Suitability of fly ash and Its derivatives as a raw material in the manufacture of cement-based roofing materials

Abstract

In this research work, fly ash produced in Norochcholai power plant, Puttalam, Sri Lanka had been characterized and investigated to be used in manufacture of cement based roofing materials. The fly ash sample has a non-homogenized particle size distribution ranging from 200 µm to Nano level and a major fraction belonged to particle size range between 150µm-63µm. The specific gravity and fineness values were 2.06 and 299 m2/kg respectively. The main chemical constituent of fly ash was SiO2 with a 79% by weight. Scanning electron microscopy (SEM) analysis revealed that fly ash samples consist of solid spheres, hollow spheres known as cenospheres, and irregular unburnt carbon. These cenospheres are hollow and have low particle densities relative to water. Cenospheres were extracted by the sink –float method using water and acetone as mediums. The SEM image of extracted samples were completely embedded with spherical particles. Further, SEM images were analyzed for the fly ash fractions passed through the sieve sizes of 53 µm and 45µm. It was observed that the concentration of spherical particles was higher in 45µm particle fraction when compared to the 53 µm fraction. Fly ash was added to the mix design for casting flat tiles in three different proportions; such as fly ash as it is, fly ash below 45 µm size and extracted cenospheres. They were used to replace Portland cement in the mix design by 0%, 10%, 20%, and 30% by weight. Modulus of Rupture (MOR), density and thermal conductivity were measured after 28 days of curing at 27°C and relative humidity of 80%. Considerable reduction in density and thermal conductivity were observed in cenosphere incorporated cast samples and the MOR was in the acceptable level for a roofing material.