Influence of recycled coarse aggregates incorporation on the fracture properties of concrete

Abstract

This paper presents the mechanical and fracture properties of a structural concrete incorporating coarse recycled aggregate. Four mixes were designed according to the standard EN 206-1 to achieve S4 consistence class and C35/45 class of strength. Concrete specimens were prepared with different recycled gravel content of 0%, 30%, 65% and 100% by volume of the total coarse gravel.Three points bending tests were performed on 10×10×40cm pre-notched samples in order to determine the flexural strength and fracture properties according to the RILEM recommendations. From experimental Force-CMOD curves, the intrinsic fracture properties were obtained by an inverse analysis using an analytical model and a power law strain-softening relationship. The strain-softening law is described by two parameters being respectively the power n and the critical crack opening displacement wc. It was found that the difference between the calculated fracture energy, GF, and the RILEM fracture energy, GFRILEM, is more pronounced for recycled aggregate concrete.The evolution of n and wc, the parameters of the power strain-softening law, was also studied. It appeared that the power, n, depends on the compressive strength, the aggregate size and the water to binder ratio. For the same class of compressive strength, it remains substantially unchanged when the recycled aggregates content increases. For the critical crack opening wc, it decreases when the substitution ratio increases. Finally, the relationship between fracture properties and the tensile strength has been established.