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

## TL;DR

This study examines how sulfate ions affect potassium magnesium phosphate cement paste, finding that adding fly ash improves its resistance to sulfate corrosion.

## Contribution

The study introduces a new experimental comparison of sulfate corrosion resistance in PMPC with and without fly ash.

## Key findings

- The sulfate diffusion coefficient in PMPC with 20% fly ash was 64.2% of the reference specimen.
- FM2 specimens showed higher strength and lower expansion rates compared to FM0 after 360 days of immersion.
- Residual strength ratios of both PMPC specimens remained above 95% after long-term sulfate exposure.

## Abstract

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 SO42− corrosion, the relation between the diffusion depth of SO42− (h) and the SO42− concentration (c (h, t)) can be referred by a polynomial very well. The sulfate diffusion coefficient (D) of PMPC specimens was one order of magnitude lower than Portland cement concrete (on the order of 10−7 mm2/s). The surface SO42− concentration c (0, t), the SO42− computed corrosion depth h00, and D of FM2 specimen containing 20% fly ash (FA) were all less than those of the FM0 specimen (reference). At 360-day immersion ages, the c (0, 360 d) and h00 in FM2 were obviously smaller than those in FM0, and the D 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 (Sn) of PMPC specimens continued to increase with the immersion age, and Sn 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.