Research On Compressive Strength And Shrinkage Of Bottom Ash Based Geopolymer

Cement is not only the most important and widely used cementitious material in construction,but also an industry of high energy consumption,high pollution and high emissions,which has attracted deep concern of government.Geopolymerization can transform a wide range of industrial waste into building materials.As a low-carbon and environmental friendly cementitious material,geopolymer is considered to be a construction material to promote the sustainable development.Based on the analysis of the character of the ground bottom ash powder,geopolymers were synthetized from bottom ash using sodium hydroxide(NaOH)and sodium silicate(Na2SiO3)solutions as activators.The influence of metakaolin dosage,cure conditions,silica modulus,activator dosage and water to solid on the compressive strength of geopolymers were explored.And the microstructure was characterized by X-ray diffraction,FTIR and SEM.Finally,the shrinkage of bottom ash-metakaolin based geopolymers was studied and compared with the cement paste shrinkage.The results of the analysis of bottom ash showed that the content of SiO2 and Al2O3 is high,the mineral composition are mainly quartz and mullite with high crystallinity,and the glass content is not much.The strength index of bottom ash is low and the alkali excitation activity is difficult in room temperature.Heat curing contributes to the excitation of the strength activity,and the long-time heat curing can significantly improve the alkali excitation activity of bottom ash.The incorporation of metakaolin can greatly increase the compressive strength of the geopolymer.When the metakaolin dosage is 50%,the compressive strength of the bottom ash-metakaolin geopolymer reaches more than 80%of the metakaolin geopolymer.High temperature curing is beneficial for the development of compressive,but if too high,it will lead to a decrease.Prolonged curing time will greatly promote the compressive strength of the geopolymer.A suitable water to solid is necessary for geopolymer.Microscopic analysis indicates a granular product is produced.The geopolymer material is composed of amorphous phase and semi-crystalline phase and the bottom ash participates in geopolymerization.Compared with the pure bottom ash geopolymers,the phenomenon that crystal diffaction peaks are weakened is more obvious,more peaks disappear and a stronger absorption peak of Si-O-T stretching vibration in MK50.There is little difference in the peak height and peak area of Si-O-T stretching vibration between MK50 and MK100.The shrinkage of bottom ash geopolymer is large,especially the dry shrinkage.Compared with the cement paste with a water-to-binder ratio of 0.30～0.35,autogenous shrinkage of the bottom geopolymer is lower and dry shrinkage is similar.