Study On Microstructure Of High Strength Geopolymer And Solidification/Stabilization Of Organic Pollutants By Geopolymer

Geopolymer is a new type of cementitious material with great potential.Compared with the traditional inorganic cementitious material cement,the preparation process of fly ash geopolymers does not need to consume a lot of energy,and solid wastes produced by metallurgy and thermal power generation can also be used.The study of geopolymer is of great significance to resource utilization and environmental protection.Fly ash based and fly ash-slag based geopolymers of high strength were prepared,the influences of Si/Al ratio,curing temperature,slag content and age on the compressive strength of geopolymers were studied in this paper.The microstructure and composition of fly ash geopolymers at different ages were studied by scanning electron microscopy（SEM）,X-ray diffraction（XRD）,X-ray fluorescence spectroscopy（XRF）and mercury intrusion porosimetry（MIP）.The influence of amorphous content on the strength of geopolymer is analyzed by XRD-Rietveld refinement method.The reason of decline of geopolymers’long-term strength and the organic pollutants solidified by geopolymers were also studied in this paper.The main results are as follows:（1）Si/Al ratio and curing temperature are the main factors which influence compressive strength of fly ash geopolymers.By adjusting the modulus of alkaline activator,the Si/Al ratio and water solid ratio of geopolymers can be controlled within a reasonable range,so as to prepare high strength-fly ash geopolymers.The curing conditions of high temperature can effectively promote the formation of polymer reaction,and the long-term strength can be increased by two times.The addition of moderate slag can significantly improve the strength of geopolymers,and C-S-H and C-A-S-H gel are produced in fly ash-slag geopolymer.（2）As the leading variable,amorphous content has a significant positive correlation with the compressive strength of fly ash geopolymers.With the increase of amorphous content,the compressive strength of geopolymers also presents an increasing trend.The relationship between amorphous content and strength of geopolymers can be regressed by logarithmic function model.（3）The reasons for decline of geopolymers’long-term strength were analyzed by SEM,XRD,MIP and other microscopic testing methods:cracks of geopolymers produced by water evaporation and volume shrinkage;precipitation of Na₂CO₃·H₂O leads to the decomposition of hydration products of geopolymers,which resulted in the deterioration of microscopic pore structure.（4）Cement solidified body was control group and fly ash geopolymers modified by different admixtures were experimental groups,the solidification ability of geopolymers for organic pollutants was studied.The solidification ability for organic pollutants can be improved by addition of porous materials such as diatomite tailings and zeolite.