Research On Cracking Resistance And Impermeability Of Basalt Fiber High Performance Concrete In Underground Structure

In recent years,with the speeding up of urbanization,more underground space is utilized in many cities because of the lack of the construction space.In response to the harsh environment with rich groundwater and erosional material,high performance concrete with excellent durability is widely applied in underground engineering.In order to improve the crack resistance and impermeability of high performance concrete,basalt fiber as reinforcing material is mixed in high performance concret.So the research on the crack resistance and impermeability of basalt fiber high performance concrete applied in underground engineering should be made penetratingly.Some aspects are researched as follows:(1)In order to investigate how mixing amount of basalt fiber and fly ash impact on the workability and mechanical property of high performance concrete,the compressive strength test and splitting tensile strength test are conducted.The result shows that,with the increase of dosage of fly ash,slump increases.And the incorporation of basalt fiber makes the decrease of concrete slump,the increase of splitting tensile strength and the transition of form of damage from brittleness to toughness.It has a inapparent effect on compressive strength.(2)In order to investigate how mixing amount of basalt fiber and fly ash impact on the early age crack resistance of high performance concrete,the slab crack test with the inducing crack method is conducted.The result shows that,with the increase of the dosage of fly ash,the cracking area of concrete decreases.Therefore,for the early crack resistance of concrete,the optimal dosage of fly ash is 30%of amount of the total gelation in this paper.The incorporation of basalt fiber makes the cracking area less.With the increase of dosage of basalt fiber,the extent of the loss increases.Even the crack could not run through when the dosage of basalt fiber is high.So 1.6kg/ml,the dosage of basalt fiber,is the optimal dosage for the early age crack resistance of high performance concrete in this paper.(3)In order to investigate how dosage of basalt fiber and fly ash impact on the impermeability of high performance concrete,the impermeability tests with electric flux method and the Autoclam permeability system are conducted.The result shows that the general electric flux value of the concrete has a fluctuant trend with the increase of mixing amount of fly ash.Based on considering the slump synthetically,it could be determined that 30%is the optimal dosage of fly ash for impermeability of high performance concrete in this paper.The incorporation of basalt fiber improves impermeability of high performance concrete.Considering the slump and the economic benefits of the actual project,1.2kg/m3 is determined to be the optimal dosage of basalt fiber for impermeability of high performance concrete in this paper.Considering air permeability,water absorption coefficient and water permeability coefficient of Autoclam permeability test system,it could be determined that 20%is the optimal dosage of fly ash for the above three evaluation index.(4)In order to investigate the effect of basalt fiber in high performance concrete on process of the matrix stress and how dosage of basalt fiber impact on stress-stress distribution of concrete,the model of concrete with basalt fiber distributed at random was established by using finite element analysis software ANSYS on the mesoscopic level to simulate the compression test of composite materials.The stress-strain curves and stress distribution was gained by the analysis.The results show that the fiber don't share stress apparently in linear elastic stage.The stress distribution of concrete is relatively uniform in the stage.The nonlinear phase fiber gradually share the stress on the substrate in the nonlinear stage.The stress concentration phenomenon appears,while it can be dispersed by fiber.With the increase of dosage of fiber,the effect of dispersion increased.In the decline stage after the peak,the effect of crack resistance of fibre embodies fully.And the effect would increase with the increase of dosage of fiber.