| Alkali-activated geopolymer is a new type of inorganic polymer material,which is synthesized from aluminosilicate materials under alkaline environment.During the progress of the geopolymerization,alkali activator cannot be completely consumed.Therefore,geopolymer is confronted with a serious problem of efflorescence,and this issue becomes one of the factors limiting the practical application of geopolymer.In this paper,to study the migration and distribution of Na’ in slag-based geopolymer activated by sodium silicate solution,to discuss the effect of n(M2O)/n(Al2O3)or n(H2O)/n(M2O)on efflorescence of slag-based geopolymer(M is Na,K),and to investigate efflorescence of these two types of geopolmer prepared by sodium silicate solution and potassium silicate solution respectively,including the substance precipitated by efflorescence,research methods such as XRF、SEM、XRD、EDX、BET、efflorescence test、leaching test et.al were used.The results of this study are as follows:(1)Adjusting the water contents of slag-based geopolymer to increase n(H2O)/n(Na2O),the porosity and water loss rate of geopolymer gradually increased,Na contents of geopolymer samples showed an upward trend from bottom to top(evaporated end)overall,and alkali leaching rate at differet height of geopolymer showed similar trend.Top end got the maximum Na contents and alkali leaching rate at the same time.Increasingn(H2O)/n(Na2O)promotes the migration of Na’.Top end of geopolymer exposured to environment and the prolongation of curing time could promote the migration of Na+ in a limited way.(2)Improvingn(Na2O)/n(Al2O3)through changing the contents of sodium silicate solution,the compressive strength of slag-based geopolymer gradually decreased,the shrinkage rate gradually became larger,the pore size got finer and the porosity,decreased first and then rised gradually;Improving n(H2O)/n(Na2O)through adjusting water contents,the compressive strength diminished,the shrinkage became stronger,and the pore size tended to increase slightly after decreasing,while the porosity increased gradually.Serious efflorescence occurred in slag-based geopolymer activated by sodium silicate solution,and many white powdery and flocculent substances precipitated on the surface.With the increase of n(Na2O)/n(Al2O3),the extent of efflorescence decreased initially and then aggravated,while it weakened with the increase of n(H2O)/n(Na2O).(3)Changing the dosage of potassium silicate solution to increase n(K2O)/n(Al2O3)of slag-based geopolymer,the compressive strength of geopolymer increased first and then decreased,the shrinkage rate became larger,the pore distribution was more concentrated and the pore diameter got narrower,and the porosity got less gradually;During the progress of promoting n(H2O)/n(K2O),the compressive strength became lower,and the shrinkage became stronger.Besides,the pore distribution got more concentrated first and then got wider slightly,and the porosity decreased initially and then increased.Slag-based geopolymer activated by potassium silicate solution didn’t present obvious efflorescence on the surface.The concentration of K+ of solution washed geopolymer after efflorescence test became less with the increase of n(K2O)/n(Al2O3)overall,and it diminished obviously with the increase of n(H2O)/n(K2O).(4)Analyzing the deposited substances precipitated by efflorescence of slag-based geopolymer through XRD,SEM,and EDX,the consequences demonstrated that sodium carbonate and sodium bicarbonate were the main white substances produced by efflorescence of slag-based geopolymer activated by sodium silicate solution.However,only a small amount substances precipitated from the slag-based geopolymer activated by potassium silicate solution after efflorescence test,mainly consisting of potassium sulfate,potassium bicarbonate and calcium carbonate.Geopolymer prepared by these two types of alkali activators showed significantly different efflorescence phenomenon,and the use of potassium silicate solution can effectively inhibit efflorescence. |
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