Effects of varied building solid wastes, particle sizes and substitution ratios on the performance and impedance spectrum of recycled fine aggregate mortar and the feasibility of developing a prediction method

In this study, three solid waste materials (sintered bricks (SB), aerated blocks (AB) and cementitious mortar (CM)) were studied to analysis the influence on the impedance characteristics and mechanical properties of recycled sand mortar. Mortar containing recycled sand obtained similar or even higher compressive strengths as to the control group at 15% substitution rate. The density of the mortar decreased with the substitution rate of recycled sand. The porosity increased by 18% compared to the control group with an inclusion of 45% of SB. The bulk density of recycled mortar was found to be related to the particle size of the recycled sand, for instance, the bulk density of ABCS45 was 6% less than ABFS45. The AC impedance spectrum results showed that the high-frequency arc was the smallest for AB and the largest for CM. The R1 values of AB were 0.27 and 0.14 times that of SB and CM, respectively. The high-frequency arc of the mortar increased with hydration, consuming OH− ions and raising R0 values, while the compacting matrix led to a rise in R1 values. After 28 days curing, mortars containing SB and CM sands displayed higher R1 values, with CMCS45 being approximately 50% higher than the control group. Through analyzing the physical, mechanical, and impedance properties, it revealed a correlation coefficient −0.88 between porosity and R0 values, with bulk density and compressive strength demonstrating stronger correlation with R1 values. These findings offer valuable guidance for utilizing and nondestructively testing recycled materials.