Study on the Chloride-Sulfate Resistance of a Metakaolin-Based Geopolymer Mortar.

The chloride-sulfate corrosion environment of concrete is a significant engineering problem. This paper investigates the effect of the complete/semi-immersion mode on the durability of concrete in a chloride-sulfate environment by using different granulated blast furnace slag (GBFS) dosage rates (10-50%) of a metakaolin (MK)-based geopolymer mortar. The chloride-sulfate corrosion environment is discussed by analyzing the apparent morphology, mass change, and mechanical property change in specimens at the age of 120 d of erosion combined with XRD and SEM. The high Ca content in GBFS has an important effect on the strength and erosion resistance of the metakaolin geopolymer (MGP) group mortar; an increase in the GBFS dosage makes the MGP group mortar denser, and the initial strength of the MGP group mortar is positively correlated with the dosage of GBFS. After 120 d of erosion, the GBFS dosage is negatively correlated with erosion resistance, with the high GBFS dosage groups showing more severe damage. Semi-immersion resulted in more severe deterioration at the immersion-evaporation interface zone due to the difference in the ionic concentration and the 'wick effect' at the immersion-evaporation interface zone. Compared with the commonly used OPC mortar, the M40 and M50 groups have improved strength and corrosion resistance and are suitable for engineering environments in highly erosive areas.