TABLE OF CONTENTS
Title page i
Table of Contents vi
List of Figures xi
List of Tables xv
List of Plates xx
List of Appendences xxi
1.1 Background 1
1.1.1 Cement 1
1.1.2 Concrete 4
1.1.3 Sandcrete hollow block (SHB) 5
1.2 Problem Statement and Justification of Study 7
1.2.1 Statement of the problem 7
1.2.2 Justifications 8
1.3 Aim and Objectives 10
1.3.1 Aim 10
1.3.2 Objectives 10
1.4 Scope and Limitations 11
1.4.1 Scope 11
1.4.2 Limitations 11
1.5 Study Area 12
1.6 Expected Research Outcome 12
2.0 Preamble 14
2.1 Water 14
2.2 Aggregate 15
2.2.1 Assessment on quality of sand and its substitutes 15
2.2.2 Studies on coarse aggregate in Nigeria 19
2.3 Cement 20
2.3.1 Raw aterials of portland cement 20
2.3.2 Process of manufacture of cement 20
2.3.3 Types of Portland Cement 21
2.3.4 Common brands of Portland available in Nigerian markets. 22
2.3.5 Current studies on some cement brands in Nigerian markets 28
2.3.6 Studies on blending materials in ordinary Portland cement 31
2.4 Sandcrete Hollow Block 43
2.4.1 Definitions of block 43
2.4.2 Methods of manufacturing sandcrete blocks 44
2.4.3 Curing 47
2.4.4 Standard test requirements 48
2.4.5 Assessments of Quality of Commercially Produced Sandcrete Blocks 49
2.4.6 Two- factor analysis of variance (ANOVA) 65
2.5 Concrete 67
MATERIALS, METHODS AND PRELIMINARY RESULTS
3.1 Preamble 74
3.2 Materials 74
3.3 Methods 74
3.3.1 Water quality 75
3.3.2 Sand 75
3.3.3 Cement tests 77
3.3.4 Sandcrete Hollow Block Tests 84
3.3.5 Coarse Aggregate Tests 105
3.3.6 Concrete Tests 109
RESULT AND DISCUSSION
4.0 Preamble 111
4.1 Chemical Analysis of the Water 111
4.2 Sand 112
4.3 Cement 114
4.3.1 Comparison of physical and mechanical properties of the cement brands 114
4.3.2 Chemical oxide characterization of the seven cement brands compared
to standard 123
4.3.3 Computation of lime saturation factor (LSF) of cement samples 130
4.3.4 Chemical compound characterization of the seven cement brands
compared to standard 131
4.4 Sandcrete hollow block tests 138
4.4.1 Optimum Water to cement ratio 138
4.4.2 Dry and wet development strength tests for sandcrete hollow
9” blocks made with machine 142
4.4.3 Comparison of tested block result with standards 149
4.4.4 Comparison of tested blocks results with Nigerian Industrial Standard,
NIS 87:2004 149
4.4.5 Comparison of blocks compressive strength with BS2028: 1985 Standard 150
4.4.6 Comparison of blocks compressive strength with BS 771-3: 2006 150
4.4.7 Comparison of results of Olanitori (2005) study with this study 150
4.4.8 Wet compressive strength of the blocks were lower than their dry strength 152
4.4.9 Minimum soaking strength of sandcrete hollow blocks made from
cement brands 152
4.4.10 Comparison of minimum soaked strength results with block industry results 153
4.4.11 Analysis of variance for mix ratio and cement brand on minimum
strength of blocks 154
4.4.12 Dry density development of 9” sandcrete hollow blocks 156
4.4.13 Wet density development of 9” hollow blocks made with vibrating machine 160
4.4.14 Water absorption of blocks 165
4.4.15 Estimation of cost production sandcrete hollow block 165
4.5 Coarse Aggregate 168
4.5.1 Physical characterization of coarse aggregate – test results 167
4.5.2 Chemical characterization of the coarse aggregate 172
4.6 Concrete Tests 173
4.6.1 Slump and compaction factor test results 173
4.6.2 Concrete cube strength of cement brands 173
4.6.3 Comparison of compressive strength of concrete cubes with standard 174
4.6.4 Performance of the seven cement brands in concrete and sandcrete
block production 175
4.6.5 Density development of concrete 178
4.7 Discussions on Cement and their Products 183
4.7.1 Cement brand A 183
4.7.2 Cement brand B 184
4.7.3 Cement brand C 185
4.7.4 Cement brand D 187
4.7.5 Cement brand E 189
4.7.6 Cement brand F 190
4.7.7 Cement brand G 192
4.8 Structural characterization of cement, SHB and concrete in Nigeria 194
CONCLUSION AND RECOMMENDATION
5.1 Findings 196
5.2 Conclusion 198
5.3 Recommendations 200
Cement is a major and binding component of concrete and sandcrete hollow blocks which are widely used for building and other structures in Nigeria. The major problem is that the measured compressive strengths of the two construction materials are lower than the minimum strengths (Adewole et al., 2015; Bamigboye et al., 2015) specified in the standards (BS EN 206: 2000 for concrete and BS EN 771-3: 2006 for sandcrete hollow block) in recent time in Nigeria and other developing countries.
Cement is the most expensive component of concrete and sandcrete block. The high cost of cement in Nigeria is attributed to (Pan African Plc, 2010) the failure of its supply to meet the demand which forced its price to go up, lack of stable power supply, its hoarding to encourage importation, monopoly of its supply by few people, high cost of its importation and huge capital required to set its production factory.
The other problem is that in 2014, the stakeholders of the construction and building industry traded blame with the local manufacturers of cement on the frequent collapse of buildings in Nigeria (The Guardian Newspaper, 2014). The stakeholders alleged that the wide spread use of a weaker grade 32.5 cement was a major cause of building collapse. They claimed that the bags of cement sold in the markets did not carry the label. The cement manufacturers on the other hand, insisted that cement grade had nothing to do with building collapse. They claimed that the professionals or consultants handling the jobs did not follow specifications as well as poor quality application of
cement, poor construction methods, inadequate supervision and corruption were the reasons responsible for the building failures (The Guardian Newspaper, 2014). This trading of blame between the stakeholders of building industry and cement manufacturers gave rise to the question: “Can the grade of cement affect the structural integrity of a building?”
The questionnaires administered by Standard Organisation of Nigeria revealed that most stakeholders and professionals in the building/ construction industries, academics and researchers did not know the grade of cement they buy from the market (Adewale, 2015). Also, the local cement industries producing the grade 32.5 cement were given approval by SON after ensuring the compliance of their product with the standard (NIS 444 – 1: 2003). It was revealed that cement grade 32.5 has been phased out in many countries and its importation has been banned even before 2003 (NIS 444-1: 2003).
The standard, BS EN 197-1: 2011 classified cement into three classes or grades: 32.5, 42.5 and 52.5. This means that the minimum 28-day mortar strengths of the cement grades are 32.5N/mm2, 42.5N/mm2 and 52.5N/mm2 respectively. The standard also specified that cement class 32.5 can have mortar strength between 42.5N/mm2 and 52.5N/mm2 while class 42.5 can have mortar strength between 42.5N/mm2 and 62.5N/mm2. This is what the manufacturers of cement in Nigeria capitalize on and believe that the class of cement does not make any difference in its quality.
The local cement industries producing grade 32.5 before 2014 were Larfarge West African Cement Company, Ashaka Cement Plc, Cement Company of Northern Nigeria (CCNN) and UniCem (2015). The imported cement dealers import class 42.5 cement.
Burham cement, Atlas cement, Ibeto cement, Eagle cement and others are imported CEM I cement brands which are class 42.5N, ordinary Portland cement. It was also observed that while the 50kg bags of class 32.5 cement were readily available, the 50kg bags of class 42.5 cement were not readily available in the market except in jumbo form and are usually supplied to the big industries (Adewole et al., 20014). Current market survey however, indicates that class 42.5 is now available in 50 kg bags and with the label as specified in the revised NIS 444-1: 2014.
Another problem of the cement brands produced locally and supplied to the markets is the introduction of Portland limestone cement types which are sold in two types: CEM II /A-L and CEM II / B-L instead of Portland cement (CEM I) which was originally being used in Nigeria (Adewole, 2014; uniCem, 2015). CEM II / A-L type is a cement produced by replacing 6 – 20% of the clinkers in Portland cement with limestone while CEM II / B-L is produced by replacing 21 – 35% of the clinkers in Portland cement with limestone (BS EN 197-1: 2011).
Based on the above problems of cement brands produced and sold in the Nigerian markets and the inability of the standard mortar tests at 2 days and 28 days to distinguish between the class 32.5 cement and the class 42.5 cement as well as the introduction of Portland limestone in the Nigerian markets it became imperative that the only reliable option is to test and characterise the products of the cement brands sold in the Nigerian markets and determine the fineness of the brands of cement. The products are mainly concrete and sandcrete hollow block which are widely used in Nigerian building and construction industry.
Adewole et al. (2014), Adewole et al. (2015) and Bamigboye et al. (2015) had extensively worked on Portland Limestone cement and its concrete grades. They had not worked on the ordinary Portland cement brands sold in the Nigerian markets and their products such as concrete and sandcrete hollow blocks to be in position to compare their strengths with those of Portland Limestone cements currently flooding most of the Nigerian markets. There is therefore the need to characterize the concrete and sandcrete hollow block produced from ordinary Portland cement present in Nigerian Markets.
Concrete is one of the major products of cement that is widely used for constructing buildings and other structures. The major problem is that the tested concretes (Adewole et al., 2015; Bamigboye, 2015; Yahaya 2009 and others) produced from cement brands sold in the Nigerian markets did not measure up to the strength requirement of the grades 20/25 and 25/30 (BS EN 206: 2000). This was attributed to the Portland limestone cement types recently introduced to the Nigerian markets (Adewole et al., 2015). According to BS EN 206: 2000, Portland limestone cement can only produce the standard minimum strength of concrete if the replacement level of clinker in the ordinary Portland cement does not exceed 15%. But the Nigerian cement manufacturers are producing classes 32.5R and 42.5R Portland limestone (CEM II /B-L 32.R and CEM II / B-L 42.5R) where the level of replacement is between 21% and 35% and recommend them for structural works (uniCem, 2015).
Studies carried out by Bamigboye et al. (2015) also revealed that the 28-day compressive strength test results for concretes produced from three of the four tested brands of cement in Nigeria failed to meet the required minimum standard for mix ratios 1:2:4 and 1:3:6. Studies carried out by Yahaya (2009) revealed that concretes produced from two imported cement brands and two local cement brands did not meet the minimum standard specifications. It was observed that the mix ratio used was 0.7. The improper water cement ratio and lack of adherence to the standard specifications of the chemical compound might have contributed to the poor results of the concrete strengths in addition to the above reason which was not considered in the previous studies. There is therefore, the need to characterise the concrete and sandcrete hollow blocks produced from selected cement brands sold in Nigerian markets considering the gaps highlighted above.
1.1.3 Sandcrete hollow block (SHB)
The major problem facing the production of sandcrete hollow block is that the tested compressive strength of sandcrete hollow blocks produced by most commercial block making industries did not meet the required standard. Studies carried out on the assessment of the quality of the blocks produced by commercial block-making industries revealed that majority of their blocks had 28- day dry strengths in the range of 0.50 to 1.5 N/mm2 in Nigeria (Ejeh and Abubakar, 2008; Ewa and Ukpata, 2013; Onwuka et al., 2013).
Several reasons were advanced for the commercial production of substandard sandcrete hollow blocks. The major reasons were poor cement to sand mix ratio, inadequate
curing and poor workmanship. The contribution made to the problem by improper use of water to cement ratio which are presently based on trial and error method was not considered by previous works. Odeyemi et al. (2015) carried out a research on sandcrete hollow blocks produced from Dangote and Elephant cement brands with a mix ratio of 1:6. Manual and vibrating machine were used to produce the blocks.
The results obtained for the 28-day dry compressive strength of SHB produced manually from Dangote and Elephant cement brands were 1.70N/mm2 and1.73N/mm2 respectively. The SHB produced from the vibrating machine had strengths of 1.78N/mm2 and 1.82N/mm2 for Dangote and Elephant brands of cement respectively. These values failed to meet the BS EN 771-3: 2006 and NIS 87: 2004 standard specifications of 2.9N/mm2 and 2.5N/mm2 respectively. They did not consider using optimum water to cement ratio but used trial and error instead as the two standards made no provision for it.
Ejeh and Abubakar (2008) and others had carried out studies on the assessment of commercial sandcrete hollow blocks produced by block making industries. The test results indicated that most of these commercial blocks were substandard because the average 28-day strength was 0.50N/mm2. They further reported that a drop in compressive strength was observed when the sandcrete hollow block was cured for 28 days and then immersed in water.
They did not consider treating standard blocks in the same way as the substandard commercial blocks. Also the effect of mix ratio, curing and cement brand on the drop had not been studied. Standard sandcrete hollow blocks need to be produced and
subjected to the same condition as in the above studies on substandard blocks varying the mix ratio, cement brand and curing periods.
1.2 Statement of the problems and Justifications
1.2.1 Statement of the problem
Concrete and sandcrete hollow block are two major materials used in Nigeria and other countries. The major problem is that the tested strength of concrete (Adewole et al., 2015 and Bamigboye et al., 2015) and sandcrete hollow block (Odeyemi et al., 2015; Ewa and Ukpata, 2013 and Onwuka et al., 2013) produced from cement brands in Nigeria do not always meet the required standards for the two materials (BS EN 206: 2000 for concrete and BS EN 771-3: 2006 for sandcrete hollow block). These observations are more common with sandcrete hollow blocks produced by commercial block making industries (Ewa and Ukpata, 2013 and Onwuka et al., 2013) and concretes produced by concrete practitioners. Some of the major reasons advanced for the low strength of the two materials (Samson et al. 2002) were poor mix ratio, inadequate curing and poor workmanship. The effect of water to cement ratio (which is currently largely based on trial and error method) on sandcrete production (Onwuka et al., 2013; Samson et al., 2002) was not considered in the previous studies as a contributing factor to the observed low strengths. While the standards for concrete made provision for water cement ratio, the standards for sandcrete hollow blocks did not provide for water to cement ratio. Also the specifications for the cement used for sandcrete and concrete productions are normally based on physical and mechanical
properties such as setting times and 28-day strengths. Chemical analyses of cement were seldom carried out.
Another problem is that previous studies (Odeyemi, 2015; OLanitori, 2006 and Samson et al., 2002) had based the assessment and suitability of the sandcrete hollow block on its 28-day dry and wet strengths. But, sandcrete hollow block wall inundated in flood water may not reach 28-days before it fails. Therefore, the assessment of wet block based on the 28-days did not represent the actual situation. Ejeh and Abubakar (2008), Ejeh and Ayinmode (2000) and others carried out studies on commercial sandcrete hollow blocks which were all substandard. The observed drops in compressive strength of the soaked blocks were not significant because the blocks were substandard. The previous studies did not cover standard blocks. Also the effects of mix ratio, cement brand and curing on the drops were not studied. All these observed parameters are important in structural characterisation of concrete and sandcrete hollow block. These observed gaps in the previous studies form the basis of this thesis.
1. The cement brands produced locally and those imported before 2003 were purely ordinary Portland cement (CEM I) class 42.5N. In 2003, the Standard Organisation of Nigeria (SON) introduced the cement standard specification NIS 444-1: 2003 which allowed the local production of Portland Limestone cement of types CEM II /A-L 42.5 N, CEM II /B -L 42.5R and CEM II/B –L 32.5R which have minimum 28-day mortar cube strengths of 42.5, 42.5 and 32.5N/mm2 respectvely. The imported cement brands have been largely
Portland cement (CEM I). There have been complaints by the stakeholders of the building and construction industry about the low quality of the cement sold in Nigerian markets particularly the Portland Limestone cements as well as the low strengths of concretes and sandcrete hollow blocks produced from them. There is therefore, the need to characterise the cement brands sold in Nigerian markets and the two products, concrete and sandcrete hollow block.
Nigeria has been experiencing flood which usually affect walls of buildings and fences constructed with sandcrete hollow block. Such walls are sometimes inundated with flood water for few days and may lead to large cracks or their collapse. The same applies to walls of buildings along coastal areas. The present method of simulating this incidence with 28-day wet compressive strength of sandcrete hollow block may not be sufficient as some walls may not survive the flood inundation for up to 28 days before failure. There is the need to characterise sandcrete hollow block immersed in water to determine the period at which the compressive strength of such flood inundated wall is a minimum. The result of such research may lead to a new approach in method of design of load bearing walls.
Majority of sandcrete hollow blocks produced by the block making industries are substandard and this has led to huge losses in the process of placement and transportation of the product. Structural characterization of sandcrete block may lead to production of standard blocks which will reduce the losses.
1.3 Aim and Objectives
The aim of the study is to characterise concrete and sandcrete hollow blocks produced from selected cement brands in Nigeria. This is pursued through the objectives below.
The objectives of the studies are to:
(i) Characterise the water, sand and gravel used for production of sandcrete hollow blocks and concretes.
(ii) Determine the physical, mechanical and chemical characteristics of selected seven cement brands labeled A to G purchased from local markets in Nigeria.
(iii) Determine the optimum water to cement ratio to be used in production of sandcrete hollow block by testing the strengths of sandcrete hollow blocks produced under varied water to cement ratio.
(iv) Determine the strength and density development profile of sandcrete hollow blocks produced from cement brands A to G and cured in the dry state by spraying with water for 28 days.
(v) Determine the economical cement to sand mix ratio and curing period to be used to produce sandcrete hollow block of compressive strength that satisfy the minimum strength of 2.9N/mm2 (BS EN 771-3:2006) and an average compressive strength of 3.5N/mm2.
(vi) Determine the strength and density development profile of sandcrete hollow blocks produced from cement brands A to G; cured in the dry state by spraying with water for 28 days and then immersed in water for another 28 days,
(vii) Determine the water absorption of the sandcrete hollow blocks produced from cement brands A to G.
(viii) Determine the strength and density development of concretes produced from cement brands A to G and its characteristic strength.
1.4 Scope and Limitations
This research work is centered on the modes of production of hollow sandcrete blocks of standard sizes 450mm x 225mm x 225mm (9”) and concrete cubes of size 150mm and grade 25/30 commonly used in the construction industries. The study is focused on the principal properties of the blocks and concrete such as compressive strength, density and water absorption and the curing method employed. Blocks and concretes were made from seven ordinary Portland cement brands of class 42.5, which means that the strength of the Portland cement at 28 days is 42.5N/mm2.
The ages of the cement brands were unknown to the researcher as the bags did not carry any date of manufacture.
1.5 Study Area
Seven brands of ordinary Portland cement labeled A, B, C, D, E, F and G were used to carry out the study. The cement brands studied were selected and purchased from Bauchi, Port Harcourt, Abuja, Lokoja, Onitsha, Lagos and Kaduna markets in Nigeria as presented in Table 1.0
Table1: Selected Cement Brands Used for Study and the Purchased Markets Sources in Nigeria
Brand of cement
Geopolitical Zone in Nigeria
Federal Capital Territory
1.6 Expected Research Outcome
The expected outcomes of the research are that the:
i. compressive strengths of the mortar cubes produced from each of the seven cement brands A, B, C, D, E, F and G at 2 days curing age exceed 10N/mm2 while the 28-day compressive strengths should exceed 42.5N/mm2,
ii. percentage of the tricalcium silicate compound in each of the seven cement brands should be in the range of 42% to 67% while that of the dicalcium silicate should be in the range of 8% to 31%,
iii. optimum water to cement ratio should produce the highest strength at all the mix ratio studied,
iv. average 28-day dry strengths of the blocks produced from the seven brands of cement at mix ratio range of 1:6 to 1:8 should meet the standard BS EN 771-3:2006,
v. standard blocks which meet the BS EN 771-3:2006 standard requirements should not show any noticeable drop in strength when soaked in water like the substandard block did in the previous studies with commercial,
vi. water absorption of the blocks produced from each of the seven ordinary Portland cement brands at mix ratio of 1:6 should not exceed 6%,
vii. characteristic strength of the concrete cubes produced from each of the seven cement brands studied exceeds 30N/mm2.
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