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 intercalating 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.