Partially-exposed cast-in-situ concrete degradation induced by internal-external sulfate and magnesium multiple coupled attack

Abstract

The safety of partially exposed concrete structures is threatened by the complicated corrosive sources in sulfate-rich saline areas. Experimental tests were conducted in the present study, taking internal sulfate, external sulfate-magnesium multiple combined attack into consideration, to simulate the corrosion process of partially exposed concrete. The diameter, weight and compressive strength were measured during the immersion period. Sulfate concentration of concrete samples was measured by chemical method. Microstructural and mineral properties were analyzed by SEM, XRD and TG tests after immersion. Results show that internal sulfate attack speeds up corrosion process to a large extent, bring great expansion and damage. Partially exposed condition further accelerates the degradation and failure process of concrete. Magnesium in the environments retards the degradation caused by both internal and external sulfate attack, enhancing the resistance ability of cast-in-situ concrete against cracking. Also, the diffusion of sulfates is slowed by magnesium induced corrosion products since the diffusion paths are blocked. Partially exposed working condition and internal sulfate attack greatly accelerate the degradation induced by sulfate attack. Magnesium in the environments could retard the degradation process and enhance the resistance ability of cast-in-situ concrete against sulfate attack.