Improved thermal performance, frost resistance, and pore structure of cement–based composites by binary modification with mPCMs/nano–SiO2

A novel binary composite–modified concrete using microencapsulated phase change materials (mPCM) and nano–SiO2 (NS) was employed to enhance the overall performance and extend the service life of concrete in high–cold regions. The following results were obtained: thermal diffusivity, adiabatic temperature rise, and thermal conductivity of the composite–modified concrete are significantly lower than those of conventional concrete. When the curing time reaches 28d, internal temperature of 10 % microencapsulated phase–change materials and a 1.5 % nanoSiO2 (10 mPCMs/1.5 NS) composite–modified concrete has been reduced by 20.6 %. Binary composite–modified concrete exhibits a notably reduced temperature drop rate during freezing (15 to −15 °C) and a slower temperature increase rate during thawing in comparison to ordinary concrete. Meanwhile, the volume change of internal pores in binary composite modified concrete is relatively small, and the pore morphology is more simplified. As freeze–thaw cycles progress, the compressive strength of the binary composite–modified concrete exhibits a slight decline. The mechanical characteristics of binary composite–modified concrete exhibit marked superiority over conventional concrete, particularly under freeze–thaw conditions. Finally, freeze–thaw tests revealed that ordinary concrete endures 100 cycles, while the binary composite–modified concrete withstands 300 cycles. A damage prediction model incorporating porosity, compressive strength, and fractal dimension was developed. The findings of this research offer new insights and a theoretical foundation for predicting the lifespan of phase–change composite–modified concrete structures in cold regions and addressing frost damage issues.