Comparative study on the effect of crystalline agents for improving frost resistance of concrete from the perspective of reaction mechanism

The crystalline agents can be used to improve the concrete frost resistance by its densification effect on the microstructure of concrete, while the effect of which depends on the type and penetration process of the crystalline agents. This study, therefore, aimed to investigate the effect of two types of crystalline materials, in terms of organic and inorganic one, and two kinds of penetration methods including surface coating and soaking, in concrete. In addition to freeze-thaw test and electric flux test, the thermal gravity analysis, mercury intrusion porosimetry and scanning electron microscope were carried out. The results showed that after vacuum drying and soaking treatment, the material’s penetration depth has reached 7 mm. Deeper penetration depth shifted the freeze-thaw failure mode sudden to gradual, significantly enhancing frost resistance as a result. Among them, organic crystalline agent increased frost resistance by 2.5 times and decreased electrical flux by approximately 90 %, while inorganic crystalline agent only enhanced frost resistance by 1.5 times and reduced electrical flux by only about 37 %. From a reaction mechanism perspective, the hydrophobic layer within the pores formed by organic crystalline material has the most contribution, in which the needle-like substances generated by inorganic one filled the pores with limited effect to barrier water.