Thomas Bennert

Bio: Thomas Bennert is an academic researcher from Rutgers University. The author has contributed to research in topics: Asphalt & Aggregate (composite). The author has an hindex of 21, co-authored 93 publications receiving 1581 citations.

Performance characteristics of plant produced high RAP mixtures

Abstract: 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 mixture...

Utilization of Construction and Demolition Debris Under Traffic-Type Loading in Base and Subbase Applications

Abstract: 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

Abstract: 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 indicat...

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

Abstract: 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 indicate...

The Development of a Performance Specification for Granular Base and Subbase Material

Abstract: The research project encompassed evaluating the performance of New Jersey Department of Transportation (NJDOT) specified aggregates at the respective NJDOT gradation ranges (high end, middle, and low end) and providing guidance as how to modify the gradation ranges to provide better performance in the field. Currently, the NJDOT specifies the use of granular materials by gradation only. However, it is well known that the gradation of granular materials has a dramatic impact on its performance. Therefore, base and subbase materials were sampled from three regions in the state and evaluated under the following performance tests: permeability (falling and constant head conditions), triaxial shear strength, cyclic triaxial loading, California Bearing Ratio (CBR) and resilient modulus. Testing was also conducted on recycled asphalt pavement (RAP) and recycled concrete (RCA) to evaluate their potential use as base and subbase materials. Materials were tested at their respective natural gradations and at manufactured gradations which represented the NJDOT high, middle, and low areas of the gradation specification in order to provide guidance as how to better refine the current NJDOT gradation specification. Testing concluded that the gradation has an impact on each material and source tested. On average, permeability increased with increasing coarse fraction and decreasing percent fines. The triaxial strength increased as coarse fraction increased; however, the permanent deformation measured from the cyclic triaxial test indicated that at the gap-graded high end of the gradation band, instability was prevalent for the rounded subbase aggregates. This is most likely due to rounded aggregate particles not interlocking during loading (The gradation of this type of material is very similar to the non-stabilized open graded base layer that the NJDOT has used in the past). The resilient modulus testing followed a similar trend. Overall, the closer the aggregate gradation was to the middle/high side of the NJDOT gradation specification, the better the performance. The testing of the RAP, RCA, and their blends with the base material, showed that as the % RAP increased in the blend, both the CBR value and permeability decreased. RAP also caused larger permanent deformations during the cyclic triaxial testing. The inclusion of RCA provided the largest CBR, largest resilient modulus, and lowest permanent deformation values. However, as the % RCA increased, the blend’s permeability decreased.

Geotechnical and geoenvironmental properties of recycled construction and demolition materials in pavement subbase applications

Abstract: A comprehensive laboratory evaluation of the geotechnical and geoenvironmental properties of five predominant types of construction and demolition (C&D) waste materials was undertaken in th...