Exploratory Investigation into a Chemically Activated Fly Ash Binder for Mortars

Abstract

This paper explores the beneficial use of low-reactivity coal fly ashes as cementitious binder in mortars without heat activation. A uniform design scheme was employed for the statistical design of experiments. Predictive models were developed to quantify the influence of mix design parameters on the compressive strength of fly ash mortars and enable the optimization of mortar designs. The slump flow and the 28-day surface resistivity of fly ash mortars were also studied. The first group of mortar specimens was fabricated using Class C and Class F coal fly ashes and admixtures intended to improve the strength and durability of hardened mortar. In the absence of chemical activation, these fly ash mortars exhibited a relatively low 28-day compressive strength in the range of 2.9–20.5 MPa. The second group of mortar specimens was fabricated using the same Class C fly ash along with the following chemical activators: sodium silicate, quicklime, calcium chloride, and sodium sulfate. Admixing chemical activators into fly ash mortars led to a noticeable improvement in their mechanical properties, with a 28-day compressive strength in the range of 16.8–33.6 MPa. Microscopic examination was conducted to shed light on the hydration behavior of fly ash particles using an electron probe microanalyzer. The results revealed the active role of chemical activators in promoting the dissolution of fly ash particles and the formation of hydration products.