Mechanical Fracture Properties of Alkali-Activated Slag with Graphite Filler

Alkali-activated slag is a building material considered as alternative to ordinary Portland cement based materials. Addition of graphite powder increases its electric conductivity, hence, introducing new functionality to building materials such as self-sensing and self-heating properties. In this study, the effect of graphite filler on the mechanical fracture properties of alkali-activated slag composite is investigated. Graphite powder was added in the amount of 5, 10 and 15% with respect to the slag mass. Modulus of elasticity, fracture toughness and fracture energy were determined using standard three-point bending test on prismatic specimens with central edge notch. The course of fracture tests was also monitored by acoustic emission (AE) method. Compressive strength was determined on the fragments remaining after the fracture tests. Results showed that addition of graphite caused a decrease in compressive strength, fracture toughness and fracture energy but modulus of elasticity increased. Addition of graphite also caused a decrease in AE events and increase in amplitude of signals. This implies that mortars with graphite filler is more brittle than the reference mortar, and lower number of much larger cracks is formed during the fracture test.