Study on dynamic mechanical properties and meso-damage mechanism of carbon fibers recycled aggregate concrete under freeze-thaw environment

Abstract

The uniaxial compression mechanical properties tests of carbon fibers recycled aggregate concrete (CFRAC) were carried out in order to investigate the effect law of coupling freeze-thaw cycles (FTCs) and dynamic strain rates on the mechanical properties of CFRAC. Two cases of carbon fibers (CFs) doping of 0% and 0.3% were considered. The full CFRAC uniaxial compressive stress-strain curves at different strain rates (10−5/s, 10−4/s, 10−3/s, 10−2/s) after different FTCs (0, 50, 100) were obtained. The microscopic characteristics and microcrack propagation process of the specimens were analyzed by means of nuclear magnetic resonance (NMR), scanning electron microscope (SEM) and acoustic emission (AE). The results showed that the specimens still had significant strain rate sensitivity after FTCs. With the same amount of CFs doping and strain rate, the strength and elastic mode (E) of the specimens kept decreasing as the number of freeze-thaw cycles (N) increased. With the same N, the strength and E of the specimens increased and the deformation capacity decreased as strain rate increased. With the addition of 0.3% CFs, the frost resistance and crack resistance of the specimens were significantly enhanced. Combined with the statistical damage constitutive model, the influence of FTCs and dynamic strain rates coupling on the meso-damage mechanism of CFRAC was analyzed. The meso damage evolution process was characterized by five characteristic parameters E0, εa, εh, εb and H. The results showed that there was an obvious regularity between the change of characteristic parameters and CFs content, dynamic strain rate and the N. An effective link between the fine-scale damage mechanism and the macroscopic nonlinear intrinsic behavior was established. The phenomenon of AE signal lag in uniaxial compression was explained from the perspective of effective stress.