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The gamma nuclear gauging technique used for monitoring the sediment load suspended in water, is based on the detection of /spl gamma/ rays emitted by a radioactive source. The GEANT321 Monte Carlo simulation tool, originally developed at CERN for high energy physics experiments, is used for the evaluation and calibration of gamma nuclear gauges. A set of parameters, principally the source energy, the source-detector separation, the lead block thickness and the energy threshold below which the sediments elemental composition affects the measurement or the energy corresponding to the Compton and photoelectric windows separation, are discussed and evaluated in the case of the gamma scattering gauge. For the gamma transmission gauge, the GEANT321 code has been used to define the optimal source detector distance interval, particularly for the Moroccan sediment samplers, and to check the influence of the radionuclide existing in the suspension, on the gauge response accuracy. Experimental calibration was also carried out using a gamma transmission gauge and a good agreement was found between experimental and simulated results.

Most fills when compacted in layers will, to some degree, experience variations in density with depth. When measured using a nuclear density gauge in direct transmission mode, such variations in density through the layer will lead to unrepresentative density–depth profiles. This is because each measurement used to generate the profile is the mean density between the surface and the depth of measurement, and no correction for this is currently made. Uniform sands and silts, and pulverised fuel ash (PFA), often go through a process of over-stressing during compaction, leading to significantly lower densities in the upper part of a compacted layer. Under these circumstances the errors recorded in nuclear density gauge determinations of the density–depth profile may become significant. In extreme cases the usual guidance is to remove the upper part of the compacted layer prior to density testing. This paper describes numerical techniques to determine the mean density between successive measurement depths for the cases of both equal and unequal depth increments, thus giving a density–depth profile that is much closer to reality.

The pavement quality indicator (PQI) produced by TransTech Systems, Inc., uses principles of electrical impedance and the dielectric constants of materials to determine the densities of asphalt pavements. The Model 300 PQI device was recently evaluated in Illinois as a potential alternative to nuclear density gauges for quality control/quality assurance of asphalt pavement construction. Both laboratory and field testing were conducted to meet these objectives. The PQI has several appealing features relative to the nuclear density gauge, including its light weight and rapid operation in the field without the need for special licensing, handling, or training. The density determined with the nuclear density gauge generally exhibited a closer correlation with the density determined from pavement cores, as denoted by significantly lower squared error of the regression values in the regression analyses performed. Also, although the Model 300 PQI has been improved from earlier models to account for moisture and temperature, the data suggest that the device is still influenced by environmental conditions. On the other hand, the PQI proved to be more operationally convenient for the field technician, being significantly lighter and less time-consuming to operate in the field. On the basis of analysis of the information obtained from the studies, the Illinois Department of Transportation has chosen to base acceptance and statistical pay factors on density values obtained by the AASHTO T166 method with pavement cores. At present, the nuclear density gauge is still the specified device for quality control/quality assurance of asphalt pavement projects in Illinois.

A pavement quality indicator device developed through an NCHRP project, the Corelok device, and laboratory and field permeability index devices were evaluated for their potential to improve the Virginia Department of Transportation’s density specification or to be designated for use in a replacement specification. Fifteen samples were taken from six projects representing three nominal maximum aggregate sizes. Densities measured by a nuclear gauge correlated well with core densities measured in accordance with AASHTO T166 and by the Corelok device. Pavement quality indicator readings appeared to be repeatable but did not correlate with the densities measured in accordance with AASHTO T166 or with the Corelok device. A fair correlation was obtained for two projects. Laboratory permeability and field permeability indices were correlated with pavement density. A good correlation was found between the laboratory permeability and field permeability indices. The relationship appears to be linear in the range agencies typically specify.

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.

The Missouri Department of Transportation's (MoDOT) past and present quality control and quality assurance programs for construction are examined. MoDOT's present quality management program along with a small number of grading projects has lowered the number of quality assurance (QA) soil compaction tests completed in the past two years. The department would like to rid itself of using the nuclear density gauges because of burdensome federal regulations, required training, security and licensing fees. Linear and multiple regression analysis was performed to see if a correlation between nuclear density gauge dry densities values and light weight deflectometer modulus values/clegg hammer clegg impact values exist. These relationships or lack thereof will determine the technology used by construction contractors to perform compaction quality control testing if MoDOT moves away from using nuclear density gauges for soil density verification.

A series of density-based and modulus-based quality control tests were performed to evaluate and compare the performance of a number of in situ testing methods for control of soil compaction. This paper highlights the results from the study that focus on three in situ testing tools for compaction control: the lightweight deflectometer (LWD), the dynamic cone penetrometer (DCP), and the nuclear density gauge (NDG). In situ tests conducted using these tools were performed during construction of an embankment built with a coarse-grained soil in a series of lifts. Comparison of the in situ test results shows that that there is a notable variability in measured soil properties for each of the testing methods that were performed. All three in situ tests showed an increasing trend in the measured properties from pass-to-pass of the compactor, which indicates the suitability of these tests for proper control of the compaction process. However, the soil moduli measured by the LWD and DCP correlated poorly to the NDG dry unit weights. This lack of agreement was likely caused by a variety of factors, including variations in the tested soil volume between these devices and variations in the local moisture content and matric suction conditions. The effect of soil moisture content was shown to be particularly significant when interpreting the results of LWD and DCP tests, and the usefulness of multivariate regression analyses was explored for including this effect.

During the reconstruction of the Ohio Turnpike, data were collected from construction sites using non-destructive tools. This study was done in two phases: the first one included using the Light Weight Deflectometer (LWD) and Automatic Dynamic Cone Penetrometer (ADCP) to evaluate the subgrade, which was recommended to be stabilized. The second phase included using the Falling Weight Deflectometer (FWD) and Ground Penetration Radar (GPR) to evaluate the structural capacity of the entire pavement. The data generated from these tests were statistically analyzed and compared with traditional measurements to develop QA/QC procedures that optimize risk and cost. This article sheds lights on the first phase of the study, which was mainly concerned with subgrade characterization using LWD and ADCP. The ADCP and LWD data correlated fairly well. Both the ADCP and LWD provide a measure of stiffness, whereby the nuclear density gauge provides a measure of density. In comparison, the LWD seems to be the most promising QA/QC candidate. It was the most cost-effective among the three tests, had the highest rate of production, and was the most reliable.

Proper compaction of unbound materials, such as soils, aggregate, and recycled materials, is a critical component in the performance of highway pavements and embankments. The most commonly used device to test for proper compaction is the nuclear density gauge. However, due to the costs associated with regulatory compliance and radiation safety training, there is an increased effort to find acceptable non-nuclear devices. This synthesis documents information on national and international experience with non-nuclear devices and methods for measuring compaction of unbound materials. Information used in this study was gathered through a literature review, a survey of state departments of transportation (DOTs) and Canadian provincial transportation agencies, and interviews with selected state DOTs.

Measurement of forest soil bulk density is often hampered by coarse fragments. In this study, five methods to determine total and fine bulk density and coarse-fragment content of a rocky forest soil in western Montana were evaluated. Two methods of core sampling (small and large diameter cylinders), two methods of soil excavation and volume determination (water and polyurethane foam), and a nuclear source moisture gauge were tested at two depths (0-10 cm and 10-20 cm) on a soil with a 35% slope and 45% rock content. In the surface 10 cm, total and fine soil bulk density values were greatest from the nuclear gauge. The two excavation techniques gave similar results. Volumetric rock-fragment content calculations using the small diameter cylinder were significantly lower than those using the other methods. At the 10- to 20-cm depth, all methods except the large diameter cylinder gave comparable results for total soil bulk density. The small diameter core method gave the highest estimate of fine bulk density at this depth. All methods are easy to use. Soil excavation using the polyurethane foam for volume determinations is the simplest method and has low standard errors.

A study was conducted to evaluate the feasibility of compacting unbound aggregate base courses in lifts thicker than those permitted by state departments of transportation (DOTs). At present, the majority of the state DOTs allow a maximum lift thickness of 20.3 cm (8 in.) or less. Work conducted in conjunction with the widening of a state road in Georgia is described. Three test pads of the same base material were constructed and evaluated: one Target Strip and two Test Sections. The Target Strip was placed in two lifts: a 17.8-cm (7-in.) lift followed by a 15.2-cm (6-in.) lift. Each test section was constructed in a single, 33-cm (13-in.) lift. Compaction of the unbound aggregate base courses was evaluated by conventional nuclear density gauge (NDG) testing. Additionally, nondestructive seismic testing was used to evaluate stiffness profiles within the base and supporting subgrade. Spectral-analysis-of-surface-waves (SASW) tests were used for this purpose. Both the NDG and the SASW test results show that a 33-cm (13-in.)-thick layer of unbound aggregate base can be compacted as dense and as stiff as a 15-cm (6-in.)-thick layer. The seismic results also show that the upper 7.6 cm (3 in.) of all three test pads have lower stiffnesses than the bottom 25.4 cm (10 in.). This near-surface layer exhibits a lower stiffness, presumably from lower effective stresses and possibly from some disturbance caused by the compaction equipment. Also, higher moisture contents during compaction of the base yielded lower stiffnesses, even at the same in situ density.

Presented are the findings of an investigation performed to identify possible correlations between nuclear density gauge readings and core density results. The nuclear density data were collected on a Superpave section of I-95 in Brevard County, Florida. Core samples also were obtained from this section for laboratory density determination. Five gauge units [Troxler models 3401, 3440 (two units), 3450, and 4640] and three core density methods (Florida test method FM 1-T 166, ASTM D1188, and dimensional analysis) were considered. The relationships among the core density results were analyzed, then an investigation of the correlation among the different gauges used in this study was evaluated. Finally, the performance of each of the units with respect to the core density results was assessed. The findings indicated that the five nuclear gauge density units did not always produce similar results and did not consistently correlate with the core densities. In addition, the nuclear density testing variability differed not only from gauge to gauge but also from location to location within each gauge.

A method was identified to determine asphalt content to replace chlorinated solvent extraction. Production of trichloroethane was banned on December 31, 1995, as part of the 1990 Clean Air Act Amendments. Initially, the study focused on evaluating the nuclear asphalt content gauge with Marshall plugs. During the course of the research, early data from the National Center for Asphalt Technology (NCAT) indicated that the ignition method was a promising alternative. Testing was conducted with three generations of ignition furnaces. Four aggregate types were evaluated with typical surface mix and base mix gradations found in Virginia. Samples for evaluation were produced at four asphalt contents for each mix design representing typical field variation around the optimum. Operator variance samples were tested nondestructively in the nuclear gauge and then destructively by solvent extraction and the ignition method. As a result of the research, a test method was developed using the ignition furnace with an internal weighing system. This method has been specified as a replacement for solvent extraction in Virginia.

The pavement behavior under 630,000 axle repetitions from the Texas Mobile Load Simulator (TxMLS) was studied. During the course of TxMLS testing, nondestructive testing and in situ instrumentation (pressure cell, strain gauge, and multidepth deflectometers) were applied to monitor and assess the pavement condition. In addition, pavement distress data, such as measurements of permanent deformation, rutting, and cracking, were collected and analyzed. At the end of 630,000 axle repetitions, the maximum permanent deformation was approximately 22 mm. A forensic study was then performed by cutting a 1.8-m by 3-m trench in the middle of the test pad and three nuclear density gauge (NDG) tests were performed on top of each layer to determine the densities and moisture contents. It was found that the lime-treated gravel base (LTB) layer contributed the most to rutting. The axle-load applications increased the density of the LTB layer in the pit area, which caused the pavement structure to settle and consolidate. The highest rate of rutting was observed at the early stages of loading, between 10,000 and 20,000 axle repetitions. The higher deflections on the left wheelpath as observed from falling weight deflectometer data were probably due to the higher moisture content and the instrumented pit. NDG data showed that the LTB, lime-stabilized subgrade (LTS), and subgrade in the left wheelpath all had higher moisture contents than those in the right wheelpath.

A Step Frequency Radar (SFR) is used for assessing the compaction of Hot Mix Asphalt (HMA) layers. The system is composed of a network analyser and an Ultra Wide Band (UWB) antenna placed above the road surface. The measurements are carried out on a new-paved road in Cagny (Normandie, France). The SFR system provides the permittivity of the first overlay. The data is corrected from vehicle vibrations and calibrated at fixed locations. Then, the HMA compaction is deduced with a Lichteneker-Rother (LR) model. The results are compared with standard tests (gamma bench testing on cores and in-place nuclear gauge). We show that the SFR system allows the nondestructive assessment of HMA overlay with a high density of points, and with an accuracy close to the compaction provided by standard tests.

Foamed asphalt stabilized base (FASB) combines reclaimed asphalt pavement (RAP) and/or recycled concrete (RC) with a foamed asphalt binder. The pavement structural properties of FASB fall somewhere between conventional graded aggregate base (GAB) and hot mix asphalt (HMA). Therefore, the required thickness of the pavement section can be reduced, resulting in cost savings in addition to recycling benefits. This case study was conducted on an 8 inch FASB layer constructed during May to July 2011 on MD Route 295 near Baltimore-Washington International (BWI) Airport. The primary objective of the project was to evaluate the suitability of using this material in high traffic volume pavements and to assess its fundamental engineering properties. FASB density, moisture content and hydraulic properties were evaluated in the field and its stiffness was monitored as the material dried and cured during the first week and at 4 to 6 months after placement. Field tests included nuclear moisture and density gauge readings, permeability assessment, and stiffness measurements using a lightweight deflectometer (LWD), a GeoGauge, and a falling weight deflectometer (FWD). Of particular interest was the increase in stiffness of the FASB with time during curing and the comparison of this increase with that observed in a companion GAB control section at the site. Overall, the final field cured stiffness of the FASB was found to be substantially higher than that for GAB. Recommendations on appropriate installation methodologies, weather constraints, and QC/QA methods are provided.

This report presents results from an evaluation of a non-nuclear soil moisture-density gauge, the Soil Density Gauge (SDG 200), tested on a series of 16 different fine-grained soils. If the results were successful, the device would serve as a replacement to the standard nuclear moisture-density gauge. Results from a standard nuclear moisture-density gauge were used for comparison. Results of the tests are presented and include comparisons of the dry densities obtained from the SDG and the nuclear gauge. Correlations between the two devices showed a strong dependence on plasticity characteristics to distinguish among soil types. The lack of internal calibration for fine soils demonstrated poor correlation between moisture conditions for a given soil. Similar to SDG studies on coarser soils, the proper response from the SDG for fine-grained soils requires calibration of the dry density using at least one independent density sample obtained in the field with an alternative device such as a sand cone or a nuclear moisture-density gauge.

During the period May-August 2010, researchers of the U.S. Army Engineer Research and Development Center in Vicksburg, MS, tested the effectiveness of various devices to determine the dry density, or modulus, of soils for horizontal construction. These tests were conducted to determine a usable alternative to the soil nuclear density gauge. The accuracy and precision of the different testing devices were compared to the density values obtained from the soil nuclear density gauge. The devices and techniques that were tested are grouped into four broad families: nuclear, electrical, volume replacement, and modulus-based. The nuclear device was the nuclear density gauge that was included for comparison purposes. Electrical devices that were tested were the electrical density gauge, the moisture + density indicator, and the soil density gauge. Volume replacement density-determining techniques; were the sand cone, the steel shot, and the water balloon tests. Modulus-based devices were two different lightweight deflectometers, a dynamic cone penetrometer, the Clegg hammer, and the GeoGauge. This investigation consisted of full-scale construction of seven soils representing a range of materials encountered in operational construction activities. Soils ranged from fine-grained silts and clays to coarse-grained gravels and crushed limestone. The test results indicated that the soil density gauge corrected with a sand cone density measurement, demonstrated the optimal combination of precision and accuracy compared to the nuclear density gauge. Results of the tests are presented and include (a) comparisons of the dry densities of the various devices to the reported dry densities of the nuclear gauge, (b) ranking of the density devices according to agreement with the nuclear density gauge, and (c) field results of modulus-based devices. Results will be used to provide further guidance for selection of appropriate devices for field determination of soil density.

This paper describes the results from a comprehensive evaluation of a relatively new non-nuclear method for compaction control. The device utilized in this study is a complex-impedance measuring instrument (CIMI), more commonly known by its manufacturer’s trade name: the “Electrical Density Gauge” (EDG). In its current form, the CIMI device uses a series of electrical measurements in conjunction with calibrated soil models to infer in situ soil unit weight and moisture content. Two approaches currently exist for building soil models with a CIMI: the first is the ASTM-approved method of calibration with in situ measurements of unit weight and moisture content provided by the nuclear density gauge (NDG), sand cone, or other similar type of in situ test, and the second is calibration with large “Proctor-type” mold tests in a controlled laboratory environment. In this study, the two calibration methods were evaluated using NDG tests that were conducted in a large rigid box in the field (to simulate field compaction conditions), and large “Proctor-type” mold tests that were conducted in a lab-controlled environment. In order to evaluate the accuracy of both calibration methods, drive cylinder tests and sand cone tests were conducted at the same locations as the CIMI and NDG tests for comparison purposes. The findings from this study are useful for engineers that may be considering the use of CIMI technology for compaction control.

The flocculation of mine tailing slurries to facilitate the consolidation of the slurries and separation of water was studied by using kaolin slurry as a model material. The mixing and reactions between kaolin slurry with flocculants (Magnafloc 336) occurred in a coiled Plug Flow Reactor (cPFR) which was constructed from 2.54 cm inner diameter plastic tubing, 10 m long, and coiled at a diameter of 20 cm. The flocculant was added into the slurry stream through two or four flocculant injection points along the cPFR. The kaolin slurries used during the experiment were set at 3 wt% and 8 wt%, while the flocculant application was varied between 26–75 g/ton (dry weight solid based). The performance of the cPFR was characterised by calculating various parameters that included the Reynolds number, as well as Dean number and Germano number to accommodate the effects of the curvature and torsion of the cPFR. Shear could also be evaluated based on the measured pressure drop across the reactor. The flocculated slurry that was produced in the cPFR was then sent to a settling column (17.6 cm diameter, 140 cm high) where settling rates were measured. The settling column was also equipped with a gamma-radiation-based density gauge. The results showed that despite the short residence time (14.8 s) within the cPFR, the reaction could occur to a sufficient extent to produce settling rates of 10.3–25.7 m/hour, at initial kaolin concentration of 3 wt% with flocculant concentrations between 26–75 g/ton. At an initial kaolin concentration of 8 wt%, the settling rate was found to be between 0.6–25.1 m/hr. Furthermore, it was also observed that settling rates did not only increase with concentration of flocculant, but also increased when the flocculant injection points were changed from two points to four points along the cPFR. The impact of the changes in the flocculant injection points was more significant at higher solids concentration. The higher settling rate was correlated with optical microscopy data, which clearly showed larger size of particles of the flocculated slurry at higher settling rates. The density gauge also showed that slurry density was not uniform with height. The bottom of the sedimented slurry consistently showed higher density than the layer above it. Moreover, the distribution of the slurry density with height continued to change during settling, while some sudden increase in density could be observed following raking.

A compaction quality control (QC) in highway construction in Thailand is typically based on an in-place density measurement using the sand replacement method. Although monitoring compaction quality through a sand cone density test is relatively simple, such method is generally time consuming, labor intensive, less cost-effective, and destructive. This paper presents the laboratory evaluation of an innovative QC tool called the soil density gauge (SDG), which provides rapid and instantaneous measurement of density and moisture content based on the electrical impedance spectroscopy. The SDG was evaluated in a test box. Six highway materials were used in the study. The variation of SDG measurements along with its measurement characteristics was investigated herein. The paper also compared the SDG density and moisture content measurements with other tests such as the nuclear gauge, the soil stiffness gauge, and the sand cone method etc.

One primary quality control parameter for asphalt concrete pavements is density, which can be measured by core sampling or nuclear gauge. The present study evaluates the use of the nuclear gauge as a quality control tool by comparing its performance with core density measurements. Nuclear gauge and core density measurements were recorded by contractors and highway departments at four paving projects and then analyzed statistically for comparison purposes. Researchers found no statistical difference for the testers or the variability of the measurements obtained by different methods. The means of the measurements obtained by the different methods, however, were different. Also, density variability depends on the type of mix. A multiple regression model was developed by investigators that correlates core density with nuclear gauge readings and type of pavement.

Summary High spatial resolution is obtained from a gamma-ray transmission density gauge by restricting the measured counts to a narrow band of the energy spectrum, close to the emission energy peak. The effect on measurement accuracy of any movement of this measurement window relative to the energy peak was investigated. The findings were related to anticipated energy peak movements in a proposed LED-based gain-stabilization system. Movements of the energy peaks during recording of unstabilized spectra prevented direct comparisons of spectra at different positions. A simulation procedure was, therefore, developed in which movements of the measurement window relative to sets of stable calibration spectra were examined. When analysing spectra, recorded using a gauge with a different gain-stabilization system, accuracy was found to be unaffected by simulated peak movements of up to 0.03 MeV in the direction of increasing energy. However, movements of stabilized spectra in the direction of decreasing energy, and of unstabilized spectra in either direction, increased measurement errors to twice the level of inherent measurement errors within 0.02 MeV, with errors in bulk density of up to 0.7 Mg m−3 for movements of 0.1 MeV. The spectra of the new LED-based stabilization system are expected to behave in a manner similar to the unstabilized system, therefore requiring regular monitoring of the peak position.

During the period May 2010-August 2010, researchers of the U.S. Army Engineer Research and Development Center in Vicksburg, MS tested the effectiveness of various devices in determining the moisture content of soil for horizontal construction. These tests were conducted to determine a usable alternative to the nuclear soil density gauge. The accuracy and precision of the different testing devices was compared to the standard laboratory oven soil moisture determination. The devices and techniques tested are grouped into four broad families: gravimetric, electrical, chemical, and nuclear. Gravimetric devices and techniques tested were the laboratory oven, gas stove and fry pan, standard microwave oven, battery-powered field microwave oven, and moisture analyzer. Electrical devices tested were the electrical density gauge, and the soil density gauge. The chemical device tested was the Speedy Calcium Carbide soil moisture test. The nuclear device tested was the nuclear density gauge, included for comparison purposes. This investigation consisted of full-scale construction of seven soils representing a range of materials encountered in operational construction activities. Soils ranged from fine-grained silts and clays to coarse-grained gravels and crushed limestone. This testing showed that the devices showing the optimal combination of precision and accuracy compared to the laboratory oven are the soil density gauge and the gas stove with fry pan technique. Results of the moisture content tests are presented and include (a) comparison of the individual moisture contents to the results obtained using the standard laboratory oven, and (b) ranking of devices versus laboratory oven. Results will be used to provide further guidance for selection of appropriate devices for field determination of soil moisture content.

A non-nuclear, non-invasive instrument capable of measuring density and moisture content of soil using electromagnetic impedance spectroscopy (EIS) is currently being developed. During the development of the empirical soil model, it was found that the model was sensitive to the specific surface area of the material being measured. With the material’s specific surface area being accounted for, in six test compactions a 119% increase in accuracy was seen by the soil density gauge’s (SDG) wet density calculation when compared to the Nuclear Density Gauge’s wet density calculation.

The DCP (Dynamic Cone Penetrometer) and LWD (Light Weight Deflectometer) are becoming ever more popular as mechanistic-empirical pavement design/construct procedures evolve. These instruments provide the ability to quickly, accurately, and economically measure shear strength and stiffness of in-place base course and subgrade material, thus obviating the need for density testing. These instruments are rugged, portable, easy to operate and do not have the regulatory disadvantages of a Nuclear Density Gauge. This paper outlines the genesis of the DCP for soil testing and the respective applications for various DCP configurations. The various types of LWDs and the results they produce are described. Finally, on going efforts in the use of these instruments as well as standards for QC/QA (Quality Control /Quality Assurance) for subgrade and aggregate base for roads are discussed.

Nuclear gauge density measurements (NGDMs) are regularly used for compliance verification with specifications for road and construction projects. The density of construction materials is an important indicator of structural performance and quality. Due to speed of measurement, flexibility, and accuracy, NGDMs methods are becoming the preferred standard the world over. Requirements dictate that gauges be verified or calibrated once every 12 to 18 months. At present, there are no field portable devices available for verification of the gauge calibration. In addition, the density references used for calibration of gauges are large and not designed for field portability. Therefore, to meet the present standards users are required to ship gauges to a service facility for calibration. This paper presents results obtained by a newly developed device for field verification and calibration of nuclear density gauges from 3 different manufacturers. The calibrations obtained by this device are compared to the factory calibration methods and accuracies are reported for each model.

This paper presents a study that compared test results of a modified Impact Soil Tester (IST) on compacted soil with data obtained from the same soil using a nuclear density gauge at the U.S. Army Corp of Engineer's Buena Vista Flood Wall project in Buena Vista, Virginia. This comparison testing demonstrated the credibility of the procedure developed for the IST as a compaction testing device. The comparison data was obtained on a variety of soils ranging from silty sands to clays. The Flood Wall comparison compaction data for 90% Standard Proctor shows that the results of the IST as modified are consistent with the nuclear density gauge 89% of the time for all types of soil tested; however, if the soils are more cohesive, then the results are consistent 97% of the time. These comparison tests are in general agreement with earlier testing using the same techniques and methods on compacted backfill in utility trenches.

Over compaction of mine spoil after the Surface Mining Control and Reclamation Act of 1977 has led to reclaimed mine lands which will not grow economically viable native hardwood forests. This has been remedied by using the low compaction grading technique. This construction technique attempts to balance stability which utilizes compaction, and tree growth which needs a looser growing medium. The physical characteristics of reclaimed mine slopes using the low compaction grading technique were studied. Several methods to measure unit weight were examined including using a nuclear density gauge and two different replacement methods similar to the sand cone density test. Also, grain size distributions were calculated for the three areas studied. The in-situ angle of the material and the internal friction angle of the material were measured and used in a simple infinite slope analysis to determine slope stability. It was found that the unit weight reading were highly variable which is mainly due to the variable nature of the material. Also, it was found that there was no correlation between density and depth which suggests that the material had not been heavily compacted. Next, it was found that the low compaction grading technique provides a suitable tree root growth medium due to low unit weights and high void ratios. Lastly, it was found that the infinite slope analysis provided sufficient factor of safety values with an upper bound of 1.9. These values were acceptable because of the low cost and consequences of failure of a surface mine slope.

Nondestructive density measurement of ground and fill materials by means of field nuclear gauges is widely known in civil engineering but its laboratory counterpart is given less attention. This paper describes the adaptation of a two-probe field nuclear gauge into a laboratory device for density measurement of cylindrical specimens. Considerations for its adaptation for laboratory use include the influence of specimen geometry comparing cylindrical to slab type specimens where the basic attenuation law applies directly, specimen position between source and detector, source to detector spacing, and specimen diameter. Density is obtained by calibration to a basic radiation attenuation law based on parallel rays passing through a slab specimen. It is found that the curvature and obliquity effects of a diverging beam passing through a cylindrical specimen can be accounted for by a ‘ c ’ factor which is approximately the volume ratio of the irradiated portion of the cylinder to the slab of the same external dimension. From the modified attenuation law a diameter ratio to a count ratio relationship is established. This diameter relationship can be used to determine the density of specimens of other diameters from the calibration curve of a single diameter. The validity of the diameter correction rule is found to be applicable for a practical working source-detector spacing of 280 mm to 450 mm.

Proper construction of longitudinal joints in asphalt pavements significantly contributes to their longevity and reduces joint-related pavement distresses, such as surface raveling, joint cracking and opening. Despite the apparent importance of the joint, there is no single construction practice that is widely accepted in the US. Most states have their own approaches and requirements regarding the construction techniques and quality assurance (QA) activities associated with longitudinal joints. Recently, the Connecticut Department of Transportation and Federal Highway Administration sponsored a research study that investigated two types of longitudinal joints: traditional vertical butt joints and notched wedge joints. The data was collected from two re-surfacing projects in Connecticut that utilized both joint types. Each project was divided randomly into multiple sections and the density data was collected from each section. The density was measured at the joint location as well as on both sides of the joint immediately after compaction. Two methods were employed to determine the density. First, the in-place density was measured using the nuclear density gauge. Next, the cores were taken from the same locations to measure the density in the laboratory using the vacuum seal method. This paper presents the experimental setup and the construction details on both joint types. The collected data is statistically analyzed and factors influencing the final density for each project are discussed. Both density measurement methods are compared and the correction factor was established between the two methods using additional cores taken from the mat away from the joint.

Backscatter gauges are used to obtain a nonintrusive measurement of the density of bulk materials from the surface. A mathematical model, which accurately represents the detector in its working environment, has been developed. Since the initial conception of a moving source albedo density gauge, there has been speculation that a broadening of the peak or multipeaking exists with hydrogen containing materials. A more sensitive version of this gauge was designed to facilitate a detailed investigation of these materials. Any difference in a detector characteristic is highlighted by a comparison of the theoretical maximum and normalised shape provided by the three-dimensional surface model. This has allowed the presence of larger than previously experienced hydrogen peaks to be verified. A simple explanation of this distortion of the three-dimensional surface model by hydrogen containing materials is given.

Nowadays, the use of nuclear density gauges, due to the ability to work in harsh industrial environments, is very common. In this study, to reduce error related to the ρ of continuous measuring density, the combination of backscatter and transmission are used simultaneously. For this reason, a 137 Cs source for Compton scattering dominance and two detectors are simulated by MCNP4C code for measuring the density of 3 materials. Important advantages of this combined radiometric gauge are diminished influence of μ and therefore improving linear regression.

This paper presents the study to characterize the performance of a new non-nuclear density gauge for real-time determination of in-place density of asphalt pavements using the PaveTracker™ (PT). Laboratory results indicated that significant factors affecting the PT gauge readings were mix type, surface moisture content, internal moisture content, and pavement thickness in relation to the probing depth of the PT gauge. The size of the surface area of the specimen was also a significant factor affecting the PT reading. From the field study, it was found that the densities measured using the PT gauge were statistically different from core densities and nuclear densities. When a pay factor schedule being used by Ohio Department of Transportation was applied to field projects, the three types of density measurements (nuclear, non-nuclear, and coring methods) resulted in slightly different pay factors. It was recommended that the non-nuclear methods for in-place density may be useful for quality control purposes but not for quality assurance testing.

Controlled test sections were constructed using a prototype CP-533 vibratory padfoot roller to evaluate relationships between machine drive power and measures of soil compaction. Machine power determined from internal sensors and number of roller passes was logged nearly continuously during construction of the test sections using an onboard computer and GPS mapping system. In this paper, machine power results are compared to spot measurements of nuclear density gauge moisture/density and dynamic cone penetration (DCP) index measurements. A framework for statistically analyzing power-based compaction monitoring data is presented with broader implications for other intelligent compaction and continuous compaction control systems that generate near continuous spatial data.

Crushed concrete (CC) and recycled asphalt pavement (RAP) are sometimes used as substitute fill material in retaining wall and pavement applications. The accuracy of the nuclear gauge device for density and moisture content measurements on these two recycled materials may be unreliable, due to their chemical compositions being different than typical earth fill. An experimental study was initiated to compare moist density and water content measured from the nuclear gauge with those from traditional rubber balloon and test pit methods. Test results show that the nuclear gauge consistently measured larger moist densities than the rubber balloon method for all materials tested. However, the discrepancies were most likely due to the inadequate size of the hole used in the rubber balloon test relative to the maximum particle size of the materials. This result was confirmed with test pit measurements, which showed closer correspondence with the nuclear gauge results. Water content measurements indicate that the nuclear gauge reports larger values of moisture content than oven drying for CC and RAP. This difference can be attributed to the misinterpretation by the nuclear gauge of inherit hydrogen atoms in CC and RAP as water molecules.

Several reconstructed Portland Cement Concrete (PCC) pavement projects in Iowa were recently studied and to evaluate the influence of subgrade/subbase non-uniformity on pavement performance. Crack surveys and field tests to evaluate the subgrade/subbase were conducted. Dynamic cone penetrometer, nuclear density gauge, Geogauge vibration, and Clegg Impact Hammer tests were performed in a grid pattern (2.5 m x 2.5 m over an area of about 7.5 m wide by 30 m long) to develop a database of the subgrade/subbase engineering property values. Results of stiffness, moisture and density, strength, and soil classification were used to produce plots indicating spatial variability of a given property. Natural subgrade soils, fly ash stabilized subgrade, reclaimed hydrated fly ash subbase, and aggregate subbase were studied. The influence of spatial variability of subgrade/subbase was evaluated by modeling elastic properties of the pavement and subgrade using the ISLAB2000 finite element analysis program. Results show that non-uniform subgrade/subbase stiffness increased localized deflections and causes stress concentrations in the pavement, which lead to fatigue cracking and other type of pavement distresses.

When several different instruments have been used on the same satellite to measure the thermospheric density, significantly different results have been obtained. For 40 years, there have been efforts to resolve these disagreements. Recent improvements in the analysis of drag coefficients and in-track winds have led us to reexamine the measurements of density made by an accelerometer, mass spectrometer, and density gauge deployed together on the S3-1 satellite. A simultaneous solution using data from the mass spectrometer and accelerometer significantly reduces the error caused by winds in the Auroral Zone during geomagnetic storms. A dramatic improvement is obtained among the three instruments by calculating the drag coefficients appropriate to the shape and altitude of the satellite instead of using the previously assumed value of 2.2 at all altitudes. A comparison of several recent studies in which 2.2 was replaced by corrected drag coefficients shows that much of the reported statistical discrepancy of 15% between density measurements and models could be removed by using appropriate drag coefficients in constructing models and in analyzing data. Nomenclature

In-situ penetration tests have been widely used in geotechnical and foundation engineering for site investigation in support of analysis and design. The standard penetration test (SPT) and the cone penetration test (CPT) are two typical in-situ penetration tests. The dynamic cone penetration test (DCPT) shows features of both the CPT and the SPT. The DCPT is performed by dropping a hammer from a certain fall height and measuring penetration depth per blow for each tested depth. The DCPT is a quick test to set up, run, and evaluate on site. Due to its economy and simplicity, better understanding of DCPT results can reduce efforts and cost for evaluation of pavement and subgrade soils. Present practice in determining the adequacy of a compacted subgrade is to determine the dry density and water content by either the sand-cone method or the nuclear gauge. The use of the resilient modulus (M sub r) has recently become mandatory for pavement design. To find the M sub r, a time-consuming test is required which demands significant effort. Therefore, a faster and easier alternative for compaction control in road construction practice is desired. To this end, the present project is a step towards the generation of sufficient data to create appropriate correlations between subgrade parameters and DCPT results. The present research considers several subgrade soils at different road construction sites. Each soil is tested in the field and in the laboratory. The field testing includes the DCPT and nuclear density gauge tests. Based on analysis of this testing, the relationships between the DCPT results and the subgrade parameters such as unconfined compression strength and resilient modulus are obtained.

There are several factors that lead to segregation. Segregation can occur during stockpiling and handling of aggregate and during mixing, storage, transport, and laydown of the asphalt mixture. Sometimes segregation may result from a single source or from a combination of sources. Nondestructive test methods have been examined to determine their effectiveness in detecting segregation. These methods include thermal imaging, air permeability, nuclear moisture (asphalt) and density, and permitivity. Based on the effectiveness of these technologies in a laboratory environment, the standard moisture/density nuclear gauge technology was field tested with a high degree of success. Use of four minute gauge readings is recommended. Field testing with the nuclear moisture/density gauge was conducted on four projects. Random locations and areas visually identified as segregated were tested with a nuclear moisture/density gauge. Subsequently, cores from the same locations as the nuclear gauge moisture (asphalt) content and density readings were taken for laboratory evaluation. A draft specification for detecting segregation is recommended using a nuclear moisture/density gauge. Asphalt mixture segregation results in distresses such as raveling, stripping, rutting, and cracking developing prematurely. Relative performance of mixtures with varying levels of segregation was determined through repeated flexural fatigue and accelerated wheel track testing. The most significant reduction in pavement performance through flexural fatigue and accelerated wheel track testing comes from coarse segregation. A training video was prepared for the Indiana Department of Transportation as one of the research tasks. Recommendations for future research from this study are also outlined.

The objective of this project was to assess the environmental and geotechnical performance of two highway embankments constructed using coal combustion fly ash. The environmental work focused on monitoring well water samples from the site before, during, and after construction. In addition, a number of in-situ lysimeter water samples were also tested during and after construction. In each case, water samples were evaluated in terms of their constitutive organic and metal concentrations, as well as their relative bioassay response using a Microtox (trademark) protocol. The geotechnical work included monitoring of ash water content and unit weight during placement, settlement analysis, and in-situ testing of the completed ash fills using the Standard Penetration Test. Analysis of the groundwater and lysimeter water samples indicated that the coal ash had not adversely affected the environmental quality of the 56th Street overpass site. The embankments also performed well from a geotechnical perspective both during and after construction. The only difficulty was the measurement of coal ash water content and unit weight using the nuclear density gauge. The benefits of reusing coal combustion fly ash for highway construction are: 1) low-cost source material for the Indiana Department of Transportation, ii) reduced disposal costs for Indiana utilities, and iii) savings of Indiana landfill capacity.

In situ measurements of soil unit weight and moisture content play a critical role in conventional compaction quality assurance and quality control procedures. Recently, there have been a number of attempts to develop alternative electrically-based test devices that can be used to measure the in situ unit weight and/or moisture content of a compacted soil; these devices are intended to serve as alternatives to more traditional tests such as sand cone, rubber balloon, drive cylinder, or nuclear density gauge tests. The study described in this paper focuses on the use of a relatively new electrically-based in situ soil test device that uses measurements of soil complex impedance, soil capacitance, and soil resistance to infer in situ soil unit weight and moisture content; this device is typically referred to as a complex-impedance measuring instrument (CIMI). This paper provides a detailed explanation of current CIMI operating principles and also describes the utilization of a CIMI for field- and laboratory-based testing. The CIMI used in this study was calibrated and assessed in two field compaction projects in which different silty sands were used for construction. A mold-based calibration approach was developed for building an electrically-based soil model using the CIMI; this approach provides an alternative to field calibration of the device. In order to perform a more complete assessment of the CIMI in a controlled environment, a series of CIMI tests were conducted in a large “field box,” and the resulting in situ measurements of soil unit weight and moisture content made using the CIMI are compared with the results from nuclear density gauge, sand cone, and drive cylinder tests. The advantages and disadvantages of field versus mold calibration of the CIMI are discussed, and side-by-side assessment of the CIMI relative to other conventionally used compaction control tests allows the reader to assess the accuracy of this device.

This paper presents and compares the results from a series of in situ density-based and modulus-based compaction control tests that were conducted during construction of a coarse-grained soil embankment. To simulate current construction practices as closely as possible, these in situ tests were performed on an embankment that was constructed and compacted by a vibratory smooth drum roller in a series of lifts. During construction of the test embankment, the compaction process was monitored using the nuclear density gauge device and a number of alternative modulus-based devices, including the lightweight deflectometer, the dynamic cone penetrometer, and the soil stiffness gauge. Comparison of the in situ test results illustrates that point-to-point variability in measured values is quite common for each of these test devices, to varying degrees for the different devices that were examined. Consistent increases in measured soil properties from pass-to-pass of the compactor are considered critical for proper control of the compaction process, with some devices faring better than others in this area of performance. The measured modulus values correlated poorly to the nuclear density gauge dry unit weights, and also correlated poorly with other measured moduli when the results from different devices were compared. This lack of agreement was likely caused by a variety of factors including: variations in the magnitude of strain and rate of strain application between the different modulus-based devices, variations in the tested volume between the different devices, and variations in the local moisture content and matrix suction conditions. Finally, the effect of soil moisture content was shown to be critically important when interpreting the results from modulus-based tests, and the utility of multiple regression analyses was explored for including this effect.

The "nuclear" asphalt content gage was used with bituminous mixes containing slag aggregates to assess its applicability as a rapid analysis tool for these types of mixes. It was found to work as well, or better, than the standard extraction technique. It was also found to have additional advantages over the extraction technique since it is about an order to magnitude faster, requires no solvent and involves no decisions on the part of the user.

This review paper on the measurement of liquid density is included to illustrate the wide range of techniques available for sensing a single measurand. The techniques described range from some of very long standing (the pneumatic bubbler) to some which are very modern (the fibre-optic interferometry density gauge). (Eds.)

This paper reviews the basic principles of nuclear gauging, and provides clear definitions of many of the terms in common usage in connection with nuclear radiation sources and detectors. The application of the basic principles to the sensing of liquid density and liquid level is described. For each measurand some practical guidelines are given relating to good installation practice and required precautions. This paper was selected from many on this topic because of its accessibility to non-physicist readers. (Eds.)