Gregory A. Sholar

Field Evaluation of High Reclaimed Asphalt Pavement–Warm-Mix Asphalt Project in Florida: Case Study

In December 2007, a portion of State Route 11 in Deland, Florida, was milled and repaved with 45% reclaimed asphalt pavement (RAP). These high RAP mixes were produced at lower than normal hot-mix temperatures and with foamed warm-mix asphalt (WMA) technology. This project was the first large production in which the Florida Department of Transportation (DOT) allowed the use of high RAP in combination with WMA. FHWA, in cooperation with Florida DOT and the National Center for Asphalt Technology, was on site for production and placement of the high RAP-WMA. Plant-produced mix was collected by FHWA for performance testing evaluation. Two mixes were produced: a high RAP–hot-mix asphalt (HMA) control mix and a high RAP-WMA mix. Performance tests conducted by FHWA included performance grade (PG) determination of binders, dynamic modulus, and flow number. PG results of the binders indicate that the high RAP-WMA mix is softer than the high RAP-HMA control mix. This is further confirmed by flow number results, where the high RAP-WMA mix had a lower flow number than the high RAP-HMA control mix did. Dynamic modulus results indicate that the high RAP-WMA mix is slightly softer than the high RAP-HMA control mix, especially at intermediate temperatures. Comparison of measured dynamic modulus results with those predicted using the Hirsch and Witczak models confirm that complete blending occurred in the high RAP-HMA control mix. However, incomplete mixing of RAP and virgin binders may have occurred in the high RAP-WMA mix.

Evaluation of a Predicted Dynamic Modulus for Florida Mixtures

The new 2002 AASHTO guide for the design of pavement structures is based on mechanistic principles and requires the dynamic modulus as input to compute stress, strain, and rutting and cracking dama ...

Performance of Polymer-Modified Asphalt Mixture with Reclaimed Asphalt Pavement

Reclaimed asphalt pavement (RAP) mixtures have shown good resistance to rutting for hot-mix asphalt (HMA) pavement. Mixtures with polymer-modified binders such as styrene-butadiene-styrene (SBS) have also shown good performance against rutting and cracking. This paper presents the laboratory evaluations used to determine the rutting and cracking performance of the RAP mixtures with SBS polymer-modified binders as virgin binders. The asphalt pavement analyzer (APA) test and indirect tensile (IDT) test were conducted for the laboratory evaluation. The properties of SBS polymer-modified binders blended with recovered RAP binders were also investigated. The binder tests included G*/sinδ as the rutting parameter and G*sinδ as the cracking parameter of the Super-pave® PG grade system. The multiple stress creep and recovery test, which has recently received attention as an indicator of the rutting potential of polymer-modified asphalt binders, was also performed. RAP mixtures with SBS polymer-modified binders were fabricated containing different amounts of RAP materials: 0%, 15%, 25%, and 35%. From the APA and Superpave IDT tests, RAP mixtures with modified binders showed good performance regardless of the amounts of RAP materials in HMA. Even though the parameters, G*/sinδ and G*sinδ, and the percentage of recovery indicated the different amounts of RAP binders in polymer-modified binders, the relationship between these parameters and mixture performance was not clearly identified.

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.

Evaluation of Coarse- and Fine-Graded Superpave Mixtures Under Accelerated Pavement Testing

Initial Superpave® implementation guidelines encouraged mix designers to develop coarse gradations for higher-traffic-level mixtures, as this was thought to produce a more robust aggregate structure. Consequently, many agencies have specified the use of a coarse-graded asphalt mixture on high-volume facilities. However, target density can be difficult to obtain while compacting coarse-graded mixtures, and control of volumetric properties is harder to maintain than it is for fine-graded mixtures. The Florida Department of Transportation (FDOT) conducted an experiment to assess the rutting performance of coarse- and fine-graded Superpave mixtures under accelerated pavement testing (APT). Both mixtures consisted of aggregate from the same source and were made with virgin binder meeting the requirements of performance grade 67-22. Both mixtures contained the same effective binder content and were designed for 10 million to 30 million equivalent single axle loads, according to the standard Superpave mix design...

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...

Forensic Investigation and Validation of Energy Ratio Concept

The energy ratio (ER) concept was recently introduced as an accurate predictor of top-down cracking performance in Florida. Initial evaluation of ER with field projects in Florida confirmed its ability to distinguish between cracked and uncracked sections. To evaluate and validate the ER concept further, the Florida Department of Transportation designed and constructed two test sections at the National Center for Asphalt Technology test track. The primary difference between the two sections was the binder used in the upper two lifts. The first section used PG 67-22 and the second section used PG 76-22, which resulted in an ER of about twice the size. The section with the lower ER value cracked first and more extensively, though both sections experienced top-down cracking. This study was intended not only to look at ER as the primary factor to differences in performance but also to evaluate forensically the sections by using in situ strain measurements, coring, and interface bond strength testing. The strain regimes and bond strengths were found to be approximately equal between the sections, a finding that further validated the ER as a good predictor of top-down cracking performance.

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...

Field Conditioning of Superpave Asphalt Mixes

Failing volumetric properties (low air voids and voids in mineral aggregate) have been a common occurrence in the production of Superpave mixes in Florida and nationally. There are several potential causes of this problem including the effect of asphalt absorption as related to conditioning time. Research was done to determine (a) whether the 2-h force-draft oven conditioning adequately simulates actual roadway conditions and (b) how actual roadway conditions can best be simulated when the asphalt mixture is sampled and tested immediately following production at the plant. The results indicate the following: (a) 3 h of conditioning during design best correlated with roadway conditions; (b) a 1-h conditioning time at the asphalt plant resulted in maximum specific gravity values that best correlated with roadway conditions; (c) 1 h of conditioning at the asphalt plant increased the air voids of the mix by 0.5 percent for absorptive materials and 0.25 percent for nonabsorptive materials; and (d) conditioning had minimal effect on bulk density values.

The Effect of Aging on the Cracking Resistance of Recycled Asphalt

Fatigue cracking is an important concern when a high percentage of Reclaimed Asphalt Pavement (RAP) is used in an asphalt mixture. The aging of the asphalt binder reduces its ductility and makes the pavement more susceptible to cracking. Rejuvenators are often added to high-RAP mixtures to enhance their performance. The aging of a rejuvenated binder is different from virgin asphalt. Therefore, the effect of aging on a recycled asphalt mixture can be different from its effect on a new one. This study evaluated the cracking resistance of 100% recycled asphalt binders and mixtures and investigated the effect of aging on this performance parameter. The cracking resistance of the binder samples was tested by a Bending Beam Rheometer. An accelerated pavement weathering system was used to age the asphalt mixtures and their cracking resistance was evaluated by the Texas Overlay Test. The results from binder and mixture tests mutually indicated that rejuvenated asphalt has a significantly better cracking resistance than virgin asphalt. Rejuvenated mixtures generally aged more rapidly, and the rate of aging was different for different rejuvenators.