Structural evolution of silicate tetrahedral polymerization in C–(A)–S–H gels subjected to rare earth leaching environments

Structural polymerization is a primary factor driving intrinsic property changes in calcium silicate (aluminate) hydrate (C–(A)–S–H). However, the mechanisms by which erosive media induce structural polymerization of C–(A)–S–H gel during the service life of cement-based materials remain unclear. This study investigates the effects of both alkaline and acidic sulfates on the composition and microstructural evolution of C–(A)–S–H through various physical and microstructural analyses. The findings indicate that dehydration condensation reactions of Si–OH groups, resulting from decalcification and carbonation processes, are the main contributors to the polymerization silicate tetrahedra. As the aluminum phase increases, the leaching of Al[IV] from the C–(A)–S–H gel after sulfate erosion becomes more pronounced, leading to a tendency for the original silicate–aluminate chain structure to undergo polymerization and reconstruction. Furthermore, aluminum can only promote the polymerization of silicate tetrahedra within a specific range. This study provides a theoretical foundation for regulating concrete microstructure and optimizing its durability.