ABSTRACT The previous freeze-thaw damage model for macroporous recycled concrete (MRC) neglected the pore structure damage that can reduce permeability. Furthermore, macro–mesoscopic factors, such as the old paste on recycled aggregates (RA), were not adequately considered. To address the aforementioned issues and establish a macro–meso coupled freeze-thaw damage model for MRC, freeze-thaw tests were conducted on saturated MRC and its meso-components, namely paste, interface transition zone (ITZ), and RA, in an air environment. The compressive strength, shear strength, indentation elastic modulus, ITZ thickness, old paste exfoliation rate, pore size distribution parameters, and average pore size of the paste, ITZ, RA, and MRC were measured. The test results indicated that, in an air environment, the freeze-thaw damage rates of the paste, ITZ, RA, and MRC were relatively low. Initially, their performance improved before gradually declining. When the paste compressive strength reached 62.5 MPa, the central region of the ITZ specimen exhibited earlier damage compared to the surface region. A novel method for quantifying the damage degree of MRC was developed by integrating changes in both macrolevel mechanical properties and mesolevel pore structure. The damage degree of the MRC was regressed by incorporating the damage degrees of the paste, ITZ, and RA, as well as the filling ratio. The damage degree of the MRC under any number of freeze-thaw cycles can be accurately predicted using the filling ratio of paste and the initial meso parameters of the paste, ITZ, and RA, with a calculation error ranging from 0.004 to 0.080.
Xu et al. (Wed,) studied this question.