Influence Of Tensile Strain And Crack Patterns Of ECC On Its Bulk Resistivity

The piezoresistivity of cement-based material has already been investigated, but mainly restricted to sensing compressive stress due to the brittleness of concrete. Engineered Cementitious Composites(ECC) exhibit superb ductility and saturated controlled-width cracks, which provides a chance for investigating the change in bulk resistivity under tensile and flexural stress and the relationship between resistivity and crack patterns. This sensor utilizing the electric resistivity of ECC itself to sense the tensile strain has an advantage over traditional embedded sensors in wider detecting strain range, not having effect in structural properties as well as monitoring the whole structure. Hence, it is of great significance to develop this new sensor.First, Ground Granulated Blast-furnace Slag(GGBS), an industrial by-product, was used in replacement of fly ash to produce ECC. Air Entraining Agent(AEA) and Rubber Crumb was chosen to improve the ultimate tensile capacity of GGBS-ECC. Carbon Black(CB) was incorporated into GGBS-ECC to enhance the conductivity of CB-ECC, but simultaneously decrease the ductility ECC. The proportion of AEA and Rubber Crumb and w/b were changed to obtain the good ductile performance.Secondly, the resistance was measured by two-probe method. It was observed that the material polarization happened in the beginning of test, and gradually slowed down with the measuring time. Additionally, increasing CB content facilitated the conductivity of CB-ECC.Finally, it was investigated that the change in resistivity with strain and time under uniaxial tensile test and four-point bending test separately. In addition, it was studied that the change in resistivity in stable polarization, elastic, inelastic and tension-softening segment.