Effects of creep recovery on the fracture properties of concrete

Abstract

To study the influence of creep recovery on the fracture properties of concrete, the pre-notched specimens were firstly subjected to three-point bending (TPB) loading at 60% peak load (Pmax) over 30 days. Afterwards, the load was removed and the creep recovery tests were performed for 1, 2, 3 and 15 days, respectively. Thereafter, the quasi-static TPB tests were conducted on the creep recovery specimens. The deformation versus time curves, initial cracking load (Pini), peak load and fracture energy in the quasi-static TPB tests after creep recovery were obtained. Also, the numerical analyses were conducted by combining with the Norton-Bailey model to investigate the stress variations at the crack tip and the time-dependent behaviour of concrete. By comparing the fracture parameters for the specimens with and without undergoing creep recovery, the effects of creep recovery on the fracture characteristics of concrete were assessed. The results showed that during the creep stage, the stress relaxation generated at the crack tip due to viscoelastic characteristics of concrete enlarged the deformation. In contrast, the reversed stress would occur at the crack tip during the recovery stage, and its relaxation over the time contributed to the time-dependent deformation during the creep recovery stage. By comparing with the specimens under the quasi-static TPB loading, Pini and Pmax for the creep recovery specimens would increase, and the increments slowed down over the recovery time. However, the increases in Pini and Pmax for the creep recovery specimens could not enhance the initial and critical fracture toughnesses and these toughnesses were approximately equal to those under the quasi-static tests.