Optimization, synthesis, and properties of foamed graphene reinforced slag/fly ash-based geopolymer composites

Abstract

To obtain hybrid foams with higher porosity and better performance, a novel lightweight foamed slag/fly ash-based graphene/geopolymer composite was prepared using a foaming method with graphene nanoplatelets (GNPs). The synergistic effects of the foaming agent (H2O2) and GNPs content on the phase structure, pore distribution, and mechanical and thermal properties of the obtained foamed graphene/geopolymer composites were investigated. The GNPs were well-dispersed in the final foamed composites. The non-crystalline structure of the foamed composites was maintained with the addition of GNPs. The mean pore size of the foamed samples obtained by adding 1.25 wt% GNPs and 3 wt% H2O2 to the geopolymer was ~340 μm. The total porosity of the samples was 13.1–76.2 %. The total porosity increased as the H2O2 ratio increased and declined with the addition of the GNPs because greater GNPs addition increased the solid content of the slurry, which affected the foaming process of the geopolymer matrix. The compressive strength of the 28-day aged foamed samples increased relative to that of the 7-day samples, attributed to the geopolymerization of the matrix, pull-out, and crack deflection of the GNPs. The thermal conductivity of samples decreased with the H2O2 addition, and achieved the thermal conductivity of 0.191 W/(m·K) with the addition of 1.250 wt% GNPs and 5 wt% H2O2. These samples have potential applications in construction, thermal insulation, etc.