A facile approach to disperse metakaolin for promoting compressive strength of cement composites

Abstract

Metakaolin (MK), a highly reactive supplementary cementitious material, is extensively employed in cement composites to improve their compressive strength. Nevertheless, MK suffers from extremely poor dispersion, resulting in agglomerating in the cement-based materials, thus failing to exhibit its positive effects fully. To overcome this drawback, for the first time, this work elaborately developed a facile graphene quantum dots (GQDs)-assisted ultrasonic dispersion approach to improve the dispersity of MK effectively. Furthermore, it investigated effect of as-obtained MK (GMK) on compressive strength of cement composites. More specifically, GMK owned a smaller size and a larger specific surface area and presented a higher dispersity than UMK (namely, MK was identically treated by ultrasonic dispersion only without GQDs) and original MK. And in light of the characteristics of three types of MKs, the dispersing mechanism of MK caused by GQDs-assisted ultrasonic treatment was rationally ascribed to intercalation, exfoliation and surfactant effects of GQDs. Crucially, GMK purely by the incorporation of 1.0 wt.% (by weight of cement) demonstrated a significant enhancement of 31.03% for the 28-day compressive strength of mortar; While UMK had little influence on the compressive strength of mortar under the identical conditions. And based on the comprehensive analyses of hydration heat, phase composition and microstructure of different cement pastes, the most significant positive effect of highly dispersed GMK purely by a dosage of 1.0 wt.% on the compressive strength of cement composites was accredited to the fact that GMK was able to accelerate hydration process, boost the formation of C−(A)−S−H and refine the microstructure. This study firstly provided a facile, efficient and low-cost method to fabricate high-dispersity GMK, and verified its remarkable promotion effect on compressive strength of cement composites. These observations would improve the benefits and reduce the cost of MK-like materials applied to cement-based materials.