James Greene

Impact of Wide-Base Single Tires on Pavement Damage

Dual tires have traditionally been used to limit pavement damage by efficiently distributing axle loads over a larger contact area than single tires. However, in recent years, the trucking industry, stating economic and safety benefits, has promoted the use of wide-base single tires. The Super Single tire, an early type of wide-base tire, proved inadequate and induced excessive pavement damage. By contrast, the new generation wide-base tires have contact areas that approach those of dual tires and offer the potential for improved performance. The Florida Department of Transportation investigated the pavement damage potential of four tire types, including a conventional dual tire (11R22.5), a Super Single (425/65R22.5), and two newly designed wide-base single tires (445/50R22.5 and 455/55R22.5 respectively). A controlled accelerated pavement testing program, in addition to theoretical modeling, was performed to determine critical pavement response parameters. Pavement damage was measured in terms of rutting and fatigue cracking (bottom-up or top-down), the predominant distresses in Florida. The investigation revealed that the 455-mm wide-base tire performed as well as the dual tire. By comparison, the 445-mm wide-base tire was shown to create more rut damage on a dense-graded pavement surface and was predicted to create more bottom-up cracking than a dual tire. As expected, the Super Single induced the most damage to the pavement.

Evaluation and Implementation of PG 76-22 Asphalt Rubber Binder in Florida

The Florida Department of Transportation (DOT) has had a long history of recycling ground tire rubber (GTR) from waste tires in highway projects. The Florida DOT first experimented with asphalt rubber binder (ARB) more than 35 years ago. In 1988, the Florida legislature mandated the investigation of using recyclable materials such as GTR in roadway construction. For more than 25 years, the Florida DOT has effectively satisfied the intent of the legislature. However, the ARB has often been associated with unpredictable performance and handling issues, such as the separation of the GTR from the binder. These performance and handling issues have resulted in higher construction costs and have made ARB less appealing because a more reliable alternative, PG 76-22 polymer modified asphalt (PMA), is available. As a result, a task team of the Florida DOT and industry members was formed with the goal of finding a way to make ARB handle and perform similarly to PG 76-22 (PMA), Floridas gold standard binder. This paper documents an accelerated pavement testing (APT) study to compare hot-mix asphalt mixtures constructed with PG 76-22 (PMA) and PG 76-22 (ARB). This APT study represents the final stage of the implementation of a new PG 76-22 (ARB) specification.

Accelerated Pavement Testing and Gradation-Based Performance Evaluation Method

Particle size distribution is a critical property that greatly influences an asphalt mixtures resistance to permanent deformation and cracking as well as a mixtures workability, permeability, and durability. The Superpave® mix design method attempts to address some of these issues by requiring that an aggregate gradation pass within control points. The control points concern: (a) the top size of the aggregate, (b) the relative proportion of coarse and fine aggregate, and (c) the dust proportion. Little additional guidance is given about suitable aggregate gradations. Some blends may pass the required Superpave criteria but perform poorly. A new theoretical approach for evaluation and specification of aggregate gradations was recently developed in Florida. The approach provides a framework to ensure that the resulting mixtures will have sufficient aggregate interlock to resist permanent deformation. Therefore, this method might be used at the mix design phase to assess the field performance of an asphalt mixture on the basis of aggregate gradation. A study was conducted to assess the appropriateness of, and to validate, this proposed approach through use of a controlled accelerated pavement testing experiment. The aggregate-based performance evaluation method is described, as are the subsequent experimental validation efforts and findings of the accelerated pavement testing.

Enhanced Gradation Guidelines to Improve Asphalt Mixture Performance

In 2010 a theoretical approach to the evaluation and specification of aggregate gradations to resist rutting was evaluated by the Florida Department of Transportation by accelerated pavement testing. This approach, known as the dominant aggregate size range (DASR) gradation model, provides a framework to ensure that the coarse aggregate of the resulting mixture has sufficient aggregate interlock to resist permanent deformation. Further research by the University of Florida and the Department of Transportation found that the properties of the interstitial components (ICs) within the DASR voids were strongly related to the durability and fracture resistance of asphalt mixtures. Parameters that made up the combined DASR-IC model included the DASR porosity, disruption factor (DF), effective film thickness (EFT), and fine aggregate ratio (FAR). The original evaluation of the DASR model was recently extended to include DASR gradations that might have had marginal aggregate interlock (i.e., marginal DASR porosity) and the effect of IC properties on mixture fracture resistance. The results confirmed that the rutting performance of the asphalt mixture was primarily controlled by the DASR porosity and that mixtures with marginal DASR porosity might still have had significantly better rutting performance than mixtures with poor DASR porosity. In addition, it was shown that the DASR porosity, DF, EFT, and FAR parameters played a critical role in mixture cracking performance. The validation of the combined DASR–IC model was documented, and the acceptable range of each parameter for improved mixture rutting and cracking performance was confirmed.

Evaluation of Structural Behavior of Precast Prestressed Concrete Pavement with Finite Element Analysis

A full-scale precast prestressed concrete pavement (PPCP) system was constructed and evaluated under actual traffic load conditions to develop the design guideline under Florida conditions. This test section showed good load transfer efficiency and riding quality. However, information was lacking about its structural response and potential performance. A three-dimensional finite element model was developed for stress analysis of PPCP under critical loading conditions. The developed three-dimensional model was calibrated by using deflection data obtained with a falling weight deflectometer. The model was used to perform a parametric analysis to determine the effects of critical loading location, concrete modulus, coefficient of thermal expansion of concrete, loss of prestress force, and subgrade stiffness under typical Florida conditions. Results of the parametric study indicate that the maximum stresses in the concrete increased significantly as the concrete modulus and coefficient thermal expansion increased. Because of the increase in flexural strength associated with the increase in elastic modulus of the concrete, an increase in elastic modulus of the concrete results in a decrease in the computed stress-to-strength ratio under critical load–temperature conditions. The PPCP system that was evaluated appeared to have a good predicted pavement performance with a computed stress-to-strength ratio of less than 0.5, with up to an additional loss of 20% of prestress force in the longitudinal and transverse directions. Variations in the base and subbase properties were found to have a minimal effect on the maximum induced stresses in concrete. This finding indicates that the PPCP system is appropriate for a wide variety of subbase and subgrade conditions.

A Long-Term Performance Evaluation of an Experimental Concrete Overlay

Flexible pavements are often rehabilitated by milling distressed asphalt and placing new asphalt at a thickness that accounts for expected traffic growth and pavement life. However, there are many reported benefits to concrete overlays as a method to rehabilitate and preserve distressed asphalt pavements. In 1988, the Florida Department of Transportation designed and constructed an unbonded concrete overlay on US-1 between Daytona Beach and Titusville. The 1.9-mile concrete overlay was part of a larger 8-mile milling and resurfacing of a deteriorated asphalt pavement. The concrete overlay test sections were divided into three groups based on design thicknesses of 6, 7, and 8 inches. Each of these groups included subsections with three joint spacing levels and two dowel bar configurations consisting of standard 12-inch spacing and wheel path only. The overlay sections are still in service with no major rehabilitation effort. The primary distress is pavement roughness found in sections with wheel path dowels only. The section with the most cracked slabs had joint spacings of 20 ft, which is no longer recommended. This paper documents the experimental program and presents the analysis and findings.

Evaluation of top-down cracking potential for asphalt pavements with 4.75 mm nominal maximum aggregate size mixture layer using full-scale field tests and finite element analysis

This study primarily focused on evaluating top-down cracking resistance for pavement structures with 4.75 mm nominal maximum aggregate size asphalt mixtures (i.e. SP-4.75) that will help determine more effective application of these mixes for layered flexible pavement system. Crack evaluation and pavement surface response measurements were conducted using full-scale field test sections. In addition, a three-dimensional (3-D) viscoelastic finite-element (FE) pavement model was developed to further validate the results of field tests using analytical solution. The results indicated that the pavement structure with SP-4.75 mixture at the top becomes more prone to top-down cracking when a thin layer with unmodified asphalt binder is applied. It was found that both layer thickness and binder type are key parameters to control top-down cracking potential. Also, the comparative observations between analytical and experimental results confirm that the FE model developed was able to provide accurate, reliable, and realistic prediction for change in pavement surface strain responses due to different conditions of SP-4.75 layer application. It was concluded that adequate thickness and binder type should be considered for proper application of SP-4.75 mixture as a surface course of layered flexible pavement system to effectively resist top-down cracking.

Strategies to reduce flexible pavement cracking in Florida

Abstract Cracking of flexible pavements, particularly top-down cracking, is the predominant distress in Florida. However, pavement failures due to cracking have reduced by ten per cent over the last ten years. This improvement in cracking resistance is primarily due to a focused and multifaceted research effort that includes laboratory studies, field test sections, and accelerated pavement testing. Most research efforts can be grouped into three main categories: asphalt binder modification, reflection cracking mitigation, and tack coat application rates and type. This paper presents the findings of these research studies and the strategies the Florida Department of Transportation has implemented to improve cracking resistance of flexible pavements.

Performance Characteristics of Fiber-Optic Strain Sensors as Compared With Electrical Resistance and Vibrating Wire Strain Gauges

This paper presented experimental results of fiber-optic sensor performance in terms of its accuracy, repeatability, and reproducibility. Strain sensors were embedded in concrete specimens, which were then subjected to the same known static and dynamic load, and their responses were compared to each other on the same basis. In addition to evaluating the response due to load, the measurements due to concrete drying shrinkage were also evaluated. According to the experimental test results, the fiber-optic strain sensor (FOS) showed an average error of 2.7 μe, as compared with average errors of 5.7 and 5.6 μe for an electrical resistance strain gauge and a vibrating wire strain gauge (VWSG), respectively. In addition, the repeatability of the FOS in terms of coefficient of variation (COV) was 7.5 % as compared with COVs of 4.4, 5.6, and 9.6 % for three different electrical resistance strain gauges and the reproducibility of the FOS in terms of COV was 9.8 % as compared with COVs of 5.4, 5.7, and 10.1 % for three different electrical resistance gauges. When compared with the strains measured by a calibrated LVDT in a concrete drying shrinkage test where the strains varied from 0 to around 250 μe, the FOS showed an average difference of 30.37 μe, whereas the VWSG showed an average difference of 34.04 μe. However, these difference were statistically insignificant at 95 % confidence level. Based on these results, it can be concluded that the FOS is found to have similar accuracy, repeatability, and reproducibility as compared to electrical resistance and VWSG.

Probabilistic Analysis to Quantify the Effect of the Use of a Material Transfer Device on a Smoothness Pay Incentive

Use of a material transfer device (MTD) during asphalt paving to provide smoother pavement while eliminating thermal and material segregation is well known. However, the additional operating cost may prevent contractors from investing in an MTD. This study evaluated the effect of MTDs on the smoothness of the finished friction course layer and predicted the incentives or disincentives a contractor may receive by using an MTD. Two empirical models were developed by using simple linear regression analysis to predict the smoothness of the final friction course on the basis of the underlying structural layer smoothness and whether or not an MTD was used. The regression model results were used in Monte Carlo simulations in conjunction with residual analysis techniques to predict, in a probabilistic fashion, the incentives or disincentives that a contractor could receive as a result of the Florida Department of Transportation’s new developmental specification for smoothness. Finally, expected incentives were predicted as a simulation result. Two validation projects with a normalized length of 10 mi showed additional expected incentives of