Characterization of self-compacting concrete incorporating fly ash and rice husk ash at fresh and hardened state

Caracterização de concreto autoadensável no estado fresco e endurecido incorporando cinza volante e cinza de casca de arroz

Abstract

This work studies the feasibility of using rice husk ash (RHA) as a partial replacement for Brazilian Portland cement in producing self-compacting concrete for structural purposes. The RHA used is produced under controlled burning conditions in a fluidized bed. The concrete mix design is presented in detail to show how to find the best combination of the regional material to produce self-compacting concretes with good fresh and hardened characteristics. Concretes produced in the proportions of 5%, 10%, 15%, 20%, and 25% of replacement of cement by RHA have been studied, with the addition of 15% of fly ash and w/b of 0.45. In the fresh state, flowability, viscosity, and passing ability tests have been conducted. Additionally, mechanical tests were performed to assess the axial compressive strength and splitting tensile strength in the hardened state. The fresh state properties are influenced by the RHA content, reducing its flowability and passing ability with the increase of this material. The hardened state properties of the mixtures with RHA have shown increased resistance when compared to plain concrete. The mixture with 15% replacement had the best results. Concretes of 20% and 25% had their strength increased to a lesser degree. However, they remain a good option when increasing the superplasticizer quantity to improve the fluid state's properties.

Keywords:
self-compacting concrete; rice husk ash; fly ash; fresh properties; hardened properties; concrete mix design