Workability and compressive strength of self-compacting concrete containing rice husk ash from controlled and uncontrolled burning condition

Rice husk as an agricultural waste material has a large amount of amorphous silica, adding its ash to concrete increases the pozzolanic property of concrete and consequently increases the strength and durability of reinforced concrete structures. The quality and method of rice husk ash preparation greatly influence the final properties of the concrete prepared from it. In this article, rice husk ash has been burned in controlled, semi-controlled, and uncontrolled conditions in terms of temperature conditions, and the resulting ash has been used as a 10% substitute for cement in self-compacting concrete. Properties related to concrete performance and compressive strength of samples containing rice husk ash at different ages have been evaluated. The properties of rice husk ash powder have been determined through XRF, FESEM, and the determination of grain size range. The results show that in all cases the sum of SiO2, Al2O3 and Fe2O3 is higher than 70%; which indicates being within the standard range of pozzolanic cement materials. In the semi-controlled state, the amorphous silica is more than 8%. Based on the results, adding rice husk ash increases the long-term compressive strength (90 days) and decreases the short-term compressive strength of self-compacting concrete. The increase in long-term strength for samples with ash produced in controlled conditions was more and up to 18%. The reduction of short-term compressive strength for samples with uncontrolled ash has been obtained up to 25%.