The Deterioration of Cement Mortar under the Coupled Conditions of Stray Current and Sulfate

Subway engineering often suffers varieties of corroding environments. This article investigated the effects of stray current and external sulfate coupled conditions on the deterioration of cement mortar. The cement mortar specimens suffered from one-dimensional sulfate attack. Simultaneously, a direct current electric field was applied to both ends of the specimen to simulate stray current. By contrast, a group of mortar specimens was immersed in the same concentration of sodium sulfate (Na2SO4) solution. In order to investigate the effect of stray current on the sulfate attack of cement mortar, the compressive strength of specimens was tested. In addition, the sulfate ions profile in the cement mortar specimen was tested. Corrosion products and the microstructure of specimens were investigated using x-ray diffraction, Fourier-transform infrared spectroscopy, and scanning electron microscope. Experimental results showed that stray current could exacerbate strength degradation and accelerate the sulfate ions' migration into the cement mortar, which led to the number of total sulfate ions and free sulfate ions at the same depth being higher than that of the immersion group, and quantities of corrosion products (gypsum and ettringite) were also higher than those of the immersion group. In a word, the stray current aggravated the sulfate attack of cement mortar. Therefore, the durability of cement mortar exposed to the stray current and sulfate coupled conditions should be given more attention.