Performance analysis of cement-based sandwich composites with fiber-reinforced skins and rubberized concrete core from waste tire recycling

The demand for lightweight, energy-efficient, and sustainable construction materials has driven interest in cement-based sandwich composites incorporating waste-derived components. This study explores multi-layer sandwich systems integrating a rubberized cementitious core, made from 70% rubber powder and 30% granules derived from waste tires, with fiber-reinforced mortar skins. Short glass fibers and nanoclay-treated recycled carbon microfibers were investigated as reinforcements to enhance mechanical performance. The produced composites achieved lightweight concrete densities (1745–1781 kg/m3, per ACI 213R), making them ideal for semi-structural applications. Sandwich configuration successfully combined the high energy absorption of the rubberized cementitious core (up to 270% higher than reference mortars) with the structural role of the fiber-reinforced skins. Flexural strength of the sandwich composites improved by up to 195% over monolithic rubberized concrete samples, demonstrating the mechanical efficiency of the layered approach. However, challenges emerged at the interface between core and skins, where fiber-induced changes in fresh-state rheology compromised adhesion and caused interfacial microcracking, as confirmed by scanning electron microscopy. Thermal testing revealed that fiber-reinforced skins, particularly those incorporating short glass fibers, retained higher residual strength after exposure to elevated temperatures and, when integrated into the sandwich configuration, effectively counteracted the strength degradation of the rubberized cementitious core induced by thermal exposure. Moreover, the sandwich structure exhibited lower thermal conductivity, with skin-core delamination disrupting heat transfer and enhancing insulation. These findings confirm that sandwich composites with fiber-reinforced skins represent a promising and smart solution for manufacturing lightweight, thermally insulating, and impact-resistant construction components. Further optimization of fiber dispersion and interfacial bonding is essential to fully exploit their structural potential.