Effects Of Phase Change Materials On Properties And Microstructure Of Steam-Cured Cement-Based Materials And The Mechanisms

With the implementation of the construction industrialization strategy,the prefabricated concrete industry is booming.Steam-cured concrete is widely used in the production of prefabricated components because of its high early strength and high production efficiency,so it has a broad development prospect.However,the steam curing process at higher temperature often leads to quality defects such as increased brittleness of concrete,coarsening of internal pore structure and surface micro-cracks,which affect the long-term durability of steam-cured concrete and its components.Traditional technical measures such as optimizing the steam curing system and optimizing the composition of cementitious materials are difficult to avoid the above-mentioned quality defects of steam-cured concrete.Therefore,combined with the characteristics of phase change materials and their transformation characteristics during the steam curing process,the modification effect of phase change materials on steam-cured cement-based materials was explored in this paper.The influence of different phase change materials on mechanical properties,durability and microstructure of steam-cured mortar and concrete was investigated,and the corresponding influence mechanism was revealed,in order to prepare high-performance steam-cured cement-based materials with excellent performance.The main innovative achievements of the paper are as follows:1.The influence of six pure phase change materials,such as paraffin,fatty acid and polyethylene glycol,on the workability,mechanical properties and durability of steam-cured mortar was studied,and the hydrophobic modification effect of phase change materials on pores in steam-cured cement-based materials was revealed.The results show that paraffin can improve the durability of steam-cured cement mortar.2.Three kinds of inorganic porous carrier composite phase change materials with diatomite,expanded graphite and their composites as carriers and paraffin as phase change materials were prepared by vacuum impregnation method.Compared with pure paraffin,the composite phase change material(diatomite/paraffin)with small particle size and good bonding properties with the cement matrix can significantly improve the mechanical and durability properties and optimize the microstructure of the steam-cured cement-based material.3.Two microcapsule phase change materials of type I and II were prepared by sol-gel method and temperature-assisted method,respectively,using amorphous silica as encapsulation material and paraffin as phase change material.The key parameters for the preparation of microencapsulated phase change materials were determined.Compared with type I,type II microcapsule phase change material has better effect on improving the toughness,durability and microstructure of steam-cured cement-based material.4.The steam-cured concrete with excellent permeability resistance and freeze-thaw resistance was prepared by mixing type II microcapsule phase change material.The multiple action mechanisms of phase change materials to improve the performance and microstructure of steam-cured cement-based materials,such as pore surface hydrophobic modification,temperature regulation and chemical activity of encapsulation materials,were revealed.The preparation method of composite phase change material which can effectively improve the durability of steam-cured concrete was established.Figures 158,Tables 24,References 293...