Evaluation of Crumb Rubber Modification on Specification Compliance of Asphalt Mixtures

Since 2008, the Louisiana Department of Transportation and Development (LaDOTD) has allowed the use of crumb rubber modification (CRM) as per the specifications. However, the introduction of CRM has presented unique challenges during design and production. LaDOTD districts have reported early cracking for dense-graded mixtures. Adhesion and stability issues have been reported for open-graded friction course (OGFC) and stone matrix asphalt (SMA) mixtures. Currently, LaDOTD specifications allow the contractor to switch asphalt cement supplies without redesigning the mixture. This study evaluated several CRM-modified mixture designs to address design and performance concerns; it also evaluated the volumetric and mechanistic properties of dense, SMA, and OGFC mixtures designed with unmodified asphalt cement, styrene-butadiene-styrene-modified asphalt cement and five crumb rubber sources. SuperPave volumetric parameters were evaluated to ascertain the impact of CRM on the design of these mixtures. Rutting and intermediate temperature cracking susceptibility were determined using the Hamburg Loaded Wheel Tracker (LWT) and semi-circular bend test (SCB), respectively. Solvent extraction and the ignition furnace were used to determine the asphalt content of the modified mixtures. The results showed that CRM improved the laboratory rutting resistance of the mixtures. However, the laboratory cracking resistance was decreased for the CRM-modified mixtures. Based on statistical analysis, additional asphalt content, reduced CRM dosage, and the use of polymer additives may mitigate the reduced laboratory cracking performance of the CRM-modified mixtures. The volumetric parameters were also affected by CRMs. The mixtures should be re-designed if the contractor anticipates using a CRM-modified asphalt cement.

Kajian Penambahan RejIRE pada Aspal Modifikasi Crumb Rubber serta Kinerjanya pada Campuran Beraspal Panas

Asphalt polymer has superior characteristics than conventional asphalt. Styrene Butadiene Styrene (SBS) is a polymer that has proven its performance in heavy traffic, but it must be imported and expensive. Crumb rubber have high potential to be used as an asphalt modifier. Asphalt modified crumb rubber has high viscosity and is not homogeneous, so that the utilization cannot be delayed. This reduces workability in the field. This study aims to obtain asphalt modified crumb rubber which is easier to use by adding materials that do not affect its performance. RejIRE is a low viscosity additive to restore the properties of bitumen on crumb rubber modified. Experiments were carried out by adding variations in RejIRE levels to crumb rubber modified asphalt to determine its characteristics. Continued investigation of the performance of hot paved mixtures for wearing courses compared to asphalt mixtures with Pen 60/70 asphalt and SBS modified asphalt mixtures. The result is the addition of 0.75% RejIRE on asphalt crumb rubber modification have high workability. Overall the performance of the mix with SBS modified asphalt is better, but the mixture of hot paved with modified asphalt crumb rubber has a resistance to permanent deformation superior to the other paved mixtures.