Investigating the synergistic effect of graphene nanoplatelets and fly ash on the mechanical properties and microstructure of calcium aluminate cement composites

Nanomaterials like graphene nanoplatelets (GNP) have been extensively applied in various fields as reinforcing materials offering excellent mechanical properties. However, for calcium aluminate cement (CAC) composites, the investigation of the GNP reinforcing effect is lacking. The synergistic effects of GNP and fly ash (FA) in CAC composites were evaluated in this study. The GNP was initially dispersed in mixing water using a dispersant combined with ultrasonication. The CAC composites with different GNP contents were prepared and their mechanical performance was investigated. In addition, partial replacement of CAC with FA was investigated for increasing sustainability and material cost of GNP-CAC composites. Their fresh properties, mechanical properties, and microstructural performance were analyzed using different techniques involving flowability, bulk density, volume of permeable void, water absorption, compressive strength, splitting tensile strength, flexural strength, nitrogen adsorption, TGA, and SEM-EDS tests. Using FA and GNP in CAC composites offers a positive impact by significantly increasing their strengths. Optimized mix was achieved by replacing 20% of FA and adding 0.3% of GNP in CAC composites. Results revealed that the 20% FA replacement of cement with 0.3% GNP addition remarkably increased the compressive, splitting tensile and flexural strengths at 28 days by about 57.2%, 35.5%, and 21.7%, respectively. The results suggest that using FA and GNP contributes to synergistic effects to promote the formation of silica tetrahedron in calcium aluminate silicate hydrate (CASH) gel, to refine pore characteristics, and to reduce conversion effects of metastable phases of CAC such that it can ultimately produce a green rapid-set high-performance concrete system. © 2023 Elsevier Ltd