Study on the physical mechanical properties and freeze-thaw resistance of energy storage concrete with artificial phase change aggregate

As the main material for major infrastructure in cold regions, the mechanical properties and freeze-thaw resistance of concrete have become key scientific issues affecting the safety and normal operation and maintenance of infrastructure in cold regions. Energy storage concrete with phase change materials (PCM) has high thermal storage performance, which is beneficial to improving the frost resistance of concrete. In our preliminary research work, the artificial phase change aggregate (APCA) containing PCM with high latent heat, good mechanical properties and frost resistance were made and tested. The APCA was added to the concrete and replaced with natural coarse aggregate in different proportions, resulting in several energy storage concrete schemes with different APCA contents. The water absorption characteristics, microstructure and pore characteristics of energy storage concrete with different APCA contents were tested and analyzed through negative pressure saturation test, SEM and MIP. The effects of APCA replacement on the composition, mechanical properties, failure morphology characteristics and frost resistance durability of energy storage concrete at various ages were analyzed through XRD test, strength test and freeze-thaw cycle test. The results showed that replacing natural coarse aggregates with APCA changed the pore characteristics of concrete, reduced its saturation water absorption rate, but did not change the composition of hydration products at various ages of concrete. Replacing with an appropriate amount of APCA in concrete is beneficial for reducing the total porosity, the total number of more-harmful pores and harmful pores. APCA reduce the compressive strength and splitting tensile strength of energy storage concrete at various ages. The early splitting strength of energy storage concrete increases rapidly, while the later growth is relatively slow. APCA are beneficial for suppressing the expansion of pores and cracks under freeze-thaw action of concrete. APCA is helpful to improve the freeze-thaw resistance of the energy storage concrete. After 100 freeze-thaw cycles, their compressive strength is still 96 % of Tthe 28 day strength, with about 35 MPa. This study provides a reliable experimental and theo- retical basis for improving the freezing resistance of concrete in cold area.