Analysis of Sandcrete Blocks Production by Using Different Sources of Sharp Sands in Some Parts of South-East Geo-political Zones: Case Study; Enugu and Ebonyi State
Chapter One
Objectives of the Study
The main objectives of this study are:
- To ascertain the grading of different sharp sands obtained from different sources and to check their suitability in the production of sandcrete blocks.
- To find out the possible effect of chemical compositions of river sand on the compressive strength of sandcrete blocks.
- To compare the compressive strength of sandcrete blocks produced from selected river sand from different sources with the standard values specified by Nigerian Industrial Standard (NIS) and other Civil Engineering bodies.
- To classify the selected sharp sands into different zones using sieve analysis results obtained.
CHAPTER TWO
LITERATURE REVIEW
General
Many people have conducted research on the constituent elements of sandcrete blocks and on its use in building construction. The construction industry is a very important sector of the economy. It plays critical role in a nation’s economy such as Nigerian economy because of the transient trend in national growth. The rapid growth in the country’s economy and population requires additional physical infrastructures to accommodate additional various component of the Gross National Product (GDP). These physical infrastructures include residential and commercial buildings, agricultural and health facilities to mention but a few. On the other hand, it requires the integration of engineering, project, and production management techniques. Over 90% of physical infrastructures in Nigeria are being constructed using sandcrete blocks (Baiden and Tuuli, 2004). This makes sandcrete blocks a very important material in building construction. It is widely used in Nigeria, Ghana, and other African countries as load bearing and non-load bearing walling units. The British Standard 6073( 1981) defines a block as a masonry unit of larger size in all dimensions than specified for bricks, but no dimension should exceed 650mm nor should the height exceed either its length or six times its thickness.
For a long time in Nigeria, sandcrete blocks are manufactured in many parts of the country without any effort to satisfy local building requirements or good quality work. In the year 2000, and in an attempt to enhance the use of the best materials and manufacturing practice, the Standard Organization of Nigeria developed a reference document which prescribed the minimum requirements and uses of different kinds of sandcrete blocks (NIS 87,2000). Among the objectives of this NIS document, are the need to ensure that all block manufacturers meet minimum specified standard, as well as to control the quality of blocks produced by these manufacturers.
Many Years after the introduction of the standards, variations in quality still exist in the quality of blocks being produced by these manufacturers. According to the NIS document, chance and assignable variations are two factors known to cause variations in the quality of sandcrete blocks. Chance variations are variations in quality as a result of environmental influences such as temperature, radiation, noise etc. The effects of chance variations are usually unnoticed. Assignable variations on the other hand, are the sources of variation that can be attributed to man, machine, raw materials and method.
Blocks are those building unit used in the construction of wall and partitions. They are of sizes and weights that can be easily handled by the bricklayer, with the facing surface layer than that of a brick but conveniently dimensioned. Sandcrete blocks are available for the construction of load bearing and non-load bearing structures (Hodge, 1971). Load bearing blocks must conform to building by- law regarding their crushing and to the amount of solid mineral contained in section.
Sandcrete block is a building material made from Portland cement and sharp sand. It is similar to,but weaker than mortar, and its mix ratio is circa 1:6. Sandcrete is usually used as hollow rectangular blocks, often 45 cm wide, 15 cm thick, and 30 cm with hollows that run from top to bottom and occupy around one third of the volume of the block. The blocks can be joined together with mortar. The final compressive strength of sandcrete can be as high as 4.6 N/mm2, which is much less than that concrete’s 40 N/mm2 (Wikipedia on sandcrete). Sandcrete is unsuitable for load-bearing columns, and is mainly used for walls, or for foundations if no suitable alternative is available. As a material for walls, its strength is less than that of fired clay bricks, but sandcrete is considerably cheaper. Sandcrete block is the main building material for walls of single-storey buildings (such as houses and schools) in countries such as Ghana and Nigeria (Wikipedia on sandcrete). Measured strengths of commercially available sandcrete blocks in Nigeria were found to be between 0.5 and 1N/mm2, which is well below the 3.5 N/mm2 that is legally required. This low strength may be due to the need of the manufacturers to keep the price low, and since the main cost-factor is the portland cement, manufacturers reduce it, which results in a block that behaves more like loose sand. Addition of coarse aggregates has been tried, since this is a cheap way to increase compressive strength. But since the cement content of sandcrete is small, so also is the amount of water that is added to the sand/cement mix to cure it. Adding more solid materials makes the mix much less fluid, and more difficult to cast into blocks.
CHAPTER THREE
MATERIALS AND METHODS
The material constituents, their mix, presence of admixtures and manufacturing process are important factors that determine the properties of sandcrete blocks. This chapter discusses the materials used and method of manufacture and testing employed in this study.
Materials
The sandcrete blocks are made of sand, cement and water. These materials are discussed as follows:
Cement
The cement used in this work is the ordinary portland cement (OPC) from the – Portland Cement Company, Ogun State, Nigeria with properties conforming to BS 12 (British Standards Institution, 1971). For constructional purposes, cement is a term restricted to the bonding materials used with stones, bricks and sand. The principal constituents of this type of cement are compounds of lime. On adding water to the cement a chemical reaction known as hydration takes place and a large quantity of heat is released. On hydration, gel is formed which binds the sand particles together and provides strength and water tightness to the sandcrete on hardening. Ordinary portland cement (OPC), is the most common cement used in general concrete construction work. American society for testing materials i.e ASTM C150, has specified certain physical requirement for each type of cement. These properties include fineness, soundness and consistency, setting time, compressive strength, heat of hydration, specific gravity and loss of ignition. Each of these properties has influence on the performance of cement. The fineness of cement, for example, affects the rate of hydration and the degree of fineness of cement is the measure of the mean size of the grain in it. Any Portland cement to be used for the production of sandcrete blocks must comply with all the prescribed requirements of BS 12(1971) and NIS: (2003) respectively.
CHAPTER FOUR
ANALYSIS OF RESULTS
Description of different sand types
Ikwo sand
From sieve analysis result of these sample 500g was measured accurately with an electronic weigh measure, 35.0g was retained on sieve number 8, 25.0g retained on number 10, 12.0g retained on number 12, 185.0 retained on number 22, 113.0g retained on number 30, and 25.0g retained on the sieve number 44, 59.0g retained on sieve number 60, 37.0g retained on sieve number 85, 3g retainend on sieve number 150, 1g retained on sieve number 170, 0g were retainend on sieve number 200 and 300 respectively. The colour definition of ikwo sample looks more whitish compared to other samples. The specific gravity obtained is 2.308 with a approximately rough texture.
CHAPTER FIVE
SUMMARY, CONCLUTION AND RECOMMENDATION
Compressive Strength
The minimum prescribed value for load bearing sandcrete block specified by NIS 87:2006 is 2.5N/m2 and 1.75N/m2 by building code (2006) and the compressive strength of sandcrete block for building requirements should be as high as 4.6N/mn2.
From the first(1st) and second(2nd) week compressive strength result obtained, all the samples fall below the minimum prescribed value for load bearing sandcrete block specified by NIS 87:200. However only Opi Agu sample among all also failed the condition for building code (2006).
The compressive strength results obtained from third (3rd) and fourth (4th) week for all the samples met the conditions for both minimum prescribed value for load bearing sandcrete block, specified by NIS 87:2000 and building code (2006). This implies that the compressive strength for the whole samples fall within the acceptable national and international standards.
DISCUSSION
From the results obtained on chemical composition of different samples shows that Obollo-Etiti River Sand and Coal Mine River Sand gives more redish pink colour because of the higher proportion of Mg2+ which is 1544.40mg/l for both samples. Ikwo and Asu Amenu were dark grey in color after production because of the higher proportion of Fe(iron) in the sand which is 343mg/l and 371mg/l respectively, while the mixture of coal mine and ikwo sample has a greyish colour because of the proportion of fe (ion) which is 305mg/l.
Taking the average of the total compressive strength results for all the samples, Asu Amenu has the higher strength which is 3.195; followed by Ikwo sample with 3.0825, Obollo Etiti 3.0225, mixture of coal mine with ikwo and Opi Agu having 3.01 and 2.58 respectively.
Ca2+, Fe, Mg2+ and SO4 helps in improving the strength of the concrete by reacting with that present in ordinary Portland Cement. But Ca2+ helps in increasing the initial setting time of the sandcrete block. Due to the higher proportion of Fe on the Asu-Amenu Sample it has the higher strength i.e. taking the average compressive strength for all the samples.
CONCLUSION/RECOMENDATION
This study has shown that the compressive strengths of sandcrete blocks produced in some parts of south east region falls within the acceptable national and international standards. the findings from this study also agree with similar studies in other parts of Nigeria. A sandcrete block accounts for virtually all wall construction in Nigeria building industry, there is no much danger in using sandcrete blocks produced in some parts of these south east region, if commercial industries abides by the standard mix proportion designed for sandcrete block production which is 1: 6 as required. There is urgent need for various arms of civil engineering bodies and government to actions in regulating the production of commercial blocks in Nigeria. This will ensure that blocks which do not meet minimum requirements are destroyed before being sold to public.
REFERENCE
- Abdullahi, M. 2005. Compressive Strength of Sandcrete Blocks in Bosso and Shiroro Areas of Minna, Nigeria. AU Journal of Technology. 9(2). Pp. 126-132.
- Baiden, B. K and Tuul, M. M. 2004. Impact of Quality Control Practices in Sandcrete Blocks Production. J. Archit. Eng. 10, 53 (2004); doi:10.1061/ (ASCE) 1076-0431(2004)10:2(53).
- British Standards Institution, BS 882: 1992, Specification for aggregates from natural sources for concrete, 1992.
- Barry, R. 1969. The construction of building. Vol.1. pp 54-55 & 94. Crosby lockwood, London, England.
- British standards institution. 1965. BS 3921: Bricks and Blocks of brick Earth clay or shale; British Standards institution, London, England.
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- F. W. Taylor and Thomas Telford, Jan 1, 1997 – Science – 459 pages
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