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The durability of C3S-C3A paste with varied C3A content (0%, 5%, 10%, and 20%) against sulfate attack at various attack ages (3 d, 7 d, 28 d, and 180 d) was investigated in this study through the examinations of corrosion product composition, Ca/Si and Al/Si of calcium-(aluminum)-silicate-hydrate (C-(A)-S-H) gel, formation and evolution of microstructure, migration and transformation of Al containing phase products, and pore structure. The results indicated that sulfate attack can promote the hydration reaction in C3S-C3A paste, thus accelerating the production of C-(A)-S-H gel in the paste. With the increase of C3A content, the acceleration effect becomes more significant. In addition, sulfate attack led to the dealumination and decalcification of C-(A)-S-H gel, resulting in the reduction of the gelling power of C-(A)-S-H gel. The degree of dealumination and decalcification of C-(A)-S-H gel increases with the increase of C3A content. At the same time, free Al and Ca promote the formation of expansive products such as ettringite and gypsum. Finally, under the action of sulfate, the pore characterization of C3S-C3A paste deteriorated, showing a decrease in specific surface area, cumulative pore volume and average pore diameter.

Chloride ion corrosion of steel bars is one of the important reasons for the decline of durability and service life of concrete structures. Due to the complexity of concrete structure, the migration process of chloride ions in concrete is diversified. Therefore, it is difficult to show the transport mechanism of chloride ions in concrete by a single experimental study. It is necessary to explore the transmission process and mechanism of chloride ions in concrete through theoretical simulation on the basis of experimental research. This paper summarizes the relevant models and methods of chloride transport, points out the advantages and disadvantages of existing models, and prospects the research direction of chloride transport models.

C35 pier concrete was prepared with natural limestone powder and fly ash, and the effect of the proportion of limestone powder and fly ash on hydration heat of composite cementitious material system was studied At the same time, the effects of different proportions of natural limestone powder and fly ash on adiabatic temperature rise, early shrinkage, drying shrinkage and early cracking of concrete were studied. The results show that the hydration heat of composite cementitious material system can be reduced by adding natural limestone powder and fly ash, the early shrinkage and dry shrinkage of concrete can be reduced, and the cracking of concrete can be reduced. On the contrary, when natural limestone powder and fly ash replace cement by 20%, 10% mass ratio, C35 concrete has the best indexes and better crack resistance.