Electrical-resistance-based sensing of impact damage in carbon fiber reinforced cement-based materials

Damage monitoring of the civil infrastructure is critically needed. This article provides the first report of impact damage self-sensing in cement-based materials. Cement mortar reinforced with short (5-7 mm) carbon fiber and in bulk or coating (5-10 mm thick) form is effective for sensing its own impact damage through DC/AC electrical resistance measurement, provided that the region of resistance measurement contains the point of impact. The mortar resistivity needs to be 10⁴-10⁵ ω cm, as provided by pitch-based fiber (15 μm diameter, unsized) at 0.5% or 1.0% by mass of cement, or type A PAN-based fiber (7 μm diameter, desized) at 0.5%. Due to the low mortar resistivity of 10³ ω cm, pitch-based fiber at 1.5% and type B PAN-based fiber (7 μm diameter, unsized) at 0.5% are less effective. Without fiber, there is no sensing ability. The surface resistance of the surface receiving the impact is an effective indicator of the damage, even for minor damage without cracking, inflicted by impact at 880 J. The oblique or longitudinal volume resistance is much less effective. The surface resistance increases abruptly upon impact, but it decreases abruptly upon impact after 5-40 impacts (number decreasing with increasing impact energy) have been inflicted.