Effect of a novel hybrid TiO2-graphene composite on enhancing mechanical and durability characteristics of alkali-activated slag mortar

A highly dispersed hybrid TiO2-graphene composite was synthesized in-situ and for the first time utilized in alkali-activated slag (AAS) mortars. The effects of the TiO2-graphene composite in different dosages of 0.0, 0.1%, 0.3% and 0.5% on the mechanical and durability properties of AAS mortars were investigated. The results showed that an optimal dosage of the TiO2-graphene composite exists which was 0.03 wt% in this study, leading to about 26.6%, 11.3% and 13.6% increase in compressive strength, flexural strength and flexural-to-compressive strength ratio, respectively. In addition, the capillary sorptivity, chloride penetration depth and diffusion coefficients were significantly reduced via TiO2-graphene additions. Similarly, 0.03 wt% dosage led to the best performance by decreasing these values by upto 32.0%, 66.5%, 68.7% respectively. All these experimental results were due to a densified microstructure of AAS incorporated TiO2-graphene composite, verified by lower porosity, especially at meso-capillary pore levels and also probably due to wrinkled surface of TiO2-graphene nanosheets. It was also noticed that an overdosage of the TiO2-graphene composite would compromise these beneficial effects due in large part to agglomerations. The well-dispersed hybrid TiO2-graphene composite assisted by the in-situ inter-calating method improves the AAS binder in terms of mechanical and durability performances, thus making it more promising in partial replacement of ordinary Portland cement counterparts. (C) 2020 Elsevier Ltd. All rights reserved.