Evaluating Consistency of Nondestructive Evaluation of Flexible Pavement by GPR and PSPA

Consistency is one of the major issues during the Nondestructive Test & Evaluation (NDT & E) of flexible pavement, i.e., asphalt pavement, by Ground Penetrating Radar (GPR) and Portable Seismic Property Analyzer (PSPA). In some recent nondestructive tests on instrumented pavement section at Milepost (MP) 141 on Interstate-40 (I-40), New Mexico, it is observed that 2-way travel time of GPR signal in unbound layers transmitted by Ground-Coupled Antenna (GCA) varies in different months which leads to different values of layer thickness at a same section and it is believed that the reason is moisture variation. In case of PSPA, tests on Asphalt Concrete (AC) surface show higher level of inconsistency at repeated drops on the same test locations which is believed due to irregular contact between the sensors and surface. To date, unbound materials were collected from the pavement section to measure dielectric constant by Percoemeter in laboratory at varying moisture content. Later, the dielectric constants at varying moisture content are incorporated during the post-processing of GPR data, and thus, the level of consistency is improved. In case of PSPA, quick-setting capping, i.e., a mixture of Plaster of Paris and fine content, is made on AC surface at different locations prior to the tests to ensure firm and smooth contact surfaces. It is observed that consistency of PSPA measurements and interpreted results is improved significantly. Based on the observations, it is recommended to incorporate dielectric constants at varying moisture content to the GPR post-processing. In addition, incorporate capping before a PSPA test on an AC surface

Structural Responses Data Measured in an Instrumented Flexible Pavement

 This study presents and analyses the stress-strain responses data measured under real traffic conditions measured between Oct. 2012 to Oct. 2013 on an instrumented flexible pavement section on Interstate 40 (I-40) in the state of New Mexico, USA. Some weather variations data such as moisture and temperature variations at different depths of the pavement over the entire year are also discussed. The moduli of different layers determined using laboratory and field tests are also presented. It is expected that results of this study will be greatly useful to understand the behaviour of flexible pavement. The data presented in this study can be used to validate any constitutive or numerical model developed by readers

Pavement maintenance procedures with and without milling materials

AbstractThis study evaluates maintenance treatment followed by different Districts of New Mexico Department of Transportation (NMDOT). In addition, two case studies on the use of old pavement materials, called the “millings”, in maintenance projects are reported. Based on this study, it is observed that none of the Districts have a written procedure for maintenance work. Rather Districts rely on the experience of the maintenance crew for conducting maintenance projects. All Districts prefer to use chip seal for maintenance irrespective of distress conditions of the pavements. Patching and crack sealing are usually done before chip sealing to extend the life of the chip seals. Sand seal, scrub seal, and slurry seal projects are not done by District maintenance crews but by outside contractors. It is also observed that all Districts are interested in using millings in maintenance projects and most have already used millings in at least one maintenance project with some success and failure. Most of the Districts have used coarse fraction of millings in chip seal projects successfully. However, they failed to find a proper way to process the fine fractions of millings. Case Study I shows that fine millings can be used to construct thin overlay when mixed with emulsion in pug mill or hot drums. Case Study II concludes that fine millings can be used as fine/sand seal successfully following the same procedure and using the same equipment as chip seal

Determining and Validating Thermal Strain in Asphalt Concrete

AbstractThermal strain causes transverse cracks in Asphalt Concrete (AC) pavements. In this study, thermal strain is determined by developing a three-dimensional Finite Element Method (FEM) model and validates the model with measured data using the field installed Horizontal Asphalt Strain Gauge (HASG) in Interstate 40 (I-40) located near the city of Albuquerque in the state of New Mexico. Materials’ properties of the pavement section were determined by laboratory testing on field collected cores from the pavement section after the construction. Viscoelastic material properties of AC were determined from the creep test on the field cored samples. Coefficient of thermal expansion (CTE) and contraction (CTC) of AC were also determined in the laboratory and in the field. Results show that the FEM model can predict thermal strain with maximum variation of 6.0% compared to measured thermal strain in the field, which is very promising

Evaluation of rutting potential of hot mix asphalt using the asphalt pavement analyzer

A comprehensive study involving rut potential of Hot Mix Asphalt (HMA) was conducted. Both cylindrical and beam specimens of HMA were prepared using a Superpave Gyratory Compactor (SGC) and an Asphalt Vibratory Compactor (A VC), respectively. Mixture rutting performance was determined in the Asphalt Pavement Analyzer (AP A). Initially, rut tests were conducted on three laboratory-prepared HMA for 8000 cycles of loading with I 00 psi hose pressure, 100 lb wheel load, and 50 seating cycles. The rut values (8,000 cycles) varied between 2.0 mm and 6.4 mm. Rut depths were found to be sensitive to temperature when compared that to asphalt content. Subsequently, this study evaluated rut potential of ten plant-produced mixes. Three of these mixes were of type A and six type B insoluble and one Type C. Only one mix showed a rut depth of more than 4 mm. The A VC beam specimens showed higher rut depth compared to cylindrical specimens. The AP A rut test data were analyzed to identify the important contributing factors. Type A mixes were sensitive to percent asphalt content, where as Type B insoluble mixes were sensitive to material passing number 200 sieve. This research investigated the relationship between rheological and mechanical properties for various Oklahoma unmodified and modified binders based on the asphalt mixture's rutting performance. The tests result showed that binder's Performance Grade (PG) affects mixture performance significantly. In general, modified binder showed better performance compared to the unmodified binders. Modified binders of same PG grade did not show the same performance when test parameters were held constant. Binder's viscosity and rut factor (G'/sin8) did not show significant effects on rutting performance of both modified and unmodified binders. Linear and nonlinear regression analyses were performed to investigate the contribution of binder properties to rutting. The nonlinear regression prediction of rutting was better than the linear prediction. This study identified the most significant factors from a number of factors, which affect rut potential of HMA. Seven factors: binders PG, specimen type, test temperature, moisture, wheel load, asphalt content, and hose pressure,. each at two defined levels were incorporated in a Superpave mix. Rut tests were designed to be the elements of an experimental matrix. The matrix test results were analyzed statistically. The analysis results showed that binders PG, specimen type, test temperature, and moisture, affected a mixture's rutting performance significantly. This study developed and described a statistical procedure to design and analyze an experimental matrix of test results. This research investigated the repeatability and reproducibility of laboratory test data. An inter-laboratory study was performed on rut tests using the AP A between the 'asphalt design laboratory' at the Oklahoma Department of Transportation (ODOT) and the 'asphalt laboratory' at the University of Oklahoma (OU). The tests result showed no significant variability in the collected data from two laboratories. This study developed a rut database for future model development. The AP A rut results ofHMA materials, which were used in a road section (funded by ODOT) of the National Center for Asphalt Technology (NCAT) Test Track at Alabama, were also included in the rut database.Final Report (September 1999-September 2001)N

Comparing laboratory dynamic modulus values with long term pavement performance predictions

This study compares laboratory dynamic modulus value of Superpave mixes with the dynamic modulus obtained from Long Term Pavement Performance (LTPP) database. The comparison shows that the dynamic modulus from LTPP database, which were determined by using different types of artificial neural network (ANN) models, differs from the laboratory tested dynamic modulus. The dynamic modulus data of five LTPP test sections are considered. Mixes similar to those five sections were collected from the field and tested in the laboratory. Based on the findings of this study, it can be said that dynamic modulus from ANN models are less than the laboratory dynamic modulus for New Mexico Superpave mixes. Therefore, as an important design parameter, the use of dynamic modulus predicted from Neural Network models can result in outcomes different from those using laboratory dynamic modulus

Backcalculated Modulus of Asphalt Concrete

Asphalt Concrete (AC) is considered a spatially homogeneous material when analyzing and designing asphalt pavement. However, the modulus of AC along the wheel path and the middle of the wheel path may not be the same considering the continuous compaction by wheel loading. This study conducted monthly Falling Weight Deflectometer (FWD) tests to determine the AC modulus of a pavement section on Interstate 40 (I-40) in the state of New Mexico, USA from 2013 to 2015. The AC moduli on the wheel path, on the middle of the wheel path, on the shoulder with friction course, and on the shoulder without friction course are determined. It is mentionable that the driving lane and the shoulder have the same geometry, materials, and compaction effort. Results show that the modulus along the wheel path is almost the same as that of along the middle of the wheel path. The shoulder without friction course has a modulus greater than that of the lane AC modulus and the shoulder with the friction course. In addition, FWD backcalculated moduli at different temperatures are compared with the dynamic modulus values of the AC layer. It is found that the dynamic modulus at a loading frequency of 5 Hz is 1.7 to 1.9 times the backcalculated AC modulus