Abstract
Sulfate attack is a key factor limiting the durability of concrete in aggressive environments, primarily through the degradation of calcium silicate hydrate (C–S–H), the main binding phase of cement. This study investigates the molecular mechanisms of C–S–H decalcification under sulfate exposure by combining semi-empirical Born–Oppenheimer molecular dynamics (BOMD) with density functional theory (DFT). A C–S–H model with a Ca/Si ratio of 1.5 was simulated in aqueous environments with and without sulfate ions. BOMD trajectories revealed that while C–S–H remained largely stable in pure water, sulfate ions rapidly promoted Ca²⁺ desorption, leading to silicate chain fragmentation and Q²→Q¹ transitions. Electronic structure analyses, including reduced density gradient (RDG), electron localisation function (ELF), and bond critical point (BCP) methods, confirmed stronger Ca²⁺–sulfate interactions compared to Ca²⁺–silicate, driving competitive calcium extraction. DFT calculations showed that sulfate significantly lowers the energy barriers for decalcification and silicate chain fracture, with water amplifying these effects by enhancing polarity and hydrogen bonding. These results reveal how sulfate ions destabilise C–S–H at the molecular level, providing fundamental insights into the mechanisms of concrete deterioration in aggressive environments and guiding strategies for designing more durable cementitious materials.
Keywords
sulfate attack, concrete damage, C-S-H decalcification, quantum chemistry.
DOI
10.5703/1288284318113
Recommended Citation
Wang, Muhan; Zhou, Xiangming; Liu, Chengbo; Wang, Pan; and Hou, Dongshuai, "Decalcification of Calcium Silicate Hydrate by Sulfate Attack: Material Degradation by Heterogeneous Charges" (2025). International Conference on Durability of Concrete Structures. 11.
https://docs.lib.purdue.edu/icdcs/2025/ddm/11
Decalcification of Calcium Silicate Hydrate by Sulfate Attack: Material Degradation by Heterogeneous Charges
Sulfate attack is a key factor limiting the durability of concrete in aggressive environments, primarily through the degradation of calcium silicate hydrate (C–S–H), the main binding phase of cement. This study investigates the molecular mechanisms of C–S–H decalcification under sulfate exposure by combining semi-empirical Born–Oppenheimer molecular dynamics (BOMD) with density functional theory (DFT). A C–S–H model with a Ca/Si ratio of 1.5 was simulated in aqueous environments with and without sulfate ions. BOMD trajectories revealed that while C–S–H remained largely stable in pure water, sulfate ions rapidly promoted Ca²⁺ desorption, leading to silicate chain fragmentation and Q²→Q¹ transitions. Electronic structure analyses, including reduced density gradient (RDG), electron localisation function (ELF), and bond critical point (BCP) methods, confirmed stronger Ca²⁺–sulfate interactions compared to Ca²⁺–silicate, driving competitive calcium extraction. DFT calculations showed that sulfate significantly lowers the energy barriers for decalcification and silicate chain fracture, with water amplifying these effects by enhancing polarity and hydrogen bonding. These results reveal how sulfate ions destabilise C–S–H at the molecular level, providing fundamental insights into the mechanisms of concrete deterioration in aggressive environments and guiding strategies for designing more durable cementitious materials.
