Acceleration Effect of Chemical Solution Immersion on Calcium Leaching of Cement-Based Materials

To quantify a relationship between the accelerated calcium leaching effect and the concentration of nitric acid solution ranging from 0.01 to 0.50 mol/L, leaching experiments and numerical simulation were conducted for cement paste, mortar and concrete specimens at a water-cement ratio of 0.50, and the evolutions of the macro- and micro-leaching indicators were analyzed. The results show that the proportional coefficients in Fick's diffusion law based on leaching depth and cumulative relative leached calcium ion exhibit a linear and negative exponential growth relationship with the concentration of nitric acid solution. The diffraction peak of calcium carbonate at the same depth of each leached paste specimen linearly decreases. The equivalent accelerated diffusion coefficients of cement paste, mortar and concrete are linearly proportional to the concentration of nitric acid solution, and the acceleration ratios are 3.9×103, 1.6×103 and 1.0×103 times of the concentrations (measured in mol/L), respectively. For cement paste with a water-cement ratio of 0.50, acceleration ratios of 6.00 mol/L ammonium nitrate, 0.50 mol/L nitric acid, 6.00 mol/L ammonium chloride and deionized water are 4 507, 2 018, 464 and 47, respectively. The equivalent accelerated diffusion coefficient of cement paste is 2.3 times greater than that of the concrete at the same water-cement ratio. If the concentration of chemical immersion solution is too high, the calcium dissolution-diffusion process will deviate from the dissolution mechanism in fresh water environment. When nitric acid solution is used for an accelerated calcium leaching experiment, an appropriate concentration is 0.10 mol/L. © 2022, Editorial Department of Journal of the Chinese Ceramic Society. All right reserved.