Mechanical and thermal properties of recycled coarse aggregate concrete incorporating microencapsulated phase change materials and recycled tire rubber granules and its freeze-thaw resistance

For the recycling and reuse of construction waste and scrap tires based on the strategy of limiting carbon emissions in response to warming, a study was performed on the performance of recycled coarse aggregate concrete (RCAC) by replacing natural sand with different volume contents of recycled tire rubber granules (RTRGs) and microencapsulated phase change materials (mPCMs). The results show that the mechanical strength and dynamic elastic modulus of RCAC specimens reduce slowly with increasing RTRGs or mPCMs. All other mechanical strengths significantly reduce compared to the reference RCAC specimens without admixture, while the splitting tensile strengths of RCAC specimens with 4-6% RTRG and 4-8% mPCM contents show an increase of 0.12-0.34 MPa. The thermal conductivities of RCAC specimens with different RTRG and mPCM contents at -0.2 or -5 degrees C ambient temperature decrease significantly compared to those at 20 degrees C, and these decreasing values all decrease with increasing RTRGs and mPCMs. The CT scanning results show that incorporating RTRGs with a larger grain size of 0.30-1.18 mm tends to affect the larger 3D pore structures in RCACs, whereas incorporating mPCMs with a grain size of 5-10 mu m tends to affect the smaller pores because the microcapsules easily fill the capillary pores with pore sizes <10 mu m. With increasing freeze-thaw cycles, the relative dynamic elastic modulus and damage of RCAC specimens decrease slowly in the early stages of 1-50 cycles and rapidly after 50 cycles. After 175 cycles, Specimen No. R-4-6 with 4 % RTRGs and 6 % mPCMs has the lowest damage value of 0.61, which is 0.13 lower than Specimen No. R-4-8. Therefore, the simultaneous use of RTRGs and mPCMs with appropriate contents can improve the freeze-thaw durability of RCAC.