Moisture susceptibility of high and low compaction dry process crumb rubber modified asphalt mixtures

The field performance of dry process crumb rubber-modified (CRM) asphalt mixtures has been reported to be inconsistent with stripping and premature cracking on the surfacing. One of the concerns is that, because achieving field compaction of CRM material is difficult due to the inherent resilient nature of the rubber particle, nonuniform field compaction may lead to a deficient bond between rubber and bitumen. To assess the influence of compaction, a series of CRM and control mixtures was produced and compacted at two levels: 4% (low, optimum laboratory compaction) and 8% (high, field experience) air void content. The long-term durability, in regard to moisture susceptibility of the mixtures, was assessed by conducting repeated moisture conditioning cycles. Mechanical properties (stiffness, fatigue, and resistance to permanent deformation) were determined in the Nottingham Asphalt Tester. Results indicated that compared with conventional mixtures, the CRM mixtures, regardless of compaction effort, are more susceptible to moisture with the degree of susceptibility primarily depending on the amount of rubber in the mixture, rather than the difference in compaction. This behavior is different from that of conventional mixtures in which, as expected, poorly compacted mixtures were found to be more susceptible to moisture than were well-compacted mixtures

Renewable biomass-derived lignin in transportation infrastructure strengthening applications

Lignin is considered as nature's most abundant aromatic polymer co-generated during papermaking and biomass fractionation. There are different types of lignins depending on the source (hardwood, softwood, annual crops, etc.) and recovery process. Recently, an emerging class of lignin products, namely sulphur-free lignins, from biomass conversion processes, solvent pulping and soda pulping, have generated interesting new applications owing to their versatility. As the renewable energy industry is expanding into developing the next generation of biofuels based on cellulosic biomass (e.g. corn stover, forest products waste, switch grass), abundant supply of sulphur-free lignin will become available as co-products for which value-added engineering applications are being sought. This paper discusses the potential for utilising lignin-containing biofuel co-products for stabilisation of geo-foundation beneath road pavements. Laboratory test results indicate that the biofuel co-products were effective in stabilising the Iowa class 10 soil (CL or A-6(8) soil classification). Utilisation of cellulosic biomass-derived lignin in transportation infrastructure strengthening applications appears to be one of the many viable answers to the profitability of the bio-based products and the bioenergy business from the perspectives of sustainable infrastructure systems.This is an accepted manuscript of an article published by Taylor & Francis in International Journal of Sustainable Engineering on November 2, 2012, available online: http://www.tandf.com/10.1080/19397038.2012.730069.</p