Graduation Year

2018

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Civil and Environmental Engineering

Major Professor

Qing Lu, Ph.D.

Committee Member

Manjriker Gunaratne, Ph.D.

Committee Member

Jing Wang, Ph.D.

Committee Member

Andres E. Tejada-Martinez, Ph.D.

Committee Member

Gabriel Picone, Ph.D.

Keywords

electromechanical model, finite element model, laboratory test, optimization

Abstract

A novel design of a piezoelectric-based energy harvesting pavement system (PZ-EHPS) is introduced in this dissertation work. The design concept of this PZ-EHPS is to transform asphalt layers into a piezoelectric energy harvester to collect dissipated vehicle kinetic energy in a large-scale system, relying on two conductive asphalt layers and one piezoelectric material layer. To verify the feasibility of the above design concept, this dissertation work practically fabricated and tested a series of PZ-EHPS specimens under the loads from a Material Testing System (MTS) in the laboratory, and theoretically analyzed one typical PZ-EHPS specimen via a three-degree-of-freedom electromechanical model and a series of finite element models (FEMs). As a result, the voltage output from the PZ-EHPS specimen captured in the laboratory matched those estimated in the theoretical models. Considering that the PZ-EHPS segments will be paved in the field on a large scale, another series of finite element models at a system level were built to simulate the operation of PZ-EHPS segments under traffic conditions.

During laboratory tests on the PZ-EHPS specimens fabricated in this dissertation work, three conductive asphalt mixture specimens of different mixture types (i.e., DGAC, SMA-12.5, SMA-19) were built as conductive layers, and PZT disks with or without plaster of Paris (POP) were built as the piezoelectric layer. Through measuring and comparing the resistance of those three conductive asphalt mixtures used in this PZ-EHPS specimen, it was observed that the conductive SMA-12.5 mixture has a better overall conductance with less average resistance (8.57 kΩ) and smaller deviation (5.31 kΩ) based on the repeated measurements. For the piezoelectric layer design, the filler, especially the stiff one, did play an essential role in the performance of the PZ-EHPS specimen: it can lead to a poor contact condition between the PZT disks and the conductive asphalt mixtures. Such a poor contact condition can weaken the voltage output from the PZ-EHPS specimen. The maximum voltage output from the PZ-EHPS specimen was captured when the POP filler was removed: without POP, the voltage output from the proposed energy harvesting layer could reach 7.6 V when the amplitude of the sinusoidal load was increased to 133 N at 1 Hz.

Regarding general design parameters of the PZ-EHPS at a component level, the results from the electromechanical model showed that using more flexible conductive asphalt mixtures and using piezoelectric elements with higher piezoelectric stress constant can increase electrical outputs from the PZ-EHPS. Meanwhile, for the PZT element with a high natural frequency in such a three-layered structure, adding more PZT elements can compensate for the limitation of decreasing natural frequency of a PZT disk to produce higher voltage output from the PZ-EHPS under very low frequency (1 Hz) vibration. Under relatively high frequency (30 Hz) vibration, the benefit from adding more PZT disks to produce higher voltage outputs disappears, however, the positive effect of each piezoelectric element’s capacitance on increasing the voltage output from the PZ-EHPS specimen turns to be significant.

Compared to the electromechanical model, FEMs are capable of better analyzing some detailed PZT element designs with or without insulative fillers in the PZ-EHPS at a component level. The results from the FEMs of the PZ-EHPS specimens in the laboratory found that a thin piezoelectric layer with piezo ball elements and a low stiffness insulative filler has the significant advantage of producing up to 85 V electricity. Piezo cylinder elements may fit a thick and stiff piezoelectric layer better than the piezo ball and lead to a high voltage output up to 50 V. To strike a balance between structural performance and electricity generation of the PZ-EHPS, tall piezo cylinder elements may be used.

Through simulating the operation of PZ-EHPS segments under traffic conditions in another series of finite element models, it confirmed that the PZ-EHPS with a rigid piezoelectric layer produces more electricity than the one with a flexible piezoelectric layer. For a single-vehicle scenario, if each PZ-EHPS segment length equals the vehicle wheelbase length, consecutive PZ-EHPS segments may constantly supply high electricity as the vehicle moves over the segments. Higher vehicle speed can result in higher voltage output from the PZ-EHPS. For a multiple-vehicle scenario, however, the voltage output generated by a second vehicle will be reduced if the first vehicle is still on the same PZ-EHPS segment.

Based on the results from the three-degree-of-freedom electromechanical model of the three-layered structure of a PZ-EHPS specimen under vibration, after optimizing this PZ-EHPS prototype by adding more piezoelectric elements with higher piezoelectric stress constant and improving the flexibility of conductive asphalt mixtures, the maximum electric power from the proposed EHPS can be increased from approximately 1.2 mW to 300 mW under a high frequency (30 Hz) external vibration. The levelized cost of electricity of this EHPS can be $19.15/kWh on a high-volume roadway within a 15-year service life.

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