Durability and mechanism of high-salt resistance concrete exposed to sewage-contaminated seawater.

• High-salt resistance concretes were prepared by mixing GBFS, basalt power and desulfurized gypsum. • Relative chloride permeability coefficient was used to evaluate the resistance of concrete to chloride ion. • Corrosion products of samples were identified by DTA, XRD, FTIR and SEM-EDS. • Corrosion mechanism of concrete exposed to high-salt sewage was revealed. To improve the durability of concrete structures used in offshore sewage treatment plants (STPs), a high-salt resistance concrete (HSRC) prepared by mixing multiple mineral admixtures was developed in this study. The effect of artificial high-salt sewage, simulated "wastewater" on properties of the HSRC was investigated and the mechanism of salt resistance was proposed. The results show that the corrosion resistance coefficient (K f) of concretes cured in wastewater decreased and their relative chloride permeability coefficient (P n) increased as the curing age from 7 to 150 d. Moreover, the K f of the HSRC composed of slag, basalt powder and desulfurized gypsum by 69.4% replacement of cement, was 47.8% higher than that of normal concrete after 150 d of curing, while the P n of the HSRC was 12.5% lower than that of normal concrete. However, excessive replacement basalt powder in cement probably resulted in negative effects. Furthermore, when cured in wastewater, the Ca(OH) 2 and C-S-H gel produced in pastes, which were the concretes with aggregates removed, were consumed by corrosive ions and formed corrosion products consisting of gypsum, syngenite, and thaumasite crystals, etc., which were generated in the HSRC pastes with aggregates removed, were fewer than those of other samples. Further, the porosity of the HSRC pastes in freshwater was smaller than that of other samples, which contributed to pastes' ability to resist permeation of corrosive ions. The results of this study have practical engineering significance to the safety of concrete structures used in the high salt environments of offshore STPs. [ABSTRACT FROM AUTHOR]