Study On Repair And Reinforcement Performance Of Basalt Fiber UHPC

Ultra-high performance concrete(UHPC)is new type of high performance cementbased materials,which has excellent mechanical properties and durability.The UHPC as a high performance repair material in the repair and reinforcement of existing structures has a good development prospect,which is also one of the most important engineering applications of UHPC in recent years.At present,Steel fiber is frequently adopted as the reinforcing material for UHPC.However,the low corrosion and heat-resistant as well as the high price of the steel fiber was the major constraint for the promotion.the environment friendly basalt fiber with excellent performance was adopted in this paper as the substitute of steel fiber.And related experimental studies are carried out against the background of repairing and reinforcing existing concrete structures.The main research contents and conclusions are as follows:(1)The influence of the content of silica fume,cenosphere and basalt fiber as well as the cement-sand ratio on mechanical properties were explored by orthogonal experiment.The results show that the binder-sand ratio and silica fume content were the dominant factors affecting the mechanical strength at the age of 28 days.On the basis of optimized mixture proportion,the basalt fiber influence on mechanical properties was investigated,subsequently.The results show that there is optimal basalt fiber content for mechanical properties,and with the incorporation of this optimal fiber content,the compressive,the splitting tensile as well as the flexural strength of concrete can be markedly improved.(2)Four different mixtures including basalt fiber UHPC were selected as repair materials,based on the mechanical test results.The permeability resistance of the repair material was comprehensively evaluated by the coulomb electric flux test and capillary water absorption test.The results showed that RM3 had the best permeability resistance,and the order of permeability resistance of repair materials was RM3 > RM2 > RM4 > RM1.In addition,pore structure characteristics of the repair material were investigated by using CT(Computer tomography)technology.The results show that: 1)RM1 has the worst pore structure;2)The incorporation of basalt fiber can optimize the pore structure parameters of concrete.(3)Two types of bonding specimens,i.e.,the cube and prism specimen were made to explore the mechanical properties of the interface between new to old concrete.The main conclusions include: 1)The interfacial bond strength of specimens cured at room temperature(20°C)was higher than that of specimens cured at low temperature(5°C);2)The interfacial bond strength of specimens with rough interface is higher than that of specimens with smooth interface;3)Among the four repair materials,the bonding strength of RM3 was the highest;4)The interfacial splitting tensile strength model was established and verified by experimental data.(4)Different corrosion conditions were applied to the cube composite specimens to investigate the durability of the interface between new to old concrete.The results showed that: 1)With the increase of cycles,the damage degree of interfacial bond strength increased gradually;2)Compared with RM1 bonded specimens,the interfacial durability of RM2,RM3 and RM4 bonded specimens is significantly improved;3)Under the action of sulfate dry-wet cycle corrosion,the deterioration of pore structure was obvious with the increase of cycles;4)For the salt freeze-thaw cycle corrosion environment,the damage degree model of interfacial bond splitting tensile strength was established based on damage mechanics.The predicted curve of the model was in good agreement with the experimental value.(5)Seven composite short columns were designed and manufactured.The axial compression bearing capacity test of short columns was conducted.Results showed: 1)The type of cladding repair material has great influence on the bearing capacity of short columns.However,the influence of the thickness of cladding layer and protective layer on the bearing capacity of short columns was much smaller;2)The axial compression bearing capacity model of composite short columns was established based on the Mander model,and this model was verified to be accurate by experimental data.;3)The bearing capacity of the cladding layer accounts for 41% ～ 61% of the total bearing capacity,which indicates that the four repair materials have excellent reinforcement performance.