Prediction of fracture parameters and strain-softening behavior of concrete: effect of frost action

摘要

The aim of this study is to investigate the effect of frost damage on the strength and fracture properties of concrete formulated according to the standard NF EN 206-1 without air entraining agent. Prismatic 8 × 15 × 70 cm and cylindrical 16 × 32 cm specimens were subjected to various repeated freeze-thaw cycles according to the standard NF P 18-425 to induce different degrees of deterioration and the change in material properties was evaluated. Mechanical experiments were carried out on the specimens before and after their exposure to freezing-thawing cycles. The Young's modulus was determined through compressive tests conducted on 16 × 32 cm cylindrical specimens. Flexure strength and fracture parameters were obtained according to RILEM recommendations from three point bending tests conducted on prenotched samples. Tensile strengths were obtained by split tensile tests conducted on 16 × 32 cylindrical specimens. The correlations between the number of freezing-thawing cycles and the mechanical properties reveal that the change in the tensile strength gives a better indication of degradation due to frost action. From force-crack mouth opening curves, F-CMOD, the intrinsic fracture properties were obtained using the cracked hinge model based on a power law strain-softening curve and an inverse analysis algorithm. It was observed that the fracture energy, G_F~(RILEM), calculated according to the RILEM recommendations decreases by increasing the ratio a_0/H (notch length/beam's height). When a_0/H exceeds 0.45, G_F~(RILEM) reaches a value of 0.15 N/mm which is equal to the one obtained using the inverse analysis. Moreover, it has been established that the fracture energy, G_F, and the critical crack opening displacement, w_c, increase with freezing-thawing cycles.