Research On The Effect Of Fluosilicate On The Properties Of Cement And Its Dissolution Behavior

As a by-product of phosphorus fertilizer,fluosilicate has better economic and environmental benefits.Fluosilicates can be used to improve the working performance and service performance of cementitious materials to a certain extent,so it is an important utilization way of fluorine-silicon resources in by-product of phosphate fertilizer that fluorine products are effectively used in cementitious materials.First,the effect of sodium fluosilicate on coagulation time was systematically studied,The results show that sodium fluosilicate has retarding effect and an optimal dosage.When the dosage of sodium fluosilicate is less than 0.5%at water-cement 0.26,the coagulation time is increased with the increase of the content,when the dosage is more than 0.5%,the setting time is decreased with the dosage increasing,and even procoagulant effect occurs;the optimal dosage is increased with the increase of water cement ratio.The effect of sodium fluosilicate on the coagulation time of different varieties of Portland cement shows the same trend,but the optimal dosage is changed,which is related to the C₃A content in cement.The retarding effect of different fluoride was also compared.In the case of the same amount of fluorine,the retarding effect from strong to weak is potassium fluosilicate,sodium fluosilicate and magnesium fluosilicate;the retarding effect of fluosilicate is better than that of fluoride.Second,the effect of sodium fluosilicate on the mechanical properties and acid resistance of the motar were discussed.It was found that in the range of 1%,the incorporation of sodium fluosilicate has little effect,even enhancement on the 3d,28d and 90d strength of the cement-based materials.When the content exceeds a certain value,the incorporation of sodium fluosilicate is unfavorable to the development of the strength,and the compressive strength at 3d and 28d is significantly lower than that of the blank.The effect of different fluosilicates on the strength of mortar shows the same trend,but the optimum content was different.In addition,the appropriate amount of sodium fluosilicate can improve the acid resistance of cement-based materials.Thirdly,the effects of sodium fluosilicate on the phase composition andmicrostructure of cement hydration products were analyzed The main function of this kind of material in the process of cement hydration is to capture the Ca²⁺in the liquid phase,to form a new precipitated substance?CaF₂?and silicic acid gel,and no obvious chemical action with C-S-H.In the initial hydration period,incorporation of sodium fluosilicate inhibits the nucleation of Ca?OH?₂ and delay the hydration of C₃S;when the content is increased to a certain value,it accelerates the dissolution of gypsum,so that promote the hydrolysis of C₃A and a large number Afts formation,causing the slurry coagulation rapidly.Finally,Finally,the leaching behavior of fluorine containing cement based samples under different environmental conditions was investigated.The results show that the large volume of bulk cement-based material has a better fluorine fixation capacity;Dissolution of fluoride ion is increased with the increase of immersion time,temperature and dosage after the sample was crushed;sodium carbonate solution will promote fluorine ion dissolution from cement-based materials.