Gale C. Page

PERFORMANCE-BASED FRACTURE CRITERION FOR EVALUATION OF MOISTURE SUSCEPTIBILITY IN HOT-MIX ASPHALT

The laboratory testing procedures currently available for testing hot-mix asphalt moisture susceptibility all evaluate the effects of moisture damage in the laboratory by measuring the relative change of a single parameter before and after conditioning (i.e., tensile strength ratio, resilient modulus ratio). The use of a single parameter to evaluate moisture damage must be questioned. Instead, a single unified framework that accounts for changes in key mixture properties is needed to evaluate the effects of moisture damage in mixtures effectively. The use of a new performance-based fracture parameter, the energy ratio (ER), for quantifying the effects of moisture damage on the fracture resistance of mixtures is evaluated here. ER is used to determine the effects of moisture damage on changes in the fracture resistance of six granite mixtures prepared with and without the use of an antistripping additive. The granite aggregate used is a known stripping aggregate. In addition, one limestone mixture with a known high resistance to stripping was used. The results indicate that not only is the ER capable of detecting the effects of moisture damage on the fracture resistance of mixtures, it is also shown to detect the presence of antistripping agents in mixtures. Results indicate that the ER may form the basis of a promising combined performance-based fracture criterion for evaluating the effects of moisture damage in mixtures as well as the overall resistance to fracture.

SUITABILITY OF ASPHALT PAVEMENT ANALYZER FOR PREDICTING PAVEMENT RUTTING

Findings are summarized from an investigation performed to evaluate the suitability of a wheel-tracking device known as the asphalt pavement analyzer (APA) for assessing the rutting potential of asphalt mixes. The evaluation process consisted of correlating the APA’s predicted rutting with known field measurements. The correlation between beam and gyratory samples and the testing variability were also investigated. In addition, the APA test results were compared with those obtained using the Georgia loaded-wheel tester. The findings of this investigation indicated that the APA may be an effective tool to rank asphalt mixtures in terms of their respective rut performance. However, for each mixture type, the APA testing variability was significant between tests and between the three testing locations within each test. Differences in rut measurements of up to 4.7 and 6.3 mm were recorded for beam and gyratory samples, respectively. Therefore, using the APA as a clear pass-or-fail criterion for performance prediction purposes of asphalt mixtures may not be appropriate at this time. It should be noted that these findings are based on data collected on three mixes. Therefore, it is suggested that the APA testing variability (testing and testing locations within the device) be further assessed with a wider range of mixtures. The intent of such an assessment should not only be to correlate the APA results with field data but also to develop potential pass-or-fail limits and procedures.

Effect of Tire Rubber Grinding Method on Asphalt-Rubber Binder Characteristics

The results of a study carried out to evaluate the effect of rubber grinding processes on the properties and characteristics of the resulting asphalt-rubber binder are presented. Several ambient and cryogenic ground tire rubber (GTR) materials were evaluated using measurements of surface areas and bulk densities. The rubber materials were then, respectively, mixed with an AC-30 asphalt; the resulting blends were tested to determine the corresponding viscosity, settlement during storage, and potential for binder draindown. The findings indicate that the asphalt-rubber binders produced with rubber from the different grinding processes have measurable differences in properties and storage characteristics that are critical to the performance of the binder in open-graded mixtures. The wet-ground rubber material had substantially lower bulk densities and larger surface areas than rubber resulting from other grinding methods. GTR materials with greater specific surface areas and more irregularly shaped particles produced asphalt-rubber binders with higher viscosities. Binders with the cryogenic ground rubber had the greatest amount of settlement and the least resistance to draindown.

Effects of Water Saturation Level on Resistance of Compacted Hot-Mix Asphalt Samples to Moisture-Induced Damage

The Florida Department of Transportation (FDOT) initiated monitoring of its first Superpave section on I-75 in Columbia County for stripping potential using AASHTO T 283, which specifies that all conditioned test samples be saturated to between 55 and 80 percent based on 7 ± 1 percent air voids. A fairly large saturation range is allowed because it was thought that mixtures may have different percentages of permeable air voids. However, the potential interaction between air void content and the level of saturation has not been fully investigated. It is also not clear whether test results from samples saturated to 55 percent are comparable with those of the same mixture saturated to 80 percent for a similar air void content. Therefore, although FDOT adopted AASHTO T 283, it also initiated a parallel study on the effects of different degrees of saturation on moisture damage. Findings are reported of both the ongoing monitoring of the I-75 project for potential stripping and the investigation of the effects of different levels of saturation on moisture susceptibility test results as determined using AASHTO T 283.

Nuclear Density Readings and Core Densities: A Comparative Study

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.

Development of New Moisture-Conditioning Procedure for Hot-Mix Asphalt

The presence of pore water in mixtures can cause premature failure of hot-mix asphalt pavements. The processes typically associated with moisture damage are complex and occur over a long period of time in the field. Short of being able to simulate each of the possible mechanisms of moisture damage directly, the ideal laboratory-based conditioning system should accelerate the penetration of moisture through the asphalt film and at the same time minimize complicating effects. This paper presents the results of an experiment conducted to determine whether it was possible to use cyclic pore pressures to induce enough damage to distinguish between mixtures known to be highly resistant from mixtures known to be susceptible to moisture damage. Experimental constraints included requirements that conditioning be accomplished within a reasonable length of time and that typical laboratory equipment be used. Evaluation of the resulting effects of moisture damage included the use of the Superpave® indirect tension test and the energy ratio parameter. Findings show that cyclic pore pressures can be used to accelerate moisture damage enough to distinguish between mixtures known to be strippers and those known to be highly resistant to moisture damage. The use of cyclic pore pressures to accelerate moisture damage in mixtures may minimize the introduction of other confounding damage effects on the mixtures.

Superpave Field Implementation: Florida's Early Experience

Over the past 10 to 15 years, Interstate pavements in northern Florida have experienced a significant number of failures, primarily due to rutting. It was believed that the present fine-graded, 50-blow Marshall-designed mixes were inadequate to withstand current loading conditions. The newly developed Superpave system represented an opportunity to address several of Florida’s asphalt pavement problems. Thus, the Florida Department of Transportation made a concerted effort to implement Superpave technology in 1996. During this period, eight projects were changed from the traditional Marshall mix designs to Superpave. Although the new procedure offers potential for improved pavement performance, there has been very little experience nationally with its field application. Florida’s early experiences with the field implementation of Superpave are documented.

Development of the Florida Department of Transportation's Percent Within Limits Hot-Mix Asphalt Specification

The Florida Department of Transportation adopted a percent within limits approach in July 2002 for the acceptance and payment of all hot-mix asphalt. Contractor test data, after being verified by the department, are used to calculate payment. Acceptance and payment for dense-graded Superpave® mixtures are based on the following five asphalt material properties: roadway density, percent air voids, asphalt binder content, percent passing the No. 8 sieve, and percent passing the No. 200 sieve. Acceptance and payment for open-graded friction course mixtures are based on the following four asphalt material properties: asphalt binder content, percent passing the 3/8-in. sieve, percent passing the No. 4 sieve, and percent passing the No. 8 sieve. Contractor test data from recently completed construction projects were used to develop representative standard deviations of the asphalt material properties used for payment and acceptance. These standard deviations were then used to develop tolerance values for the pe...

Evaluation of High-Speed Profilers for Measurement of Asphalt Pavement Smoothness in Florida

The Florida Department of Transportation initiated a field study to assess the feasibility and appropriateness of implementing the use of laser-based high-speed profilers to automate its process of determination of ride acceptance. If a high-speed profiler is to be considered for determination of ride acceptance, it is essential that its level of accuracy and precision be assessed. For such a purpose, profile measurements were acquired by using five profilers concurrently on a large number of asphalt pavement sections. Also, to evaluate the effects of surface texture on these measurements, the test sections were randomly selected to include both open-and dense-graded surface mixtures. The profile data collected were first analyzed to determine the profile indices in terms of the ride number and the international roughness index at each test site. The results were then used as a basis for an evaluation of the repeatability and reproducibility of the profiling units. In addition, the effects of a profiler operating speed gradient as well as those of the pavement surface texture on roughness measurements were assessed.

Investigation of the CoreLok for Maximum, Aggregate, and Bulk Specific Gravity Tests

The Florida Department of Transportation uses long-established test procedures to determine the maximum specific gravity (Gmm) and bulk specific gravity (Gmb) of asphalt mixtures and the bulk specific gravity (Gsb) of aggregates. The CoreLok, a vacuum-sealing device that can be used to determine these properties, was evaluated by the department for these test procedures. With respect to the Gmm test procedure, for mixtures containing nonabsorptive granites, the CoreLok determined results equivalent to those of the departments test procedure. However, for mixtures containing absorptive limestones, the CoreLok determined higher Gmm values than did the departments test procedure. The apparent reason for the discrepancy is that the CoreLok does not determine a saturated surface dry condition of the sample. With respect to the aggregate specific gravity test procedures, the CoreLok provided test results equivalent to the departments test procedure for the nonabsorptive fine aggregates only. For the absorpti...