Experimental Study of the Product Layer Effect in the Process of Mortar under Corrosion in Sulfuric Acid

Abstract

A product layer will grow on the surface of cement mortar when the sulfuric acid attacks the former, which created the blocking effect to the corrosion process and damps the reaction rate. To investigate the surface coating effect, long time immersion tests in sulfuric acid were conducted on two batches of cement mortar specimens. For comparison, product layer removal and acid replacement were conducted regularly on one batch, while the other batch remained unchanged during the whole process. The apparent diffusion coefficients of mortar at different immersion time were calculated by the model of dissolution reaction and experiment datum. The changing of the apparent diffusion coefficients in different batch and at different immersion time was obtained. Scanning electron microscopy and X-ray diffraction were used for analysis of the morphology and phase composition of the product layer. The results indicate that the surface coating effect exists no matter the immersion acid was replaced or not. However, by replacing the immersion acid and removing the product layer, the influence of the blocking effect is reduced and the corrosion rate is increased. The apparent diffusion coefficients observed in both batches will decrease according to the power law of immersion time.

Keywords

• cement mortar
• corrosion
• microstructure
• sulfuric acid
• surface coating effect