Study On The Modification Of Nano-SiO₂ And Carbon Nanotubes In Fly Ash Based Geopolymer

Fly ash based geopolymer has many engineering performances over the traditional cementitious materials,and its outstanding properties in the sustainable development are becoming the research focus of scholars at home and abroad.However,this material has shortcomings such as severe efflorescence,low toughness and unstable strength development etc.,which restrict their large-scale application in road engineering.With the rapid development of nanotechnology,the introduction of nano-scale componets into the cementitious materials has brought new vitality to the building materials industry.However,there are few reports about the modification of nanoparticles in fly ash based geopolymer.Fly ash based geopolymer has been successfully prepared by using fly ash as the main raw material in this passage.Two different types of nano-materials(nano-SiO2 and carbon nanotubes)were selected to carry out the flowability,setting time and the microstructure of fly ash based geopolymer was analyzed by XRD,FTIR and SEM.The main conclusions are as follows:1.With the increase of nano-SiO2 or carbon nanotubes,the fluidity and setting time of the system decrease significantly.The minimum fluidity of the geopolymer paste is reduced to 119 mm and 83 mm,and the mortar fluidity is 98 mm and 71 mm;the initial setting time of the paste is shortened to 62 min and 65 min,and the final setting time is reduced to 75 min and 81 min.Both nano-materials can effectively enhance the flexural and compressive strength of fly ash based geopolymer.The optimum content of nano-SiO2 is 2.0%,and the flexural and compressive strength of the paste is increased by 74.64%and 47.60%in 28 day.The 28 day's flexural and compressive strength of mortar increased by 42.20%and 42.52%.The optimum content of carbon nanotubes is 0.10%,the flexural and compressive strength of the paste increased by 127.92%and 158.44%in 3 day;the 3 day's flexural and compressive strength of the mortar increased by 59.78%and 129.05%.At the same time,under the optimal dosage of the two nano-materials,the fly ash based geopolymer has the best crack resistance,the lowest efflorescence and the better durability.2.The incorporation of the two nanomaterials does not significantly affect the type of geopolymerization products,but the nano-SiO2 will participate in the geopolymerization and change the content of geopolymerization products,while the carbon nanotubes will not.The carbon nanotubes are distributed in the reactant matrix by fiber bridging and network filling.3.Based on the above research and the results of microcosmic test,the modification mechanism of two nanomaterials to geopolymerization is proposed:the nano-SiO2 particles are dispersed in the matrix phase to provide nucleation position for the formation of the gel phase in the reaction system.The ion enrichment region forms around it,accelerating the dissolution rate of each phase in the raw material and intensifying the reaction.Carbon nanotubes can be filled with fine pores of fly ash based geopolymer,greatly compacting their whole structure,and their excellent mechanical properties and toughness can effectively prevent and control matrix defects by their bridging and pull-out effects.