The non-invasive assessment of the condition of paved areas using electrical resistivity techniques

Yan, Ting (2020). The non-invasive assessment of the condition of paved areas using electrical resistivity techniques. University of Birmingham. Ph.D.

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Abstract

This work to detect wet areas below a paved surface is part of a 10-year research programme “ATU” (Assessing the Underworld), sponsored by EPSRC to assess the condition of the underworld by various techniques [1]. A low-frequency (5 kHz to 15 kHz) non invasive electrical resistivity technique was applied to a paved surface to assess the condition of upper layers of the asphalt. Generally, the paved surface (e.g. an asphalt pavement) is constructed using a base layer, a sub-base layer and a sub-grade layer or the natural soil foundation. The thickness of the upper typically ranges from 18 mm to 40 mm according to the standards for highway construction in the UK [2].

The electrical resistivity technique applied in this research has been implemented using a capacitive-coupled resistivity (CCR) system. Four square-plate electrodes C1, P1, P2 and C2, of large dimensions compared to the electrode spacing, are operated as inline capacitive sensors: electrodes C1 and C2 act as current sources coupling electrical current into the pavement; while electrodes P1 and P2 operate as receiver sensors to measure the voltage in the media. By this method, the quantity of electrical impedance could be estimated. It is assumed that as the moisture content of the wearing layer increases, its resistivity decreases and its dielectric constant increases. It is believed that this is the first time that this capacitive-coupled resistivity technique has been researched and applied to the condition assessment of asphalt pavement. The separation between the electrode plate and the ground surface affects the capacitance value, and hence, the coupling of the electrical signal into the ground. Thus, the surface roughness of the wearing layer could reasonably be expected to influence the capacitance. Surface roughness effects on capacitors have been studied in the nanoscale integrated circuit (IC) application area. However, no research has been published about the impact of the pavement surface roughness on the impedance measurements, obtained by the capacitive-coupled resistivity technique. In this research a laser profiling instrument with an along-track resolution of 0.125 mm and a typical height resolution of 50 μm has been utilised to measure the asphalt pavement surface roughness height distribution of the areas surveyed using the capacitive coupled resistivity technique. These surface roughness height distribution data will be incorporated into the measurement data processing as correction factors, to achieve more accurate survey results. The moisture content of the wearing layer of asphalt pavements will be estimated using the Cole-Cole model for these corrected results.

According to the experiments conducted within the laboratory and field surveys on asphalt pavements in different locations, it is concluded that the measured reactance is an indication of surface roughness (with a typical maximum peak-peak roughness of 1.2 cm for the results presented within this thesis); while the real part of the measured impedance indicates the moisture content of the wearing layer of the asphalt pavement. A larger measured reactance indicates a rougher pavement surface. A smaller real part of the measured impedance indicates a higher moisture content within the sub-surface layer.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):