Experimental study on sulfate corrosion behavior in water saturated PMPC paste and effect of W/C

Abstract

The paper investigates the sulfate corrosion behavior in potassium magnesium phosphate cement (PMPC) paste immersed in a 5 % Na₂SO₄ solution and effect of W/C. The conclusions are as follows: the concentration of sulfate ions decreases significantly with increasing erosion depth, the PMPC specimen with large W/C (P1) exhibited a higher content of SO₄²⁻ at the same depth compared to the PMPC specimen with small W/C (P0). Both the SO₄²⁻penetration depth and the SO₄²⁻ content inside PMPC specimen gradually increase with erosion ages. when soaked for 360 days, the measured erosion depth (h₀) in the P1 specimen is 1.43 times that of the P0 specimen, and the SO₄²⁻ content at a depth of 2 mm is 1.11 times that of the P0 specimen. The relationship between the diffusion depth x (mm) of the SO₄²⁻ and the SO₄²⁻ content c (x, t) in PMPC specimens is well described by a polynomial with R² ≥ 0.999. The surface sulfate content (c_s (0, t)) gradually increases with soaking time (t). The c_s (0, t) of P1 specimens is significantly larger than that of P0 specimens, and its calculated erosion depth of the SO₄²⁻ (h₀₀) exceeds that in P0 specimens. After 360 days of immersion, the c_s (0, t) of the P1 specimen is slightly larger than that of the P0 specimen, the h₀₀ of P1 and P0 specimens is 14 mm and 19 mm, respectively. The diffusion coefficient of SO₄²⁻ (D) in PMPC specimens is on the order of 10⁻⁷ mm²/s (1/10 D of Portland cement concrete reported in previous studies). The D first increases and then decreases with t. At the same soaking age, the D of P1 specimens is significantly larger than that of P0 specimens. Specifically, the D of P1 specimens is 1.65 times that of P0 specimens when the soaking age is 360 days. As the immersing age increases, the strengths of PMPC test pieces first increase and then decrease. After immersing in the solution for 360 days, the strength residual rate of P0 test pieces is higher than 95 %, while the strength residual rate of P1 test pieces, though lower than that of P0, is still greater than 90 %. The development trend of the total porosity, diffusion coefficient and strength of PMPC specimens with different sulfate solution soaking ages is consistent.