Effect of aged binder on piezoelectric properties of cement-based piezoelectric composites

Age-dependent piezoelectric properties of cement piezoelectric composites containing cement-based binder and 50 vol. % PZT piezoelectric inclusions are conducted. The effect of binder with 10 to 50 % cement replaced by slag and fly ash is investigated. Specimens are polarized by 1.5 kV/mm for 30 min when the curing time reaches 7, 28 and 56 days, respectively. Experimental values are measured daily till 120 days after the polarization. Prior to polarization, dielectric loss needs to be less than 0.73 to guarantee the feasibility of polarization. Piezoelectric properties including d33, g33 and ɛr are age-dependent unless the age is higher than 60 days after the polarization. The electromechanical coupling coefficient κt is independent of the ages. The curing time shows less efficient to piezoelectric properties while hydration reaction is completed. 20 vol. % cement replaced by slag or fly ash provides optimum d33 and g33. Compared with slag replacement, fly ash replacement can diminish ɛr, but increase κt. In addition, a modified equation to calculate the dielectric constant of PZT/cement composites is also proposed.