Enhancing Sulfuric Acid Resistance of Cement Paste through Incorporation of CMK with Different Specific Surface Areas: An Analysis of Mechanical Properties and Durability

This study investigates the impact of two different coal-bearing metakaolin (CMK) powders, characterized by varying specific surface areas, on the partial replacement of cement and its resultant effect on the sulfuric acid resistance of cement paste. The CMK-cement paste specimens underwent exposure to a 5% sulfuric acid solution, with subsequent analysis of degradation kinetics, phase composition, and microstructure. The degradation kinetics, encompassing appearance alteration and strength loss, revealed that both particle sizes of CMK contributed to a reduction in the degradation rate of the specimens, with finer CMK demonstrating a more pronounced effect. Moreover, the compressive strengths of the two CMK-cement pastes surpassed those of the pure cement paste by 8.5% and 16% at the 180-day mark. Moreover, resistivity and scanning electron microscope (SEM) tests unveiled a significant decrease in specimen porosity due to the addition of CMK, resulting in a greater retention of hydration products following acid curing. This improvement in structural compactness was particularly prominent for the finer CMK, with the porosity of coarser and finer CMK-cement paste found to be 20.66% and 57.80% lower, specifically, than that of pure cement paste after exposure to sulfuric acid. Furthermore, X-ray diffraction (XRD) patterns illustrated a heightened presence of hydration products and reduced levels of corrosion products, such as gypsum, in the cement paste featuring the addition of finer CMK post-sulfuric acid curing. In summary, this study underscores that the incorporation of CMK with a smaller specific surface area replacing part of the portland cement not only mitigates the degradation rate of cement paste through chemical and microstructural optimization but also demonstrates an even more pronounced enhancement effect when utilizing CMK with a larger specific surface area.