Ambarish Banerjee

Calibration of "Mechanistic–Empirical Pavement Design Guide" Permanent Deformation Models: Texas Experience with Long-Term Pavement Performance

The performance models in the Mechanistic–Empirical Pavement Design Guide (MEPDG), developed under NCHRP 1-37A and 1-40D, are calibrated with sections throughout the United States. Hence, it is necessary to calibrate these models for specific states and regional conditions because of the differences in materials, environmental conditions, and construction practices. In general, a pavement design based on the nationally calibrated MEPDG will result in either an overestimate or underestimate of the pavement layer thicknesses because of systematic errors arising from local differences. This deficiency calls for local calibration of the performance models in the MEPDG so that they can be used to design pavements at a regional level. The calibration procedure described in this paper concentrates on finding two bias correction factors for the asphalt concrete (AC) permanent deformation performance model after values derived from expert knowledge have been assumed for the subgrade permanent deformation calibration factors. Pavement data from the Texas Specific Pavement Study (SPS)-1 and SPS-3 experiments of the Long-Term Pavement Performance database were used to run the MEPDG and calibrate the guide to Texas conditions. The regional calibration factors were obtained by minimizing the sum of squared errors between the observed and predicted surface permanent deformation. In this case, a simultaneous joint optimization routine was applied because it was theoretically sound. Finally, an average of the regional calibration coefficients for AC and subgrade permanent deformation was computed to obtain the set of state-default calibration coefficients for Texas.

Evaluating the Effect of Natural Gas Developments on Highways

The natural gas reserve in the Barnett Shale geological formation is one of the largest onshore natural gas reserves in the United States. The development of a natural gas well is a traffic-intensive operation that involves high volumes of truck traffic; saltwater traffic generated during the production phase is a major contributor to truck volume. The effect of traffic related to the natural gas industry on Texas highways is quantified. The oversized and overweight database maintained by the Texas Department of Transportation (DOT) was used to quantify several key characteristics of the rig traffic. In addition, personnel from the Texas DOTs Fort Worth District provided critical information about construction and saltwater traffic, including truck types used, gross vehicular weights, number of trips, and haul distances. Pavement sections were located along the busiest trucking corridors to evaluate damage caused by the truck traffic associated with natural gas development. Results indicated the approximate damage due to rig traffic was 1.6%, to construction traffic was 13%, and to saltwater traffic was 6%, relative to the damage caused by design traffic in terms of rutting. Additional damage caused by the natural gas truck traffic translated into reduced service life for pavements in the region. Results indicated a reduced service life of approximately 5.6%, 29%, and 16% associated with rig, construction, and saltwater traffic, respectively, in terms of rutting.

Framework for Determining Load Equivalencies with DARWin-ME

This paper presents a methodology for use of mechanistic–empirical design procedures to determine load equivalencies for various axle configurations and loads with a focus on oversize and overweight vehicles. The study uses the DARWin-ME system for pavement analysis and computation of equivalent damage factors (EDFs). In the context of the study, the EDFs for a given axle load and configuration consist of two partial factors: the axle load factor and the group equivalency factor. The framework adopted in this study defines a given axle load and configuration equivalent to a reference axle load based on equivalent pavement responses that results in the same distress level. The EDFs for single, tandem, tridem, and quad axles were evaluated for a wide spectrum of varying loads, and three failure criteria were applied: rutting, fatigue cracking, and roughness. Except in the case of rutting, there was no evidence that EDFs are affected by the structural capacity of the pavement sections. For single axles, it was found that thicker pavement structures are less sensitive to traffic loads. For tandem, tridem, and quad axles, the relationship was nonmonotonic. For fatigue cracking, a linear relationship between the axle load factor and the number of axles per axle group was observed. Finally, for roughness, the EDFs showed no systematic trend for the different structural numbers.

Characterizing Stability of Asphalt Emulsions Using Electrokinetic Techniques

This paper presents the findings from a study conducted to develop a simple quantitative test method to characterize the stability of asphalt emulsions. The proposed method uses electrokinetic techniques to determine the rate at which an asphalt emulsion breaks when subjected to an electric field. The test method was used with different types of emulsion as well as emulsions that were modified by further dilution or mechanical agitation. Results demonstrate that the parameters obtained from these tests were repeatable and different for different types of asphalt emulsions. Results also demonstrate that for a given type of emulsion the test method is sensitive to factors such as water content and partial breaking due to mechanical agitation. The proposed electrokinetics-based method and concomitant parameters provide a repeatable, rapid, and quantitative method by which to characterize asphalt emulsions.

Practical Approach for Determining Permit Fees for Overweight Trucks

A practical approach is presented for determining permit fees for overweight (OW) trucks based on consumption of service life of highways. A mechanistic–empirical design philosophy is used to estimate deterioration of the pavement structure. The methodology uses permanent deformation, load-related fatigue damage, and roughness scores as descriptors to estimate service life consumption for flexible pavements and punchouts and roughness measures for rigid pavements. The experiment included flexible and rigid pavement sections with varying structural numbers and slab thicknesses from sections across Texas to account for climatic and geographical differences. Each pavement section was simulated under different loading conditions reflecting the full spectrum of axle weights characteristic of single, tandem, tridem, and quad axles. The exercise provided the basis for developing group equivalency factors and axle load factors for individual axle groups. Axle-specific parameters enabled a modular approach toward determining gross load equivalencies for any truck category without restriction on axle weights or configuration. Consumption of service life was calculated as the additional pavement structure required to accommodate OW traffic in excess of the design truck volume while ensuring the same terminal distress condition. The cost incurred in providing the additional structure to offset the accelerated consumption was assigned to the responsible truck fleet in proportion to the marginal load equivalency over the legal gross vehicle weight and axle weight tolerances. Permit fees of 3.7¢/mi per equivalent single-axle load for flexible pavements and 2.9¢/mi per equivalent single-axle load for rigid pavements were found to be practical.

Evaluation of the Benefits of Diamond Grinding of a Continuously Reinforced Concrete Pavement

This paper discusses a study to evaluate the benefits on a continuously reinforced concrete pavement (CRCP) of diamond grinding used specifically for improving pavement functionality in surface macrotexture, skid resistance, roughness, and noise. The effectiveness of diamond grinding in improving those properties is calculated on the basis of in-field observations. The effect of three preexisting conditions (carpet drag, burlap drag, and transverse tining) on the effectiveness of diamond grinding is also evaluated. The results of the analysis indicate that diamond grinding improved the surface macrotexture by 0.6 mm and skid resistance by about 60%. The surface roughness of the diamond-ground sections was, on average, appreciably reduced, from 124 to 80 in./mi. An average overall reduction in noise level of 3.2 dB(A) was evident. A maximum reduction in the region of the noise frequencies (1,000 to 2,500 Hz) was observed, with a maximum noise reduction of 5.6 dB(A) at 1,600 Hz. The grinding operation produced a relatively uniform surface in relation to these properties despite the varying preexisting conditions across the CRCP.

A Rational Framework for Determination of Tariff Rates for Overweight Trucks

This paper presents a rational approach for determination of permit fees for truck traffic based on consumption of service life of highways. The prescribed approach uses mechanistic-empirical design philosophy for estimation of deterioration of the pavement structure. The methodology uses permanent deformation, load-related fatigue damage, and roughness scores as primary descriptors for estimation of the service life consumption. The experiment factorial included flexible pavement sections with varying structural numbers and sampled across Texas to account for climatic and geographical differences. Each of the pavement sections were simulated under different loading conditions to reflect the full spectrum of axle weights that are characteristic of single, tandem, tridem, and quad axles. The aforementioned exercise provided the basis for developing the group equivalency (GEF) and axle load factors (ALF) for individual axle groups. The determination of axle specific parameters enabled adoption of a modular approach towards determination of gross load equivalencies for any truck category without any restriction on axle weights or configuration. The consumption of the service life was calculated as the additional pavement structure that would be required to accommodate traffic in excess of the design truck volume. The cost incurred in the process of providing the additional structure was assigned to the responsible truck fleet in proportion to the marginal load equivalency over the legal gross vehicle weight (GVW) and axle weight tolerances. Results indicate that a permit fee of 3.7 ¢/mile/ESAL is equitable based on the findings from this study.