Mechanical Behavior And Self-sensing Property Of Multi-Walled Carbon Nanotubes Reinforced Engineered Cementitious Composites

With the modern society paying more attention to the functionality and durability of architectures,the exploitation and application of high-performance concrete provide appropriate raw materials for construction and monitoring of ordinary and special architectures.ECC is a kind of malleable concrete and appreciated by many researches around the world,which was invented by Victor Li.Because of addition of 2%fiber,ECC has excellent tension toughness and crack control capacity.The ultimate tensile strain of ECC is more than 3%.Therefore,ECC overcomes the brittleness of ordinary concrete,and can be applied to special architectures.CNTs is a kind of burgeoning nano-materials,which have outstanding mechanical and electrical conductive properties and are applied in many fields.Researchers has applied CNTs into cement concrete to improve the mechanical property and self-sensing property of concrete,which makes it possible to achieve self-monitoring of architectures.For the CNTs-ECC composite,the main research is as follows:(1)Dispersion process of CNTs in water.This thesis used surfactants and ultrasonic to disperse CNTs into water and absorbance to characterize degree of dispersion.This thesis also researched the optimal dosage of PVP and TNWDIS,and optimal ultrasonic time of CNTa and CNTb.The optimal dosage of PVP is 8%(by weight of CNTs),and the optimal dosage of TNWDIS is 21%(by weight of CNTs).Moreover,optimal ultrasonic time for CNTa is 90min,and for CNTb is 30min.(2)Mechanical property of CNTs-matrix composite.This thesis tested the influence of different content of PVP and TNWDIS on density of ECC matrix,and different content of PVP,TNWDIS,CNTa and CNTb on flexural property and compressive of ECC,and different content of CNTa and CNTb on fracture toughness of ECC matrix.It was concluded that PVP didn’t introduce bubble into ECC matrix during mixing procedure,and had no effect on density and strength of ECC matrix.However,TNWDIS would introduce bubble into ECC matrix during mixing procedure,and did harm to strength of ECC matrix though adding TBP to eliminate bubble.Therefore,it was appropriate to choose PVP as dispersant.What’ more,both CNTa and CNTb improved strength of ECC matrix.(3)Mechanical property of CNTs-ECC composite.This thesis used a certain mix proportion to test different content of CNTa and CNTb on mechanical property of ECC by means of uniaxial tensile test and four-point flexural test.It was concluded that,in the uniaxial tensile test,CNTa and CNTb improved first cracking tensile strength and ultimate tensile strength of CNTs reinforced ECC,while reducing tensile strain.In the four-point flexural test,CNTa and CNTb improved first cracking flexural strength and ultimate flexural strength,while reducing mid-span first cracking deflection and mid-span ultimate deflection.(4)Self-sensing property of CNTs-ECC composite.This thesis used 2-probe method to test the influence of different content of CNTa and CNTb on self-sensing property of ECC by means of uniaxial tensile test uniaxial tensile test and four-point flexural test.It was concluded that the percolation threshold of CNTs-ECC composite was beyond 0.3wt%.CNTs-ECC performed excellent self-sensing property during cyclic loading.