Size Effect in Thermally Damaged Concrete

Detailed experimental observations and numerical simulations are presented for the evaluation of residual properties of high-strength concrete specimens after exposure to high temperatures. Heated and nonheated notched four-point bending specimens were tested at ambient conditions approximately 1 month after exposure to the high temperature. Residual strength and post-peak response were monitored using a closed-loop load frame, and the fracture process zone was observed using Electronic Speckle Interferometry. The symmetric over-nonlocal formulation of a microplane model was used for interpreting the experimental investigation. The size-effect results were used to identify the true tensile strength and the initial fracture energy corresponding to the peak and the initial post-peak slope of a linear cohesive crack law. This study reveals that the material ductility increases with the thermal damage, which is explained by the increase of the fracture process zone size and the characteristic length.