Investigation of Electromagnetic Gauges for Determining In-Place HMA Density, 2007

Density is an important component of hot-mix asphalt (HMA) pavement quality and long-term performance. Insufficient density of an in-place HMA pavement is the most frequently cited construction-related performance problem. This study evaluated the use of electromagnetic gauges to nondestructively determine densities. Field and laboratory measurements were taken with two electromagnetic gauges—a PaveTracker and a Pavement Quality Indicator (PQI). Test data were collected in the field during and after paving operations and also in a laboratory on field mixes compacted in the lab. This study revealed that several mix- and project-specific factors affect electromagnetic gauge readings. Consequently, the implementation of these gauges will likely need to be done utilizing a test strip on a project- and mix-specific basis to appropriately identify an adjustment factor for the specific electromagnetic gauge being used for quality control and quality assurance (QC/QA) testing. The substantial reduction in testing time that results from employing electromagnetic gauges rather than coring makes it possible for more readings to be used in the QC/QA process with real-time information without increasing the testing costs.

Investigation of Electromagnetic Gauges for Determining In-Place HMA Density, Final Report, May 2007

Density is an important component of hot-mix asphalt (HMA) pavement quality and long-term performance. Insufficient density of an in-place HMA pavement is the most frequently cited construction-related performance problem. This study evaluated the use of electromagnetic gauges to nondestructively determine densities. Field and laboratory measurements were taken with two electromagnetic gauges—a PaveTracker and a Pavement Quality Indicator (PQI). Test data were collected in the field during and after paving operations and also in a laboratory on field mixes compacted in the lab. This study revealed that several mix- and project-specific factors affect electromagnetic gauge readings. Consequently, the implementation of these gauges will likely need to be done utilizing a test strip on a project- and mix-specific basis to appropriately identify an adjustment factor for the specific electromagnetic gauge being used for quality control and quality assurance (QC/QA) testing. The substantial reduction in testing time that results from employing electromagnetic gauges rather than coring makes it possible for more readings to be used in the QC/QA process with real-time information without increasing the testing costs.

Assessment of Nondestructive Testing Technologies for Quality Control/Quality Assurance of Asphalt Mixtures, TR-653, 2015

Asphalt pavements suffer various failures due to insufficient quality within their design lives. The American Association of State Highway and Transportation Officials (AASHTO) Mechanistic-Empirical Pavement Design Guide (MEPDG) has been proposed to improve pavement quality through quantitative performance prediction. Evaluation of the actual performance (quality) of pavements requires in situ nondestructive testing (NDT) techniques that can accurately measure the most critical, objective, and sensitive properties of pavement systems. The purpose of this study is to assess existing as well as promising new NDT technologies for quality control/quality assurance (QC/QA) of asphalt mixtures. Specifically, this study examined field measurements of density via the PaveTracker electromagnetic gage, shear-wave velocity via surface-wave testing methods, and dynamic stiffness via the Humboldt GeoGauge for five representative paving projects covering a range of mixes and traffic loads. The in situ tests were compared against laboratory measurements of core density and dynamic modulus. The in situ PaveTracker density had a low correlation with laboratory density and was not sensitive to variations in temperature or asphalt mix type. The in situ shear-wave velocity measured by surface-wave methods was most sensitive to variations in temperature and asphalt mix type. The in situ density and in situ shear-wave velocity were combined to calculate an in situ dynamic modulus, which is a performance-based quality measurement. The in situ GeoGauge stiffness measured on hot asphalt mixtures several hours after paving had a high correlation with the in situ dynamic modulus and the laboratory density, whereas the stiffness measurement of asphalt mixtures cooled with dry ice or at ambient temperature one or more days after paving had a very low correlation with the other measurements. To transform the in situ moduli from surface-wave testing into quantitative quality measurements, a QC/QA procedure was developed to first correct the in situ moduli measured at different field temperatures to the moduli at a common reference temperature based on master curves from laboratory dynamic modulus tests. The corrected in situ moduli can then be compared against the design moduli for an assessment of the actual pavement performance. A preliminary study of microelectromechanical systems- (MEMS)-based sensors for QC/QA and health monitoring of asphalt pavements was also performed.

Embankment Quality Phase IV: Application to Unsuitable Soils, TR-492, 2007

The Quality Management Earthwork (QM-E) special provision was implemented on a pilot project to evaluate quality control (QC) and quality assurance (QA) testing in predominately unsuitable soils. Control limits implemented on this pilot project included the following: 95% relative compaction, moisture content not exceeding +/- 2% of optimum moisture content, soil strength not exceeding a dynamic cone penetrometer (DCP) index of 70 mm/blow, vertical uniformity not exceeding a variation in DCP index of 40 mm/blow, and lift thickness not exceeding depth determined through construction of control strips. Four-point moving averages were used to allow for some variability in the measured parameter values. Management of the QC/QA data proved to be one of the most challenging aspects of the pilot project. Implementing use of the G-RAD data collection system has considerable potential to reduce the time required to develop and maintain QC/QA records for projects using the QM-E special provision. In many cases, results of a single Proctor test were used to establish control limits that were used for several months without retesting. While the data collected for the pilot project indicated that the DCP index control limits could be set more tightly, there is not enough evidence to support making a change. In situ borings, sampling, and testing in natural unsuitable cut material and compacted fill material revealed that the compacted fill had similar strength characteristics to that of the natural cut material after less than three months from the start of construction.

Identification of Practices, Design, Construction, and Repair Using Trenchless Technology, TR-570, 2010

Trenchless technologies are methods used for the construction and rehabilitation of underground utility pipes. These methods are growing increasingly popular due to their versatility and their potential to lower project costs. However, the use of trenchless technologies in Iowa and their effects on surrounding soil and nearby structures has not been adequately documented. Surveys of and interviews with professionals working in trenchless-related industries in Iowa were conducted, and the results were analyzed and compared to survey results from the United States as a whole. The surveys focused on method familiarity, pavement distress observed, reliability of trenchless methods, and future improvements. Results indicate that the frequency of pavement distress or other trenchless-related issues are an ongoing problem in the industry. Inadequate soil information and quality control/quality assurance (QC/QA) are partially to blame. Fieldwork involving the observation of trenchless construction projects was undertaken with the purpose of documenting current practices and applications of trenchless technology in the United States and Iowa. Field tests were performed in which push-in pressure cells were used to measure the soil stresses induced by trenchless construction methods. A program of laboratory soil testing was carried out in conjunction with the field testing. Soil testing showed that the installations were made in sandy clay or well-graded sand with silt and gravel. Pipes were installed primarily using horizontal directional drilling with pipe diameters from 3 to 12 inches. Pressure cell monitoring was conducted during the following construction phases: pilot bore, pre-reaming, and combined pipe pulling and reaming. The greatest increase in lateral earth pressure was 5.6 psi and was detected 2.1 feet from the centerline of the bore during a pilot hole operation in sandy lean clay. Measurements from 1.0 to 2.5 psi were common. Comparisons were made between field measurements and analytical and finite element calculation methods.

Embankment Quality: Phase III, TR-401, 2002

This report describes test results from a full-scale embankment pilot study conducted in Iowa. The intent of the pilot project was to field test and refine the proposed soil classification system and construction specifications developed in Phase II of this research and to evaluate the feasibility of implementing a contractor quality control (QC) and Iowa DOT quality assurance (QA) program for earthwork grading in the future. One of the primary questions for Phase III is “Was embankment quality improved?” The project involved a “quality conscious” contractor, well-qualified and experienced Iowa Department of Transportation field personnel, a good QC consultant technician, and some of our best soils in the state. If the answer to the above question is “yes” for this project, it would unquestionably be “yes” for other projects as well. The answer is yes, the quality was improved, even for this project, as evidenced by dynamic cone penetrometer test data and the amount of disking required to reduce the moisture content to within acceptable control limits (approximately 29% of soils by volume required disking). Perhaps as important is that we know what quality we have. Increased QC/QA field testing, however, increases construction costs, as expected. The quality management-earthwork program resulted in an additional $0.03 per cubic meter, or 1.6%, of the total construction costs. Disking added about $0.04 per cubic meter, or 1.7%, to the total project costs. In our opinion this is a nominal cost increase to improve quality. It is envisioned that future contractor innovations have the potential for negating this increase. The Phase III results show that the new soil classification system and the proposed field test methods worked well during the Iowa Department of Transportation soils design phase and during the construction phase. Recommendations are provided for future implementation of the results of this study by city, county, and state agencies.

Field Evaluation of Compaction Monitoring Technology: Phase I, 2004

This Phase I report describes a preliminary evaluation of a new compaction monitoring system developed by Caterpillar, Inc. (CAT), for use as a quality control and quality assurance (QC/QA) tool during earthwork construction operations. The CAT compaction monitoring system consists of an instrumented roller with sensors to monitor machine power output in response to changes in soil machine interaction and is fitted with a global positioning system (GPS) to monitor roller location in real time. Three pilot tests were conducted using CAT’s compaction monitoring technology. Two of the sites were located in Peoria, Illinois, at the Caterpillar facilities. The third project was an actual earthwork grading project in West Des Moines, Iowa. Typical construction operations for all tests included the following steps: (1) aerate/till existing soil; (2) moisture condition soil with water truck (if too dry); (3) remix; (4) blade to level surface; and (5) compact soil using the CAT CP-533E roller instrumented with the compaction monitoring sensors and display screen. Test strips varied in loose lift thickness, water content, and length. The results of the study show that it is possible to evaluate soil compaction with relatively good accuracy using machine energy as an indicator, with the advantage of 100% coverage with results in real time. Additional field trials are necessary, however, to expand the range of correlations to other soil types, different roller configurations, roller speeds, lift thicknesses, and water contents. Further, with increased use of this technology, new QC/QA guidelines will need to be developed with a framework in statistical analysis. Results from Phase I revealed that the CAT compaction monitoring method has a high level of promise for use as a QC/QA tool but that additional testing is necessary in order to prove its validity under a wide range of field conditions. The Phase II work plan involves establishing a Technical Advisor Committee, developing a better understanding of the algorithms used, performing further testing in a controlled environment, testing on project sites in the Midwest, and developing QC/QA procedures.

Development and Evaluation of a Portable Device for Measuring Curling and Warping in Concrete Pavements, 2016

Portland cement concrete (PCC) pavement undergoes repeated environmental load-related deflection resulting from temperature and moisture variations across pavement depth. This has been recognized as resulting in PCC pavement curling and warping since the mid-1920s. Slab curvature can be further magnified under repeated traffic loads and may ultimately lead to fatigue failures, including top-down and bottom-up transverse, longitudinal, and corner cracking. It is therefore significant to measure the “true” degree of curling and warping in PCC pavements, not only for quality control (QC) and quality assurance (QA) purposes, but also for better understanding of its relationship to long-term pavement performance. Although several approaches and devices—including linear variable differential transducers (LVDTs), digital indicators, and some profilers—have been proposed for measuring curling and warping, their application in the field is subject to cost, inconvenience, and complexity of operation. This research therefore explores developing an economical and simple device for measuring curling and warping in concrete pavements with accuracy comparable to or better than existing methodologies. Technical requirements were identified to establish assessment criteria for development, and field tests were conducted to modify the device to further enhancement. The finalized device is about 12 inches in height and 18 pounds in weight, and its manufacturing cost is just $320. Detailed development procedures and evaluation results for the new curling and warping measuring device are presented and discussed, with a focus on achieving reliable curling and warping measurements in a cost effective manner.

Embankment Quality and Assessment of Moisture Control Implementation, TR-677, 2016

A specification for contractor moisture quality control (QC) in roadway embankment construction has been in use for approximately 10 years in Iowa on about 190 projects. The use of this QC specification and the development of the soils certification program for the Iowa Department of Transportation (DOT) originated from Iowa Highway Research Board (IHRB) embankment quality research projects. Since this research, the Iowa DOT has applied compaction with moisture control on most embankment work under pavements. This study set out to independently evaluate the actual quality of compaction using the current specifications. Results show that Proctor tests conducted by Iowa State University (ISU) using representative material obtained from each test section where field testing was conducted had optimum moisture contents and maximum dry densities that are different from what was selected by the Iowa DOT for QC/quality assurance (QA) testing. Comparisons between the measured and selected values showed a standard error of 2.9 lb/ft3 for maximum dry density and 2.1% for optimum moisture content. The difference in optimum moisture content was as high as 4% and the difference in maximum dry density was as high as 6.5 lb/ft3 . The difference at most test locations, however, were within the allowable variation suggested in AASHTO T 99 for test results between different laboratories. The ISU testing results showed higher rates of data outside of the target limits specified based on the available contractor QC data for cohesive materials. Also, during construction observations, wet fill materials were often observed. Several test points indicated that materials were placed and accepted at wet of the target moisture contents. The statistical analysis results indicate that the results obtained from this study showed improvements over results from previous embankment quality research projects (TR-401 Phases I through III and TR-492) in terms of the percentage of data that fell within the specification limits. Although there was evidence of improvement, QC/QA results are not consistently meeting the target limits/values. Recommendations are provided in this report for Iowa DOT consideration with three proposed options for improvements to the current specifications. Option 1 provides enhancements to current specifications in terms of material-dependent control limits, training, sampling, and process control. Option 2 addresses development of alternative specifications that incorporate dynamic cone penetrometer or light weight deflectometer testing into QC/QA. Option 3 addresses incorporating calibrated intelligent compaction measurements into QC/QA.

Impact of Curling and Warping on Concrete Pavement, TR-668, 2016

Portland cement concrete (PCC) pavement undergoes repeated environmental load-related deflection resulting from temperature and moisture variations across the pavement depth. This phenomenon, referred to as PCC pavement curling and warping, has been known and studied since the mid-1920s. Slab curvature can be further magnified under repeated traffic loads and may ultimately lead to fatigue failures, including top-down and bottom-up transverse, longitudinal, and corner cracking. It is therefore important to measure the “true” degree of curling and warping in PCC pavements, not only for quality control (QC) and quality assurance (QA) purposes, but also to achieve a better understanding of its relationship to long-term pavement performance. In order to better understand the curling and warping behavior of PCC pavements in Iowa and provide recommendations to mitigate curling and warping deflections, field investigations were performed at six existing sites during the late fall of 2015. These sites included PCC pavements with various ages, slab shapes, mix design aspects, and environmental conditions during construction. A stationary light detection and ranging (LiDAR) device was used to scan the slab surfaces. The degree of curling and warping along the longitudinal, transverse, and diagonal directions was calculated for the selected slabs based on the point clouds acquired using LiDAR. The results and findings are correlated to variations in pavement performance, mix design, pavement design, and construction details at each site. Recommendations regarding how to minimize curling and warping are provided based on a literature review and this field study. Some examples of using point cloud data to build three-dimensional (3D) models of the overall curvature of the slab shape are presented to show the feasibility of using this 3D analysis method for curling and warping analysis.