Experimental Study On Sulfate Corrosion Resistance Of Potassium Magnesium Phosphate Cement

Potassium magnesium phosphate cement?MKPC?is a new inorganic cementitious materialformed by mixing magnesiapowderandsoluble phosphate in proportion.Through the long-term immersion test of fresh water and sodium sulfate solution,it was found that the strength loss of the MKPC specimen in fresh water immersion for 360 days was 3⁴%,and the strength increased by 5⁶%in the sodium sulfate solution for the same time,reflecting the good resistance to sulphate resistance.The addition of fly ash and slag powder reduces the linear expansion rate of MKPC in soaking with sodium sulfate by 0.198%and 0.058%respectively,and the fly ash can also help to improve the strength of MKPC in soaking sodium sulfate.The freeze-thaw cycle tests of MKPC were carried out in fresh water,sodium sulfate,Magnesium Sulfate and Sodium Chloride Solution respectively.After 400 cycles,the loss rate of compressive strength?22%?and mass loss rate?1.03%?in the freezing thawing of sodium sulfate did not reach the standard of freezing and thawing damage,which showed that the MKPC base group had good frost resistance.In the freeze-thaw of sodium sulfate solution,the maximum expansion rate of the specimen is 0.275%,and the part of the specimen is fractured,and the main part of the sodium chloride freeze-thaw is surface erosion,and the angle of the Magnesium Sulfate freeze-thaw is slightly damaged.The addition of steel slag powder and fly ash reduces the initial water absorption of MKPC specimens by 0.17%and 0.07%respectively.After 400 cycles of the same sodium sulfate freezing and thawing environment,the increase of water absorption rate is reduced by 0.11%.The loss of compressive strength of the specimens is reduced by 26%and 15%,and the loss rate of mass is reduced by 0.4%and 0.17%,respectively,with the same sodium sulphate freezing and thawing environment.The expansion rate is reduced by 0.201%and 0.075%,indicating that fly ash and steel slag powder are beneficial to improve the sulfate resistance and freeze-thaw properties of MKPC.The diffusion concentration of SO₄^2-in MKPC increased with the increase of erosion time in the three erosion conditions of long-term immersion,freezing thawing cycle and electric pulse,and gradually decreased with the increase of depth.The SO₄^2-diffusion depth x and the erosion time t satisfy the x=at^brelation of power function.In the same corrosive environment,the SO₄^2-diffusion coefficient in MKPC decreases with the increase of erosion time due to the change of internal and external concentration difference.The SO₄^2-diffusion coefficient of MKPC is 10^-7mm²/s orders of magnitude in the long term immersion,and it is 10^-6mm²/s orders of magnitude in the freeze-thaw cycle and electric pulse.It shows that the diffusion of SO₄^2-in MKPC can be accelerated by the freezing thawing cycle and the electric pulse environment.Under the conditions of freeze-thaw cycle and electric pulse,the addition of fly ash obviously slows the diffusion of SO₄^2-,and the addition of steel slag powder helps to reduce the SO₄^2-diffusion rate of MKPC in the long-term soaking and freeze-thaw cycle.