A Study On The New Type Of Construction Material-Carbon Nanofiber Concrete

Concrete is the most widely used construction material and has experienced the developing stages of normal strength concrete, high strength concrete and high performance concrete. Due to the nano size, concrete with nano particles is superior to normal strength concrete because of the special properties of nano-engineered concrete and as a result, the development of Nano technology today greatly diversify the application of traditional concrete. On the other hand, carbon nanofibers (CNFs) have many advantages in both mechanical and electrical properties such as high strength, high Young's modulus and high conductivity. In this paper, an innovative carbon nanofiber reinforced concrete is proposed by mixing nanofiber into normal concrete to produce nano-engineered concrete. The mechanical properties and strain self-monitoring properties based on variation of electrical resistance (ERV) of the proposed carbon nanofiber reinforced concrete have been studied. Finally, a reasonable concentration of CNF is obtained for use in concrete which not only enhances compressive strength, but also improves the electrical properties required for strain monitoring, damage evaluation and self-health monitoring of concrete and the test results show it is attractive to make smart, high performance concrete using CNFs. The main research contents are as follows:(1) How to dissolve the carbon nanofiber into concrete was studied. The test results indicate that it is feasible to disperse CNFs in Self-Consolidating Concrete (SCC) using the polycarboxylate high range water reducer solution. The enhancement of concrete's strength and functionality can also be achieved.(2) The optimal concentration of CNFs in concrete has been found by conducting compressive test?four point bending test?split tensile test?cyclic loading with various stress amplitudes test and SEM test. Well-dispersed CNFs in the appropriate concentration allows for the significant mechanical enhancement of concrete such as compressive strength?split tensile strength?flexural strength and ductility.(3) Based on the theoretical analysis of electrical resistance property and electrical conductivity mechanism of CNF-concrete composite, the behavior of composite's ERV under loading and the correlations between ERV and strain (stress) was experimentally investigated simultaneously by conducting compressive test?four point bending test?split tensile test?cyclic loading with various stress amplitudes test. It was found that the ERV was strain dependent and strain self-monitoring because its electric resistance changes linearily with applied strain, which is named as "piezoresistivity", and consequently, may be used in applications that require strain monitoring and make concrete itself a smart sensor.(4) The pulse velocity method was used to characterize properties of concrete containing CNFs. Concrete strength correlations between pulse velocity, ERV in nondestructive and destructive tests were analyzed for each mix proportions and in each series. These correlations are presented in the form of regression equations. The tests results indicate that the compressive strength, pulse velocity and percent reduction in electrical resistance while loading concrete containing CNF are much greater than those of plain concrete. This regularity may be used for predicting the strength and nondestructive detection of CNF-Concrete composite.(5) The stress-strain curves of concrete containing CNFs are similar to those of plain concrete; therefore, the uniaxial constitutive law of plain concrete in Cyclic Softened Membrane Model (CSMM) is also applicable for concrete containing CNFs. The seismic performance of two framed shear walls was analyzed using cyclic load with the CSMM-based finite element program. Both of the shear force capacity and ductility of shear walls with carbon nanofibers were improved significantly. It shows CNFC can be used to enhance the seismic performance of framed shear walls.(6) Only normal concrete containing CNFs without rebar were investigated in the preliminary research, therefore, the further studies on behavior of ERV of concrete beam with rebar containing CNFs and concrete bridge column with rebar containing CNFs under flexural loading and cyclic laoding are experimentally conducted. It shows similar results to those of plain concrete containing CNFs and verified the feasibility of adding CNFs into concrete structure to make it superior and smart.