Effects And Mechanism Analysis Of PVA Fibers And Carbon Nanotubes On Geopolymers

This paper studies preparation technology of geopolymers and multiscale analysis of effects of PVA fibers and carbon nanotubes on geopolymers.During the process of studying preparation technology of geopolymers,it was discovered that under different loading forms,mechanical properties of geopolymer had different performance,when n(Si2O)/n(Al2O3),n(Na2O)/n(Al2O3)and n(H2O)/n(Na2O)were changed.When studying the problems of large viscosity and poor flowability of geopolymers,deformers and Na2CO3 were used to improve workability,microstructure and mechanical properties.When studying mechanical properties and mechanisms of geopolymers with PVA fiber and carbon nanotubes,it was found that PVA fiber and carbon nanotubes had a very good effect on mechanical properties of geopolymers,especially bending strength and flexutural strength.Microscopic analysis techniques were used to analyze mechanism,and then double fibers modification based on multiscale was proposed,which laid the preliminary theoretical foundation for future engineering application and technological improvement.The main conclusions from the experimental study were as follows.1.The three key molar ratios of n(Si2O)/n(Al2O3),n(Na2O)/n(Al2O3)and n(H2O)/n(Na2O)had a significant influence on mechanical properties and microstructure of geopolymers.Different loading forms were also important for mechanical properties of geopolymers.The change of molar ratios affected microstructure of geopolymers and different mechanical performance of geopolymers under different loading forms.Under normal circumstances,the increase of the ratio of n(Si2O)/n(Al2O3)or the decrease of n(Na2O)/n(Al2O3)and n(H2O)/n(Na2O)made higher compressive strength and lower bending strength.2.Defoamers could improve pore structure of geopolymers to improve the macroscopic mechanical properties of geopolymers.In this study,the optimum amount of defoamer was 1 ‰ of metakaolin dosage.Na2CO3 could improve workability of geopolymers.In this study,the optimal dosage of Na2CO3 was 3.3‰of metakaolin dosage.3.PVA fiber and carbon nanotubes had a good effect on mechanical properties and microstructure of geopolymers,especially bending strength and flexural strength of geopolymers.Bending strength of geopolymers with PVA fibers and carbon nanotubes was increased by up to 30.1%and 30.3%,respectively.Geopolymer with both PVA fiber and carbon nanotubes had a very good "mixing effect".PVA fibers and carbon nanotubes changed microstructure of geopolymers,which leading to mechanical performance changing.Compared with geopolymers without PVA fibers and carbon nanotubes,the highest increase rates o of bending strength,compressive strength and flexural strength of geopolymers f geopolymers for 28 ages were 33.3%,10.7%and 20.9%respectively.4.The chemical modification of carbon nanotubes to geopolymers showed that few carbon nanotubes participated in the reaction of geopolymers to form a firm bond.And then carbon nanotubes played roles of cracking action,filling effects and mechanical interlocking.With PVA fiber extraction,extraction and debonding,forces need to do more works to detroy the matrix,causing better toughness.PVA fiber still can change the internal stress distribution of geopolymers,resulting in different failure morphology.