Evaluating The Impact of Partially Replacing Cement with Rice Husk Ash and Metakaolin on the Rheological Behavior and Mechanical Strength of Self-Compacting Concrete

Although self-compacting concrete (SCC) is a unique concrete that can spread and fill formwork without the need for mechanical vibration, researchers are now using supplementary cementitious materials (SCMs) to partially replace cement in SCC production because of the high cement content required to produce SCC. Based on the aforementioned, the rheological and strength properties of SCC admixed with Rice Husk Ash (RHA) and Metakaolin (MK) at 0.4, 0.5, and 0.6 water-cement (W/C) ratios was investigated. The materials used in the study are cement, water, fine aggregate, coarse aggregate, Metakaolin (MK), Rice Husk Ash (RHA), and superplasticizer. Mechanical tests were conducted on the cement, fine and coarse aggregate, RHA and MK. SCC was produced by partially replacing cement with RHA and MK separately and in blend at 2.5, 5, 7.5, 10, 12.5, and 15 %, yielding a total of four hundred and twenty (420) concrete cubes, and all cubes were cured for 3, 7, 14, 28, 56, 90, and 120 days before crushing. The Marsh cone test was adopted to determine the optimum superplasticizer (SP) content, while the rheological tests conducted on the fresh SCC are the slump test, V-funnel test, L- Box test, and J-Ring test, whereas the mechanical tests conducted on the hardened SCC are the compressive, flexural, and split tensile strength test. Results from the findings showed that the rheological properties of SCC admixed with RHA and MK separately and in blend at 0.9 % superplasticizer content, exhibits adequate workability and flowability at 0.4, 0.5, and 0.6 water-cement ratios. Also, at 0.4, 0.5, and 0.6 W/C ratios, the maximum compressive strength of SCC was achieved at 5- 10 % for RHA, and 5-15 % for MK, and was achieved at 10 % when MK and RHA was used in blend. More also, the maximum 28 days split tensile strength was achieved at 7.5-10 % for RHA, and 10 % for MK, and was achieved at 10 % when MK and RHA blend replaced cement. Furthermore, the maximum 28 days flexural strength was achieved at 12.5-15 % for RHA, and 15 % for MK, and was achieved at 12.5 % when MK and RHA blend replaced cement. Hence it was concluded that the workable rheological, and maximum strength properties of SCC can be achieved when blend of RHA and MK replaces cement between 10 – 12.5 %.