Combined influence and mechanism of superabsorbent polymers and waterborne epoxy coatings on the durability of self-curing concrete under compound sodium and magnesium sulfate attacks

The corrosion of concrete structures near seawater leads to severe performance deterioration and significant economic losses. A novel method to enhance resistance to compound sulfate attack in concrete was investigated, where superabsorbent polymer (SAP) was incorporated as an internal curing material and waterborne epoxy coating (WEC) was applied as an external curing material. The mass loss, compressive strength, and dynamic elastic modulus were measured to evaluate the deterioration of specimens exposed to compound sulfate solutions of Na 2 SO 4 and MgSO 4 . X-ray diffraction, thermogravimetric analysis and mercury intrusion porosimetry were employed to explore the deterioration characteristics and mechanisms. Results demonstrate that the combined use of SAP and WEC significantly reduces mass loss, degradation of relative dynamic elastic modulus, and compressive strength loss under sulfate attack. Additionally, the combined curing improves the compactness and pore structure of concrete. The compressive strength of control and Self3 specimens decreased by 32.91 % and 8.73 %, respectively, compared to those in sodium sulfate solution. This demonstrates that concrete exhibits lower resistance to compound sulfate attack compared to single sodium sulfate exposure. The synergy of SAP and WEC slows sulfate attack by preventing calcium hydroxide from expanding into gypsum. Furthermore, WEC effectively blocks the ingress of corrosive ions, while SAP refines internal pores and inhibits sulfate ion transport. These findings reveal the protective mechanism of self-curing concrete against compound sulfate attack, providing insights for engineering applications in harsh environments.