Can crumb rubber modifier effectively replace the use of polymer- modified bitumen in asphalt mixture?

Laboratory scale mechanical performances on six plant produced mixtures; three semi-dense surface courses and three dense binder courses modified with engineered crumb rubber (ECR) using the dry process are presented. The two types of mixtures produced and investigated fulfilled for the most part, the requirements of the Swiss and/or US standards regarding volumetric properties, water sensitivity and rutting. In advanced testing where no requirements exist, the dense ECR mixtures performed similar to the reference polymer modified mixtures and slightly worse for semi-dense mixtures in high temperature tests, where the binder becomes viscous in the rubber-binder composite and its ability to transfer loads is reduced. The ECR mixtures performed similarly or better than the reference in low temperature tests.  Across the advanced testing data set, all obtained results were well within acceptable values for both ECR and reference polymer mixtures indicating that crumb rubber can effectively replace polymer in asphalt mixtures

Designing, Producing, and Constructing Fine-Graded Hot Mix Asphalt on Illinois Roadways

Fine-graded (F-G) asphalt concrete mixtures are composed of an aggregate structure in which the fine fraction controls the load-carrying capacity of the mix. Other states have reported benefits in using F-G mixtures, including improved compaction, lower segregation, and lower permeability—resulting in longer life. Rutting concerns have been mitigated through the use of manufactured sand. This study investigates the feasibility of using F-G mixtures for IL 19.0 mm (3/4 in) asphalt binder courses in Illinois. A careful laboratory investigation, including mix designs guided by the Bailey Method, was conducted, then followed by extensive laboratory performance testing. Performance tests indicated that the F-G mixtures had equivalent or superior rut and crack resistance to a reference coarse-graded (C-G) control mixture. Limited field trials demonstrated the F-G mixtures were easier to compact, led to higher pay factors, and had significantly lower permeability than traditional C G mixtures, while being similar in cost. Whether designing a coarse- or fine-graded mixture, optimum asphalt content will be the same when using the same materials and targeting the same VMA and voids level, provided asphalt absorption remains constant. Limited full-scale accelerated pavement tests also demonstrated similarity in rutting resistance between the C-G and F-G mixtures investigated. Recommendations for implementation of F-G mixtures are provided, along with a revised draft specification for 19.0 mm mixtures. The revised specification provides upward adjustments to the lower side of the gradation band at the primary control sieve to lessen the likelihood of designing segregation-prone binder mixtures and raises the upper band to permit F-G mixtures to be designed. These principles apply to surface course mixtures as well.Illinois Department of Transportation, R27-079Ope

Cost-Effectiveness and Performance of Overlay Systems in Illinois Volume 2: Guidelines for Interlayer System Selection Decision When Used in HMA Overlays

In an effort to control reflective cracking in hot-mix asphalt (HMA) overlays placed over Portland Cement Concrete (PCC) pavements, several reflective crack control (RCC) systems, including interlayer systems, have been used. However, the cost-effectiveness of interlayer systems is still in doubt due their performance and additional costs. In this project, a decision making procedure to aid in the selection of cost-effective interlayer systems was developed. As a core step in evaluating the benefit-cost ratio (B/C) of interlayer systems, a user-friendly life-cycle cost analysis (LCCA) program, CIND (Cost-effective INterlayer system Decision program) was developed. Based on sensitivity analysis, a B/C prediction model was proposed, which takes into account a performance benefit ratio (PBR) parameter, a material cost ratio (MCR), and a construction time ratio (CTR). Using the B/C model, a table was developed which allows the user to determine the most cost-effective interlayer system in a rehabilitation project for a given equivalent single-axle load (ESAL) level, representative low temperature (TL), and existing concrete pavement joint spacing (JS). Finally, a decision making tree was constructed to simplify the process of determining the most cost-effective and compatible interlayer system for a given project. Depending on project significance and/or information availability, pavement engineers can select from one of three newly developed B/C evaluation tools (in order of sophistication): application tables, B/C prediction model, and the CIND computer program. Using these tools, it was found that B/C increases as PBR increases or MCR and CTR decrease. In general, System D is cost-effective in a wide range of ESALs and TL values; especially in a cold region with lower traffic volume. The application range is reduced with the increase of JS, however. System E is relatively cost-effective only in warm regions having higher traffic volume.ICT-R58published or submitted for publicationis peer reviewe

Cost-Effectiveness and Performance of Overlay Systems in Illinois Volume 1: Effectiveness Assessment of HMA Overlay Interlayer Systems Used to Retard Reflective Cracking

This project evaluated the ability of interlayer systems used in HMA overlays to retard reflective cracking. Field crack surveys and forensic investigation, including video imaging and ground penetrating radar surveys as well as laboratory testing of cored specimens, were conducted to examine the behavior of reflective cracking and reflective cracking control systems applied in Illinois. Crack extent and severity were recorded at 24 locations across Illinois. The performance evaluation focused on five types of interlayer systems: area- and strip-type nonwoven fabric; two strip-type composite; and a fine, high polymer content HMA interlayer system. Two reflective cracking indices were developed to characterize the condition of HMA overlays regarding reflective cracking as well as transverse cracking. In addition, a performance benefit ratio parameter, PBR, was developed to assess the performance of treated pavements relative to control sections. The study provided a quantitative assessment for various types of reflective cracking interlayer systems. In addition, it provides a means to predict the performance of several interlayer systems under various vehicular and environmental loading conditions through a simple ESALs-TL chart. A companion report (volume 2) provides tools for the selection of appropriate reflective crack control treatments based upon traffic, climate, and life cycle costs using a user-friendly life cycle cost analysis program (CIND ??? Cost-effective INnterlayer system Decision program).ICT-R58published or submitted for publicationis peer reviewe