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US-12618883-B2 - Methods for calculating a relative change in percent voids using electromagnetic wave reflection coefficients

US12618883B2US 12618883 B2US12618883 B2US 12618883B2US-12618883-B2

Abstract

A method for calculating the change in percent voids between a reference location and a second location in a medium. The method includes obtaining a reference reflection coefficient of an electromagnetic wave reflection at the reference location, and a second reflection coefficient of an electromagnetic wave reflection at the second location. The obtained reflection coefficients are used to calculate a percent change in reflection coefficient. A reflection conversion factor correlating the change in the reflection coefficient to a change in percent voids in the medium is calculated and is used to calculate a change in percent voids between the reference and second locations based on the calculated percent change in reflection coefficients.

Inventors

  • Roger Roberts

Assignees

  • GEOPHYSICAL SURVEY SYSTEMS, INC.

Dates

Publication Date
20260505
Application Date
20230215

Claims (5)

  1. 1 . A method for determining calculating a change in percent voids between a reference location and a second location in a medium, the method comprising: (a) using a radar system having a transmitting antenna and a receiving antenna, transmitting and receiving at least one electromagnetic wave to obtain a reference radar measurement for a reference location of a medium, the at least one electromagnetic wave being transmitted at a predetermined incidence angle; (b) using the predetermined incidence angle, an effective dielectric of the medium, and the reference radar measurement, calculating a transmission angle of the electromagnetic wave through the medium at the reference location and calculating a reference reflection coefficient of an electromagnetic wave reflection at the reference location; (c) using the radar system transmitting and receiving another electromagnetic wave to obtain a second radar measurement at a second location in the medium, the another electromagnetic wave being transmitted at the predetermined incidence angle; (d) using the predetermined incidence angle, the effective dielectric of the medium, and the second radar measurement, calculating a transmission angle of the electromagnetic wave through the medium at the second location and calculating a second reflection coefficient of the electromagnetic wave reflection at the second location; (e) calculating a percent change of reflection coefficients between the reference reflection coefficient and the second reflection coefficient; (f) graphically generating a % void-percent reflection coefficient (PV-PRC) plot and extracting from the plot a reflection conversion factor correlating changes in reflection coefficient to changes in percent voids in the medium; (g) using the reflection conversion factor, calculating the change in percent voids between the reference location and the second location based on the determined percent change of reflection coefficients; (h) repeating steps (c) to (g) for multiple sample locations in an area of the medium, each sample location comprising a said second location; and (i) generating a spatial distribution map of the area of the medium, the spatial distribution map indicating the change in percent voids at the multiple sample locations in the area of the medium.
  2. 2 . The method of claim 1 , wherein calculating the reference reflection coefficient comprises using the radar system to obtain multiple radar measurements over an area, and determining the reference reflection coefficient is based on an average of reflection coefficients for the multiple radar measurements.
  3. 3 . The method of claim 1 , wherein obtaining calculating the reference reflection coefficient comprises determining a dielectric of the medium based on a known Gmm dielectric of the medium and a specified percent voids.
  4. 4 . The method of claim 1 , wherein calculating the reference reflection coefficient and calculating the second reflection coefficients comprise obtaining a ratio of respective reflection amplitudes from an asphalt surface to a reflection amplitude from a conducting surface.
  5. 5 . The method of claim 4 , wherein obtaining a percent change in reflection coefficients from the reference reflection coefficient and the second reflection coefficient comprises calculating the percent change in surface reflection amplitudes between measurements at the reference and second locations.

Description

FIELD OF THE DISCLOSED TECHNOLOGY The disclosed technology relates generally to methods for computing a change in compaction of asphalt concrete, and, more specifically, to methods for calculating a relative change in compaction of asphalt concrete measured at two measurement locations. BACKGROUND OF THE DISCLOSED TECHNOLOGY There is a need easily and accurately to know the variation in density of a new asphalt road as it is being placed, since controlling its density can double the life of the road. Ground Penetrating Radar (GPR) technology is often used to measure the effective dielectric of asphalt of road surfaces. Knowledge of the effective dielectric of asphalt is useful in calculating the density of the asphalt. Once a calibration equation mapping dielectric to air void content is created, the density can be known simply by measuring the dielectric value at a given location on the road. The prior art describes a method of generating the calibration equation mapping between air void content and dielectric, based only on a known percent compaction and associated dielectric of a single sample of asphalt. This calibration method, though efficient, requires the procurement of at least one sample of asphalt with associated measured dielectric and % voids. The step of obtaining a sample of material with these known values may, at times, be difficult or impossible, for example due to lack of access to, or availability of, the equipment necessary for obtaining the sample. Even when calibration is unavailable, knowledge of the spatial variation in % voids can help reveal problems in the placement of asphalt. These problems can be corrected once known. For example, measuring the expected range in % voids between the center of a paved area and edges of the paved area can help identify problems in the placement of the asphalt. More generally, mapping of the relative change in compaction over a paved area enables adjusting of the roller compaction strategy accordingly, and assists in avoiding over-compaction or under-compaction. A stakeholder may also decide to reward or penalize the paving contractor based on the uniformity in % void content. There is thus a need in the art for a method of calculating the relative change in air void content between two or more measurement locations, when the measurement is conducted in situ. SUMMARY OF THE DISCLOSED TECHNOLOGY The disclosed technology relates generally to methods for computing relative percent voids, and, more specifically, to methods for calculating a relative percent voids at two asphalt locations, in situ, using radar reflection amplitudes. This disclosure should be interpreted according to the definitions below. In case of a contradiction between the definitions in this Definitions section and other sections of this disclosure, this section should prevail. Dielectric—an electromagnetic property that relates to the ability of a material to store energy in the presence of an electric field. Effective Dielectric—an average dielectric of a micro-inhomogeneous medium, i.e. a medium whose dielectric is not homogeneous on a small scale. Asphalt—a composite material comprising and having at least 90% aggregate (i.e. rock fragments) and bitumen, and, in some cases, also including additional materials. Also known as “pavement” in North America and as “asphalt concrete” in technical papers. These terms are used interchangeably. Dielectric Mixing Equation—an equation that calculates the effective dielectric of a dielectrically inhomogeneous medium, given volume percentages and dielectrics of constituents in the medium. Asphalt Air Void Content—the percentage or volume ratio of air in an asphalt sample. Bitumen—a black viscous mixture of hydrocarbons obtained naturally or as a residue from petroleum distillation. Bitumen is commonly used as a constituent in asphalt concrete. It may also be called tar or binder. Aggregate—rock and sand constituents typically included in asphalt concrete. Aggregates may be taken from nearby quarries, and as such, have highly regional material properties (shape, density, dielectric, porosity etc.). Air Void—air trapped inside asphalt concrete. The total air void content is typically expressed as a percentage of the total volume of asphalt concrete. Puck—a cylindrical-shaped asphalt sample that is typically compacted to a pre-determined amount using gyratory compactor. Percent Compaction—the inverse of the percent voids in a sample, or the percent of the sample which is not air voids. A sample of asphalt that has one hundred percent compaction contains no air voids. Percent compaction is calculated from % Voids using the relation: % Compaction=100−% Voids. Magnetic Permeability—an electromagnetic property that relates the magnetic induction inside a material to the magnetic field intensity. Mix Design—a particular combination of aggregate, bitumen and possibly other constituents that are mixed together to make asphalt. Different mix designs a