A strategy for in situ determination of self-healing state for strain hardening cementitious composites

Abstract

In strain-hardening cementitious composites, the bridging effect of fibers can control crack openings to very small values so the cracks can be self-healed in the presence of water. To rely on autogeneous self-healing to enhance the durability of structures, a method to assess the state of self-healing is required. A new strategy is presented in this paper for in-situ measurement of the healing effect without pre-knowledge of the environmental condition (such as moisture). Exploiting the fact that the electrical conductivity in the crack is lower than that of the undamaged section, the effective macroscopic cracking effect is first distinguished by frequency dependent impedance measurements both along (parallel to) and across the cracks. Dielectric spectroscopy along the cracks is found to correlate well with gravimetric measurements and can therefore, be used for inverse approximation of moisture content. The effect of moisture change on the equivalent resistance in the direction across the cracks can then be derived approximately from measurements under various moisture contents. The approximated resistance vs moisture curve is found to reflect the evolution of autogenous self-healing, and a curve indicating almost complete healing agrees well with the recovery in member stiffness measured from loading test.