Quality of Sandcrete Hollow Blocks in Plateau State

Quality of Sandcrete Hollow Blocks in Plateau State

Chapter One

Aim and Objectives

This research work is aimed at assessing the quality of sandcrete hollow blocks produced commercially in Plateau State with the following objectives.

To carry out survey of the manufacturing block industries in Plateau
To determine the particle size distribution by sieve analysis and silt and clay content of the sand materials used for the production of these
To determine the varying mix proportion used by the block producing industries and compare with
To determine the dry and wet compressive strengths of the sandcrete blocks produced with age, in the state and compare with the international and local standards.
To determine the density of the finished sandcrete

CHAPTER TWO

LITERATURE REVIEW

Sandcrete Hollow Blocks

The use of sandcrete hollow blocks in building construction, especially in shelter provision as stressed byOmopariola (2014), as a walling unit in Nigeria, has come a long way. It is as old as the construction industry itself. For a long time until perhaps a few years ago, these blocks were manufactured in many parts of this country without any reference to any specification either to suit local building requirements or for good quality work. It is interesting to observe that the situation has changed, as the Standard Organization of Nigeria now has a document in place giving the specification both for the manufacture and use of these blocks in Nigeria, (SON 1976). Therefore, studies have been carried out by different researches from various parts of this country to determine its quality in comparison with the quality set by the local and international standards.

Ejeh and Banuso (2008), assessed the quality of sandcrete blocks produced in Kaduna state and concluded that the blocks were of lower quality when compared with the BS and NIS standards. A research work carried out by Afolayan et al (2008) indicated that the compressive strengths of sandcrete hollow blocks produced in Ondo State of Nigeria were sub-standard. Abdullahi (2005) studied the compressive strength of sandcrete blocks produced in some parts of Minna, Niger State, and discovered that they were below the minimum standard requirement. Florek (1985) also said that the quality of sandcrete hollow blocks produced in Kaduna, Zaria, Saminaka, Ikara, Bauchi and Mubi were very low compared to the standard. Omoreregie (2012) also reported that investigations into the compressive strength of blocks were carried out in Benin City, Ekpoma, Ughelle, Effurum and Warri town, and the results also revealed low compressive strength as compared to the standerd. The standard compressive strength, when produced by machine moulding and under the standard production requirement is 2.9N/mm², BS EN 771-3:2006. Measured strength of commercially available sandcrete blocks in Nigeria was found to be between 0.5 and 1 N/mm², which is well below the 3.45N/mm²(BS) and 2.5N/mm2, NIS (2007) that is legally required. This may be due to the need of the manufacturers to keep the price low, and since the main cost- factor is the Portland cement, they reduce that, which results in a block that behaves more like loose sand. Most of the manufacturing industries do not care to provide adequate enabling environment for the production of sandcreteblocks. They are, in most cases, trying to maximize their profit. The manufacturing of sandcrete hollow block was always in the hands of the illiterates, sandcrete blocks depend on some variables during production which are: amount of cement, fine aggregate, water, degree of compaction, curing condition and etc”. Frank (1982), observed that “the physical properties of sandcrete hollow blocks are affected to high degree by the properties of the constituent materials” that is cement, aggregate and water. Oyekan and Kamiyo (2011), The material constituents, their mix, presence of admixtures, if needed, and the manufacturing process are important factors that determine the properties of sandcrete blocks.

These conventional constituent materials; cement, sand (fine aggregate) and water, are discussed as follow:

Cement

This binds the other constituent materials together and also fills up the voids in between them in the presence of water. Ma‟aruf et al(2017) observed that „the cement glues the aggregates(sand) together, fills voids with it and makes it flow freely‟.

Therefore, it is the most essential constituent material of sandcrete blocks. Neville (2012), stressed the fact that cement binds aggregates together and fills up the voids in between them. It has been observed that Ordinary Portland Cement (OPC) is the most common cement generally used in this country for building construction and it comes in different brands; from Dangote, Sokoto, Ashaka cements etc.

Whichever brand of cement is used in the production of sandcrete block, it should meet the BS EN 197-1:2011 and NIS87:2004 requirements. These codes specify the following physical properties of cement.

The soundness expansion should not be more than 10mm and 5mm if
The fineness of an average specific surface of range bewteen200 and 300cm²/g

Initial setting time should not be less than 45 minutes and final setting time of more than 10hrs, BS12(1996).

The Portland cement that is commonly used in Nigeria in the manufacture of sandcrete blocks is often deficient in basic characteristics such as soundness, leading to excessive change in volume, particularly expansion of the cementpaste after setting, as reported by Omoregie (2012).

Cement is the most important material for the production of sandcrete hollow blocks, because it binds the other constituent materials together in the presence of water into a cohesive strong mass. Ola and Owoleye (2002), after their tests concluded that the compressive strength of sandctete blocks increase appreciably with increase in cement content.

The principal requirement is that the cement should be able to produce strong, dense, durable sandcrete hollow block with definite setting and hardening characteristics. The cement should conform to the standard recommendations of BS EN 197-1: 2011and NIS87:2004, Portland cement (ordinary and rapid hardening).

Aggregate

According to NIS 87:2004, the sand to be used for producing sandcrete blocks shall be approved clean, sharp, fresh water or pit sand free from clay, loam, dirt, organic or chemical matter of any description and shall mainly pass through 4.70mm or fall within zones 1 and 2 of British standard test sieves.

Abdullahi (2005), said „The most widely used aggregates for moulding sandcrete blocks is the natural sharp sand usually from the riverbed‟. BS EN 12620:2013, specifies that the maximum quantity of clay, silt and fine dust should not be more than 6% . The grading for sizes and the shape of particles are important, because they affect the workability of the mix as well as the density and impermeability of sandcrete hollow block. Jackson and Dhir (1996), said aggregate from some parents rock should not be used for sandcrete block because they may be physically and chemically unsuitable. In general, aggregate to be used in any construction work or manufacturing should conform to the standards.

CHAPTER THREE

METHODOLOGY

Survey of Existing Block Industries

The methodology involves general survey of the entire state to determine the total number of 121 functional block industries and spread all over the state. The state has seventeen Local Government Areas and they were divided into four different zones. These zones are: North East Zone, North West Zone South West Zone and South East Zone. Five block industries were selected, based on consistency in production; two from North East Zone and one from each of the other Zones. Three(3) number of block samples were collected per ages of 1, 3, 7, 14 and 28 days of curing; that is, fifteen (15) numbers of blocks per industry. The fifteen (15) number of blocks, were used for the test of Dry development compressive strength, Wet development compressive strength, Wet compressive strength and Density of these block samples. That is, 60 pieces of sandcrete hollow block samples of size 450mm x 230mm x 230mm were purchased from each of the five selected block industries. A total number of 300 blocks, produced by the block industries, were purchased and collected for laboratory test. „Tippett‟s (2004), „random sampling technique‟ was adopted for selection of these block specimen. Sand materials used by the block industries, were also collected. Laboratory tests were performed on the samples collected in accordance with the relevant code of practice.

The following listed laboratory tests were conducted:

Dry development compressive
Wet development compressive

Wet compressivestrength

Density

Sieve analysis, Clay and silt content and Cement

Summary of the excisingfunctional block industries

Extensive survey of the existing block industries in the entire state was conducted between February and May 2016. This was done to obtain detail information on sandcrete hollow blocks production in the state and to ascertain the number and spread of block industries across the entire state.After general survey of the entire state, it was observed that there were one hundred and twenty one total number of block functioning industries within the state, the breakdown of which is shown in the table below:

CHAPTER FOUR

ANALYSIS AND DISCUSSION OF RESULTS.

Particle Size

The sieve analysis results of the sand materials used for the production of the block samples are shown in Tables 3.4 to 3.8 and plotted in figure4.1below:

CHAPTER FIVE

CONCLUSION AND RECOMMENDATIONS

CONCLUSION

This research work considered the materials and method of production of sandcrete hollow blocks produced in Plateau state. All the tests and analyses carried outwere aimed at determining the quality of the sandcrete hollow blocks produced in the state.The following conclusions are therefore reached:

There were 121 block industries observed in Plateau
The sand material used for the production of the sandcrete hollow blocks in all the industries considered were generally sharp and clean materials. They are mainly graded into zone 1 and 2 of the grading standard of BS EN: 2013 12620 812:part 103 and complied with the requirement of the NIS standard for blocks

Results of the silt content of the sand materials were all within the 6% limit specified byBS EN 12620:2013. Therefore the silt content is

The proportion of sand material in the mix for the production of blocks in all the industries wastoo All the industries were using between 1:10 to 1:12 mix ratio of cement to sand, instead of the recommended standard of 1:6 to 1:8 as specified by thestandards.
The curing method and duration of curing in all the five industries, was done by spraying water twice in a day and for duration of two to five days in an open place. This is actually inadequate to allow for effective development of the cement
All the fiveindustries wereusing Ordinary Portland Cement (Dangote brand).From the results of the cement tests obtained for setting time,standard consistency and soundness, all conformed to BS EN197-3:2005.
The maximum twenty eight (28 day) dry development compressive strengths of the blocks for all the five industrieswere found to be less than the minimum average strength recommended by the established standards. From the analysis, industry V had the highest 28days dry development strength of 0.57N/mm^2,while industry II had the least compressive strength value of 0.21N/mm². These values were less than the 2.5N/mm² minimum average strength for individual block as specifiedby the

The average wet compressive strength values were 0.91, 0.99,0.97, 0.36 and 0.21N/mm²for industries I to V respectively. These strength values fell below the minimum national and international standards prescribed for type C sandcrete blocks.
The values of the coefficient of variation of 32.9%, 38.5%, and 24.13% for industries I, II and IV are too high when compared with the 20% limit specified for sandcrete blocks, as stated by Shettima (2006). This implies that these industries were not consistent in the variation of their strength, but there is no much variation in the level of production process in industries B and
The average density of blocks produced in the state was 916.4Kg/m³. This value is less than 1500Kg/m³but greater than 675Kg/m3 as specified by the standard for type C blocks; BS EN 771-3:2006. This means that the density value is
The values of the drying shrinkage and wetting expansion of all the five industries were within the limit specified by the standard for type C blocks. Therefore, all the blocks exhibit normal dimensional changes as water content changed.

RECOMMENDATIONS

These recommendations are either corrective or preventive aiming at improving the quality of sandcrete hollow blocks, produced commercially in the state, to meet the requirement of national and international standards.

From the analysis and conclusion made, the following recommendations are suggested:

Manufacturers of sandcrete hollow blocks should be enlightened through workshops and seminars to emphasize the need of producing blocks that meet the standard requirements, and the consequences of producing sub standard
The Federal Government in collaboration with COREN and NSE should constitute a powerful regulating body which will be monitoring the production of sandcrete blocks in the whole nation, with a powerful supervising team. This regulating body should be given the responsibility of testing and issuing a certificate of test passed, to enable the end users to demand for it when burying the
The block moulding machines as well as the driving engine device should be properly checked and service when due or on routine basis to improve the efficiency of the
Curing should be done according to the standard
Proper adherence to standard procedure of block production is highly recommended.

REFERENCES

Abdullahi, M. (2005) Compressive Strength of Sandcrete Bloks inBosso and Shiroro Areas of Minna, NigerState.Nigeria. AUJ.T.9(2) .
Adedeji, A. A., and Ejeh, S.P. (1998) Strength Characteristic of Dry-Jointed Block Assemblies Under Vertical Loads, Nigeria Journal of Construction Technology and Management Vol. 1, No. 1, pp. 102-108.Department of Building, University of Jos, Nigeria
Afolayan, J. O., Arum, C., and Characterization of the Daramola, C.M.(2008). Compressive Strength of Sandcrete Blocks in Ondo State, Nigeria, Journal of Civil Eng‟g Research and
Baiden, B. K. and Tuuli,M.M. (2004) Impact of Quality Control Practices in Sandcrete Block Production, Journal ofArchitecturalTechnology vol. ii, pp 53-60.
Banuso O.R.& S.P Eeh (2008)Assessment of Quality of Sandcrete Blocksin Kaduna state – Nigeria. Cape Town, South Africa. Journal of Construction Vol 2, No.1.
British Standard Institution. (1995). BS 812-2: Testing Aggregates: Methods of Determination of Density. London, England.
British Standard Institution. (1996). BS 12: Specification of Portland Cement,London, England.
British Standard Institution. (2000).BS 812-103.1: Testing Aggregates. Methods of Determination of Particle Size distribution: Sieve Test, London, England.
British Standard Institution. (2002). BS EN 1008:Mixing Water for Concrete. Specification, For Sampling, Testing and Assessing Suitability of Water, Including Water recoveredfrom Processes in Concrete industry As Mixing Water for concrete. London England.
British Standard Institution. (2002). BS EN 772- 1: Methods of Test for MasonryUnits: Determination of Compressive Strength.London, England.

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