Structural Characterization of Concrete and Sandcrete Hollow Block Produced From Selected Cement Brands in Nigeria

Structural Characterization of Concrete and Sandcrete Hollow Block Produced From Selected Cement Brands in Nigeria

Chapter One

Objectives of the Study

The objectives of the studies are to:

• Characterise the water, sand and gravel used for production of sandcretehollow blocks and
• Determinethe physical, mechanical and chemical characteristics of selected seven cement brands labeled A to G purchased from local markets in
• Determinethe 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
• Determinethe 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
• Determine the economical   cement to sand mix ratio and curing periodto 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 5N/mm².
• Determine the strength and density developmentprofile 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,
• Determine the water absorption of the sandcrete hollow blocks producedfrom cement brands A to
• Determine the strength and density development of concretes producedfrom cement brands A to G and its characteristic

CHAPTER TWO 

LITERATURE REVIEW

Preamble

 This chapter deals with review of related studies. The review of some of the studies previously carried out on assessments of quality of water, aggregates, cement brands, sandcrete hollow block, and concrete in Nigeria and other countries are presented.

 Water

Water from public utilities or well water fit for drinking is recommended for making sandcrete hollow blocks. If other sources of water are used, they should be stored in plastic or galvanized tanks (NIS 87: 2004). According to U.S. Army Corps Engineers (1963) water with pH in the range of 6.0 to 8.0 are suitable for concrete works. In addition such water must not contain organic matter. Water containing salts of sodium, potassium as well as other salts of natural origin in excess is regarded as unsuitable for concrete or sandcerete blocks. However, recent study (Osuji and Nwankwo, 2015) had shown that the effect of sea water on concrete is negligible.

The U.S. Army Corps Engineers (1979) specified that when the quality of water is questionable, the 7-day and 28-day mortar cubes test results should be a minimum of 90% of the mortar cube results of the same periods using distilled water. The specification for quality of mixing water is provided in ASTM C 1602-2006 and BS EN 1008:2002 codes.

Aggregate

Assessment on quality of sand and its substitutes

Olugbenga et al. (2000) carried out a research work on the study of compressive strength characteristics of laterite and sandcrete hollow blocks in Ile-Ife in Osun State of Nigeria. The objective of their study was to determine the possibility of partial replacement of sand with laterite in the production of sandcrete hollow block so as to cut down the cost. This was because laterite is more abundant and cheaper than the sand which is now widely used.   The 6” sandcrete hollow block of standard dimensions 450mm x150mm x225mm prepared with mix ratios 1:6 and 1:8 were used. The levels of replacement of sand with laterite were 0, 10%, 20%, 30%, 40%, 50% and 60% respectively. Results showed that sandcrete hollow blocks with 10% level of replacement with laterite gave the highest compressive strength and that compaction became more difficult as the percentage of laterite increased. The compressive strengths of the sandcrete hollow blocks decreased with level of replacement of laterite and therefore it is not a better material than sand.

Boeck et al. (2000) conducted a study on the effect of gradual replacement of sand with stone dust in sandcrete block making.   They used river sand which fell almost in zone 1 grading limit. The objective of the study was to determine the percentage level of replacement of sand with stone dust in sandcrete production. The stone dust was said to have the advantage of providing the finer particles smaller than 300 when added to the sand thereby ensuring good workability of sandcrete hollow block and reduce the occurrence of segregation. The mix ratio used was 1:5 while the level of replacement were 0, 20%, 40%, 60%, 80% and 100%. The results showed that the density increased with the addition of stone dust up to 40% of the fine aggregate after which it decreased. The compressive strength of the 450mm x 225mm x 225mm sandcrete blocks however, showed gradual decrease with the addition of stone dust. This was attributed to the increased surface area due to the addition of fines. They observed that for high density and good workability, the mix with 2 parts of sand to 1 part of stone dust gave good results.

Also the combined grading curve of sand and stone dust fell fully within the limits of zone 1 for fine aggregates. It can be deduced from this study that the stone dust has not been able to produce higher strength than the sand. Also stone dust is not readily available. Thus the stone dust has not been able to demonstrate any superiority and advantage over sand to justify its use.

Omoregie and Alutu, (2006), carried out a study on the influence of fine aggregate combination on particle size distribution, grading parameters and compressive strength of sandcrete blocks. They observed that low priced sand of lower quality were widely patronised in Nigeria despite its high content of silt and clay. Tests on coefficient of uniformity, C_u, curvature coefficient C_c and the fineness modulus F_m were determined from laboratory on fine sand deposits in parts of South – South, Nigeria (Benin City). The compressive strengths and other properties of the sandcrete hollow blocks produced were determined.

Results showed that the grading of the combined sand, the strength and durability characteristics of the sandcrete were greatly improved by the combination. The cost of the block was highly reduced. The high priced sand produced sandcrete block of compressive strength 6.05N/mm² and 5.59N/mm² for river sand from Okhuahia River and Ovia River respectively. The low priced sand produced sandcrete hollow blocks with strengths 2.57 and 2.47N/mm² for Ikpoba erosion sand and Okhoro erosion sand respectively. The combined sand in the ratios of 2: 1 (high priced sand: low priced sand) and 1:2 (high priced sand: low priced sand) produced sandcrete blocks of 28-day dry compressive strengths of 4.92 and 4.71N/mm² respectively. Also the grading zones of the high priced sand and low priced sand were 3 and 4 respectively. Those of the combinations in the above proportions were in zone 2. The water cement ratio used was based on trial and error method.

Agbede and Joel (2004) conducted a research on the suitability of Quarry dust as partial replacement for sand in hollow sandcrete block production. The source of the sand used for the study was River Benue at Makurdi while the quarry stone dust was sourced from Quarry at Ahua of Mkar near Gboko, Nigeria. The study revealed that the mean compressive strength of the hollow sandcrete blocks was 1.26N/mm² for blocks moulded from river sand from River Benue at Makurdi while the highest mean compressive strength of 1.97N/mm² was recorded at 28 days for blocks made from quarry dust only. The values obtained from a mixture of river sand and stone dust varied between 1.40N/mm² to 1.72N/mm² for mix ratios 1:1 to 1:4. In this study, the cement to sand mix ratio used was not stated. Also the highest compressive strength of N.97 N/mm² recorded did not meet the mimimum standard. They were just merely comparing this result with that of commercial blocks which were substandard.

Chindaprasirt et al. (2009) conducted a study on influence of fineness of rice husk ash and additives on the properties of light-weight aggregate. The objective of their study was to produce light weight aggregate (LWA) from rice husk ash (RHA). The rice husk ash was obtained from biomass power plant in Thailand with specific gravity in the range 2.0 to 2.3. The chemical composition of the RHA was as shown in Table 2.1

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CHAPTER THREE 

MATERIALS, METHODS AND RESULTS

Preamble

In Nigeria and most particularly in Kaduna State, most sandcrete blocks produced are of two types. They are the 6” and 9” hollow blocks. Their standard sizes are 450 x 150 x 225 millimetres and 450 x 225 x 225 millimetres respectively. They are produced by using hand mould or vibrating machine. Both hand moulded and machine vibrated blocks were produced with control mix and quality materials. Thus the 6” and 9” hollow blocks were produced and tested.

Materials

The materials used for the production of the sandcrete hollow blocks were water, sand and cement only. The concrete was produced using water, sand, gravel and cement. The water used was public water supply from tap while the sand was obtained from River Kaduna at Rafin Guza in Kaduna. The gravel was purchased from the market in Kaduna. Seven brands of ordinary Portland cement labeled A, B, C, D, E, F and G were used. The markets in Nigeria where the cements were purchased have been presented in chapter one, page 12, Table 1.0.

CHAPTER FOUR

 ANALYSIS AND DISCUSSION OF RESULTS

  Preamble

The test results presented in chapter three were analysed and discussed to arrive at a reasonable conclusion. These are presented below.

Chemical Analysis of the Water

The test results conducted on the public water supply (portable water) used for block   moulding in the block industry are shown on chapter three, page 75, Table 3.1.

According to BS EN 1008: 2009, as a general rule, water of chemical composition acceptable for drinking is adequate for making sandcrete hollow blocks or concrete. The chloride content of the water was found to be 99.40 mg/l. The standard chloride content allowed for concrete is a maximum of 1000mg/l. Thus the chloride content was found to be within the allowable limit.

The sulphate content of the water was 105.54mg/l while the maximum allowable value is 1000mg/l for concrete work. Thus the sulphate content was only 10.5% of the maximum allowable and this is satisfactory for block.

 

CHAPTER FIVE 

CONCLUSION AND RECOMMENDATION

Findings

1. Thepublic water supply had pH, Chloride and sulphate contents of 25, 99.4mg/l and105.54mg/l respectively. The sand from River Kaduna at Rafin Guza had silt and clay, organic contents of 3.49% and0.35% respectively and its grading curve fell in zone 2. The gravel had an aggregate crushing value, soundness and sulphate contents of 27.90%, 1.2% and 0.08% respectively.
2. The Cement brand A (a locally produced cement) had initial and final settingtimes of 142 and 310 minutes respectively. Its mortar cube strengths at 2-days and 28-days were 17.23 and 47.75N/mm² Its C₃S, C₂S, C₃A and C₄AF contents were 33, 38.39, 12.52 and 6.08% respectively.
3. The Cement brand B had initial and final setting times of 134 and 324 minutes respectively. Its mortar cube strengths at 2-days and 28-days were 25.64 and 55.30N/m
4. m² respectively. Its C₃S, C₂S, C₃A and C₄AF contents were 46.97, 16.43, 5.99 and 10.49% respectively.The Cement brand C had initial and final setting times of 139 and 321 minutes respectively. Its mortar cube strengths at 2-days and 28-days were 18.73 and 49.33N/mm² respectively. Its C₃S, C₂S, C₃A and C₄AF contents were 30.41, 37.46, 12.52 and 6.08% respectively.
5. The Cement brand D had initial and final setting times of 134 and 346 minutes respectively. Its mortar cube strengths at 2-days and 28-days were 16.32 and 47.07N/mm² respectively. Its C₃S, C₂S, C₃A and C₄AF contents were 68.99, 5.66, 6.38 and 7.60% respectively.
6. he Cement brand E had initial and final setting times of 141 and 322 minutes respectively. Its mortar cube strengths at 2-days and 28-days were 18.79 and 49.86N/mm² respectively. Its C₃S, C₂S, C₃A and C₄AF contents were 51.77, 24.17, 1.58 and 6.69% respectively.
7. The Cement brand E had initial and final setting times of 147 and 323 minutes respectively. Its mortar cube strengths at 2-days and 28-days were 16.36 and 45.05N/mm² respectively. Its C₃S, C₂S, C₃A and C₄AF contents were 34.25, 28.84, 17.82 and 6.08% respectively.
8. The Cement brand E had initial and final setting times of 145 and 381 minutes respectively. Its mortar cube strengths at 2-days and 28-days were 14.07 and 47.09N/mm² respectively. Its C₃S, C₂S, C₃A and C₄AF contents were 6.34, 49.78, 0.02 and 6.69% respectively.
9. The optimum water to cement ratio to be used in production of sandcrete hollowblock is 0.45 as it recorded the maximum strength at the mix ratios 1:4 to 1:12
10. The strength of the sandcrete hollow blocks increased parabolically with curingage up to 28 days for brands A to G. The 28-day dry strengths of the SHB were 24, 5.83, 4.62, 3.75, 5.38, 3.45 and 4.21N/mm² for A to G respectively. The density of the blocks increased with curing age up to maximum at 14 days after which it decreased with age up to 28 days.

3. Tobalance the economy and satisfy the minimum standard (BS EN 771-1: 2006) strength   of 2.9N/mm², the cement to sand mix ratio should be in the range 1:6 to 1:8 at a minimum curing age of seven
4. Strength development of SHB cured in the dry state by spraying with water for28-days and then soaked in water revealed that there was a sharp drop in the compressive strength after one day soaking period after which the strengths rose with period of  The sharp drop in strength was attributed to the disjoining pressure of the water which weakened sharply the interlocking bonds between the cement hydration products crystals and the sand particles. This was observed for blocks produced from the seven cement brands and mix ratio range of 1:4 to 1:12.The minimum soaked strengths of the blocks produced from cement brands A, B, C, D, E, F and G were 0.91, 0.98, 1.19, 1.01, 0.84, 1.06 and 0.90N/mm² respectively at mix ratio 1:6.
5. The average water absorption of the SHB were 5.61, 5.00, 7.32, 4.69, 4.92, 4.80and 5.00% for sandcrete hollow blocks produced from cement brands A, B, C, D, E, F and G respectively which are lower than 6% Except that of C-blocks.
6. The characteristic strengths of the concretes produced from cement brands A, B,C, D, E, F and G were 29.5, 31.81, 31.80, 29.74, 28.78, 29.24 and 27.90N/mm²  The characteristic strength of concretes produced from cement brands B and C were above 30N/mm² specified in BS EN 206:2000 while those from the local cement brands A, D, F and G were within the acceptable limit of 27N/mm². The average 28-day densities of the concretes produced from cement brands A to G were 2450, 2413, 2402, 2415, 2424, 2424 and 2402kg/m³ respectively.

Conclusions

Based on the above findings, the following conclusions were drawn:

1. The tap water, the sand from River Kaduna at Rafin Guza and gravel weresuitable materials for concrete and sandcrete hollow block production.
2. The locally produced cement brands A, D, F, and G did not meet the EN 197 1:2000 standard specifications for both tricalcium and dicalcium silicates while the imported cement brands B and E met the standard.
3. The optimum water to cement ratio to be used in production of sandcrete hollowblock is 45.
4. Sandcrete hollow blocks were produced from cement brands A to G and their28-day dry compressive strengths met the British standard (BS EN 771-3: 2006).
5. Economical standard blocks could be produced at mix ratio range of 1:6 to 1:8and curing age of seven
6. Sandcrete hollow blocks cured for 28 days in the dry state and then immersed inwater suffered a sharp drop in strength after one day immersion. This suggested that sandcrete hollow block wall inundated with flood water suffers the same sharp drop in strength after one day inundation no matter the initial
7. The averge water absorption of the sandcrete hollow blocks produced fromcement brands A to G was 5.33% and this is less than 6%.
8. The average compressive strengths of the concrete produced from the cement brands A, D, F and G (locally produced cement brands) were lower than 30N/mm² but within acceptable range of 27 – 30N/mm² while those of imported cement brands B and E were above 30N/mm². Lack of adherence to standard specifications of the two silicate compounds was responsible for the low concrete strengths of the local cement brands.

Recommendations

1. As floodis rampant in many parts of Nigeria, a new design approach should be developed for load bearing sandcrete block walls taking into consideration the problem of sharp drop in strength when inundated by flood
2. Assessment of wet strength of sandcrete hollow block should be based on oneday immersion instead of the current 28-day
3. Further studies are required in developing mathematic models for the estimationof the minimum soaked strengths of the sandcrete hollow block.
4. Other construction materials such as brick, concrete, should be studied undersimilar conditions to sandcrete hollow
5. The local cement industriesof cement brands A, D, F and G should improve on the quality control of the two silicate

REFERENCES

• Abdullahi, M. (2005). Compressive Strength of Sandcrete Blocks in Bosso and Shiroro Area of Minna, Nigeria, Auchi Journal of Technology, Vol. 9(2), pp. 126-132.
• Abieyuwa, O. (1998). Investigation on the strength of sandcrete blocks produced and marketed in Ekpoma town, Edo State. (Unpublished Project), Civil Engineering Department, University of Benin, Nigeria.
• Abrams,D. P,R and Uz arski, J.(1996), Out of Plane strength of reinforced masonry infill panels, Earthquake Spectra, Journal of Earthquake Engineering, Research
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• Adedeji, A. A., and Ejeh, S.P. (1998). Strength characteristic of dry-jointed Block assemblies under vertical loads, Nigerian Journal of Construction Technology and Management Vol. 1, No. 1, pp. 102-108.Department of Building, University of Jos, Nigeria.
• Adewole, K. K., Ajagbe, W. O. and Arasi, I. A. (2015), Determination of appropriate mix ratios for concrete grades using Nigerian Portland-Limestone grades 32.5 and 42.5. Leonardo Electronic Journal of Practices and Technologies, issue 26, pp. 79 – 88.
• Afolayan, J.O., Arum, C., and Daramola, C.M. (2008). Characterization of the compressive strength of sandcrete blocks in Ondo State, Nigeria, Journal of Civil Engineering Research and Practice, vol.5, No.1.
• Agbede, I. O., and Joel, M. (2004). Suitability of quarry dust as partial replacement of sand in hollow block production. Nigerian Journal of Research and Development, Vol. 3, No. 4, pp. 33-37.
• Agbede,I.O., and Joel, M. (2008). Use of cement sand admixture in laterite brick production for low cost housing, Leonardo Electronic Journal of Practices and Technologies, Issue 12,pp. 163-174.

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