Abstract:
River sand and cement are the major components of building materials used in the making of sandcrete blocks. The extraction of these materials have caused a negative impact on the environment and mining sources have been depleted. The cost of construction has also increased significantly causing a shortage of decent housing. This research investigates the structural performance of sandcrete blocks produced using lateritic sand and marine sand as complete replacement of river sand, and sugarcane bagasse ash as partial replacement of cement. The performance of dry stacked sandcrete blocks and wall models made from optimum mixture of these materials are also assessed. Sandcrete hollow blocks (450 × 225 × 225 mm) were made by blending varying contents of marine sand and lateritic sand using the nominal mix ratio of 1:6 (cement: sand). A total of 90 sandcrete blocks were casted and the compressive strengths of the blocks determined at 7, 14 and 28 days. The 28 day compressive strength of mixes containing 0%, 10%, 20%, 30%, 40%, 50%, 60%, 80% and 100% marine sand were 4.47 N/mm2, 5.10 N/mm2, 5.25 N/mm2, 5.33 N/mm2, 5.20 N/mm2, 4.63 N/mm2, 4.58 N/mm2, 3.88 N/mm2 and 3.76 N/mm2 respectively. The 28 days strength at all percentage replacement exceeded the minimum strength value of 3.45 N/mm2 specified by NIS 87 (2000). Sandcrete blocks made with 30 to 70 percent marine-lateritic sand blending produced the highest compressive strength. At 30% replacement level the smaller sized particles of marine sand fills the spaces between the bigger lateritic ones, this creates a more compact sandcrete block and increases the strength. Using the 30:70 ratio, 90 sandcrete blocks were casted by replacing cement with Sugar Bagasse Ash (SBA) in the ratio of 0%, 5%, 10%, 15%, 20% and 25% by weight of cement. The 28 day compressive strength were 5.33 N/mm2, 5.29 N/mm2, 5.18 N/mm2, 4.71 N/mm2, 3.42 N/mm2 and 3.08 N/mm2 for 0%, 5%, 10%, 15%, 20% and 25% replacement respectively. Up to 15% replacement levels met the minimum compressive strength recommended in standards. The results for water absorption and density were also within the acceptable limits of 12% and 1500 kg/m3 respectively. An optimal mixture for production of non-conventional sandcrete block was established as 15% SBA replacement of cement with a 30 to 70 percent marine to lateritic sand blended mixture i.e. the optimum of Cement/SBA: Marine/lateritic sand: water ratio was 1(0.85/0.15):2(0.30/0.70):0.5.This optimum mix was adopted in the casting of two types of dry stack hollow sandcrete blocks (DHSBs) which were identified as T-DHSBs and R-DHSBs .The T and R prefixes represents the Trapezoidal and Round shapes of the interlocking joints respectively. The 28 compressive strength of T-DHSBs and R-DHSBs were found to be 3.58 Mpa and 4.04 Mpa respectively. The water absorption values for T-DHSBs and R-DHSBs were 8.98% and 9.39% respectively. The loss of weight due to abrasion for 28 days sandcrete blocks were 0.056% and 0.051% for T-DHSB and R-DHSBs respectively. The strength and durability of the blocks met the specifications in NIS 87 (2000) and BS 5628-1 (2005) respectively. The performance of wall models made from T-DHSBs and R-DHSBs under The axial compression and shear was determined. Shear performance of DHSBs masonry walls were determined by triplet shear test set-up modified to establish shear strength of the interlocking features of the DHSBs masonry. The compressive strength for T-DHSBs and of R-DHSBs wall models were established to be 1.28 N/mm2 and 1.41 N/mm2 respectively. The ultimate load of T-DHSBs wall model under shear were
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24.8, 27.4 and 30.1 kN and that of R-DHSBs wall were 6.47, 7.90 and 9.25 kN for precompression
stresses of 0.2, 0.6 and 1.0 Mpa respectively. The cohesion ( o ) were
0.73 and 0.42 for T-DHSBs and R-DHSBs respectively whereas friction coefficient
value were 0.21 and 0.25 for T-DHSBs and R-DHSBs specimens respectively. The
general failure mode of the two DHSBs walls model under compression stress were
by formation of tensile cracks parallel to the axis of loading at approximately center
of the block units. In this research, 15% SBA replacing cement by weight in a 30:70
marine to lateritic sand matrix is established as the optimal mixture required in the
manufacture of non-conventional hollow sandcrete blocks. These optimal mixture of
SBA and blended lateritic and marine sand produces dry stacked hollow sandcrete
blocks that meets the strength and durability requirements for hollow sandcrete block.
Owing to its better shear strength properties and less volume of materials used in its
production, the study recommends T-DHSBs in preference to R-DHSBs for use as an
alternative to the existing load bearing hollow sandcrete blocks. The use of mortar-less
blocks made from non-conventional materials reduces the over reliance of river sand
and cement in blocks production, reduces environmental effects by spreading the
burden of extraction on different sources, and at same time minimizes the cost of wall
construction.