Sulfate Freeze-Thaw Resistance of Magnesium Potassium Phosphate Cement Mortar according to Hydration Age

Rong-Jian Ji; Tao Li; Jian-Ming Yang; Jun Xu

doi:10.3390/ma15124192

Sulfate Freeze-Thaw Resistance of Magnesium Potassium Phosphate Cement Mortar according to Hydration Age

Materials (Basel). 2022 Jun 13;15(12):4192. doi: 10.3390/ma15124192.

Authors

Rong-Jian Ji¹, Tao Li², Jian-Ming Yang², Jun Xu³

Affiliations

¹ Yangzhou Polytechnic Institute, College of Architecture Engineering, Yangzhou 225127, China.
² School of Civil Engineering, San Jiang University, Nanjing 210012, China.
³ College of Civil Engineering and Architecture, Jiangsu University of Science and Technology, Zhenjiang 212000, China.

Abstract

Concrete structures can be degraded by exposure to environmental stressors such as freeze-thaw cycling and salt corrosion. Magnesium potassium phosphate cement (MKPC) mortar is useful for the rapid repair of such structures but must acquire environmental resistance rapidly. In this study, the freeze-thaw resistance of MKPC mortar specimens of different hydration ages was tested in water and a 5% Na₂SO₄ solution. The strength, volume deformation, and water absorption rates were compared with those of full-age MKPC mortar specimens (28 d). The phase composition and microscopic morphology of the MKPC mortar specimens before and after corrosion were observed, and the corrosion-resistance mechanism was analyzed. After 225 freeze-thaw cycles in water and sulfate solution, the strength residual rates of the early-age specimen (1 d) were higher than those of the full-age specimen (28 d). The degree of strength attenuation in the 1 d specimen was lower in the sulfate environment than in the water environment. After 225 freeze-thaw cycles, the volume expansion rates of 1 d specimens in water or sulfate were 0.487% and 0.518%, respectively, while those of 28 d specimens were 0.963% and 1.308%. The comparison shows that the 1 d specimen had significantly better deformation resistance under freeze-thaw than the 28 d specimen. After 225 freeze-thaw cycles, the water absorption rates of 1 d specimens were 1.95% and 1.64% in water and sulfate solution, respectively, while those of 28 d specimens were 2.20% and 1.83%. This indicates that freeze-thaw cycling has a greater effect on the pore structure of fully aged mortar than on early-age mortar (1 d). Therefore, MKPC mortar is suitable for the rapid repair of concrete structures in harsh environments. The results form a theoretical basis for winter emergency repair projects. They also further the understanding of the application of MKPC-based materials in extreme environments.

Keywords: freeze–thaw resistance; hydration age; magnesium potassium phosphate cement; strength; sulfate corrosion; volume deformation; water absorption.

Grants and funding

This work was supported by the National Natural Science Foundation of China (grant no. 51578475) and the Natural Science Foundation of the Jiangsu Higher Education Institutions of China (grant no. 21KJD560001). School-level subject of Yangzhou Polytechnic Institute (grant no.2110002/124). The authors thank all the anonymous reviewers for helping improve this paper.