Studies On Reaction Mechanism And Preparation Of Kaolinite-based Geopolymer

Due to their unique structure and excellent properties,Kaolin is considered a precious natural resources and with a broader range applications.This paper,from the point of the study of the kaolin’s activity,geopolymer was prepared with metakaolin as mineral admixture by adopting the orthogonal design and obtained the greatest technology control-factors on the compress strength by the range analysis method.To explore the reaction mechanism,geopolymer was prepare by adding active Al2O3 and the process of reaction was monitored by using of various analysis and characterization methods.Activiting kaolin by three different ways: calcined at high temperature,calcined with alkali,mechanical ball-milling.The calcined at high temperature are most effective when calcined 2.5 hours at 70℃.The kaolin activation mechanism is that the three-dimensional structure had been destroyed and the activity of contact were increased.Also,the main influences of module of waterglass,curing time,curing temperature,the content of the alkali activator and fly ash,aging time and temperature on the compressive strength are investigated.According to the results of orthogonal test,the best factors are as follows: 100 g metakaolin as main raw material,the content of the alkali activator(module=1.0)and fly ash are 80 g and 30 g separately,curing 12 h at 50℃.The compression strength has reached 46.10 MPa,39.14 MPa and 73.4MPa for 1 day,7day and 28 day.Through the analysis of the technology control-factors on the compress strength by the range analysis method,the results are as follows: the main control-factors are the alkali activator in early maintenance(1day),the main control-factors are cuing time in media(7day)and advanced(28day)maintenance.The XRD analysis indicated that no new crystal phase are found in the samples and they all belong to the amorphous structure.The FITR analysis showed that the 1000 cm-1 absorption peaks shifted to lower wave numbers,indicating the Si-O-Al structure following poly-condensation.The measured hydration heat emission revealed that there is an essential difference between geopolymer’ polymerization and cement hydration reaction.What’ more,the polymerization are divided four stage by the hydration heat curves.The samples prepared by different active SiO2/ Al2O3 ratios were measured by XRD,FITR,pH,compressive strength and conductivity,and the process of reaction would be divided four stages: alkali solution stage,aluminosilicate gel forming stage,polymerization stage and net structure forming stage.