Effect of reduced graphene oxide coated sand on mechanical and electrical properties of cementitious composites

The use of smart cementitious materials with high electrical conductivity for structural health monitoring has shown significant potential in engineering applications. However, simultaneously improving both mechanical and electrical properties remains a major challenge. In this study, polydopamine (PDA) functionalized reduced graphene oxide (rGO) coating sand (PDA-rGO@Sand) was prepared by a simple water deposition process using PDA as the medium and added to the cement matrix, aiming to address the inherent trade-off between conductivity and strength. The strong adhesion of PDA ensures that the rGO remains firmly attached to the sand surface, while its catechol and amine groups chemically interact with the functional groups of rGO, further strengthening the bond of rGO with the sand particles. This improves the interfacial transition zone (ITZ) between aggregate and paste, thereby building a three-dimensional conductive network in the cement matrix and significantly increasing the mechanical strength of the mortar. The influence of PDA-rGO@Sand with varying reduction degrees on the mechanical, electrical, and piezoresistive behavior of the mortar was systematically evaluated. The results indicated that incorporating low-reduction PDA-rGO@Sand samples led to a 31.91 % increase in 28-day compressive strength and a 27.15 % improvement in flexural strength, relative to ordinary mortar. The inclusion of high-reduction samples reduced the 28-day resistivity of the mortar by about one order of magnitude (1.02 × 10⁴ Ω·cm), with a fractional resistivity change of up to 10.3 %. Notably, mortars with high-reduction samples still maintained good mechanical properties, which was 14.56 % and 10.46 % higher than that of ordinary mortar, respectively. The smart cementitious composites produced using this method will contribute to the application and dissemination of structural health monitoring. © 2025 Elsevier Ltd.