Action mechanism of rice husk ash and the effect on main performances of cement-based materials: A review

Rice husk is a kind of agricultural waste with huge yield and wide distribution, which can get rice husk ash (RHA) containing a large amount of amorphous silica and porous structure by combusting under certain conditions. As a supplementary cementitious material (SCM), the RHA has high pozzolanic activity and internal curing characteristic. It was reported that RHA can significantly improve various performances of cement-based materials. This paper presents an overview of the physicochemical properties of RHA and its effects on the main performances of cementitious materials, e.g. cement hydration, strength, chloride penetration, sulfate resistance, carbonation and shrinkage. The hydration mechanism and the universal optimal content range of RHA are further discussed in depth. The main hydration modes of RHA particles are: (i) the dissolution reaction of micro-particles and (ii) the diffusion reaction of macro-particles. The main contribution of small-size particles to the cementitious system is the chemical effect of RHA, and the main function of large-size particles presents as the internal curing effect of RHA. Based on the summary and extraction of the macro-properties, it is considered that the preferred content range of RHA is 10-20%. Through a deeper and clearer understanding of the action mechanism of RHA in cementitious materials, it can provide ideas for further studies related to RHA and promote the green and sustainable application of RHA in cement-based materials. (c) 2021 Elsevier Ltd. All rights reserved.

Automated summary

Rice husk ash (RHA) is a byproduct of agricultural waste combustion, containing high pozzolanic activity and internal curing characteristics that can significantly improve the properties of cement-based materials. The effects of RHA on various performances of cementitious materials have been investigated, with a focus on its hydration mechanism and optimal content range. Through further research, it is believed that RHA can contribute to the green and sustainable application of cement-based materials.