Study on the Transport Law and Corrosion Behavior of Sulfate Ions of a Solution Soaking FA-PMPC Paste

To study the sulfate corrosion behavior of potassium magnesium phosphate cement (PMPC) paste, the sulfate content, strength, and length of PMPC specimens were measured at different corrosion ages under 5% Na₂SO₄ solution soaking conditions, and the phase composition and microstructure were analyzed. The conclusion is as follows: In PMPC specimens subjected to one-dimensional SO₄^2- corrosion, the relation between the diffusion depth of SO₄^2- (<i>h</i>) and the SO₄^2- concentration (<i>c</i> (<i>h</i>, <i>t</i>)) can be referred by a polynomial very well. The sulfate diffusion coefficient (<i>D</i>) of PMPC specimens was one order of magnitude lower than Portland cement concrete (on the order of 10^-7 mm²/s). The surface SO₄^2- concentration <i>c</i> (0, <i>t</i>), the SO₄^2- computed corrosion depth <i>h</i>₀₀, and <i>D</i> of FM2 specimen containing 20% fly ash (FA) were all less than those of the FM0 specimen (reference). At 360-day immersion ages, the <i>c</i> (0, 360 d) and <i>h</i>₀₀ in FM2 were obviously smaller than those in FM0, and the <i>D</i> of FM2 was 64.2% of FM0. The strengths of FM2 specimens soaked for 2 days (the benchmark strength) were greater than those of FM0 specimens. At 360-day immersion ages, the residual flexural/compressive strength ratios (360-day strength/benchmark strength) of FM0 and FM2 specimens were all larger than 95%. The volume linear expansion rates (<i>S_n</i>) of PMPC specimens continued to increase with the immersion age, and <i>S_n</i> of FM2 specimen was only 49.5% of that of the FM0 specimen at 360-day immersion ages. The results provide an experimental basis for the application of PMPC-based materials.