Research status and analysis of cement and geopolymer hydrophobic composites

The long-term durability of concrete is one of the main problems it faces, and the main cause of durability damage is the migration of water in the porous structure of concrete, which makes it easier for harmful ions to enter the interior of the substrate. Modifying the cement and geopolymer with superhydrophobic materials is a valid method to avoid the transmission of water, thereby preventing the migration of harmful ions and increased its durability of concrete. This review summarized the superhydrophobic modification methods of cement and geopolymer cementitious materials and categorized into superhydrophobic surface and bulk modification; the modification mechanism of superhydrophobic modifier added to cement and geopolymer and their bonding mode with inorganic matrix in the internal modification method. Besides, the modification methods commonly used for surface modification in the present research are summarized, divided into external coating, maceration, template method, etc., and the surface modification mechanism is analyzed. Compared with the superhydrophobic composite coatings, the monolithically modified cement and geopolymer matrix composites have greater advantages in practical application scenarios. In addition, the effects of hydrophobic modification on the wettability, waterproofing, compressive properties and anti-corrosion properties of composites are concluded, and their compressive strength was reduced by about 20%~60%. Finally, some problems in the research of hydrophobic modification of cement and geopolymer composites are described and the future research direction is prospected, and it is suggested to carry out research on volumetric super-hydrophobicity, improvement of compressive strength, cost control, and homogeneous dispersion of hydrophobic admixture inside the material.