Effect of incorporation of rice husk ash and iron ore tailings on properties of concrete

Abstract

Solid wastes such as rice husks (RH) and iron ore tailings (IOT) are detrimental to the environment. It has been investigated that rice husk ash (RHA) produced by incinerating RH at a suitable temperature could possess pozzolanic activity, and IOT could be applied instead of natural sand in concrete. The purpose of this study is to evaluate the effect of simultaneously incorporating RHA and IOT into concrete. Replaced cement with various proportions of RHA (0%, 5%, 10%, and 15%) and natural sand with different ratios of IOT (0%, 20%, 40%, and 60%). The compressive strength, flexural strength, ratio of compressive strength to flexural strength, and frost resistance of concrete mixed with RHA and IOT (RIC) were analyzed and discussed. The results indicated that RHA and IOT could significantly improve the performance of concrete. The concrete prepared by substituting RHA for 10% cement and IOT for 40% natural sand exhibited the greatest performance improvement. Additionally, microscopic comparisons (SEM, EDS, porosity analysis, and nanoindentation analysis) were carried out between the benchmark group and the RIC group with RHA replacing 10% of cement and IOT replacing 40% of natural sand after 90 days of curing. In comparison, the benchmark group without RHA and IOT was found to have more CaOH2 and pores within, whereas the content of Ca elements and porosity inside the concrete prepared by replacing 10% cement with RHA and 40% natural sand with IOT were substantially reduced. As a result of pozzolanic activity in RHA and part of IOT, the concrete underwent a secondary hydration reaction that produced a large amount of calcium silicate gel, increasing bond strength between the aggregates and effectively filling the internal pores. Moreover, the fine particles of RHA and IOT could also be beneficial to filling, and the rough surface of IOT could facilitate occlusion between aggregates, thereby improving mechanical properties.