Chloride-Carbonation Durability of Low-calcium High-strength Clinker Cement Concrete

Low-calcium high-strength clinker cement and fly ash were used as the main raw materials to prepare low-calcium high-strength clinker cement concrete specimens. Three mechanisms, namely, single chloride ion erosion, single carbonation erosion and chloride ion-carbonation erosion, were set up to conduct concrete erosion test. Free chloride ion and total chloride ion mass fraction were used as evaluation indexes to analyze the chloride ion erosion resistance of concrete specimens under single chloride ion and chloride ion-carbonation, the carbonation depth and pH were used as evaluation indexes to analyze the carbonation resistance of concrete specimens under single carbonation and chloride ion-carbonation, and the pore structure of concrete specimens was analyzed by nitrogen adsorption method (BET) and scanning electron microscopy (SEM) and the micro-morphological characteristics. The results show that compared with single chloride ion erosion, the internal erosiond epth of concrete specimens under chloride ion-carbonation erosion is basically the same, which is 20-25 mm, but the content of free and total chloride ions increases, and the content of bound chloride ions decreases, and the maximum pore diameter increases by 8.1 nm, and the pore structure is coarsened. The micro morphology shows irregular cluster C—S—H gel structure and a large amount of CaCO₃, and the number of pores increases, and the connectivity increases, and the resistance to chloride erosion decreases.Compared with the single carbonation erosion, the depth of internal carbonation of concrete specimens under chloride ion-carbonation decreased, and the depths of fully carbonated and partially carbonated zones also decreased, the pore structure was refined, and the chlorine crystals and Friedel’s salts appeared in the microscopic morphology. The pore structure is refined, and chloride ion crystals and Friedel’s salt appear in the microstructure and filled in the pores, which makes the structure denser, and is conducive to the improvement of the specimen's carbonation resistance.