Investigating the compressive strength and microstructural analysis of mortar containing synthesized graphene and natural pozzolan in the face of alkali-silica reactions

Abstract

The high cost and agglomeration phenomenon of nano-graphene in cement matrix are considered major obstacles to applying graphene in the concrete industry. This research resolves both mentioned issues using synthesized graphene from graphite and surfactant by exfoliation method. On the other hand, the behavior of this material in Alkali–silica reaction (ASR) conditions is still unknown. Therefore, the main objective of this research is to investigate the performance of mortar by incorporating synthesized surfactant-based graphene and two natural pozzolans, pumice and zeolite, to mitigate ASR. First, the compressive strength of the studied mortars was measured in this study. Then, the behavior of the mixtures for 91 days in ASR conditions was assessed by measuring expansion, compressive strength loss, and various microstructure analyses. The results showed that the compressive strength of mortar containing 5 g/l of graphite and 0.56 g/l surfactant increased by 85.62% after 3 days of maturation compared with the surfactant-based mixture without graphite. The amount of expansion reduction in the graphene-based mixture with 15% replacement of cement by pumice after 28 and 91 days in ASR conditions is 215% and 194.2%, respectively, compared with the control mixture. In addition, the compressive strength loss of this mixture was negligible. The microstructure analysis showed that using synthesized graphene in mortars could mitigate ASR by forming a dense boundary structure around aggregates, and reducing OH‾ ion penetration. Furthermore, mixing pumice in the graphene-containing mixture could mitigate the ASR gel by lowering calcium silicates hydrates (C–S–H) dissolution and reducing transformation from tobermorite to polymerized C–S–H phase.