Appropriate concentration of ammonium chloride solution to accelerate calcium leaching of cement-based materials
To determine the optimum concentration of ammonium chloride solution within the range of 0.2-6.0 mol/L,accelerated leaching experiments were carried out on cement paste,and evolution laws of the leaching depth,cumulative relative leached calcium ion and porosity were studied.The mi-croscopic mechanism was then analyzed by the X-ray diffraction analysis.The results show that the calcium leaching increases with the concentration of ammonium chloride solution.When the Fick's law of diffusion is represented by leaching depth and cumulative relative leached calcium ion,respectively,the obtained proportion coefficient increases linearly and then decreases in the former and exhibits a negative exponential growth trend in the latter.At the same depth of leached specimens,the diffrac-tion peak of calcium carbonate decreases first and then increases.If the concentration of ammonium chloride solution is unreasonably high,it will make the calcium dissolution-diffusion process of ce-ment-based materials significantly deviate from that of the actual mechanism in the natural environ-ment,and the most appropriate concentration of ammonium chloride solution is 3 mol/L.
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