Strength and physico-chemical characteristics of fly ash-bottom ash mixture

Abstract

The quantity of coal combustion products, particularly fly ash (FA) and bottom ash (BA), has been increasing from coal power plants around the world. The major problem of a coal combustion-based power plant is that it produces huge quantities of solid waste. Recently, there have been efforts to use FA and BA together as a mixture in construction works. This paper investigates morphology and chemical and strength characteristics of an FA-BA mixture for various curing periods. Scanning electron microscopy (SEM), X-ray fluorescence (XRF), and consolidated undrained triaxial tests were used to determine the physico-chemical characteristics of the mixture. Based on SEM results, it was found that, with an increasing ratio of BA to FA, the number of irregular particles in the mixture increased. The results of XRF indicated noticeable changes in the surface composition of both FA and BA particles after mixing. The physico-chemical test results indicate the formation of a new gel form product in the mixture, which has been identified as calcium silicate hydrate (C-S-H). From an engineering point of view, the results indicated that the value of modulus of elasticity decreases with increasing BA content, from 30 to 70 %, in the ash mixture. However, the increase in BA from 30 to 70 % did not have any significant effect on the shear strength of the FA-BA mixture.