Synergistic effects of low-cost graphene and coal fly ash on the strength–porosity performance of cellular lightweight concrete

Abstract

Cellular lightweight concrete (CLC) is attractive for envelope and infill applications due to its low density and low thermal and sound insulation. However, its high pore volume often reduces compressive strength and limits wider application. Graphene-based additives and fly ash have been widely studied in cementitious composites. However, their combined effect in low-density CLC remains insufficiently understood, particularly regarding the strength-porosity balance, cellular pore stability, and microstructural mechanism. This study investigated the synergistic effect of low-cost graphene produced by turbulence-assisted shear exfoliation (TASE) and coal fly ash on CLC with a target density of approximately 1.1 g·cm⁻³. TASE graphene was selected because its aqueous shear-exfoliation route offered lower processing complexity, better scalability, and stronger cost potential than many commercial or oxidized graphene derivatives, making it more suitable for large-volume cementitious applications. CLC mixtures containing 0–15 wt.% graphene and 0 or 5 wt.% fly ash were cast and cured for 14 and 28 days. Compressive strength, porosity, and microstructure (SEM/TEM) were evaluated. Among the investigated mixtures, the mixture containing 10 wt.% graphene and 5 wt.% fly ash produced the best strength–porosity performance, achieving the highest 28-day compressive strength of 1.86 ± 0.20 MPa and the lowest porosity of 23.70%. Compared with the graphene-free mixture at the same fly ash level, this composition increased strength by 64.60% and reduced porosity by 14.84%. SEM/TEM observations supported a dosage-dependent mechanism involving graphene-assisted nucleation, fly ash-assisted pozzolanic densification, pore-wall refinement, and reduced reinforcement efficiency at excessive graphene loading. These findings supported the practical design of graphene–fly ash modified CLC material systems.