Study On The Anti-erosion Ability Of Iron Oxide-rich Phosphoaluminate Cement

Iron-rich phosphoaluminate cement?PAC?is a new type of special cement,which is developed on the basis of phosphoaluminate cement.It has the advantages of low calcination temperature,early strength and high strength by increasing Fe₂O₃ content.In this paper,the effects of supplementary cementitious materials,such as limestone powder,fly ash and gypsum,on the resistance to sulfate ion attack,chloride ion penetration and frost resistance of iron oxide-rich PAC were investigated deeply.The microstructures and morphology of the hardened paste were analyzed by means of XRD,SEM and MIP.The reason for the improvement of the mechanical properties and the corrosion resistance of the cement were explained.The main conclusions are as follows:Compared with Portland cement?OPC?and sulphoaluminate cement?SAC?,iron-rich PAC exhibits higher erosion resistance.The chloride ion electric flux for 6h of OPC and SAC are 6000 C and 3000 C,respectively.On contrast,the chloride ion electric flux of iron-rich PAC is only 800 C.The erosion coefficient of resistance to sulfate for three types of cement cured for 90 d were 0.84,1.31 and 1.41.After 150 cycles of freezing-thawing the quality loss rate of OPC and SAC decreased to 5% of the original value,the dynamic modulus of elasticity loss rate dropped to 60% original value.Oppositely,after 200 cycles of freezing-thawing the compressive strength of iron-rich PAC still maintains high value.The porosities of OPC,SAC and iron-rich PAC were 27.3%,16.9% and 11.21%,respectively.The porosity of iron-rich PAC was low and most of its pore belongs to less harmful pores and harmless pores,which can delay the harmful ions to penetrate into the pastes.The calcium aluminate in the iron-rich PAC can react with the C l-to form the Friedel salt,which could optimize the pore structure.The p H value of OPC,SAC and iron-rich PAC is 12.9,11.8 and 10.9.The low pH of iron-rich PAC ensures that the lower osmotic pressure.The low hydrostatic and osmotic pressure of the paste endows iron-rich PAC with good frost resistance.When the content of limestone powder was 3% and 6%,the chloride ion electric flux decreased from 800 C to 429 C and 405 C,respectively.In addition,its erosion coefficient of resistance to sulfate was 1.26 and 1.22,respectively.After 200 cycles of freeze-thaw cycles,the compressive strength of iron-rich PAC with 5% 8% can be increased 3% 6%.When the dosage is in the range of 9% to 12%,the chloride ion electric flux increases to 503 C and 860 C,and the erosion coefficient of resistance to sulfate is 0.85 and 0.52.After 200 cysles of the freezing-thawing,the loss of compressive strength for iron-rich PAC is 14% and 21% When the content of limestone powder is 3%,6%,9% and 12%,the porosity of the pastes decreased from 13.5% to 6.78%,4.42%,6.09% and 9.87%,respectively.It concludes that the suitable quantity limestone powder can improve the density of the pastes.The limestone powder can react with calcium aluminate to produce calcium carboaluminate,which can improve the resistance to erosion performance of iron-rich PAC.If the content of limestone powder is excessive,the content of ementitious phase will decreases and worsen its mechanical performce.In addition,the smooth surface of calcium carbonate is not benefit to its mechanical performance and corrosion resistance of the iron-rich PAC.The appropriate contnent of limestone powder in iron-rich PAC is in the range of 3% to 6%.When the content of fly ash was 3%,6% and 9%,the chloride ion electric flux of decreases to 892,824 and 712 C,and the erosion coefficient of resistance to sulfate is 1.51,1.55 and 1.58,respectively.After 200 cycles of freezing and thawing,the compressive strength of the paste is 50.21,50.46 and 51.30 MPa,respectively.With its dosage increases to 12%,the chloride ion electric flux increases to 917 C and the erosion coefficient o f resistance to sulfate decreases to 1.10.After 200 cycles of freezing-thawing,its compressive strength decreases to 45.2MPa.The porosity of iron-rich PAC with fly ash of 3%,6%,9% and 12% was 12.1%,4.5%,10.5% and 12.5%,respectively.Appropriate content of fly ash can optimize the pore structure of cement paste.When the content of fly ash is excessive,the hydration product is reduced,and the low alkali system is difficult to activiate the pozzolanic effect.The appropriate content of fly ash is in range of 3% to 9%.When the content of natural gypsum 2%,5%,8% and 11%,the chloride ion electric flux of iron-rich PAC is 448,463,597 and 842 C,respectively,and the erosion coefficient of resistance to sulfate is 1.10,1.21,0.89 and 0.87.After 200 cycles of freezing and thawing,the compressive strength of iron-rich PAC is 50.46,51.30,50.21 and 45.2MPa,respectively.The porosity of the pastes with different content of gypsum cured for 28 d is 4.1%,4.5%,10.6% and 15.4% respectively.Gypsum reacts with calcium aluminate to produce ettringite,which can ptimize the pore structure.The appropriate content of gypsum in iron-rich PAC is in the range of 2% to 5%.