Study Of Metakaolin-based Geopolymer Mechanism Of Reaction At Ambient And High Temperature

Geopolymer is a kind of cementitious materials obtained by alkali activation of active ingredients full of silica-alumina,such as metakaolin,fly ash,which is receiving increasing attention in the field of civil engineering applications as the advantages of low-carbon high-strength and environment-friendly.Solidification temperature one of the key factors for geopolymer synthesis and final structural engineering performance,but there still exists disagreement on the study of influence mechanism of the solidification temperature.This paper explored the mechanical properties of geopolymer composed of 9 types of metakaolin under different solidification temperature,and analyzed the functional mechanism of the solidification temperature influencing metakaolinite-based geopolymer properties by means of microcalorimetry,FTIR,SEM and other testing technologies.Research results showed that increased solidification temperature could promote the dissolution and condensation of silicon aluminum acid salt so as to effectively improve the mechanical properties of metakaolinite-based geopolymer;but the excessive heat would accelerate the reaction speed of condensation,thus the condensation precursor produced by dissolving silicon aluminum acid salt was wrapped by generated gel,not able to contact alkali inspired agent to give the condensation reaction,causing the inadequate geological aggregate reaction and the reduced geopolymer mechanical properites.High-strength geopolymers require the promotion of high temperature solidification reactions,which condition greatly limit the wide application of geopolymer.The experiment mixed the granulated blast furnace slag into the metakaolin,hoping to improve the solidification properties of geopolymer under normal terperature and revealed the reaction mechanism from the microstructure through XRD,FTIR,SEM and micro-thermal analysis.Results indicate that slag admixture can effectively promote the geopolymer solidification properties under normal temperature,as well as get Si-O-Al network-like structure and the coexisting high-strength structure of C-S-H gel and C-A-H gel,but the excessively high slag content will make the structure cracked and generate CaCO3 crystals attached to the structure,bad for the strength development.The best geopolymer structure can be obtained by adopting low activator module and 40% of slag content,with the 28 D strength of 95.17 MPa.