Experimental study on full stress-strain curve of recycled concrete after composite salt freezing

In order to reveal the influence mechanism of composite salt freezing on the stress-strain constitutive relationship of recycled concrete, uniaxial compression tests of 48 prismatic specimens in four groups after composite salt freezing were carried out with strength grades and freezing-thawing cycles as test variables. Taking ordinary concrete as the control group, the variation laws of the peak stress, peak strain, Poisson’s ratio, and elastic modulus of recycled concrete before and after composite salt freezing were analyzed aided by the SEM test, and the stress-strain constitutive relationship of recycled concrete after composite salt freezing was established. The test results show that after 90 times of composite salt freezing, the peak stress, elastic modulus, and Poisson’s ratio of ordinary concrete are 2. 5, 7. 1, and 1. 2 times that of recycled concrete, respectively. The peak stress and elastic modulus of recycled concrete decrease with the increase of composite salt freezing cycles, but the reduction decreases with the increase of strength grade, and the peak strain increases with the increase of composite salt freezing cycles. Based on the existing stress-strain constitutive models of ordinary concrete, i. e., the ascending part of the CEB-FIP model and the descending part of GUO Zhenhai model, the non-dimensional stress-strain curve is piecewise fitted. The experimental curve is in good agreement with the piecewise model curve. © 2022 Science Press. All rights reserved.