STRUCTURAL CHARACTERISATION OF CONCRETE AND SANDCRETE HOLLOW BLOCK PRODUCED FROM SELECTED CEMENT BRANDS IN NIGERIA

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Department of Engineering

ABSTRACT
The current wave of collapse of building structures all over the world including Nigeria necessitates the need to carryout research on the properties of the construction materials. Concrete and sandcrete hollow blocks are major construction materials used in the building industry. The objective of this study is to determine the properties of sandcrete hollow blocks (SHB) and concretes produced from seven selected brands of ordinary Portland cement labeled A to G. The cement brands were purchased from local markets in Nigeria. The water, sand, gravel and the cement brands were characterized and results compared with the British standards (BS EN 1008:2002 for water, BS EN 12620 for sand and gravel, and BS EN 197-1: 2011for cement) in order to determine their suitability for production of concrete and SHB. A total of 2774 SHB and 105 concrete cubes produced from the above materials were investigated. Tests were conducted on the SHB to determine: the optimum water to cement ratio, dry and wet strengths and density development and water absorption. The strength and density development tests were also carried out on the concrete cubes. Results were compared with British Standards. The average tricalcium silicate contents by mass were 33, 46.97, 30.41, 68.99, 51.77, 34.25 and 6.34% respectively for cement brands A to G. Those of dicalcium silicate contents were 38.39%, 16.43%, 37.46%, 5.66%, 24.17%, 28.84%, and 49.78%. The average 28-day dry compressive strengths of the SHB produced from cement brands A to G were 4.24, 5.83, 4.62, 3.75, 5.38, 3.45 and 4.21 N/mm2 respectively. SHB cured for 28 days in the dry state and then immersed in water, were found to suffer a sharp drop in compressive strength after one day soaking before rising in strength again. This was observed for SHB produced from the seven cement brands, A to G and mix ratio range of 1:6 to 1:12. The characteristic strengths of the concretes produced from cement brands A to G were 29.5, 31.81, 31.80, 29.74, 28.78, 29.24 and 27.90 N/mm2 respectively. The local cement brands A, D, F and G did not meet the standard specifications of tricalcium silicate content of 46% to 67% and dicalcium silicate content of 8% to 31% (EN 197 -1: 2000). The optimum water to cement ratio of SHB was 0.45. The compressive strengths of the SHB produced from cement brands A to G were higher than the minimum standard strength of 2.9N/mm2 (BS EN 771:2006). It was inferred from the study that wall constructed of SHB experiences a sharp drop in strength after one day inundation by flood. Concretes produced from the local cement brands A, D, F and G had strengths lower than the minimum standard strength of 30N/mm2 (BS EN 206: 2000) due to non-compliance of the cements silicate compounds to the standard. Concretes produced from imported cement brands B and C met the standard. It was suggested that SHB should be subjected to additional standard test after one day immersion in water based on the above established phenomenon.