Self-sensing concrete: from resistance-based sensing to capacitance-based sensing

Self-sensing uses the cement-based material without sensor incorporation to sense itself. This paper reviews self-sensing cement-based materials, with coverage of the well-studied resistance-based sensing as well as the less-studied capacitance-based sensing. This review is the first that covers capacitance-based self-sensing. Capacitance-based sensing is advantageous over resistance-based sensing in that no particular admixture is required, so that it is applicable to both existing and new structures. In contrast, resistance-based sensing that is comparable to capacitance-based sensing in stress/strain sensitivity requires conductive admixtures, such as carbon fiber. Resistance-based strain sensing is based on piezoresistivity, which is associated with the resistance increasing upon tension and decreasing upon compression. Capacitance-based strain sensing is based on piezopermittivity, which is associated with the permittivity decreasing upon tension and increasing upon compression. Damage causes the resistance to increase and causes the permittivity to decrease. Increase in temperature decreases the resistance but increases the permittivity. This review also covers the methodology of the electrical measurements.