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In-Place Hot-Mix Asphalt Density Estimation Using Ground-Penetrating Radar
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This research proposes the innovative use of ground-penetrating radar (GPR) for effectively, continuously, and rapidly estimating in-place hotmix asphalt (HMA) density. On the basis of electromagnetic mixing theories, three candidate models were developed to determine HMA's dielectric constant, considering dielectric and volumetric properties of its three major components of HMA: air, binder, and aggregate. Laboratory tests were conducted on midsize HMA slabs (60 cm × 60 cm × 7.5 cm) to evaluate the models. After evaluating and comparing the three models, it was determined that the prediction model based on the Rayleigh mixing theory was the most accurate. The selected model was calibrated with a field core and then validated using field GPR measurements of a composite pavement with an HMA surface. The selected model provided accurate HMA density within a reasonable range.
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... The main issue in this method is estimation of the velocity ν of electromagnetic (EM) wave in the layers [2]. The wave velocity in each layer is proportional to the square root of the permittivity ϵ of that layer [9], [15]. In monostatic configuration, the thickness h of a layer can be calculated by h = ν∆τ/2 where ∆τ is the time difference between the received echoes. ...
... We simulate the reflection coefficient of the antenna placed above an asphalt layer with relative permittivity of ϵ ′ 1 = [2, 6,9], conductivity of σ 1 = 0.04 S/m and thickness of h 1 = [1,4,7] cm. Thickness of the asphalt sub-layer is considered to be infinite and its relative permittivity is set equal to 4. We used the result of these simulations as the measurement data in the cost function defined by (33). ...
p>A fast analytical model for prediction of antenna S<sub>11</sub> in presence of a layered medium; This model is based on plane wave expansion of antenna field and has two appriximations. The first is neglecting the evanescent modes of plane wave and the second is neglecting the multiple reflections from the antenna to the multilayer.</p
... The main issue in this method is estimation of the velocity ν of electromagnetic (EM) wave in the layers [2]. The wave velocity in each layer is proportional to the square root of the permittivity ϵ of that layer [9], [15]. In monostatic configuration, the thickness h of a layer can be calculated by h = ν∆τ/2 where ∆τ is the time difference between the received echoes. ...
... We simulate the reflection coefficient of the antenna placed above an asphalt layer with relative permittivity of ϵ ′ 1 = [2, 6,9], conductivity of σ 1 = 0.04 S/m and thickness of h 1 = [1,4,7] cm. Thickness of the asphalt sub-layer is considered to be infinite and its relative permittivity is set equal to 4. We used the result of these simulations as the measurement data in the cost function defined by (33). ...
p>A fast analytical model for prediction of antenna S<sub>11</sub> in presence of a layered medium; This model is based on plane wave expansion of antenna field and has two appriximations. The first is neglecting the evanescent modes of plane wave and the second is neglecting the multiple reflections from the antenna to the multilayer.</p
Contractors are paid incentives/disincentives based on achieved in situ asphalt concrete (AC) density. Ground-penetrating radar (GPR) has been proven feasible for predicting in situ density of AC pavements using various empirical and fundamental approaches. However, to use fundamental equations for density prediction, aggregate dielectric constant must be known beforehand. Destructive cores are usually extracted from the pavement to back-calculate the aggregate dielectric constant. This cancels out the non-destructive benefit of the GPR technology. In this study, GPR is used to quantify the dielectric constant of 10 different aggregates commonly used in AC mixes in Illinois, U.S. The sampled aggregates included limestone, dolomite, trap rock, granite, and crushed gravel. The purpose was to initiate an aggregate dielectric constant database that would help predict AC density nondestructively and accurately. By using the aggregate database, GPR would help contractors estimate achieved density in real-time without prior calibration. This technology would save energy, time, and cost. Simulations using gprMax and a sensitivity analysis are presented to illustrate the effect of aggregate dielectric constant on AC bulk dielectric constant and, consequently, on AC density predicted by the Al-Qadi Lahouar Leng model. A new procedure to determine the aggregate dielectric constant using the electromagnetic mixing theory is detailed. Advanced chemical tests confirmed that the aggregate dielectric constant is a function of its elemental/mineral compositions. Finally, laboratory and field data were used to validate AC density prediction using the aggregate database. The establishment of an aggregate dielectric constant database would improve the accuracy of GPR in nondestructive AC density prediction.
Segregation is a serious problem in hot-mix asphalt and typically results in poor performance, poor durability, a shorter life, and higher maintenance costs for the pavement. A summary of the results and recommendations from three projects in Texas in which infrared imaging and ground-penetrating radar were used to examine the uniformity of the pavement mat is presented. Both techniques have significant advantages over currently used nuclear density techniques in that they provide virtually 100% coverage of the new surface. The effectiveness of both the infrared and radar techniques was evaluated by taking measurements on new overlays at the time of placement, coring, and then identifying relationships between changes in the infrared and radar data with changes in the measured volumetric and engineering properties of the cores. Analyses of the results showed that changes in both infrared and radar data are significantly related to changes in hot-mix asphalt properties such as air void content and gradation. On the basis of current Texas Department of Transportation specifications, significant changes in the hot-mix asphalt are expected if temperature differentials of greater than 25 degreesF (13.9 degreesC) are measured after placement but before rolling. If the surface dielectric of the in-place mat changes by more than 0.8 for coarse-graded mixes and 0.4 for dense-graded materials, significant changes in mix properties are expected. Given the promising results from this work, agencies should consider implementing both the infrared and ground-penetrating radar technologies.
This book is written primarily with the requirements of interdisciplinary researchers in mind and as a reference book for postgraduate students. This book, broadly divided into two portions, is aimed at agriculture and soil physicists and those working in the areas of remote sensing. The first portion, comprising four chapters, deals with the physical and dielectric properties of soils, methods of soil dielectric measurements using microwaves, and remote sensing techniques. In the second portion, Chapter 5 deals with some of the results on soil moisture measurements while in Chapter 6 the theoretical models of soil moisture data are discussed.
The introduction of new devices to measure pavement density requires an evaluation method that is both accurate and fair. Evaluations are commonly done by taking a density measurement with the gauge and comparing this density to the density obtained from a core taken at the same location. This approach must meet two requirements; first, enough cores must be taken at each location to make the comparisons meaningful, and second, evaluation of these devices must be done with as many projects in as many locations as possible to account for all materials used in pavement construction. Unfortunately, given the difficulties in obtaining field cores, large numbers of cores that can be used for evaluations are not available from all projects. Therefore, any evaluation of density gauges must balance rigor with practicality. The correlation coefficient was selected to evaluate the new nonnuclear pavement density gauge. However, because only a limited number of cores are available at each site for development of the correlation coefficient, this parameter by itself cannot be used to evaluate the new gauge. Instead, results from side-by-side comparisons with the accepted nuclear density gauge were used to aid in the evaluation of the new density-measuring device. It was concluded, on the basis of data from 76 projects in six different states, that the proposed nonnuclear density gauge must be further developed before it can be used to determine pavement density. In its current form, the densities obtained with the device do not correlate with the measured densities to the same degree that the densities measured with existing devices do. Use of this nonnuclear device will introduce more uncertainty in pavement density measurements than that which already exists.
Having fast computers with lots of memory makes it possible to make performance predictions using mechanics, which simply could not have been done even as recently as 3 or 4 years ago. This trend can be expected to continue. Pavement materials, whether asphalt concrete, base course, or subgrade, can now be characterized in realistic ways that were simply unavailable to pavement engineers. The dependence of these materials on stress state, moisture, temperature, strain rate, and damage is what has made their characterization difficult, if not impossible. This complexity has posed an almost insuperable problem for computational mechanics and for the linkage of these properties to construction specifications on the one hand and performance of in-service pavements on the other. Although these tasks will never be simple, the tools to work on them are becoming more adequate. Some examples are given of how one can proceed to simplicity through complexity in several areas that are important to pavement performance. In every case one must be able to measure a property of the material that can be used as input to a computer program, principally a finite element program, that allows material properties to change from point to point. Several examples are given in the categories of material properties, material behavior, materials testing in the laboratory, nondestructive testing in the field, and performance prediction models. Laboratory testing, materials characterization and properties, nondestructive testing of pavements in service, construction specifications, pavement variability and reliability, field data collection, performance prediction modeling, and prediction of pavement response and distress with modern computer methods - taken individually, these subjects look complex. Combined with the glue of mechanics, they are simplicity itself. And they confirm Alfred North Whitehead's principle, "The only simplicity that can be trusted is that which lies beyond complexity".
Ground-penetrating radar and capacitance-based dielectric surface probe measurements are used to measure fluctuations in voids, bitumen content, or both, in newly asphalted pavements without causing structural damage. Both methods rely on the compaction of asphalt to reduce the proportion of low-dielectricity air in the material, which increases the volumetric proportions of high-dielectricity bitumen and rock and thus results in higher asphalt dielectricity values. Ground-penetrating radar enables pavement thickness to be measured rapidly from a moning vehicle and information on variations in pavement voids content to be collected simultaneously on the basis of dielectricity fluctuations. The results can be calibrated against real void content by material sampling or by comparison of dielectric value with voids content values determined beforehand for the same material under laboratory conditions. This means that the subcontractor can be informed quickly of any values that exceed or fall betow the norms and can take immediate step to rectify such defects, Other advantages offered by the technique are the rapidity of the measurements and the immediate availability of the results. In addition, the one measurement provides simultaneous information on pavement and base thicknesses and the quality of the latter. The dielectric probe based on capacitance measurements lends itself to use in asphalt mass proportioning examinations performed at the laboratory stage, which enables the values to be used directly for monitoring in situ pavement compaction. The advantages of the dielectricity probe are rapidity of measurement, low-cost meters, and the avoidance of radiation. Thus far, the probe has been excessively sensitive to variations in the roughness of pavement surfaces. The theory behind these research methods is discussed, the methods are described, and the results of laboratory tests conducted at the Texas Transportation Institute in 1994-1995 and field tests performed in Finland in 1995 are presented.