Study On Steel Corrosion Mechanism Of Magnesium-potassium Phosphate Cement

Magnesium-potassium phosphate cement(MKPC)has many advantages,such as fast harding,early high strength and excellent steel protecting ablitily.There is a huge potential for development in the application of structural engineering.But because its hydration mechanism and cement materials are so special,MKPC steel bar corrosion mechanism remains to be revealed.This paper mainly studies the pH value and resistivity of MKPC;The corrosion current density and corrosion potential of steel in MKPC;the ability against cracks by steel corroison in MKPC was evaluated by the corrosion acceleration experiment.The microstructures of steel in MKPC were investigated though XRD and SEM-EDS.The main conclusions are as follows:1.Before initial setting,the slurry of MKPC is acidic,and the slurry corrodes steel.After that,pore fluid pH value of LM13 is 9.8 at 3d;it is up to 10.3 at 56d;with P/M being higher,the pH value of 3d increases;with adding silica fume,the pH value of 3d decreases;with adding fly ash,the pH value of 3d increases.All of the pH values are about 10.3 at 56d.In this low alkalinity environment,the steel can not form a passivation film on the surface.2.MKPC has resistivity with early rapid growth,and lately it becomes stable.The resistivity of LM13 is 550 ?·m at 3d,1100?·-m at 56d.The P/M is lower,the resistivity is greater.Adding silica fume improves the resistivity.Adding fly ash slightly only lowers the resistivity of 3d with little influences at 56d.The resistivity enhances MKPC obstructing ability against Ion migration that can keep steel from corrosion.3.At 3d steel in OPC remains uncorroded,steel in MKPC remains corroded,but at 56d both of them show no corrosion any more.At 3d the resistivity of LM13 is low,steel has corrosion in MKPC;Lowing P/M makes resistivity higher,making corrosion slighter;adding silica fume highs the resistivity that makes corrosion slighter.adding fly ash lows the resistivity that make corrosion severer.But the resistivity at 56d is great making corrosion stop.Lowing P/M and adding silica fume is benefit to stop corrosion,fly ash has little influence on corrosion.4.In the constant voltage accelerating corrosion experiment,steel corrosion in OPC is accelerated with appearant effects with cracks after 4 days;while the LM13 has little effects without cracked in 28days.Highing P/M makes corroison acceleration more effective;adding silica fume makes corrosion less effective;adding fly ash makes corrosion more effective;Lowing P/M is benefit to being against corrosion acceleration,but excessively low P/M is easily to making cracks.