Mechanism of macro- and microscopic performance of cement mortars influenced by municipal solid waste incineration bottom ash as sand substitution

Abstract

With growing construction work, natural sand has turned out an endangered resource for building materials, leading to a research hotspot for alternative materials as natural sand substitutes. In this paper, we investigated the effect of municipal solid waste incineration (MSWI) bottom ash replacing natural sand on macro- and microscopic performance of cement-based materials after wet treatment. The viability of bottom ash in the mortar was explored instead of conventional fine aggregates. The fluidity, flexural strength, and compressive strength of different water-cement ratios in the mortar with substitution of 0%, 25%, 50%, and 75% were investigated by using the macro-experimental method. We examined the components and micro-morphology of hydration products by using thermogravimetry–differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The results demonstrated that a large substitution amount slightly effects the strength of cement mortar, while the early strength became stronger with the increase of the substitution rate. Notably, MSWI bottom ash showed a certain pozzolanic activity, which reduces the formation of Ca(OH)2 and can improve the early strength of the mortar. Additionally, the leaching concentrations of heavy metals (Cu, Zn, Pb, Cr, etc) in the mortars containing bottom ash were all less than the identification value of solid waste leaching toxicity. The carried out research confirmed that MSWI bottom ash can successfully replace conventional sand as building materials. The proposed work enables the reuse of MSWI bottom ash and also provides a reliable and effective method for solving the shortage of conventional aggregate resources.