Use of Rice Husk Ash Blended Cement to Produce Cement Sand Blocks: Optimal Level of Cement Replacement for Compressive Strength

Abstract

This article primarily investigates the variation in compressive strength, in relation to different levels of replacement of cement with rice husk ash (RHA) when blended cement is used to produced cement sand blocks. The samples of RHA used in this study have been obtained directly from furnaces and were not further incinerated. This study considers two binders-sand ratios (1.3 and 1.6), there water-binder ratios (0.4 ,0.5 and 0.6) in its attempt to determine the optimum level of cement replacement. The study determines that at around five percent level of replacement the compressive strength exceeds that of unblended cement. The compressive strength developed when cement replacement level is 15 percent, is greater than that stipulated in SLS 855: Part 1:1989 (2.5MPa) for cement sand blocks. The study also concludes following: disregarding the level of replacement, the compressive strength steadily decreases when cement replacement levels exceed the limit of five percent; of the three water-binder ratios, 0.5 offers marginally higher compressive strengths than the other two ratios; compressive strength does not vary when cubes cast using RHA samples obtained from three districts are tested; the development in compressive strength when samples are matured beyond 28days till 60 days is only 19 percent. Finally, the study concludes that given all RHA generated in the country can be put in the use for cement replacement, the total saving to the country is approximately Rs. Billion 2.25.