Freezing and thawing resistance of MKPC paste under different corrosion solutions

This paper investigates the resistance to freezing and thawing of magnesium potassium phosphate cement (MKPC) containing limestone (LS) and silica fume (SF) exposed to water, 3.5% sodium chloride solution and 5% sodium sulfate solution compared with that of pure MKPC paste. The deterioration including compressive strength and flexural strength, weight loss, deformation and water absorption were evaluated through freeze-thaw tests. To identify the products formed under the coupling effect, the phase compositions and morphologies of hardened MKPC specimens were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM-EDS) and thermal analysis (TG). The results indicated that the rate of deterioration in MKPC was significantly dependent on the types of solutions. As for MKPC paste without any admixture, its deterioration by 5% sodium sulfate solution showed the most aggressive corrosion subjected to 400 freeze-thaw cycles. However the addition of limestone powder and silica fume led to significant improvement in the resistance of MKPC paste exposed to combined solution attack and freezing-thawing and especially in sulfate solution. The minimum strength residual ratio was more than 85% and the weight losses were all below 5% after 400 times of freeze-thaw cycles in three kinds of solutions, the volume deformation and external damage was also improved. (C) 2019 Elsevier Ltd. All rights reserved.