Axial Compressive Behavior of FRP-Confined Compression-Cast Recycled Aggregate Concrete

Abstract

With the increasing scarcity of natural gravel resources and increased production of construction and demolition waste, recycled aggregates offer prospects for concrete structures. However, the adhered loose and porous mortar and microcracks in recycled aggregates led to impaired mechanical behavior of recycled aggregate concrete (RAC) and reduced durability in harsh environments, significantly restricting its engineering application. Compression-casting can solve the problems of low strength and poor durability of RAC; however, it induces significant brittleness of concrete in compression. This study proposed an improvement in the ductility of compression-cast RAC through confinement using fiber-reinforced polymer (FRP) laminates. A total of 32 FRP-confined compression-cast cylinder specimens were tested under uniaxial compression, with variables including concrete mixture proportion, FRP thickness, and concrete casting method. The experimental results showed that the ultimate axial stresses of the unconfined RAC and FRP-confined RAC increased by up to 34.8% and 14.5%, respectively, and the ultimate axial strain decreased by up to 49.0% with compression-casting. Furthermore, the compression-casting method resulted in an 8.5% reduction in the measured average rupture strain of the FRP. The confinement efficiency was not significantly affected by compression-casting, as indicated by a slightly greater slope of the strength enhancement ratio with an increase in the confinement ratio for FRP-confined compression-cast RAC. Stress–strain models of FRP-confined compression-cast and normal RAC were proposed based on test data from this study and the literature. It was found that the proposed model improved the prediction accuracy of the stress–strain behavior compared with existing models.