Mechanical properties and damage model of modified recycled concrete under freeze-thaw cycles

The recycled aggregate contains a large amount of old mortar and interface transition zone (ITZ), resulting in poor freeze-thaw resistance of recycled concrete (RC). To improve the freeze-thaw resistance of RC, this study used nano-silica (NS) and surface-modified basalt fiber (MBF) as reinforcement materials to form modified recycled concrete (MRC). The freeze-thaw cycles (FTCs) tests and mechanical property tests were used to study the anti-freezing capability of the MRC, and the damage model to the MRC was evaluated by damage mechanics with multiple indices. Results indicated that the addition of NS and MBF improved the anti-freezing capability of MRC. After adding NS and MBF, the degree of damage and the mass loss were reduced, and the mechanical properties and the relative dynamic elastic modulus were improved considerably. Through data fitting, the relationship between the mechanical properties and the number of FTC was obtained. Through regression analysis, the damage evolution equations with compressive strength, splitting tensile strength and relative dynamic elastic modulus as the damage variables were also obtained. Comprehensively considering the NS contribution rate and MBF contribution rate, the freeze-thaw damage model was established, and the freeze-thaw damage evolution of MRC was analyzed. Compared with the addition of NS or MBF alone, the anti-freezing capability of MRC can be enhanced by adding both NS and MBF.

Automated summary

This study used nano-silica and surface-modified basalt fiber as reinforcement materials to improve the freeze-thaw resistance of recycled concrete. The results showed that the addition of nano-silica and surface-modified basalt fiber reduced the degree of damage and mass loss, and improved the mechanical properties and relative dynamic elastic modulus of the modified recycled concrete, thus enhancing its anti-freezing capability.