Analysis of alkali leaching mechanism on as-built cement concrete bridge deck pavement.

• Efflorescence of dense-graded asphalt paved on a cement concrete bridge deck. • Calcium Carbonate was found to be the main efflorescence material. • Cement concrete bridge deck provide the alkaline source for efflorescence materials. • Carbonation is the result of Ca(OH) 2 transformation in the presence of H 2 O and CO 2. • Migration model of the efflorescence material was established. A new distress type, namely alkali leaching, was recently observed to have developed on an as-built dense-graded asphalt concrete (DGAC) paved on a cement concrete bridge deck in China. Not only does alkali leaching affect the aesthetic appearance of the cement concrete bridge deck pavement (CCBDP) due to the distinctive color contrast, it also creates a potential threat to the service life of the bridge. In this paper, an alkali leaching distressed section of a CCBDP in Shaanxi Province (China) was studied. The study results indicated that whitish spots cannot be removed by natural water. In situ pH measurements indicated highly alkalinine materials appear on the surface of pavement layers. Based on these findings, the formation mechanism of alkali leaching on CCBDP was analyzed. The corresponding results showed that the main mineral of alkali leaching was Calcium Carbonate (CaCO 3). Under wet conditions, rainwater infiltrates into the cement bridge deck from the sides of the pavement. Continuous exposure to moisture or humid environments facilitates the subsequent hydration to generate Ca(OH) 2 , which is the alkaline source for alkali leaching. The generated Ca(OH) 2 migrates with rainwater to the pavement surface through capillary action. With the repeated circles of wet and dry conditions, the in-situ carbonation products lead to formation of alkali leaching on the pavement surface. [ABSTRACT FROM AUTHOR]