Study On The Durability Of Potassium Magnesium Phosphate Cement(MKPC)-based Anticorrosive Coating

Potassium magnesium phosphate cement（MKPC）based anti-corrosion coating is based on the large fluidity MKPC.Through the preliminary research,large fluidity MKPC can cooperate with related spraying equipment for spraying,which is convenient and fast in construction and has a broad application prospect.In the previous study,MKPC with large fluidity has excellent early performance,but the research on durability has not been involved.In this paper,three kinds of corrosion environments are designed:long-term immersion,freeze-thaw cycle and dry wet cycle.The corrosion media are fresh water,5%sodium sulfate solution and 3.5%sodium chloride solution,by comparing the strength,mass loss,shrinkage rate and other macro parameters of MKPC hardened body mixed with water glass and different mineral admixtures in the process of corrosion,combined with XRD and SEM-EDS,the influence of water glass and mineral admixtures on MKPC corrosion resistance in three corrosion environments was analyzed.（1）In the long-term immersion test,the strength loss rate of blank group Specimens and MKPC Specimens mixed with water glass in three media environments is not more than 17%;The strength of MKPC specimens with mineral admixtures increased to a certain extent after immersion corrosion in three media,and the volume expansion and water absorption of MKPC specimens with water glass and mineral admixtures also decreased to a certain extent;（2）In the freeze-thaw cycle test,after 300 freeze-thaw cycles,the strength loss of MKPC specimens with four mix proportions is not more than 25%,and the strength loss of MKPC specimens with water glass and mineral admixture is less than that of blank group;The mass loss of MKPC in the process of freeze-thaw is less than 5%,the highest is only 0.958%.In the process of freeze-thaw,the volume stability of MKPC is good,the volume expansion after 300 freeze-thaw cycles is only 0.043%,and the volume expansion rate and mass loss of MKPC in the process of freeze-thaw can be reduced by adding mineral admixture;（3）In the dry and wet cycle test,the strength of MKPC specimen still increased after 180d under the double erosion of dry and wet cycle and salt solution.In the blank group,the strength increased by 3.4%in fresh water,8.3%and 4.6%in 5%sodium sulfate solution and 3.5%sodium chloride solution.The strength of MKPC with water glass increased about 10%in three media environments,while that of MKPC with mineral admixture increased 12%¹3%in fresh water environment,increase about 20%in two salt solutions.The mass loss in the process of dry and wet cycle is less than 1%,and the glass and mineral admixture play a positive role in reducing the quality in the process of dry and wet cycle.The test data show that MKPC specimen has good corrosion resistance,and the durability of MKPC specimen mixed with water glass and mineral admixture has been improved in three corrosion environments,and the performance of MKPC in two salt solutions is better in three corrosion environments.Through micro test,MgSiO₃,AlPO₄and other new cementitious materials were found in MKPC hardened body with water glass and mineral admixture.The analysis should be that the active substances in the water glass and mineral admixtures combine with some ions in the hydration reaction system of MKPC hardening body,and the newly formed cementitious substances can play a role of cementation,help MKPC hardened body to form a more stable network structure,on the other hand,fill the gaps in the hardening body,and improve the internal pore structure of MKPC hardening body.Metakaolin and fly ash can be used as micro aggregate to fill the hardened body of MKPC.