Effect Of Aluminous Silica Mineral Admixture On Properties Of Potassium Magnesium Phosphate Cement(MKPC) Mortar

Potassium magnesium phosphate cement has the characteristics of fast setting and high early strength,and has been used as a rapid repairing material in civil engineering.However,it has been reported that potassium magnesium phosphate cement?MKPC?has the disadvantages of poor water resistance and short setting time;and early hydration is fast,and heat release is large,which affects its late durability.Therefore,research on the performance of modified potassium magnesium phosphate cement for the above problems has important research significance.This paper mainly studies the effects of bleed-type water reducing agent and aluminum siliceous mineral admixture?metakaolin and illite?on the water resistance and sulfate corrosion resistance of MKPC mortar.In this paper,the modified MKPC mortar is placed in water environment and sulfate environment respectively,and long-term static water and hydrodynamic water immersion,freeze-thaw cycle and salt freeze-peeling test are carried out to study the changes of physical and mechanical properties,combined with microscopic analysis of its phase composition.And microstructure to explore its corrosion and sulfate corrosion mechanisms.In addition,the effect of aluminosilicate mineral admixture on the sulfate diffusion in MKPC mortar was also determined by measuring the SO₄^2-osmotic concentration.Research indicates:1.Under the state of natural curing,the addition of bleed-type water reducing agent improves the fluidity of MKPC mortar,but it is not obvious for improving the flexural and compressive strength,improving the volume shrinkage and delaying the heat release.While the aluminum siliceous mineral admixture slightly reduces the fluidity of the mortar,it improves the 60d flexural and compressive strength of the mortar,improves the volumetric shrinkage,accelerates the reaction rate,and makes the interface of the mortar hydration product more dense.2.Long-term static water immersion,dynamic water immersion and water freeze-thaw tests on modified MKPC mortar show that the damage of MKPC mortar is the most serious,followed by long-term dynamic water immersion and static water immersion.In the three environments,the strength loss of the benchmark group is large,the volume expansion rate is large,the specimen damage is serious,and the water absorption rate is increased.The air entraining agent does not improve the mortar performance.The mortar strength loss is the smallest and the shrinkage value is modified.Small,the shape changes are not obvious,and the water absorption rate changes little.The aluminum siliceous mineral admixture has a good effect on the water corrosion resistance of MKPC mortar.The reason is that the active component in the siliceous mineral admixture participates in hydration,forms a phosphate gel,and fills the capillary pores,thereby improving its water corrosion resistance.3.In the 5%Na₂SO₄ solution,the modified MKPC mortar showed an undulating change after 300d long-term immersion and 300 freeze-thaw cycles.The air entraining agent has no obvious improvement on the strength of MKPC mortar in sulfate corrosion,and the aluminum silice mineral admixture has good improvement effect.The freeze-thaw cycle has a great influence on the volumetric deformation of the slurry,and the volume deformation of the MKPC mortar containing the aluminous siliceous mineral admixture in the sulfate environment is significantly reduced.The admixture has obvious effect on improving the pore structure of MKPC slurry.The active component in the aluminous siliceous mineral admixture participates in hydration to form a phosphate gel,which fills the capillary pores and inhibits the corrosion of the sulfate,thereby improving its resistance to sodium sulfate corrosion.4.The SO₄^2-diffusion law of MKPC mortar is basically the same during the test,that is,the concentration of SO₄^2-increases with the increase of erosion time,and the depth of the surface of the specimen is larger,the smaller the concentration of SO₄^2-is.The incorporation of bleed-type water reducer has little effect on the permeability of SO₄^2-in the mortar,while the aluminosilicate mineral admixture has a certain slowing effect on the diffusion of sulfate ions in MKPC,and the effect of metakaolin is more obvious.Under different sulfate attack environments,the SO₄^2-diffusion depth x and the erosion time both satisfy the power function relationship.In the long-term immersion environment,the diffusion coefficient D is on the order of 10^-5mm²/s;in the fast freeze-thaw environment,the diffusion coefficient D is significantly larger than the long-term immersion,and the order of magnitude is mostly10^-4mm²/s,further verifying the acceleration of the freeze-thaw cycle.The spread of SO₄^2-.