Incorporation of high loss-on-ignition fly ash into high-strength mortar: Influence on short-term engineering properties

Abstract

The re-utilization of fly ash (FA), a primary by-product of thermal power plants, in producing various types of sustainable construction materials has been studied by many researchers. The quality of FA varies depending on either the characteristics of coal or the combustion techniques. Most previous studies used FA with a low loss-on-ignition (LOI), while the use of FA with a high LOI in the production of construction materials is still limited. Finding ways to reusing of locally available FA in sustainable construction materials is crucial. Therefore, this study aims to investigate the effect of high LOI FA content on the short-term engineering properties of high-strength mortars (as a modified concept of reactive powder concrete) in terms of workability, fresh unit weight, compressive and flexural strengths, drying shrinkage, and thermal conductivity. The mortar mixtures were designed with a constant water-to-binder ratio of 0.24 and the 0–60% high LOI FA was used to replace cement (step increment of 15% by weight). Test results found that the substitution of cement with high LOI FA significantly affected the engineering properties of high-strength mortars. Increasing the high LOI FA content improved the workability while reducing fresh unit weight, mechanical strength, drying shrinkage, and thermal conductivity of high-strength mortars. Although the short-term properties of mortars were negatively affected by the incorporation of high LOI FA, the mortar samples containing 60% high LOI FA registered relatively high 28-day compressive and flexural strengths of about 34 and 6 MPa, respectively. In another aspect, using high LOI FA in the production of construction materials is beneficial in reducing the use of cement as well as limiting environmental pollution due to the disposal of this FA type, contributing to a greener environment toward a sustainable development goal.