Influence Of Water And Salt Content On The React Process And Strength Of Alkali-actived Geopolymer

There are many researches on geopolymer-solidified saline soil,but only few research on the mechanism of salt on the reaction of geopolymer.Previous studies mostly focused on the effect of solidification and the properties of solidified soil,ignoring the importance of salt content and type on the chemical reaction during solidification.This article use fly ash as a solid raw material and water glass as an alkali activator to prepare geopolymers.The mass rations of water,sodium sulfate and sodium chloride in the system were changed.The influence of the reaction process and strength of alkai-actived geopolymer were investigated.X-ray diffraction,Fourier transform,scanning electron microscopy,energy spectrum analysis,physical adsorption,and nuclear magnetic resonance were used to conduct in-depth qualitative and quantitative analysis of the chemical composition,microstructure,and pore distribution of geopolymers,respectively.The mechanism of the effect of water and salt content on the polymerization process of geopolymers was explored,and the mechanism of the effect of water and salt content on the strength of alkali-activated fly ash base polymer was described.The conclusions as follows:(1)The water-to-binder ratio significantly affects the strength and microstructure of alkali-activated geopolymers.The water-binder ratio increased from 0.25 to 0.35,and the geopolymer strength continued to decrease from 30.7 MPa to 12 MPa.With the water-binder ratio increasing,the mineral phase in the geopolymer system has not changed basically,and the solubility of fly ash and the surface erosion of the vitreous body have decreased.The continuous increasing of nano-scale pores and average pore diameters indicates that the increasing of water content in the geopolymer systems reduces the degree of polymerization reaction,which adversely affects the reaction process and microstructure development of the geopolymer.(2)Under the same water-to-binder ratio,the lower content of sodium sulfate could not affect the unconfined compressive strength significantly.However,when the sodium sulfate content is low until reaches a certain value,the unconfined compressive strength increases first,and then decreases.Meanwhile,the peak value shifts to down with the increase of the water-to-binder ratio.At the lower content of sodium sulfate,it does not substantially affect the geopolymer reaction process and microstructure due to the high dissolution and dispersion of the sodium sulfate;while at high contents,sodium sulfate can promote the polymerization reaction and improve the micro strength,but excessive sodium sulfate can limited the polymerization reaction of geopolymer.In addition,sodium sulfate crystals would produces an aerial structure,resulting the strength reduce.(3)As the content of sodium chloride increasing,the unconfined compressive strength of alkali-activated geopolymers decreases in the overall trend.With the sodium chloride content increasing,the occurrence of geopolymerization was restricted.So as the unreacted sodium chloride crystals was increased and network structure of gels was singularized,resulting in a decrease in strength.