Experimental investigation on the influence of phase change materials on properties and pore structure of steam-cured mortar

Steam-cured concrete with high early strength has been widely applied in high-speed railway. However, heat damage caused by the steam curing process brings adverse effects on the pore structure and durability of steam-cured concrete. It has been found that phase change materials (PCMs) help improve the durability of cement-based materials. Therefore, the influences of two PCMs on the strength, water absorption, and microstructure of steam-cured mortar are discussed in this study. Two PCMs used include pure paraffin and a composite phase change material composed of porous diatomite and paraffin (D/P). The results show that the addition of appropriate PCMs does not significantly reduce the strength of steam-cured mortar. The addition of a small amount of PCMs shows little influence on the pore structure of steam-cured mortar but effective in improving the water-penetration resistance. This is partially attributed to the improvement of hydrophobic characteristics in the pores, resulting from the adhesion of hydrophobic PCMs on the pores during the steam curing. Compared with specimens containing pure paraffin, the pore structure of specimens containing D/P is refined, resulting in higher compressive strength. This may be due to the uniform distribution of small particles D/P in the specimen and the pozzolanic reaction of diatomite in D/P. The use of suitable phase change materials will be helpful to improve the durability of steam-cured concrete.

Automated summary

The addition of suitable phase change materials has little effect on the strength of steam-cured mortar, but can effectively improve water-penetration resistance. The hydrophobic characteristics of the PCMs adhere to the pores during steam curing, and the composite phase change material of diatomite and paraffin further optimizes the pore structure of the mortar.