Study on the mechanical and electrical conductivity properties of waste short carbon fibers concrete and the establishment of conductivity models

Abstract

The properties of waste short carbon fibers (WSCFs) were firstly characterized in this paper, and the effects of WSCFs with different lengths and contents on the mechanical properties and electrical conductivity of concrete were mainly investigated. Conductive model for WSCFs concrete was established based on the core-shell structure. The results revealed that, in comparison to virgin carbon fibers, WSCFs contained a small amount of resin, and the microscopic surface of WSCFs was smoother, but the content of C elements was low, the wettability and graphitization were poorer. The compressive strength of concrete did not significantly change after being mixed with WSCFs. Compared with the control group (0 %), only when the WSCFs content was 1 %, the compressive strength was slightly improved. The splitting tensile strength decreased as the length of WSCFs increased at the same content. When the length of WSCFs was 10 mm or 20 mm, the resistivity of concrete decreased by 86.0 % and 90.3 %, respectively, at 0.5 % content (28 d). As curing age increased, the free water inside the concrete decreased, and fibers were wrapped by hydration products, resulting in an increase of resistivity. Increasing the length of WSCFs from 10 mm to 20 mm effectively increased the probability of fiber overlap, constructing a more connected conductive network and reducing the conductive threshold of concrete from 0.5 % to 0.4 %. The established conductivity model for WSCFs concrete exhibited high calculation accuracy. The calculation results showed that for WSCFs with a length ranging from 10 mm to 50 mm, the concrete resistivity was very close and fluctuated less for the WSCFs content greater than 0.5 %.