Experimental study on the road energy harvesting of piezoelectric ceramic in unbound granular materials based on a large-scale triaxial apparatus

As one of the methods to harvest and then reuse the traffic-induced mechanical energy or one of the materials to make specific piezoelectric sensors, the application of piezoelectric ceramic to the traffic engineering has drawn more and more attention in recent years. However, few studies have tried to install the piezoelectric ceramic especially piezoelectric patch in the unbound granular materials (UGMs) of pavement base or subbase layers, and then to investigate their coupling including the power generation characteristics of piezoelectric ceramic and the resilient behavior of UGMs under traffic loading. In this study, a special piezoelectric transducer in which the piezoelectric ceramic worked in a single 31-mode was made and it was installed in the UGMs sample. A series of resilient deformation tests based on a large-scale triaxial apparatus was performed to explore the effects of water content of UGMs, confining pressure, cyclic stress magnitude and initial deviatoric stress on the open-circuit voltage generated by piezoelectric patch, and the influences of power generation on the resilient modulus of UGMs. Test results show that the open-circuit voltage in saturated sample is larger than that in sample of optimum moisture condition. The increase in both confining pressure and cyclic stress magnitude lead to the increase in open-circuit voltage, while the influence of initial deviatoric stress is slight. However, the development patterns of open-circuit voltage over either confining pressure or cyclic stress magnitude are very different between the two water content conditions. The power generation by piezoelectric ceramic tends to lower the resilient modulus of UGMs. In general, the installation of piezoelectric ceramic in the UGMs of base or subbase layers is feasible, which provides another way to harvest the traffic-induced mechanical energy. The cyclic stress level should be the key factor influencing the power generation of piezoelectric ceramic, while the confining pressure and water content of UGMs would play minor but non-negligible roles.