The contract for this project has just been signed. This follow-on project will explore and establish technical and scale-up feasibility and market viability of bio-modified rubber (BMR) asphalt (developed in an earlier IDEA Project NCHRP-171) as a sustainable bio-based alternative to petroleum-based asphalt and test it in the field. Work in Stage 1 will focus on designing and building a prototype to perform thermochemical liquefaction of swine manure, followed by filtration and vacuum distillation to produce an amide-enriched bio-modifier. This modifier will be blended with crumb rubber to activate the rubber surfaces. During blending (at 175ºC with 20 minutes residence time), molecules of bio-modifier will cleave polysulfidic crosslinks of swollen vulcanized crumb rubber in the absence of oxygen to promote interaction between the rubber surface and the amide groups in bio-modifier molecules. Amide-type organic compounds have a polar end and a non-polar hydrocarbon tail. When BMR is added to the asphalt binder, the polar end attaches to the rubber (polar surfaces) and the tail attaches to asphalt (non-polar) promoting interaction between BMR and the asphalt matrix. This reduces the propensity of rubber segregation within the asphalt blend and enhances asphalt rheological properties. In addition, the prototype unit will be able to produce sufficient BMR for laboratory and field evaluation. Work in Stage 2 will focus on experimental evaluation of BMR asphalt, alone and within the paving mixture. Superpave PG grading will be conducted for three selected BMRs. In addition, a comprehensive analysis at both binder and mixture levels will be performed. At the binder level, chemical and rheological characteristics of bio-asphalt before and after short-term and long-term aging (RTFO and PAV) will be investigated At the mixture level, Superpave mixtures will be prepared using three different BMRs for both intermediate and low temperature performance. Tests to be performed will include a low temperature cracking test [disk-shaped compact tension (DCT) test following ASTM D7313]. Stiffness will be investigated by measuring the dynamic modulus and flow number (AASHTO TP79). Moisture resistance will be investigated using a Hamburg wheel-track tester (AASHTO T324). Finally, the compounds that leach out from each of the mixtures will be analyzed and compared with ground water standards. The best performing BMR asphalt mixture will be selected for a trial field section. The trial section will use two rubber modified asphalts -- one with BMR (surface treated rubber) and the other with un-treated rubber. Field work will be done in collaboration with the industry partner and the North Carolina DOT. The mixing temperature and level of agitation for both asphalts as well as the number of roller compaction passes will be monitored to compare the ease of application of the two mixtures. In addition, field samples will be collected before and after compaction to conduct performance testing following North Carolina DOT specifications.
The project was terminated. No final report is available.
