Thomas Bennert

Performance characteristics of plant produced high RAP mixtures

The main focus of this study was to obtain plant produced Reclaimed Asphalt Pavement (RAP) mixtures, to document the mixture production parameters and to evaluate the degree of blending between the virgin and RAP binders. The effect of mixture production parameters on the performance (in terms of stiffness, cracking, rutting, and moisture susceptibility) and workability of the mixtures was evaluated. Eighteen plant produced mixtures were obtained from three locations in the Northeast United States. RAP contents (zero to 40%) were varied and softer binders were used. The data and analysis illustrated that the degree of blending between RAP and virgin binders is a function of production parameters. The stiffness of the mixtures increased as the percentage of RAP increased, but not when the discharge temperatures of the mixtures were inconsistent. The cracking resistance was reduced as the percentage of RAP increased. The rutting and moisture damage resistance improved as the percentage of RAP in the mixtures increased. Finally, reheating the mixtures in the laboratory caused a significant increase in the stiffness of the mixtures.

UTILIZATION OF CONSTRUCTION AND DEMOLITION DEBRIS UNDER TRAFFIC-TYPE LOADING IN BASE AND SUBBASE APPLICATIONS

As construction and remediation take place throughout New Jersey, the amount of construction and demolition debris increases, while the availability of landfill space decreases. A viable solution for disposing of these materials is to incorporate them into base and subbase applications. An extensive laboratory program was conducted on two types of construction and demolition debris: recycled concrete aggregate (RCA) and recycled asphalt pavement aggregate (RAP). These two materials were compared with dense-graded aggregate base coarse (DGABC), which currently is being used in roadway base applications in New Jersey. Both RCA and RAP were mixed at various percentages with the DGABC to evaluate whether an optimum mix blend could be formulated. The materials were evaluated under a traffic-type loading scheme that included resilient modulus and permanent deformation via cyclic triaxial testing. Laboratory tests indicated that the RAP, RCA, and DGABC blended materials all obtained higher resilient modulus values than the currently used DGABC. The permanent deformation results indicated that the RCA mixed samples obtained the lowest amount of permanent deformation when the material was cyclically loaded to 100,000 cycles. In contrast, the permanent deformation testing on RAP mixed samples resulted in the highest amount of permanent deformation at the same number of cycles. Existing models currently used for quarried base and subbase materials were used to predict the permanent deformation in the recycled materials. Laboratory test results indicated that these models could be used for predicting permanent deformation in unbound recycled materials.

Assessment of Workability and Compactability of Warm-Mix Asphalt

One of the main benefits advertised about the use of warm-mix asphalt is the increased workability at conventional and lower compaction temperatures. From a field perspective, “workability” is commonly defined as the asphalt mixture property that describes the ease with which the asphalt mixture can be placed, worked by hand, and compacted to the desired mat density. Unfortunately, a laboratory property and test condition have yet to be developed to quantify these field characteristics. A research effort to evaluate the workability and compactability of different warm-mix additives preblended in a polymer-modified asphalt binder at varying percentages is summarized. Different test procedures, both asphalt binder related and asphalt mixture related, were evaluated and compared. Test results indicated that conventional mixing and compaction temperature asphalt binder tests were insensitive to the different warm-mix additives and dosage rates. Compaction data obtained with the gyratory compactor also indicated the device was generally insensitive to workability and compactability. Meanwhile, the University of Massachusetts workability device and the Marshall compaction hammer were found to rank the general workability and compactability of the mixtures in a rational order and compared favorably with one another. Not only was a promising new asphalt binder test, the lubricity test, sensitive to dosage rate and warm-mix additive, but the ranking compared favorably with mixture tests. The hope is that the information in this research effort can help in the selection and validation of warm-mix additives as a compaction aid.

Influence of Pavement Surface Type on Tire/Pavement Generated Noise

Pavement noise evaluations were conducted on 42 pavement surfaces in New Jersey using the Close Proximity Method (CPX) via the NCAT Noise Trailer. The CPX Method is a current ISO Standard that measures sound levels of the tire/pavement interface, thereby providing a method to evaluate solely the influence of pavement surface on traffic noise. The surfaces were comprised of both hot mix asphalt (HMA) and Portland cement concrete (PCC) surfaces. The HMA surfaces consisted of dense-graded asphalt mixes (DGA), open-graded friction course (OGFC) with and without crumb rubber, stone-mastic asphalt (SMA), NovaChip®, and a microsurfacing slurry mix. The PCC surfaces, pavements and bridge decks, had varying surface treatments consisting of transverse tining, saw-cut tining, diamond grinding, and broom finish. The main focus of the research was to: 1) Evaluate how different pavement surfaces influence the generation of tire/pavement noise, 2) Evaluate the effect of vehicle speed on the tire/pavement generated noise, and 3) Provide guidance as to the repeatability of the CPX method and optimal test distance on the roadway to aid in maximizing testing efficiency. Results of the testing indicated that the asphalt based surfaces provided the lowest tire/pavement noise levels. Of the HMA surfaces tested, the OGFC mixes modified with crumb rubber provided the lowest noise levels (96.5 dB(A) at 60 mph (96.5 km/h)). However, not only were these mixes modified with crumb rubber, but they also had the finest aggregate gradation. The loudest HMA surface was a 12.5mm SMA mix (100.5 dB(A) at 60 mph (96.5 km/h)). The PCC surfaces had the highest noise levels. Of all PCC surfaces tested, the transverse tined surface obtained the loudest noise levels (106.1 dB(A) at 60 mph (96.5 km/h)). It was found that if the PCC surface was diamond ground, the noise levels could be comparable, and sometimes lower, than typical HMA pavement surfaces. Typical noise levels of the diamond ground PCC surfaces were approximately 98.7 dB(A) at 60 mph (96.5 km/h). To evaluate the effect of vehicle speed, noise measurements were conducted at 55, 60, and 65 mph (88.5, 96.5, and 104.6 km/h). Test results within this range indicate that on average, the tire/pavement noise increases linearly and at a rate of approximately 0.18 dB(A) for every 1.0 mph (1.6 km/h). The NovaChip® mixes were less susceptible to the increase in vehicle speed (0.15 dB(A) increase for every 1.0 mph (1.6 km/h) increase), while the PCC broom finish (no treatment) surfaces were affected the greatest by vehicle speed (0.29 dB(A) increase for every 1.0 mph (1.6 km/h) increase). The CPX method was found to be repeatable, with an average standard deviation of approximately 0.13 dB(A), as long as the test distance was greater than 0.2 miles (0.32 km). This is most likely due to the sensitivity of the test method being influenced by the ability to track the identical wheel-path in successive test runs.

Influence of Production Temperature and Aggregate Moisture Content on the Initial Performance of Warm-Mix Asphalt

The concept and use of warm-mix asphalt (WMA) is becoming more popular in the asphalt industry. The promise of reduced energy consumption, reduced emissions, and a more workable product is appealing to an industry pressured by environmentalists with sustainability agendas and state agencies that apply pay adjustments on the bases of ride quality and pavement density. The use of WMA may come with some potential issues, however. Lower production temperatures may result in softer asphalt because of reduced oxidative aging, while poorly dried aggregates may create a problem from moisture damage. To evaluate these issues, a research project was undertaken to quantify the influence of mixing (production) temperature on the rutting and fatigue cracking performance of WMA mixtures. Stripping potential was also evaluated by using prewetted aggregate blends and by modifying the mixing procedure in the laboratory to more appropriately simulate a drum plant production of WMA. The laboratory procedure clearly indicated a decrease in rutting resistance and stiffness when evaluated in an asphalt mixture performance tester and dry Hamburg wheel tracking (HWT) tests once mixing temperatures decreased. Fatigue cracking resistance meanwhile increased in an overlay tester. Tensile strength ratio (TSR) and wet HWT tests indicated that TSR and Hamburg rutting values were able to obtain only passing results at conventional hot-mix asphalt mixing temperatures and with dry aggregates. The information presented may help state agencies to develop quality control testing plans for future implementation of WMA.

Backcalculation Method to Determine Effective Asphalt Binder Properties of Recycled Asphalt Pavement Mixtures

State departments of transportation are beginning to require the use of higher percentages of recycled asphalt pavement (RAP) in hot-mix asphalt. To help implement higher RAP contents, better procedures are needed for evaluating the binder properties of higher RAP content asphalt mixtures without chemical extraction. In particular, new and innovative methods are required to determine how the addition of RAP influences mechanical properties of the composite (RAP + virgin) asphalt mixtures. A method is summarized for determining what is referred to as the effective asphalt binder stiffness properties of asphalt mixtures blended with RAP. The proposed extraction-less procedure uses the Hirsch model to backcalculate the asphalt binder stiffness (G*) from asphalt mixture stiffness (E*). In addition, an analytical procedure to determine the phase angle (δ) is discussed. Test data comparing predicted versus measured asphalt binder properties of plant-produced asphalt mixtures with 0% RAP are presented. Additional validation data are presented for plant-produced asphalt mixtures of varying RAP percentages. Examples of implementing the backcalculated binder properties in the Mechanistic–Empirical Pavement Design Guide, as well as comparing the backcalculated asphalt binder properties with mixture fatigue test results, are also shown and discussed.

Field and Laboratory Forensic Analysis of Reflective Cracking on Massachusetts Interstate 495

In July 2007 the Massachusetts State Highway Department (Mass-Highway) began a pavement rehabilitation project involving the placement of hot-mix asphalt (HMA) over a section of portland cement concrete (PCC) pavement on Interstate 495. The pavement rehabilitation consisted of a 50.8-mm (2-in.) thick leveling course, followed by a 25.4-mm (1-in.) thick reflective crack relief interlayer (RCRI) and an overlay of another 50.8-mm (2-in.) thick intermediate course consisting of a dense-graded HMA mixture that was identical to the leveling course. Within approximately 2 months after placement, reflective cracking was observed in the area where only the initial 50.8-mm-thick leveling course had been placed. Approximately 6 months after the section that included the RCRI had been placed, reflective cracking was also observed. This paper summarizes a field and laboratory forensic effort that was aimed at determining the cause of the early reflective cracking on Interstate 495 in Massachusetts. Field testing, with the falling weight deflectometer as well as coring of PCC pavement, was used to assess the PCC joint performance in the vertical and horizontal deflection modes. Laboratory testing was conducted on laboratory-prepared HMA and evaluated for cracking resistance under vertical and horizontal deflections and for test temperatures that simulated field conditions. A general framework is introduced that can be used to assess the compatibility of different HMA and RCRI mixtures intended for use on composite pavements during the mixture selection and design phase before field placement.

Evaluation of the effects of hot mix asphalt density on mixture fatigue performance, rutting performance and MEPDG distress predictions

The purpose of this study was to evaluate the effect of density on the fatigue cracking and rutting performance of hot mix asphalt mixtures. Two plant produced Superpave mixtures, 9.5 and 12.5 mm, were utilised to fabricate specimens to target density levels of 88, 91, 94 and 97% of the theoretical maximum specific gravity. The specimens were used to evaluate the mixture stiffness in the asphalt mixture performance test device, fatigue cracking characteristics utilising the beam fatigue test and the overlay test-based fatigue cracking analysis and rutting potential using the asphalt pavement analyser and the flow number test. Additionally, the mechanistic-empirical pavement design guide (MEPDG) distress prediction equations were used to predict the mixture performance as function of density. Overall, the testing analysis and MEPDG predictions indicated that higher density specimens yielded improved fatigue and rutting performance.

Geotechnical Properties of Stabilized Dredged Material from New York-New Jersey Harbor

As a result of the ban on the disposal of contaminated dredged sediments in the New York Bight, the states of New York and New Jersey have embarked on a rigorous program of seeking environmentally friendly solutions to handling dredged material, including beneficial use of stabilized dredged material (SDM) in roadway applications. A pilot study was initiated in 1998 to construct two embankments on a site in Elizabeth, New Jersey, where SDM was successfully used as a cover for more than 100 acres of commercial development area. The pilot study included a laboratory phase for geotechnical evaluation of SDM and a field phase for monitoring and evaluating the construction process as well as the performance of the fills after construction. The results of the laboratory phase indicate that SDM satisfies most geotechnical criteria for fill construction—except those for durability—requiring proper coverage and protection similar to those provided for fills constructed on cohesive soils.

Field and Laboratory Evaluation of a Reflective Crack Interlayer in New Jersey

A research effort consisting of both field and laboratory testing was undertaken to evaluate reflective crack relief interlayer (RCRI) mixes as a means of mitigating reflective cracking in composite pavements. Extensive field testing that included falling weight deflectometer (FWD) and weigh-in-motion (WIM) sensors was used to establish applied loads and the resultant movements in the pavement structure. The resultant field movements were used to establish testing parameters for the laboratory study. The purpose of the laboratory program was to evaluate the reflective cracking potential through bending and expansion-contraction-type movements of plant-produced asphalt mixes consisting of different aggregate gradations and asphalt binder types commonly used in New Jersey for portland cement concrete pavement overlays. Results indicate that the combination of FWD and WIM data can provide valuable information for establishing realistic parameters for laboratory validation of asphalt mixes. The laboratory study clearly illustrated the benefit of using RCRI mixes that consist of a fine aggregate gradation and polymer-modified asphalt binders to minimize reflective cracking potential. However, future efforts should include more fatigue-resistant mixes that would overlay the RCRI mixtures, as well as efforts to ensure better construction practices during their placement.