Study On Mechanical Properties Of Hybrid Fiber And Nano-Particles Reinforced Geopolymer Concrete Subjected To Hygrothermal Condition And Salt Attacks

Geopolymer concrete has the advantages of green environmental protection,quick hardening and early strength,but has defects of easy cracking and low toughness.With the continuous development of marine resources in China,more marine facilities need to be built,which puts forward higher requirements for the performance of geopolymer concrete.On this basis,nano-SiO₂,polyvinyl alcohol fiber（PVA fiber）and steel fiber were adopted to modify and strengthen geopolymer concrete.The effects of nano-SiO₂and hybrid fiber on the mechanical properties of geopolymer concrete subjected to hygrothermal condition and salt attacks were proved by the experiments,and the damage mechanism of geopolymer composite concrete subjected to hygrothermal condition and salt attacks was revealed.The following are the main contents and achievements of this thesis:（1）Through the compressive test,splitting tensile test and elasticity modulus test,the effects of nano-SiO₂,PVA fibers and hybrid fibers on the basic mechanical properties of geopolymer concrete subjected to hygrothermal condition and salt attacks were explored.According to the results,it indicates that the compressive strength,splitting tensile strength and elasticity modulus of geopolymer concrete first increase and then decrease with the increase of nano-SiO₂ content,PVA fiber content and hybrid fiber content.When the content of nano-SiO₂,PVA fiber and hybrid fiber are 1.5%,0.6%and 1.6%respectively,geopolymer concrete can obtain the best mechanical properties.（2）By conducting the drop hammer impact test,the effects of nano-SiO₂,PVA fibers and hybrid fibers on the impact resistance of geopolymer concrete subjected to hygrothermal condition and salt attacks were explored.The two-parameter Weibull model was used to calculate the initial cracking impact times,failure impact times and impact toughness of geopolymer concrete under different failure probabilities,and the evaluation on the impact resistance of geopolymer concrete was conducted on the basis of these indexes.According to the results,the initial cracking impact times,failure impact times and impact toughness of geopolymer concrete first increase and then decrease with the increase of the content of nano-SiO₂,PVA fiber and hybrid fiber.After the addition of nano-SiO₂,the impact resistance of geopolymer concrete is improved.After the addition of PVA fiber and hybrid fiber,the impact toughness of geopolymer concrete has the significant improvement.（3）By taking the microscopic test results as the basis,the analysis on the failure mechanism of the hybrid fiber and nano-SiO₂ reinforced geopolymer concrete subjected to hygrothermal condition and salt attacks was conducted.From the results,it indicated that the geopolymer concrete was degraded under the combined action of chloride ions and water when it was subjected to hygrothermal condition and salt attacks.The deterioration of chloride ions and water on geopolymer concrete would be accelerated by the defects caused by PVA fibers and steel fiber microfilaments,the loss of nano-SiO₂ and the corrosion of steel fiber microfilaments.The loss of nano-SiO₂,the corrosion of steel fiber microfilaments and the weakening of the fiber-matrix interface transition zone would be aggravated by the deterioration of geopolymer concrete.So the change of the internal structure of geopolymer composite concrete and the decrease of its mechanical properties were caused.