Influence of Structural Characterization of C(3)S-C(3)A Paste under Sulfate Attack

The durability of C(3)S-C(3)A paste with varied C(3)A 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 C(3)S-C(3)A paste, thus accelerating the production of C-(A)-S-H gel in the paste. With the increase of C(3)A 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 C(3)S-C(3)A paste deteriorated, showing a decrease in specific surface area, cumulative pore volume and average pore diameter.