Relationship between chloride ion permeation resistance of recycled aggregate thermal insulation concrete and pore structure parameters

The incorporation of recycled coarse aggregate (RCA) and glazed hollow bead (GHB) leads to a different internal pore structure of recycled aggregate thermal insulating concrete (RATIC) than that of normal concrete (NC), which is the fundamental reason for the different chloride ion transport mechanisms between the two. To investigate the quantitative relationship between the fine pore structure of RATIC and its resistance to chloride ion permeation in this study, chloride ion permeation tests were conducted on 10 sets of RATIC specimens with different RCA replacement ratios and GHB contents. The pore structure of the specimens, including their quantity and porosity, was also systematically analyzed using nuclear magnetic resonance (NMR) spectroscopy. A model for chloride ion permeation resistance of RATIC that considered RCA replacement and GHB content was pro-posed, and grey correlation analysis was used to relate the chloride ion permeation resistance of RATIC to the pore structure and establish a suitable chloride ion diffusion coefficient model for RATIC. The results showed that: (1) increasing RCA replacement weakened the resistance of RATIC to chloride ion permeation. Compared to normal concrete (NC), the chloride diffusion coefficient of RATIC increased by 18.73 % when the RCA substi-tution ratio rose from 0 % to 100 %, while the overall number of internal pores increased by 14.32 %, with the greatest increase in harmful pores under the same RCA replacement conditions; (2) increasing the GHB content effectively improved the chloride ion permeation resistance of RATIC, and the chloride ion diffusion coefficient decreased by 11.49 % when the GHB ratio rose from 0 kg/m3 to 130 kg/m3. The number of RATIC internal pores increased by a total of 20.29 %, with the largest increase in multiple harmful pores. The present authors concluded that establishing the two-parameter model of chloride ion diffusion coefficient/pore structure of RATIC could serve to predict the resistance of RATIC to chloride ion permeation, which could in turn provide a reasonable basis for further research on the durability of RATIC.