Role of Silica Fume in Geopolymer Shrinkage Property Regulation and Geopolymerization Process
To solve the severe early dry shrinkage deformation of geopolymer and to realize the efficient use of geopolymers in road engineering,the shrinkage property and geopolymerization process of fly ash-granulated blast furnace slag(FA-GBFS)geopolymer were regulated by using silica fume.On the basis of using silica fume to improve the dry shrinkage performance of FA-GBFS geopolymer,the changes of pore distribution and microstructure inside the geopolymer were observed,as well as the effects of silica fume on the degree of reaction inside geopolymer were explored.The variation rule of silica fume reaction degree to inside geopolymer was studied.The mechanism of the effect of silica fume on the dry shrinkage behavior of geopolymer and the geopolymerization process was further revealed.The result indicates that the dry shrinkage of geopolymer is mainly concentrated in the early stage.The shrinkage strain reaches 80%-90%of the total strain in 7 d.The addition of silica fume makes the dry shrinkage strain of geopolymer decrease gradually.When the content of silica fume reaches 20%,the dry shrinkage strain of geopolymer decreases by 50%.Simultaneously,the content of 20 nm-10 μm pores in the geopolymer decreases.In addition,by changing the binding energy and relative content of Si—O—T(T is Si or Al)structure and tetrahedral coordination Al—OH bond in FA-GBFS geopolymer,the early middle stage geopolymerization reaction and calcium silicate hydration reaction in geopolymer are delayed.Therefore,the phenomenon that the moisture inside geopolymer evaporates largely due to the exothermic hydration reaction is improved.This also reduces the harmful pores amount produced by the heat of hydration in the geopolymer.When the content of silica fume reaches 20%,the silica fume has a good synergistic effect on the dry shrinkage and mechanical properties of geopolymer,which not only has the low dry shrinkage strain,but also improves the mechanical strength in 28 d.
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