag cement based aerated concrete
75
xiii
4.3
Compressive strength of wall panels at 7 days
75
4.4
Compressive strength of wall panels at 14 days
76
4.5
Compressive strength of wall panels at 28 days
76
(area 300mm x 50mm) 4.6
Compressive strength of wall panels at 28 days
76
(area 600mm x 50mm) 4.7
Rebound hammer value for wall panels tested at 7 days
77
4.8
Rebound hammer value for wall panels tested at 14 days
78
4.9
Rebound hammer value for wall panels tested at 28 days
79
4.10
Mean, standard deviation and variation value for wall panels
80
at 7,14 and 28 days 4.11
Results for the dimension stability test
80
xiv
LIST OF FIGURES
FIGURE NO.
2.1
TITLE
Relationship between compressive strength and the density
PA
34
Of Aerated Concrete 2.2
Relationship between shrinkage and moisture content of
35
Aerated Concrete 2.3
Effects of slag percentage on concrete slump
35
2.4
Effects of slag fineness on concrete workability
36
2.5
Typical dosage of superplasticizer required to produce
36
Flowing concrete 3.1
Sieve analysis for sand
57
4.1
Strength comparison between controlled sample and slag
81
cement replacement sample 4.2
Density comparison between controlled sample and slag
81
replacement sample 4.3
Compressive strength of wall panels at 7, 14 and 28 days
82
4.4
Location of points for rebound hammer test
82
4.5
The axis on the wall panels for the dimension stability test
83
4.6
Dimension changes for axis X-X
83
4.7
Dimension changes for axis Y-Y
84
xv
LIST OF PLATES
PLATE NO.
TITLE
PAGE
3.1
Layers of the panels
58
3.2
Materials for producing aerated lightweight concrete
58
3.3
Oven for drying of sand
59
3.4a
Sieve machine for sieving sand
59
3.4b
Sieving of sand
60
3.5
Los Angeles Test Machine for grinding of POFA and RHA
60
3.6
Water table used to gauge the water ratio for mortar
61
3.7
Mixing of OPC, slag (GGBFS) and sand in mixing bowl
61
3.8
Concrete mixer used in mixing of mortar
62
3.9
Aerated concrete cube
62
3.10
First layer of mortar
63
3.11a Inner layer made from aerated lightweight concrete
63
3.11b Inner layer of aerated lightweight concrete
64
3.12
Final layer of mortar
64
3.13
Curing of the panels
65
3.14
TONIPAC 300 machine used for testing compressive strength
65
Of cubes 3.15
DARETEC testing machine used for testing the wall panels
66
3.16
Wall panels being tested for 28 days strength
66
3.17
Location of the Demec disc on the wall panels
67
3.18
Shrinkage measurement by Demec gauge
67
3.19
Rebound hammer used to conduct non-destructive test on the
68
wall panels
xvi
3.20
Points on the wall panels for the rebound hammer test
68
4.1
Typical failure of wall panels tested at 7 days strength
85
4.2
Typical failure of wall panels tested at 14 days strength
85
4.3
Typical failure of wall panels tested at 28 days strength
86
(area 300mm x 50mm) 4.4
Typical failure of wall panels tested at 28 days strength (area 600mm x 50mm)
86
xvii
LIST OF ABBREVIATIONS
AAC
-
Autoclaved Aerated Concrete
CSH
-
Calcium Silicate Hydrate
GGBFS
-
Ground Granulated Blast Furnace Slag
PFA
-
Pulverised Fuel Ash
POFA
-
Palm Oil Fuel Ash
RHA
-
Rice Husk Ash
OPC
-
Ordinary Portland Cement
NDT
-
Non-Destructive Test
ASTM
-
American Society of Testing and Materials
BS
-
British Standard
Demec
-
Demountable Mechanical Strain
kN
-
Load in kilo Newton
N/mm2/ MPA -
Strength
Kg/m2
Density
-
CHAPTER 1
INTRODUCTION
1.1
Introduction
Lightweight concrete can simply be defined as concrete, which by one means or another has been made lighter than conventional concrete, the very familiar product made from sand and gravel which has so long been a major building material. Lightweight concrete has been found to be in use as early as Roman times and has in recent years gained popularity. One of the main properties that are associated with lightweight concrete is its low density. Lower density translates into a reduction in weight and this means reduction in dead load. In a construction perspective, buildings made with lighter material will indirectly reduce the overall size in the foundations, an important factor especially in the construction of high rise buildings, and therefore reduce construction cost as a whole. With its lightweight characteristics, the use of lightweight concrete will also result in faster building rates because of lower haulage and easy handling. Lightweight concrete also possesses low thermal conductivity, which improves with a decrease in density.
There are three basic ways in which a lightweight concrete can be produced, by omitting finer sizes from aggregate grading termed as no fines concrete, by
2
replacing the gravel or crushed rock aggregate with a hollow cellular or porous aggregates, termed as lightweight aggregate concrete, and lastly aerated concrete which can be produced by creating gas bubbles in the cement slurry (Andrew Short, 1968). In this research, the use of aerated concrete has been employed. Aerated concrete was first commercialized in Sweden in 1929 (CEB Manual, 1978). By appropriate method of production, a wide range of density of 300 - 1800 kg/m3 can be obtained, thus giving it flexibility and versatility in manufacturing products for different application purposes (Narayanan and Ramamurty, 1999).
Other than the properties mention above, aerated concrete also has a higher fire resistance and good sound absorbing properties as well (www.litebuilt.com). In addition to that, aerated concrete can be sawn, cut, nailed and drilled with ordinary woodworking tools. Because of its properties mentioned above, this study will incorporate aerated concrete with ground granulated blast furnace slag in producing non-load bearing wall panels. The reason for using ground granulated blast furnace, as cementitious material is because of its outstanding result in concrete durability, strength and workability. The non-load bearing wall panels will be produced as a sandwich panel in which it is made up of an aerated lightweight concrete layer and also a mortar layer. The aerated lightweight concrete will be the inner layer and covered with the mortar as the outer layers.
1.2
Research Problem
This study is concerned with obtaining a mix proportion for aerated lightweight concrete using ground granulated blast furnace slag and also a mix proportion for the mortar. In addition to this, the mix proportions will be used to produce non-load bearing wall panels. The wall panels will then be tested on its engineering properties namely compressive strength, dimension stability and uniformity.
3
1.3
Objectives
The objectives of this study are:
1. To test the engineering properties of the aerated concrete and mortar develop with the specified mix proportions.
2. To produce non-load bearing wall panels using slag based aerated concrete and mortar.
3. To test the wall panels constructed, on aspects such as compressive strength, drying shrinkage, and non destructive test (NDT).
1.4
Scope
The scope of this study is to determined the used of ground granulated blast furnace slag, aluminium powder, superplasticizer, sand, cement and water in producing durable aerated concrete with the required density (1000-1200 kg/m3) and strength. This can be satisfied by conducting compressive strength and density tests on the sample cubes produced. When the mix proportion of the aerated concrete is obtained, it is then used in the making of the non-load bearing wall panels. Thereafter, the wall panels will then be tested for its compressive strength, drying shrinkage, and non-destructive tests such as Schmidt rebound hammer test.
CHAPTER 2
LITERATURE REVIEW
2.1
Introduction
The non-load bearing wall panel is basically made up of two materials which are mortar for the outer skin layer and aerated lightweight concrete for the inner layer. The mortar layer will be 15mm in thickness and the aerated lightweight concrete layer will be 20mm in thickness. In this chapter, the materials used for the production of the wall panels will be discussed. The materials that will be looked into are ground granulated blast furnace slag, aerated concrete, superplasticizer, mortar and pulverised fuel ash. The literature review is done to give an insight to the materials that will be used and to better understand their respective nature and characteristics.
5
2.2
Aerated Concrete
Aerated concrete can be describe as a mortar, with pulverized sand and/or industrial waste like fly ash as filler, in which air is trapped artificially by chemical means such as using metallic powders like aluminium or zinc, or mechanical means by using foaming agents, resulting in significant reduction in density of the concrete (Narayanan and Ramamurthy, 1999). One of the most important factor of an aerated concrete is definitely its lightweight property, which if use as a construction material, will result in the reduction of the dead load of the structure and also the reduction of the size of the foundations, thus saving in the cost of construction. This is more evident in the construction of taller buildings. The high thermal insulation of the aerated concrete also makes it a suitable material as wall partitions.
With the use of appropriate method of production, a wide range of density can be obtained that will give it flexibility when it comes to producing for various applications. Aerated concrete is also used as a fireproofing material as it offers better fire resistance compared to ordinary concrete (A.M. Neville, 1981). Even though aerated concrete was first produce mainly as an insulation material, its lightweight property, savings in material and potential for large scale utilization of wastes like pulverized fuel ash, has renewed interest in it as a structural material (Narayanan and Ramamurthy, 2000). There are two basic methods of producing aeration with appropriate name being given to each end product.
2.2.1
Gas Concrete
Gas concrete is obtained by a chemical reaction generating gas in the fresh mortar, so that when it sets, it contains a large volume of gas bubbles. The mortar used must be of the right consistence so that the gas is allowed to expand but not
6
escape. Therefore, the speed of gas evolution, consistence of mortar and its setting time must all be matched properly. Aluminium powder which is finely divided is commonly used to produce the required gas bubbles, with its proportion being of the order of 0.2 percent of the cement weight (A.M. Neville, 1981). The reaction of the active powder with a hydroxide of calcium or alkali produces hydrogen which in turn forms bubbles. Powdered zinc or aluminium alloy can also be used for the same purposes. In some cases, hydrogen peroxide is employed but this will generate oxygen instead of hydrogen gases.
2.2.2
Foamed Concrete
Foamed concrete is reported as the most economical and controllable pore forming process, as there are no chemical reactions involved. Foamed concrete is produced by adding to the cement mix a foaming agent, which is normally some form of hydrolysed protein or resin soap. The foaming agent will introduces and stabilizes air bubbles during mixing at a high speed. In certain cases, stable pre formed foam is added to the mortar during mixing in an ordinary mixer.
2.3
Properties Of Aerated Concrete
This section will look into the various properties and characteristics of aerated lightweight concrete. The properties are density, compressive strength, tensile strength, drying shrinkage, water absorption, fire resistance, thermal conductivity, and workability.
7
2.3.1
Density
The density of an aerated concrete can be related to the amount of aeration obtained and is greatly influenced by the water-cementitious ratio. For Autoclaved Aerated Concrete with pozzolans, water-solids ratio seems to be more important than the water-cementitious ratio regardless to the method of pore formation. In gas concrete, a lesser water-solids ratio lead to insufficient aeration while a higher one will lead to rupture of the voids (Narayanan and Ramamurthy, 1999). In this aspect, the water amount is to be gauged by the consistency of the fresh mix rather than by a pre determined water-cement or water-solids ratio. The density of steam-cured aerated concrete is within the range of 300 -1000 kg/m3 with the most common density for load-bearing products being 500 kg/m3 or more (CEB Manual, 1978). However, as mention earlier, a wide range of density can be obtained by varying the composition, which in turn affects the pore structures, size and distribution. A stable and preferably spherical cell structure is vital for optimum structural and functional properties. The distribution of the pores also plays and important role and must be distributed evenly to achieve a uniform density (Narayanan and Ramamurthy, 1999).
2.3.2
Compressive Strength
The strength of aerated concrete is closely related to the specimen size and shape, method of pore formation, direction of loading, age, water content, characteristics of its ingredients used and method of curing. Both pore structures of the air pores and mechanical condition of the pore shells have a great influence on the compressive strength of aerated concrete (Vagner, F., Schober, G., Mortel, H., 1995). It is also been found that a reduction in density due to formation of large micropores results in a significant drop in strength, which confirms the general view, which is, compressive strength increases linearly with density. Figure 2.1 shows the compressive strength of different densities (CEB Manual, 1978). Autoclaving
8
increases the compressive strength significantly because high temperature and pressure result in a more stable form of tobermorite and for autoclave aerated concrete, final strength is achieve depending on the pressure and duration of autoclaving.
The strength of non-autoclaved however, increases 30 to 80% between 28 days and 6 months, and marginally beyond this period. A portion of this increase is attributed to the process of carbonation. Moisture content also plays a part in the strength development of aerated concrete where strength will increase with lower water content. On drying to equilibrium with normal atmosphere, there is an increase in strength and an even larger increase on complete drying out. The use of fly ash as a partial or complete replacement for the filler has result in higher strength to density ratio.
2.3.3
Tensile Strength
The determination of tensile strength is more sensitive to the conditions of the test when compared to that of compressive strength. The ratio of flexural strength to compressive strength varies from 0.22 to 0.27 (Narayanan and Ramamurthy, 1999). For very low-density aerated concrete, this value is almost zero.
9
2.3.4
Drying Shrinkage
Drying shrinkage can be described as loss of absorbed water. This phenomenon is significant in aerated concrete because of its high porosity (40-80 %) and specific surface of pores, around 30 m2/g. Drying shrinkage of aerated concrete with only cement, as the binder is higher than that produced with lime or lime and cements with the shrinkage of lime-cement products the least. Shrinkage will also increase with the decrease of pore size along with higher percentage of smaller pores (Narayanan and Ramamurthy, 1999). The duration and method of curing, pressure of autoclaving, fineness and chemical composition of silica, additives like fly ash, the size and shape of the specimen and the time and climate of the storage affect the drying shrinkage of aerated concrete (Schubert, 1983).
Additives like superplasticizer and silica fume have little effect on shrinkage thus, conforming that the drying shrinkage of aerated concrete is dependent on the physical structure of the gel rather than the chemical composition. Air-cured specimens have very high drying shrinkage whilst moist-cured cement-sand mixes show drying shrinkage values ranging from 0.06 to over 3% when dried at ordinary temperatures, the lower values being associated with higher densities and higher percentages of sand. Tada (1992) attribute the higher shrinkage in non-autoclaved aerated concrete to its larger volume of finer pores. However, when the same product is autoclaved, fundamental changes take place in the mineral constitution, which may reduce shrinkage to one-quarter or even one fifth of that of air-cured product. This is because of the formation of well-crystallised tobermorite in AAC products. The time dependence of shrinkage is influenced by material properties, size of specimen and shrinkage climate. This apart, the final value of shrinkage depends on the initial and final moisture content. The drying shrinkage, in most cases, increases if the relative humidity decreases. In the range of higher moisture content (greater than 20% by volume), a relatively small shrinkage occurs with loss of moisture, which can be attributed to the presence of more number of large pores which do not contribute to shrinkage (Schubert, 1983). Figure 2.2 gives an example of the amount of shrinkage in relation to the moisture content (CEB Manual, 1978).
10
2.3.5
Water Absorption
Lightweight concrete, particularly those used in blocks, are somewhat porous and thus, have a higher water absorption compared to normal concrete. This however, is not considered to be of great importance in practice, since aerated concrete exposed to the weather is not generally used without a suitable protective rendering (Neville, A.M., 1981). In the dry state, pores are empty and the water vapour diffusion dominates, while some pores are filled in higher humidity regions. Capillary suction predominates for an element in contact with water. These mechanisms make it difficult to predict the influence of pore size distribution and water content on moisture migration. The water vapour transfer is explained in terms of water vapour permeability and moisture diffusion coefficient whereas capillary suction and water permeability characterise the water transfer (Prim and Wittmann, 1983, Tada, 1992). The moisture transport phenomena in porous materials, by absorbing and transmitting water by capillarity have been defined by an easily measurable property called the sorptivity, which is based on unsaturated flow theory. It has been shown that the water transmission property is better explained by sorptivity than by permeability. The concept of capillary hygroscopicity also employs the same principle as sorption. These values give a fair indication of the fineness of the pores.
2.3.6
Fire Resistance
Aerated concrete is a non-combustible material. Its low thermal conductivity and its equilibrium moisture content make it well suited to protect other structures from the effects of fire. In practice, the fire-resistance of aerated concrete is more than or as good as ordinary dense concrete and hence its use does not involve any risk of spread of fames. An important reason for such behaviour is that the material is relatively homogeneous, unlike normal concrete where the presence of coarse
11
aggregate leads to differential rates of expansion, cracking and disintegration. The good fire resisting property of aerated concrete lies in its closed pore structure which pays rich dividends, as heat transfer through radiation is an inverse function of the number of air solid interfaces traversed. This coupled with their low thermal conductivity and diffusivity gives an indication that aerated concrete possesses better fire-resisting properties.
2.3.7
Thermal Conductivity
The thermal conductivity of aerated concrete depends primarily on the density. Other factors, which may affect the thermal conductivity, include moisture content, temperature level, raw materials and pore structure (CEB Manual, 1978). As thermal conductivity is largely a function of density, it does not really matter whether the product is moist cured or autoclaved as far as thermal conductivity is concerned. The amount of pores and their distribution are also critical for thermal insulation with finer pores resulting in better insulation. It is also reported that an increase of 1 percent in moisture increases thermal conductivity by 42 percent.
2.3.8
Workability
Another attribute of aerated concrete, which has given rise in its popularity as a construction material, is its high workability. Aerated concrete can be easily bored, nailed, sawn, planed and chased. Ordinary wood working tools can be used, but special saws for scraping tools are readily available. However, members designed to carry load in bending, for example roof and floor slabs, should not be cut on site without the authorization of the manufacturer
12
2.4
Ground Granulated Blast Furnace Slag (GGBFS)
Blast furnace slag is a by-product obtained in the manufacture of pig iron in the blast furnace and is formed by the combination of earthy constituents of iron ore with limestone flux. When the molten slag is swiftly quenched with water in a pond, or cooled with powerful water jets, it forms into a fine, granular, almost fully non crystalline, glassy form known as granulated slag, having latent hydraulic properties. Such granulated slag, when finely ground and combined with Portland cement, has been found to exhibit excellent cementitious properties. The reactivity of ground granulated blast furnace slag (GGBFS) is considered to be an important parameter to assess the effectiveness of GGBFS in concrete composites.
2.5
Chemical Characteristics
The chemical composition of the slag plays a key role upon which the hydaulic index (HI) has a bearing. From a chemical standpoint, slag can be classified into two types according to their basic index. Several basicity indexes have been defined by different authors, the simplest one being the CaO/SiO2 ratio. Metallurgists classify slag as either basic or acidic: the more basic the slag, the greater its hydraulic activity in the presence of alkaline activators (Huang, W.H., 2001). At constant basicity the strength increases with the Al2O3 content, and a deficiency in CaO can be compensated by a larger amount of alumina (MgO). The influence of MgO as a replacement for CaO seems to depend both on the basicity and the MgO content of the slag. Variations in the MgO content up to about 8-10% may have little effect on strength development, but high contents have an adverse effect. Further, Frearson has mentioned that the presence of merwinite crystallites within the glass structure would improve the reactivity of slag. Moreover, it was observed that hydraulic activity increases with increasing CaO, Al2O3 and MgO and decreases with increasing SiO2 content.
13
According to European Standard ENV 197-1:1992 and British Standards, the ratio of the mass of CaO plus MgO to the mass of SiO2 must exceed 1.0. This ratio assures high alkalinity, without which the slag would be hydraulically inactive (A.M.Neville, 1981). In a later study, it is reported that the Al2O3 content of the slag influences the sulfate resistance of slag concrete and noted that an MgO level of about 13% is required for a satisfactory performance against the sulfate attack. The percentage of soluble sulfate (expressed as SO3) is stipulated to be no greater than 4% and the percentage of total sulfur to be no greater than 2.5% for reasonable durability requirements. Table 2.1 shows the range of chemical composition of GGBFS.
2.6
Hydraulic Reactivity Of Slag
Research carried out so far reveals that the hydration product that is formed when GGBFS is mixed with Portland cement and water is essentially the same as the principal product formed when Portland cement hydrates, i.e., calcium silicate hydrate (CSH). In general, Portland cement and GGBFS come together in the same field, although Portland cement is essentially in the C3S field, whereas GGBFS is found essentially in the C2S field. This is why GGBFS hydrates are generally found to be more gel-like than the products of hydration of Portland cement, and so add denseness to the cement paste.
The hydration mechanism of GGBFS is different from that of cement. When GGBFS is mixed with water, initial hydration is much slower than Portland cement mixed with water. Hydration of GGBFS in the presence of Portland cement depends upon the breakdown and dissolution of the glassy slag structure by hydroxyl ions released during the hydration of Portland cement and also the alkali content in
14
cement. The hydration of GGBFS consumes calcium hydroxide and uses it for additional CSH formation. Research by Regourd, Vanden Bosch and Roy and Idorn has suggested that, in general, hydration of GGBFS, in combination with Portland cement, at normal stage is a two-stage reaction.
Initially and during the early hydration, the predominant reaction is with alkali hydroxide, but subsequent reaction is predominantly with calcium hydroxide. The complexity of the influencing factors suggests that direct performance evaluations of workability, strength characteristics and durability are the most satisfactory measures of the effectiveness of GGBFS use. The ASTM C989-89 Slag Activity Index (SAI) is therefore recommended as a basic criterion for evaluating the relative cementitious potential of GGBFS.
2.7
Properties Of Ground Granulated Blast Furnace Slag
Properties of GGBFS can be divided into two categories which are its chemical characteristics and its physical characteristics. Chemical characteristics have been discussed previously. Therefore this section will mainly discuss the physical characteristics of GGBFS like fineness and glass content. Effects of GGBFS on the fresh and hardened concrete will also be look into.
2.7.1
Fineness
As with all cementing materials, the reactivity of slag is determined by its surface area. In general, increased fineness results in better strength development, but
15
in practice, fineness is limited by economic and performance considerations and factors such as setting times and shrinkage. In the United Kingdom, GGBFS is marketed at a surface area of 375-425 m2/kg, whereas some slags in the United States have a surface area in the range of 450-550 m2/kg. Canadian slags are about 450 m2/kg, while in India it is found to vary from 350 to 450 m2/kg. The fineness of GGBFS is a very important parameter, which is dependent on energy-saving and economic considerations, influences the reactivity of GGBFS in concrete, early strength development of concrete and water requirement. It is reported that an increase in fineness of two to three times that of normal Portland cement can preserve the benefits of material fineness on a variety of engineering properties such as bleeding, time of setting, heat evolution, high strength and excellent durability. Thus, for better performance, the fineness of GGBFS must be greater than that of cement.
2.7.2
Glass Content
The glass content of slag is considered to be the most significant variable and certainly the most critical to hydraulicity. Several factors influence the degree of vitrification achieved during quenching, but the most important variable influencing the nature of slag is the temperature at which the furnace is tapped (Pal, Mukherjee and Pathak, 2003). The rate of quenching, which influences the glass content, is thus the predominant factor affecting the strengths of slag cements. Increasing crystalline contents reduce hydraulicity, but there is no well-defined or single relationship between strength and glass content, although some research has shown linear glass content-strength relationship.
Although a glassy structure is essential to reactivity, research has shown that there is no exact correlation of glass content to hydraulicity, and therefore, there is no guarantee that high glass content will produce a highly reactive slag. Research data
16
show that slag samples with as little as 30-65% glass contents are still suitable, but no specific minimum required glass content appears to emerge from these tests. Because of these uncertainties, most international standards judge slag activity by direct strength performance tests rather than include minimum glass content criteria, although it has been reported that generally, the glass content of the slag should be in excess of 90% to show satisfactory properties.
2.7.3
Workability
It has been found that concretes containing GGBFS usually exhibits superior workability characteristics when compared to ordinary Portland cement of the same proportions (Malhorta, 1983). He also mentioned that the use of GGBFS or slag cements usually improves workability with a decrease in water demand due to the increase in paste volume caused by the lower relative density. Other factors influencing the workability of GGBFS replaced concrete are as follows:
i.
Effects of blend on workability:
Different volume of GGBFS will result in different levels of workability with the slump of all mixtures containing slag exceeds that of ordinary concrete, regardless to the water-cement ratio. Figure 2.3 shows that the slump increases with the increase of GGBFS percentage, although to a lesser degree at levels between 30 to 50 percent (Muesel and Rose, 1983).
17
ii.
Effects of slag fineness on workability:
Figure 2.4 shows that an increase in the slag fineness will result in decrease in slump of a concrete, although to a small degree (Muesel and Rose, 1983). It can be concluded, that within the normal parameters of expected production fineness of 5200±500cm2/g, no significant differences in concrete water demand will be found. Therefore, the use of high fineness in slags for optimum slag hydration does not have a significantly negative effect on workability or strength potential of concrete (Muesel and Rose, 1983).
2.7.4
Setting Time
Setting times of concretes containing slag increases as the slag content increases. An increase of slag content from 35 to 65% by mass can extend the setting time by as much as 60 minutes. This delay can be beneficial, particularly in large pours and in hot weather conditions in which this property prevents the formation of "cold joints" in successive pours. The change in setting depends on certain factors such as:
i.
Initial curing temperature
ii.
Mix proportion
iii.
The water-binder ratio
iv.
Characteristics of Portland cement
18
2.7.5
Strength Of Hardened Concrete
The compressive strength development of slag concrete depends primarily upon the type, fineness, activity index, and the proportions of slag used in concrete mixtures. In general, the strength development of concrete incorporating slags is slow at 1-5 days compared with that of the control concrete. Between 7 and 28 days, the strength approaches that of the control concrete; beyond this period, the strength of the slag concrete exceeds the strength of control concrete. Flexural strength is usually improved by the use of slag cement, which makes it beneficial to concrete paving application where flexural strengths are important. It is believed that the increased flexural strength is the result of the stronger bonds in the cement-slagaggregate system because of the shape and surface texture of the slag particles.
2.7.6
Durability
Durability can be defined as the ability to provide or sustain the required level of service for the design life of the structure in the given environment. It is essential that concrete should withstand the conditions for which it has been designed, without deterioration, over a period of time. Deterioration of concrete is rarely due to one isolated cause and for this reason; it is sometimes difficult to assign trouble to a particular factor (A.M. Neville, 1981). Factors that contribute to durability of concrete are as follows:
i.
Decreased permeability
Incorporation of granulated slag in cement paste helps in the transformation of large pores in the paste into smaller pores, resulting in decreased permeability of the matrix and of the concrete indicated that significant
19
reduction in permeability is achieved as the replacement level of the slag increases from 40 to 65% of total cementitious material by mass. Because of the reduction in permeability, concrete containing granulated slag may require less depth of cover than conventional concrete required to protect the reinforcing steel.
ii.
Freeze-thaw durability of hardened concrete
Many researchers have studied freeze-thaw durability of slag concrete. It has been reported that resistance of air-entrained concrete incorporating GGBFS is comparable to that of conventional concrete (Malhotra, 1983). He reported results of freeze-thaw tests on concrete incorporating 25-65% slag. Test results indicate that regardless of the water-to (cement + slag) ratio, airentrained slag concrete specimens performed excellently in freeze-thaw tests, with relative durability factors greater than 91%.
iii.
Alkali silica reaction
Effectiveness of slag in preventing damage due to ASR is attributed to the reduction of total alkalies in the cement-slag blend, the lower permeability of the system, and the tying up of the alkalies in the hydration process. There have been many studies of GGBFS that has been used as partial replacement for Portland cement in concrete to reduce expansion caused by alkaliaggregate reaction.
iv.
Heat of hydration
Concrete containing GGBFS exhibits a lower heat of hydration than conventional Portland cement concrete. This reduction is directly proportional to the amount of GGBFS used.
20
v.
Sulphate resistance
Use of GGBFS as a partial cement replacement gives concrete moderate resistance to sulfate attack (ASTM C 989-89).
vi.
Salt scaling
Concrete containing high concentrations of GGBFS may be susceptible to salt scaling (the loss of surface layers of cement mortar during repeated freeze-thaw cycles). Due to this problem, some agencies limit the amount of slag in a Portland cement concrete mix to 25 percent of the total cement weight.
vii.
Reduced bleeding
GGBFS usually has higher fineness compared to ordinary cement. Therefore, a given mass of GGBFS has a higher surface area than that of ordinary cement. Bleeding of concrete is subjected to the ratio of the surface area of solids to the volume of water. Hence, bleeding of GGBFS concrete would be lower than that of ordinary concrete.
2.8
Water Reducing Agent (Superplasticizer)
High-range water reducing agents (superplasticizers) are admixtures, which can give a considerable increase in the workability of mortars and concrete at constant water-cement ratio. With the addition of superplasticizers, mortars and concretes of constant workability can be produce with smaller amounts of water, saving more than 12 percent without undue retardation, excessive entrainment of air
21
or detrimental bleeding (Biagini, 1995). Superplasticizers can be divided into 4 main categories:
i.
Category A Sulphonated melamine formaldehyde condensates
ii.
Category B Sulphonated naphthalene formaldehyde condensates
iii.
Category C Modified lignosulphonates
iv.
Category D Polycarboxylate derivatives
2.8.1
Mechanism Of Action
The mechanism of high-range water reducers is mainly based on their ability to absorb on the surface of cement particles and modifies the rheological behaviour of the cement matrix. The rate of absorption of high-range water reducers depends on the chemical and mineralogical composition of the cement, its fineness and in particular on the C3A content. Studies have found that calcium aluminate absorbs very rapidly the high-range water reducer molecules, while calcium silicate in the first hours of hydration absorbs only lower amount of the water reducers. The increase in workability that can be obtained in a concrete by the use of superplasticizers can be correlated with the following properties:
22
i.
The value of zeta potential of the electric double layer that is formed on the surface of the cement particles by the polar groups of absorbed superplasticizer chains.
ii.
The molecular weight of the superplasticizer (Biagini, 1995)
2.8.2 Effects
This section will discuss the different effects of superplasticizers on concrete at fresh state, setting state and hardened state.
2.8.2.1 Fresh State
i.
Unit mass Unit mass of concrete is usually increased when superplasticizers are used.
ii.
Workability
a.
Consistency Superplasticizers dramatically increase the ability of concrete to flow and this will result in a higher workability concrete. Figure 2.5 shows the typical dosage of superplasticizer required to produce flow concrete.
23
b. Cohesion Cohesion is largely improved by the use of high range-water reducers as a consequence of the reduction of water in concretes.
iii.
Segregation
Segregation decreases when the admixture is either used as a high-range water reducer or as a superplasticizer, provided that an adequate mix design of the concrete is done.
2.8.2.2 Setting State
i.
Setting
Generally the admixture used as a superplasticizer mildly retards the setting of concrete.
ii.
Plastic shrinkage
Plastic shrinkage cracking may increase by the use of superplasticizers if the ambient conditions are such that evaporative demands are greater than the reduced bleeding capacity of the high-range water reducer concrete.
iii.
Bleeding
With the use of superplasticizers in concrete, bleeding can be reduced. However, if the aggregate size distribution is not properly designed, bleeding can be increased when superplasticizers are used
24
2.8.2.3 Hardened State
i.
Strength
The use of superplasticizers in concrete will result in higher early strength and also continued strength development with the additional use of mineral admixtures such as GGBFS (Biagini, 1995).
ii.
Durability
The permeability of concrete is directly linked to its capillary porosity which is influenced by the water-cement ratio. This permeability can be largely reduced with the use of superplasticizes. Lower permeability will result in a concrete which is more durable.
iii.
Drying shrinkage
The shrinkage in concrete is reduced by high-range water reducers mainly because of the reduction of the water content of the concrete. When a concrete is manufactured with superplasticizers, its shrinkage, for the same percentage of moisture loss, has been found to be higher than in a concrete produced with the same quantity of water but without superplasticizer (A.M., Neville, 1981). On the other hand, it has been also shown that with the same curing conditions, the shrinkage of a superplasticized concrete is similar to that of a corresponding plain concrete. The conclusion can be made that the better dispersion of cement particles in a superplasticized concrete produces finer capillary structure, which reduces the rate of moisture loss of the concrete under normal ambient conditions, so that the shrinkage of superplasticized concrete is practically similar to that of a normal concrete manufactured with the same amount of water.
25
2.9
Mortar
Mortar is the bonding agent that integrates brick into a masonry assembly. Mortar must be strong, durable, and capable of keeping the masonry intact and it must help to create a water resistant barrier. These requirements are influenced by the composition, proportions and properties of mortar. Because concrete and mortar contain the same principal ingredients, it is often assumed that good concrete practice is also good mortar practice. In reality, mortar differs from concrete in working consistencies, methods of placement, and structural performance.
Mortar is used to bind masonry units into a single element, developing a complete, strong and durable bond. Concrete, however, is usually a structural element in itself (McIntosh, J.D., 1968). Mortar is usually placed between absorbent masonry units, and loses water upon contact with the units. Concrete is usually placed in non-absorbent metal or wooden forms which absorb little if any water. The importance of the water cement ratio for concrete is significant, whereas for mortar it is less important. Mortars have a high water cement ratio when mixed, but this ratio changes to a lower value when the mortar comes in contact with the absorbent units.
2.9.2
Properties of mortar
Mortars have two distinct, important sets of properties; those in the plastic state and those in the hardened state. The plastic properties help to determine the mortar’s compatibility with brick and its construction suitability. Properties of plastic mortars include workability, water retention, initial flow and flow after suction. Properties of hardened mortars help determine the performance of the finished masonry. Hardened properties include bond strength, durability, extensibility and
26
compressive strength. Properties of plastic mortar are more important to the mason. Properties of hardened mortar are of more importance to the designer and owner.
2.9.2.1 Workability
Workability is generally a characteristic defined by the mason. There is no textbook definition of workability because there are no standardized tests for it. A "workable" mortar has a smooth, plastic quality, is easily spread with a trowel, and readily sticks to vertical surfaces. Ingredients whish can increase workability are:
•
Well graded and smooth aggregates
•
Lime
•
Air entrainment
•
Proper amount of mixing water
The lime imparts plasticity and increases the water carrying capability of the mortar. Air entrainment is an additive that creates tiny air bubbles in the mix. These air bubbles help the ingredients of the mortar move more freely. These air bubbles can reduce the strength of bond as they reduce the density and surface area of the bonding surface of the masonry unit. Air contents should be kept below 12-15% if not lower. Mortar requires a maximum amount of water for workability. Retempering should be allowed within the first 2.5 hours after mixing.
2.9.2.2 Water retentivity and flow
Other mortar characteristics that influence general performance, such as aggregate grading, water retentivity, and flow, can be accurately measured by
27
laboratory tests and are included in ASTM Standards. Water retentivity allows mortar to resist the suction of dry masonry units and maintain moisture for proper curing. It is the mortar's ability to retain its plasticity in contact with absorptive masonry so that the mason can carefully align and level the units without breaking the bond. Less retentive mixes will "bleed" moisture, creating a thin layer of water between mortar and masonry unit and substantially decreasing bond strength. Highly absorptive clay units may be prewetted at the job site, but concrete products may not be moistened, thus requiring the mortar itself to resist water loss.
Under laboratory conditions, water retention is measured by flow tests, and is expressed as the ratio of initial flow to flow after suction. The flow test is similar to a concrete slump test, but is performed on a "flow table" that is rapidly vibrated up and down for several seconds. Although they accurately reflect the properties of the mortar, laboratory values differ somewhat from field requirements. Construction mortars require initial flow values on the order of 130 to 150%. Laboratory mortars are required to have an initial flow of 100 to 115%. The amount of mixing water required to produce good workability, proper flow, and water retention are quickly and accurately adjusted by experienced masons. Results produced from assemblies prepared in the field reliably duplicate the standards set by laboratory researchers. Dry mixes lose water to the masonry units and will not cure properly. Excessively wet mixes cause units to float, and will decrease bond strength.
The "proper" amount of mixing water is universally agreed upon as the maximum compatible with "workability," and workability is best judged by the mason. Retempering (the addition of mixing water to compensate for evaporation) is acceptable practice in masonry construction. Since highest bond strengths are obtained with moist mixes having good flow values, a partially dehydrated mortar is less effective if the evaporated water is not replaced. Mortar normally begins to harden or set about 2.5 hours after initial mixing. After this point, retempering will decrease compressive strength by approximately 25%. ASTM standards require that all mortar be used within 2 .5 hours and permit retempering as frequently as needed within this time period. Tests have shown that the decrease in compressive strength
28
is minimal if retempering occurs only 1 to 2 hours after mixing. Mortar that is not used within 2.5 hours or that has begun to set should be discarded.
2.9.2.3 Bond strength
The single most important property of mortar is bond strength, and it is critical that this bond be complete, strong, and durable. The mechanical bond between individual bricks, blocks, or stones unifies the wall as a system, provides resistance to tensile stress, and seals against the penetration of moisture. The strength and extent of the bond are affected by many variables of material and workmanship. Complete and intimate contact between the mortar and the unit is essential, and workability influences the ease with which the mortar spreads and covers the surfaces. Rough units have a very porous surface that is highly receptive to the wet mortar and increases adhesion. The moisture content and suction of the units, the water retention of the mortar, and curing conditions such as temperature, relative humidity, and wind combine to influence the completeness and integrity of the mechanical and chemical bond.
Voids at the mortar-to-unit interface offer little resistance to water infiltration and facilitate subsequent disintegration and failure if freezing occurs. ASTM standards give a laboratory test method for measuring susceptibility to water penetration. The test subjects a sample wall to a pressure differential and application of water on the high pressure side. The time, location and rate of leakage is observed and interpreted. Workmanship is also very important in bonding. Full mortar beds must be laid down by the mason to assure complete coverage of all contact surfaces. Once a unit has been placed and levelled, additional movement will break or seriously weaken the bond. The high water retention of cement-lime mortars allows more time for placing units on bed joints before evaporation or the suction of adjacent units alters the plasticity and flow of the mortar. In aligning the masonry, laboratory tests show that tapping the unit to level will increase bond strength 50 to 100% over hand pressure alone.
29
2.9.2.4 Compressive strength
The compressive strength of mortar is sometimes used as a principal criterion for selecting mortar type, since compressive strength is relatively easy to measure, and it commonly relates to some other properties, such as tensile strength and absorption of the mortar. The compressive strength of mortar depends largely upon the cement content and the water-cement ratio. The accepted laboratory means for measuring compressive strength is to test 2 inches cubes of mortar. Because the referenced test in this specification is relatively simple, and because it gives consistent, reproducible results, compressive strength is considered a basis for assessing the compatibility of mortar ingredients.
Field testing compressive strength of mortar is accomplished using either 2 inches cubes or small cylindrical specimens of mortar. Perhaps because of the previously noted confusion regarding mortar and concrete the importance of compressive strength of mortar is over-emphasized. Compressive strength should not be the sole criterion for mortar selection. Bond strength is generally more important, as is good workability and water retentivity, both of which are required for maximum bond.
Flexural strength is also important because it measures the ability of a mortar to resist cracking. Often overlooked is the size/shape of mortar joints in that the ultimate compressive load carrying capacity of a typical 3/8 in. bed joint will probably be well over twice the value obtained when the mortar is tested as a 2 in. (50.8 mm) cube. Mortars should typically be weaker than the masonry units, so that any cracks will occur in the mortar joints where they can more easily be repaired. Compressive strength of mortar increases with an increase in cement content and decreases with an increase lime, sand, water or air content. Retempering is associated with a decrease in mortar compressive strength. The amount of the reduction increases with water addition and time between mixing and retempering. It is frequently desirable to sacrifice some compressive strength of the mortar in favour of
30
improved bond, consequently retempering within reasonable time limits is recommended to improve bond.
2.10
Pulverised fuel ash (PFA)
Pulverised Fuel Ash (PFA) is the ‘fine’ ash fraction produced in the furnaces of coal fired power stations when pulverised coal is fed into the boilers and burnt at high temperatures and pressures. As combustion takes place, the ash within the coal melts and solidifies in flight as rounded glassy particles (www.scotash.com). These are carried out in the flue gasses and subsequently captured in the electro-static precipitators. The PFA particles are mostly extremely fine glassy spheres and can resemble cement in appearance. When used correctly, PFA can offer many benefits in both the casting and the finished surface of concrete products.
2.10.1 Properties of pulverised fuel ash (PFA)
Pulverised fuel ash has unique physical and chemical properties due to the combustion process and the chemical composition of coal. PFA particles, particularly those below 50 microns, are spherical in shape, as a result of the way in which they are formed. As the coal is burned at temperatures approaching 1400°C, the minerals associated with it become molten and form spherical shapes. On cooling they solidify as amorphous, glassy material. Some of the physical properties of PFA are shown in Table 2.2. Fly ash has three main elements, silicon, aluminium and iron, the oxides of which account for 75 - 85% of the material. Fly ash consists principally of glassy
31
spheres together with some crystalline matter and unburned carbon. A typical range of oxides of PFA is shown in Table 2.3.
2.10.2 Role of pulverised fuel ash
Pulverised fuel ash (PFA) is a valuable resource in its own right. It is safe versatile construction material which can be used in a variety of applications. Some of the typical uses of PFA are as follows:
i.
PFA as a cement addition in concrete: Used in ready mixed concrete, concrete products and block manufacture.
ii.
PFA in cement manufacture: Used as raw material in place of clay or shale, as a Minor Additional Constituent (MAC), and to manufacture cements to the required standards.
iii.
PFA for grouting: When mixed with cement and/or lime, PFA grout is used for filling fissures, voids and cavities such as redundant mines, pipes and behind tunnel segments.
iv.
PFA as an industrial filler: PFA and cenospheres (hollow, lightweight particles with low thermal conductivity, which float to the surface of ash lagoons) are used in the
32
manufacture of plastics, rubbers, refractory products and bituminous materials.
v. PFA in stabilisation/solidification products: The stabilisation/solidification of contaminated land and soils uses much specialised cementitious products, which often incorporate PFA.
2.10.3 Benefits of pulverised fuel ash (PFA) in concrete
Pulverised fuel ash is a pozzolana, a material that reacts with lime to form a hardened mass. During the hydration process of Portland cement, lime is released. The PFA reacts with this to produce cementitious hydrates. The main benefits of using PFA as a cement enhancer are:
•
Increases strength and durability due to pozzolanic reaction
•
PFA improves sulphate resistance and reduces the risk of alkali-silica reaction
•
Reduces the water required for equal workability, which reduces permeability
•
Reduces the heat of hydration
•
Improves pumpability
•
Increases the quality of the surface finish
•
Reduces creep and shrinkage
•
Reduces efflorescence in concrete products
33
Table 2.1: Chemical composition of GGBFS (Hogan and Rose, 1986, Hwang C.H, 1991).
Constituent
Hogan and Rose
Hwang C.H
SiO2
33%-40%
28%-38%
Al2O3
6%-13%
8%-24%
CaO
35%-43%
30%-50%
MgO
6%-16%
1%-18%
S
0.9%-1.7%
1%-2.5%
Fe2O3
0.3%-1.0%
-
MnO
-
_
Table 2.2: Physical properties of PFA.
Property
Typical values
Compacted bulk density
1300 - 1500 Kg/m3
Relative Density (oven dry)
2.0 - 2.4
Specific Heat capacity
0.8 - 0.7J/Kg/°C
Water Permeability - compacted fly ash
1.0 x 10-6 - 7.0 x 10-7
Electrical conductivity
0.09 W/mK
Loss on Ignition
6 - 10%
Table 2.3: Chemical properties of PFA.
Element
Typical range of values
Silicon (% as SiO2)
38 - 52
Aluminium (% as Al2O3)
20 - 40
Iron (% as Fe2O3)
6 - 16
Calcium (% as CaO)
1.8 - 10
34
100
300
500
700
900 1 ООО
Dsrji.ity ika.-'Tr'i
Figure 2.1: Relationship between compressive strength and the density of aerated concrete (CEB Manual, 1978).
35
0.06
1
2
3
4 5
10
20
30 40 50
100
Moisture Content % by weight
Figure 2.2: Relationship between shrinkage and moisture content of aerated concrete (CEB Manual, 1978).
Figure 2.3: Effects of slag percentage on concrete slump (Muesel and Rose, 1983).
36
Figure 2.4: Effects of slag fineness on concrete workability (Muesel and Rose, 1983).
Superplasticizer dosage (% v/w cement)
Figure 2.5: Typical dosage of superplasticizer required to produce flowing concrete.
CHAPTER 3
RESEARCH METHODOLOGY
3.1
Introduction
In this chapter, the materials used, the procedures and the tests conducted is explained. The main study of this research is the strength and density of the non-load bearing wall panels that are to be produced. However, other relevant factors such as the panel uniformity and dimension stability will also be looked into. The non-load bearing wall panels are basically made up of two different layers which are the aerated concrete inner layer which is 30mm in thickness and the outer layers which are made up of mortar and is 15mm in thickness each. Plate 3.1 shows the 3 layers of the wall panel.
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3.2
Materials
As mentioned earlier, the non-load bearing wall panel is made of two different units which are the aerated concrete layer and the mortar layer. Altogether, 10 materials were used in the production of the wall panels.
3.2.1
Aerated Concrete
The materials used for the aerated lightweight concrete layer were cement, sand, ground granulated blast furnace slag, aluminium powder, superplasticizer and water. Plate 3.2 shows the materials needed to produce aerated lightweight concrete.
3.2.1.1 Sand (300цш)
For the production of the aerated lightweight concrete layer, only sand passing sieve size 600^m were used. The sand was firstly dried in the oven at a temperature of 110°C ± 5 for at least 24 hours to remove it of unwanted moisture. Plate 3.3 shows the oven in the laboratory that was used for drying purposes. After the sand was dried for 24 hours, it is then sieve using the sieve machine for at least 5 minutes. Sand passing the 600^m sieve size was than collected to be used for the making of the aerated lightweight concrete. Plate 3.4a and 3.4b shows the sieve machine and how the sieving is done.
3.2.1.2 Cement
For this study, only Ordinary Portland Cement (OPC) was used throughout the entire experiment. This is done so that a certain degree of uniformity is
39
maintained when producing the wall panels. The cement was of the Seladang brand obtained from Tenggara Cement Manufacturing Sdn. Bhd. The cement is kept in an airtight container provided by the laboratory management. The reason for storing the cement in airtight containers is because exposed cement will absorbed moisture and this will in turn affect the reaction of the concrete thus producing undesirable results. The chemical composition and the physical properties of the cement used are shown in Table 3.1.
3.2.1.3 Ground Granulated Blast Furnace Slag (GGBFS)
Ground granulated blast furnace slag as mention in Chapter 2 is a waste material of the steel industry. It is a glassy granular material which is formed during the chilling process of the molten blast furnace slag. The ground granulated blast furnace was obtained from YTL Cement Sdn. Bhd. at Pasir Gudang. Just like the cement, the GGBFS was also stored in airtight containers to decrease the chances of it being exposed to moisture in the environment. The GGBFS was sieve using the 150^m sieve size before it was used in the experiment. This is done to make sure that the GGBFS is free from larger size particles and unwanted materials. The chemical composition of the GGBFS is also shown in Table 3.1.
3.2.1.4 Aluminium Powder
The aluminium powder is used as a gas forming agent in the production of the aerated lightweight concrete. It is easily identified because of its fine silverfish coloured material. The chemical composition of the aluminium powder is shown in Table 3.2.
40
3.2.1.5 Superplasticizer
Superplasticizer is a chemical admixture, which is also known as a water reducer. The purpose of the admixture is to produce a more workable and flowable concrete using lower water content. The superplasticizer will also be used to acquire a higher early strength and ultimately a higher strength at a mature concrete age. The permeability of the concrete is also reduce with the introduction of superplasticizer because of a lower water/cement ratio that produces lesser capillary pores. The superplasticizer was supplied by Sika Kimia Sdn. Bhd.
3.2.1.6 Water
Water as we know is an important ingredient in the making of concrete. It is the reaction of water and cement that produces the CSH gel which in turn provides strength of a concrete. The water that is used throughout the experiment is ordinary tap water obtained in the laboratory itself.
3.2.2
Mortar
There were altogether 8 materials used for making mortar. The materials used were cement, sand, water, ground granulated blast furnace slag, superplasticizer, palm oil fuel ash (POFA), pulverize fuel ash (PFA) and rice husk ash (RHA). The materials are the same for making aerated lightweight concrete except for some added pozzolans and the size of sand used.
41
3.2.2.1 Palm Oil Fuel Ash (POFA)
Palm oil fuel ash (POFA) is one of the pozzolans used for the making of mortar. The palm oil fuel ash has to be grind in the Los Angeles Test Machine for two and a half hours before it can be used. The palm oil fuel ash was weigh to obtain a 5kg amount and was then poured into the machine. After that 15 roller rods was inserted and the grinding begins.
3.2.2.2 Pulverised Fuel Ash (PFA)
Pulverised fuel ash (PFA) or also known as fly ash is the fine ash fraction produced in the furnaces of coal fired power stations when pulverised coal is fed into the boilers and burnt at high temperatures and pressures. The physical and chemical properties of pulverised fuel ash are shown in Table 3.3 and Table 3.4.
3.2.2.3 Rice Husk Ash (RHA)
The rice husk ash was also grind in the same way as the palm oil fuel ash before it was used in the making of mortar. The Los Angeles Test Machine, which was used for grinding purposes, is shown in Plate 3.5.
3.2.2.4 Sand (600цт)
Sand used for the making of mortar is dried in the same way as the sand for making aerated concrete. However, the sand size used for making of mortar was sand passing sieve size 1.18 |im. The sieve analysis of the sand used is shown in Figure 3.1 and the results are shown in Table 3.5.
42
3.3
Mix Proportions
The mix proportions for both aerated lightweight concrete and mortar were determined by trial and error method. The mixes obtained were then test for strength and density and the optimum values were used for mixing.
3.3.1
Mix Proportion For Aerated Lightweight Concrete
The sand cement ratio was obtained from a previous research and the sand to cement ratio used was 50:50. From this, the ground granulated blast furnace slag was replaced to 50 percent of the cement weight. For the initial mixes, the water-dry mix ratio was taken as 0.21 from previous research. The water-dry mix ratio is important because it is related to the amount of aeration obtained and directly link to the density of the aerated lightweight concrete. The amount of aluminium powder and superplasticizer was also obtained from previous research conducted with the aluminium powder taken as 0.1 percent of the weight of the dry mix and superplasticizer as 0.6 percent of the cementitous weight. The superplasticizer was used in order to increase the early and ultimate strength of the aerated lightweight concrete.
From the result of the initial mix proportions, the density obtained was not satisfactory to the desired density which was in the range of 1000 kg/m3 to 1200 kg/m3. Therefore the volume of the aluminium powder was increase to 0.15 percent of the dry mix weight. The water-dry mix ratio was also increase, based on the consistency of the fresh mix and the value was set at 0.25. The mix proportions to produce the slag cement based aerated lightweight concrete is shown in Table 3.6 and the volume of material used to produce 1 m3 of slag cement based aerated lightweight concrete is shown in Table 3.7.
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3.3.2
Mix Proportion For Mortar
The mix proportion for mortar was determined from the sand-binder ratio. For this research three types of sand-binder ratios were tested. The sand to binder ratios was, 1:1, 2:1 and 3:1. The ratio was then chosen based on the compressive strength of the mortar cubes at 3 and 7 days. The ultimate strength and the weight of the mortar for all three ratios are shown in Tables 3.8, 3.9, 3.10 and 3.11. The water ratio for the mortar was determined using the flow test method in accordance with BS 4551:1980. The water table apparatus used to determine the water ratio is shown in Plate 3.6. Various water ratios were tested in the flow test method and the final water ratio was determined when the cement paste area measured was in the range of 110±5 %. The water ratio for each sand-binder ratio is shown in Table 3.12.
From the results obtained, the sand-binder ratio which gives the highest value of compressive strength was chosen to be used in the mix. In this research, the sandbinder ratio was 1:1 and the water ratio was 0.44 of the weight of binder. For the making of mortar, pozzolans were also used and the percentage of replacement of cement with the pozzolanic materials is shown in Table 3.13. The pozzolans used were ground granulated blast furnace slag (GGBFS), pulverised fuel ash (PFA), palm oil fuel ash (POFA) and rice husk ash (RHA). The materials used to produce 1 m3 of mortar are shown in Table 3.14.
3.4
Mixing Procedure
The mixing procedure is divided into two parts for the aerated lightweight concrete and mortar.
44
3.4.1
Procedure for Mixing Of Aerated Lightweight Concrete
The first step is to weigh all the needed materials. After that, the ordinary Portland cement (OPC), slag (GGBFS) and sand are mixed in a concrete mixer bowl by hand for about 2 minutes (Arreshvhina N. 2001) as shown in Plate 3.7. At the end of the 2 minutes, the aluminium powder is added into the dry mix. The aluminium powder is added without the presence of water because it has a tendency to float on the mixing water. The ingredients were mixed until the aluminium powder is thoroughly distributed in the mix. Finally the water and the superplasticizer were added together into the dry mix. This is done because research has shown that by adding water with superplasticizer at the same time is essential for obtaining better performance (Biagini, 1995). The aerated concrete was mix for about 2 minutes. Mixing of the aerated concrete cannot be done for too long a time because the aluminium powder would start to react with the water to produce air bubbles. Therefore, it is advisable to pour the aerated concrete mix into the mould before the reaction begins.
3.4.2
Procedure for mixing mortar
The materials needed were weigh before mixing commence. Two third to three quarter of the required water was first poured into the concrete mixer. After that, half of the required sand was added into the mix. Next, the ordinary Portland cement (OPC), slag (GGBFS), rice husk ash (RHA), pulverised fuel ash (PFA), palm oil fuel ash (POFA) and the superplasticizer were added into the mix. Finally, the remaining sand and water were added into the mix (www.cement.org/masonary/cc_fn_workable_mortar.asp) and the mix was mix for not more than 5 minutes. The concrete mixer used for the mixing of mortar is shown in Plate 3.8.
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3.5
Producing samples
The samples produced were of cubes size 75mm x 75mm x 75mm and the wall panels. The dimension of the wall panels are shown in Table 3.15.
3.5.1
Cubes
The concrete cubes were produced at the beginning stages of this research. The size of the cube moulds used was 75mm x 75mm x 75mm. The tests conducted on the aerated lightweight concrete cubes were compressive strength test and also to determined the density of the material. The cubes were also produced for the comparison of strength and density between the control sample which was made from 100 percent OPC and the slag cement based aerated lightweight concrete. The mortar cubes were used to determine the strength for each of the three sand-binder ratios to obtain the desired ratio to be used for the research. Plate 3.9 shows an aerated concrete cube. All cubes, whether it be aerated or mortar were air cured.
3.5.2
Wall panels
Producing the wall panels was the main scope for this research. The wall panels were produced to be used as non-load bearing wall partition panels. The size and dimension for the wall panels are shown in Table 3.15. The mould used to produce the wall panels was of plywood with a thickness of 12mm. The parts of the moulds were assembled by using nails because the moulds were not made to be reuse. For this research, 20 number of wall panels were produced to be tested. The
46
wall panels are made up of three layers. The inner layer is made of aerated lightweight concrete with a thickness of 20mm and the outer layer is made of mortar with a thickness of 15mm each. Before the mix is poured into the mould, it is firstly layered with a coat of oil so that the dried sample does not stick to the mould surface. The steps of producing the wall panels are as follows:
i.
The first layer of mortar is poured into the mould and left to dry for approximately 24 hours as shown in Plate 3.10.
ii.
After that the aerated lightweight concrete is poured to about 80 percent of the required volume as shown in Plate 3.11a and 3.11b. It is then left to expand for 24 hours.
iii.
Next, additional plywood for the layer of mortar is glued to the wood mould. This is done by using CA glue purchased from any hardware shop.
iv.
Finally, the last layer of mortar is poured into the mould and left to dry for approximately 24 hours before demoulding as shown in Plate 3.12.
All the wall panels produced were cured by air curing as shown in Plate 3.13. The wall panels were then used for various tests such as compressive strength test, dimension stability and uniformity test.
47
3.6
Testing done on cubes and wall panels
The aerated lightweight concrete and mortar cubes were subjected to compressive strength test. The wall panel, being the main scope of this research was subjected to compressive strength test, dimension stability and uniformity test.
3.6.1
Compressive strength
The compressive strength was the most important test because the wall panels produced had to be durable. The compressive strength was divided into two parts which were compressive strength for cubes and wall panels.
3.6.1.1 Compressive strength for cubes
The compressive strength test was done on both aerated lightweight concrete and mortar cubes. The mortar cubes were tested at 3 and 7 days whereas the aerated lightweight concrete cubes were test on 7 and 28 days according to ASTM E 447-74. The cubes were tested using the TONIPAC 300 machine as shown in Plate 3.14. The testing procedures are as follows:
i.
Before the cubes were tested, the weight of each cube was recorded. This was done to determine the density of the cubes. The cube samples were also checked to make sure that they are no deformations such as cracks and broken edges.
ii.
After that, the platens of the machine were cleaned and the cube samples were placed at the centre of the test plate.
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iii.
The loading was applied gradually without shock. The constant rate of loading used was 0.2 kN per second until the samples fail. The ultimate load was then recorded.
3.6.1.2 Compressive strength for wall panels
The wall panels were tested using the DARTEC testing machine located in the laboratory. Plate 3.15 shows a panel being tested with the DARTEC machine. The wall panels were tested at 7, 14 and 28 days according to ASTM E72-80. The wall panels at 28 days were tested in two different surface areas as shown in Plate 3.16. The procedures for testing the panels are as follows:
i.
Before testing, the panels were check for any deformations
ii.
Next, the samples were placed on the testing plate and were adjusted so that it was centred properly.
iii.
After that, the compressive test is done by gradually increasing the loading on the wall panels. The loading rate was 0.3 kN/s.
iv.
During the loading stages, the panels were observed for any physical changes.
49 v.
The samples were loaded until it fails, at which the maximum load is
recorded.
3.6.2
Drying shrinkage
Drying shrinkage was done to check the dimension stability of the wall panels during the drying stage. For this test, 3 samples were used. The samples were each fitted with Demec points to check changes in the length and width of the panels. The test procedures are as follows:
i.
The samples were first clean of any objects that
might interfere with the test
such as dust particles.
ii.
After that, the Demec discs were installed using glue as shown in Plate 3.17. The changes in the length of the panels were than measured using the Demec gauge as shown in Plate 3.18. The first measurement is then taken as the datum and is considered zero.
iii.
The measurements are then taken everyday for the first 7 days. After that, the measurements are taken at 5 day intervals.
iv.
The panels are considered to have achieved a constant length when two consecutive measurements taken give the same value.
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3.6.3
Non-destructive test
The purpose of the non-destructive test was to check the uniformity of the wall panels. For this research, the Schmidt rebound hammer method was used to conduct the tests. The hammer used is of type N as shown in Plate 3.19. The panels tested were at 7, 14 and 28 days. According to BS1881: Part 202 (1986), the measurement of hardness can be used to establish the uniformity of concrete produced. The procedures for the test are as follows:
i.
The samples were first cleaned to make sure there are no foreign materials that might interfere with the test conducted.
ii.
After that, the samples were marked with several points that were to be tested on as shown in Plate 3.20.
iii.
Next, the measurements are taken by the rebound hammer at the selected points and the rebound hammer number recorded.
iv.
The rebound hammer values were then changed into MPa units using the graph located on the rebound hammer itself.
3.7
Summary
In this chapter, the main discussion was about the tests and the method in which the tests were conducted. The materials used for the making of the wall panels
51
and cubes were also looked into. The mix proportions and the mixing procedures were also discussed in detail at the beginning of the chapter. By looking through this chapter, the materials needed and the methods to produce the wall panels are explained to get a better view of the research being conducted. The results of the tests conducted will be discussed further in Chapter 4.
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Table 3.1: Chemical compositions and physical properties of Ordinary Portland Cement and ground granulated blast furnace slag.
Chemical Composition
OPC ( % )
GGBFS ( % )
Silicon dioxide (SiO2)
20.1
28.2
Aluminium oxide (Al2O3)
4.9
10.0
Ferric oxide (Fe2O3)
2.5
1.8
Calcium oxide (CaO)
65.0
50.4
Magnesium oxide (MgO)
3.1
4.6
Sulphur oxide (SO3)
2.3
2.2
Sodium oxide (Na2O)
0.2
0.1
Potassium oxide (K2O)
0.4
0.6
Titanium oxide (TiO2)
0.2
-
Phosphorous oxide (P2O2)
< 0.9
-
Loss on ignition (LOI)
2.4
0.2
Carbon content (C)
-
-
Physical Properties Specific gravity
3.2
Fineness (% passing 45 ^m)
93.0
Table 3.2: Chemical composition of aluminium powder. Chemical Composition (%) Aluminium
Minimum 99.3
Copper
Maximum 0.1
Iron
Maximum 0.4
Silica
Maximum 0.2
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Table 3.3: Physical properties of pulverised fuel ash (PFA). Property
Typical values
Compacted bulk density
1300 - 1500 Kg/m3
Relative Density (oven dry)
2.0 - 2.4
Specific Heat capacity
0.8 - 0.7J/Kg/°C
Water Permeability - compacted fly ash
1.0 x 10-6 - 7.0 x 10-7
Electrical conductivity
0.09 W/mK
Loss on Ignition
6 - 10%
Table 3.4: Chemical properties of pulverised fuel ash (PFA). Element
Typical range of values
Silicon (% as SiO2)
38 - 52
Aluminium (% as Al2O3)
20 - 40
Iron (% as Fe2O3)
6 - 16
Calcium (% as CaO)
1.8 - 10
Table 3.5: Sieve analysis for sand. Sieve
Weight
%
Cumulative %
Cumulative %
Size
Retained (kg)
Retained
Retained
Passing
2.36
1.469
9.8
9.8
90.2
1.18
3.208
21.4
31.2
68.8
0.6
4.979
33.2
64.4
35.6
0.3
3.689
24.6
89.0
11.0
0.15
1.274
8.5
97.5
2.5
0.075
0.254
1.7
99.2
0.8
Pan
0.118
0.8
100
0
Total
14.991
100
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Table 3.6: Mix proportion of slag cement based aerated lightweight concrete. Sand : Cement ratio
50 : 50
Slag replacement
50 %
Water-Dry mix ratio
0.25
Aluminium powder
0.15 %
Superplasticizer
0.6 %
Table 3.7: Material used for 1 m3 of slag cement based aerated lightweight concrete. Material
Weight (kg)
Sand
600
Cement
300
GGBFS
300
Water
300
Aluminium powder
1.8
Superplasticizer
3.6
Table 3.8: Ultimate strength of mortar at 3 days. Strength (kN)
Ratio
Average (kN)
Sample 1
Sample 2
Sample 3
1:1
127.5
139.7
141.2
136.13
1:2
111.7
105.3
107.7
108.23
1:3
57.2
59.2
59.2
58.53
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Table 3.9: Ultimate strength of mortar at 7 days. Strength (kN)
Ratio
Average (kN)
Sample 1
Sample 2
Sample 3
1:1
191.3
190.9
192.6
191.60
1:2
147.8
152.8
149.5
150.03
1:3
95.9
101.1
100.2
99.07
Table 3.10: Weight of mortar at 3 days. Ratio
Weight (kg)
Average (kg)
Sample 1
Sample 2
Sample 3
1:1
0.745
0.745
0.750
0.747
1:2
0.765
0.755
0.760
0.760
1:3
0.746
0.746
0.748
0.747
Table 3.11: Weight of mortar at 7 days. Ratio
Weight (kg)
Average (kg)
Sample 1
Sample 2
Sample 3
1:1
0.752
0.750
0.756
0.753
1:2
0.758
0.768
0.754
0.760
1:3
0.750
0.758
0.756
0.755
Table 3.12: Water ratio for each sand-binder ratio of mortar. Ratio
Water ratio
Range (%)
1:1
0.44
112
1:2
0.53
108
1:3
0.71
104
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Table 3.13: Types of pozzolans and the percentage replacement. Type of pozzolan
Percentage replace of cement (%)
Slag (GGBFS)
30
Rice husk ash (RHA)
10
Pulverised fuel ash (PFA)
5
Palm oil fuel ash (POFA)
5
Table 3.14: Material used to produce 1 m3 of mortar. Material
Weight (kg)
Sand
1000
Cement
500
Slag (GGBFS)
300
Rice husk Ash (RHA)
100
Pulverised Fuel Ash (PFA)
50
Palm Oil Fuel Ash (POFA)
50
Water
440
Superplasticizer
1
Table 3.15: Dimension of the wall panels.
Thickness
Length
600mm
Width
300mm Aerated layer
20mm
Mortar layer
15mm (each)
Overall thickness
50mm
Volume
0.009m3
57
Figure 3.1: Sieve analysis for sand
58
Plate 3.2: Materials for producing aerated lightweight concrete.
59
Plate 3.4 a: Sieve machine for sieving sand.
60
Plate 3.4 b: Sieving of sand.
Plate 3.5: Los Angeles Test Machine for grinding of POFA and RHA.
61
Plate 3.6: Water table used to gauge the water ratio for mortar
Plate 3.7: Mixing of OPC, slag (GGBFS) and sand in mixing bowl.
62
Plate 3.9: Aerated concrete cube.
63
Plate 3.11a: Inner layer made from aerated lightweight concrete.
64
Plate 3.12: Final layer of mortar.
65
Plate 3.14: TONIPAC 300 machine used for testing compressive strength of cubes.
66
Plate 3.16: Wall panels being tested for 28 days strength.
67
Plate 3.17: Location of the Demec disc on the wall panels
Plate 3.18: Shrinkage measurement by Demec gauge.
68
Plate 3.20: Points on the wall panels for the rebound hammer test.
CHAPTER 4
RESULTS AND DISCUSSION
4.1
Introduction
In this chapter, the results of the various tests conducted on the cube samples and the wall panels will be looked into. The entire test, were conducted as mention in the previous chapter.
4.2
Comparison of Strength and Density of Cubes
The slag cement based aerated concrete cubes were compared to controlled samples to analyse the difference between the two specimens in regard to compressive strength and density. The controlled samples were made without replacement of cement with slag. The cubes were tested at 7 and 28 days. The results are shown in Table 4.1 Table 4.2 and illustrated in Figure 4.1 and Figure 4.2. Based on the results obtained, it can be concluded that the controlled samples has a higher compressive strength and higher density values than that of the slag cement
70
based aerated lightweight concrete cubes. The reason for the low strength of the slag cement based aerated concrete may be cause by the curing temperature used. The curing temperature plays a vital role in the strength obtained for slag cement based concrete (Short, A., 1978). All the cubes used in this research were cured by air.
However, the strength obtained is acceptable to be used in the production of non-load bearing wall panels because the required strength is 3.45 MPa at 28 days. The slag cement based aerated lightweight concrete has an average strength of 5.18 MPa at 7 days and 6.46 MPa at 28 days. The slag cement based concrete also shows a lower density compared to the controlled sample with an average of 1207.34 kg/m3 at 7 days and 1188.48 kg/m3 at 28 days. The density obtained is in the range set by the objectives in the beginning of the chapter, which is between 1000 kg/m3 to 1200 kg/m3. From the results of the compressive strength, the mix proportion can be used to produce the wall panels because the strength is acceptable for non-load bearing wall panels.
4.3
Compressive Strength of Wall Panels
The wall panels were tested at 7, 14 and 28 days to determine the compressive strength. For each test, 3 samples were used. However, for the 28 day test, 2 samples were used each for test conducted on to different surface area. The results obtained for the tests are shown in Tables 4.3, 4.4, 4.5 and 4.6.
For the test conducted at 7 days, the maximum loads obtained are 112.713 kN, 77.944 kN and 99.520 kN with an average of 96.73 kN. The compressive strength of the wall panels respectively are 7.51 MPa, 5.20 MPa and 6.63 MPa with an average value of 6.45 MPa. The maximum loads obtained from the test conducted for wall panels at 14 days are 118.041 kN, 122.082 kN and 116.039 kN with an
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average of 118.72 kN. The compressive strength of the wall panels respectively for 14 days are 7.87 MPa, 8.14 MPa and 7.74 MPa with an average value of 7.92 MPa. The panels tested for 28 day strength was tested at two different surface areas. For the surface area of 300mm x 50mm, the maximum loads recorded are 140.948 kN and 100.548 kN with an average result of 120.75 kN. The compressive strength values obtained from the results are 9.40 MPa and 6.70 MPa with an average value of 8.05 MPa. The maximum loads for the surface area of 600mm x 50mm are 234.486 kN and 254.311 kN with the compressive strength of 7.82 MPa and 8.48 MPa. The average value of the maximum load is 244.40 kN and 8.15 MPa for the compressive strength.
The increasing compressive strength of the wall panels is shown in Figure 4.3. From Figure 4.3, the increase of strength between 7 and 14 days was about 23%, while from 14 to 28 days, it was about 2%. Therefore, the strength of the wall panels can be assumed to increase more at the beginning stages. This may be because of the curing regime used for this research, with all the panels cured with air curing. Proper curing is needed for the hydration process to continue in concrete (Neville, A. M., 1981). In the case of air curing, the moisture in the concrete is used up and the hydration process begins to decrease, thus having only slight increase in strength at later ages. The difference in strength for the wall panels tested at 28 days for the two different test surface conducted was about 1.2%. The compressive strength of the test conducted at the surface area of 600mm x 300mm is slightly higher than that of the other. This may be due to the former having a higher buckling yield strength because it is less slender compared to the latter. Most of the panels tested, tend to crack at the mortar layer. This may be due to the mortar having lesser thickness compared to the aerated concrete layer. The mortar layer also tends to split from the aerated concrete layer suggesting a weakness in the bonding of the two materials. Plates 4.1, 4.2, 4.3 and 4.4 show the wall panels after each test. From the results obtained, it can be concluded that the wall panels produced is acceptable to be used as non-load bearing wall panels since the strength of the panel at 28 days is more than the required strength. Therefore, the objective of producing a durable wall panel has been met.
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4.4
Density of Wall Panels
The weight of the wall panels were recorded before each compressive test to obtained the density of the panels. The weight of the wall panels were between the range of 13.5 kg to 14.5 kg with a density of 1500 kg/m3 to 1611.11 kg/m3. The density of dense concrete is in the range of 2240 kg/m3 to 2480 kg/m3 (Riba, A. E., 1994). Therefore, the wall panels produced can be considered lightweight because the density is below that of dense concrete. Therefore, the objective to produce a lightweight wall panel is also satisfied.
4.5
Non-Destructive Test
The non-destructive test used in this research was the type N Schmidt rebound hammer. The wall panels were tested at ages 7, 14 and 28 days and the results are shown in Tables 4.7, 4.8 and 4.9. There were all together 28 points tested on each panel and the locations of the points tested are shown in Figure 4.4. The rebound hammer test is only a complementary test and cannot be substitute for other well established test (BS1881: Part 202: 1986). The hardness measurement of the concrete is able to provide information about the quality and uniformity of the concrete. The bigger the rebound hammer values, the harder the concrete is. From the results obtained, it can be said that the wall panels produced shows an amount of uniformity as the values do not vary much.
For the panels tested for 7 days, the rebound number range is 14 to 18. The range for panels tested for 14 and 28 days respectively are 14 to 18 and 24 to 30. The mean value, standard deviation and variation of the panels tested at 7, 14 and 28 days are shown in Table 4.10. It can also be said, that the hardness of the wall panels increase with age due to the bigger value of rebound hammer number for panels
73
tested at 28 days compared to panels tested on 7 days. This can be taken as a sign of quality concrete. Therefore, it is safe to imply that the strength of the wall panels also increase with age. The mean value for 28 days was recorded as 26.71 which is approximately 22 MPa.
4.6
Dimension Stability
The dimension stability test was conducted as discussed in the previous chapter. The main purpose of this test is to examine the small changes in dimension due to expansion or shrinkage of the wall panels. The value for this test was recorded everyday for the first ten days and subsequently taken at intervals of five days as the value does not change significantly. Three panels were used for this test at which the average value was taken at the end of the test which lasted for 42 days. The value was compared to the maximum permissible variation according to ASTM C 129-85 (1990) which states that the allowable variation does not exceed ± 3.2 mm. Figure 4.5 shows the location of the Demec disc and the axis of X-X and Y-Y.
The results of the test are show in Table 4.11. The dimension changes of the wall panels are calculated as follows:
X-X: Length of panel
600 mm
Dimension change after 42 days
-3.350 x 10-5
Current length of panel
599.999 mm
74
Y-Y: Width of panel
300 mm
Dimension change after 42 days
-1.264 x 10-6
Current length of panel
299.999 mm
Based on the calculations above, the new length of the panel is 599.999 mm with a difference of 0.00017%. The new width of the panel is 299.999 mm with a difference of 0.00033%. The dimensional changes of the panels with age are shown in Figures 4.6 and 4.7. From the test conducted, the dimension changes of the panels appear to be small. This may be due to pozzolans used in the mortar layer which may result in lower shrinkage (Neville, A. M., 1981).
4.7
Summary
Based on the tests conducted, the main objective of the research, which was to produce a light and durable non-load bearing wall panel, is satisfied. The strength of the panel at 28 days which was 8.05 MPa surpasses that of the required strength for non-load bearing wall panels which is 3.45 MPa. The panels produce also is considered lightweight with a density of 1500 kg/m3 to 1611.11 kg/m3. Other complementary tests conducted also shows that the wall panels produced are of quality and strength. The uniformity of the panel also indicated a good mix of concrete.
75
Table 4.1: Compressive strength comparison between controlled samples and slag cement based aerated concrete. 7 days (MPa) Samples
28 days (MPa)
Controlled
Slag cement
Controlled
Slag cement
samples
based samples
samples
based samples
1
9.58
5.14
11.56
6.60
2
9.63
5.20
11.69
6.48
3
9.59
5.20
12.20
6.30
Average
9.60
5.18
11.82
6.46
Table 4.2: Density comparison between controlled samples and slag cement based aerated concrete.
7 days (kg/m3) Samples
28 days (kg/m3)
Controlled
Slag cement
Controlled
Slag cement
samples
based samples
samples
based samples
1
1480.02
1216.77
1485.32
1188.48
2
1493.35
1216.77
1406.24
1188.48
3
1487.65
1188.48
1462.35
1188.48
Average
1487.01
1207.34
1452.30
1188.48
Table 4.3: Compressive strength of wall panels at 7 days.
Samples
Dimensions (mm)
Maximum Load
Compressive
Height
Width
Thickness
(kN)
Strength (MPa)
1
600
300
50
112.713
7.51
2
600
300
50
77.944
5.20
3
600
300
50
99.520
6.63
96.73
6.45
Average
76 Table 4.4: Compressive strength of wall panels at 14 days.
Samples
Dimensions (mm)
Maximum Load
Compressive
Height
Width
Thickness
(kN)
Strength (MPa)
1
600
300
50
118.041
7.87
2
600
300
50
122.082
8.14
3
600
300
50
116.039
7.74
118.72
7.92
Average
Table 4.5: Compressive strength of wall panels at 28 days (area 300mm x 50mm).
Samples
Dimensions (mm)
Maximum Load
Compressive
Height
Width
Thickness
(kN)
Strength (MPa)
1
600
300
50
140.948
9.40
2
600
300
50
100.548
6.70
120.75
8.05
Average
Table 4.6: Compressive strength of wall panels at 28 days (area 600mm x 50mm).
Samples
Dimensions (mm)
Maximum Load
Compressive
Height
Width
Thickness
(kN)
Strength (MPa)
1
600
300
50
234.486
7.82
2
600
300
50
254.311
8.48
244.40
8.15
Average
77 Table 4.7: Rebound hammer value for wall panels tested at 7 days.
Points
Rebound Number
1
16
2
16
3
16
4
14
5
14
6
18
7
14
8
14
9
16
10
16
11
14
12
14
13
16
14
16
15
18
16
18
17
18
18
18
19
18
20
16
21
16
22
14
23
14
24
16
25
14
26
14
27
14
28
16
78 Table 4.8: Rebound hammer value for wall panels tested at 14 days.
Points
Rebound Number
1
18
2
14
3
14
4
14
5
16
6
18
7
18
8
18
9
18
10
16
11
16
12
16
13
18
14
18
15
18
16
16
17
18
18
18
19
18
20
16
21
18
22
16
23
14
24
14
25
14
26
14
27
14
28
18
79 Table 4.9: Rebound hammer value for wall panels tested at 28 days
Points
Rebound Number
1
24
2
24
3
26
4
30
5
30
6
24
7
26
8
30
9
30
10
24
11
24
12
24
13
24
14
26
15
30
16
28
17
24
18
24
19
26
20
26
21
28
22
30
23
28
24
30
25
24
26
26
27
28
28
30
80
Table 4.10: Mean, standard deviation and variation value for wall panels at 7, 14 and 28 days.
7 days
14 days
28 days
Mean
15.643
16.357
26.710
Standard Deviation
1.545
1.726
2.507
Variants
2.386
2.979
6.286
Table 4.11: Results for the dimension stability test.
Dimension Changes (mm)
Days
X-X
Y-Y
1
0
0
2
3.160 x 10-7
3.160 x 10-7
3
1.264 x 10-6
1.264 x 10-6
4
1.580 x 10-6
1.580 x 10-6
5
1.580 x 10-6
2.212 x 10-6
6
2.212 x 10-6
3.160 x 10-6
7
2.212 x 10-6
2.844 x 10-6
8
1.896 x 10-6
2.528 x 10-6
9
1.580 x 10-6
2.212 x 10-6
10
9.480 x 10-7
1.896 x 10-6
16
3.160 x 10-7
1.580 x 10-6
21
-3.192 x 10-5
6.320 x 10-7
27
-3.286 x 10-5
-3.170 x 10-7
32
-3.318 x 10-5
-3.160 x 10-7
37
-3.350 x 10-5
-1.264 x 10-6
42
-3.350 x 10-5
-1.264 x 10-6
81
STRENGTH COMPARISON ет
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