Better Roads Digital Magazine
Issue link: https://read.dmtmag.com/i/119545
tages when compared to fossil fuel oils,��� the authors write. containing bio-binder from alternative feed stocks at higher ���Bio-oils are renewable, environmentally friendly, provide blending proportions (up to 50 percent replacement).��� energy security, and can be an economic opportunity for the This study determined if asphalt mixtures prepared with United States.��� high bio-binder content from pine tree feed stock have the In most cases, say Mohammed, Elseifi, Cooper, Challa and potential for increased use in transportation infrastructure. The Naidoo, the feed stocks for bio-based materials do not comresearchers conducted a comprehensive laboratory evaluation pete with food or feed supplies. Bio-based materials include of asphalt mixtures containing bio-binder technology at a industrial products, co-products, and byproducts made from content of 20, 25.5, 30 and 50 percent. agricultural or forestry feed stocks, they say. These feed stocks The mechanistic properties of asphalt mixtures containing could be wood, wood waste and residues, grasses, crops, and green asphalt technologies were evaluated in comparison to co-products of crops. conventional asphalt mixtures. A suite of laboratory tests was Technologies for converting biomass to energy can be genconducted to capture the mechanical behavior of the mixtures erally classified into either biochemical conversion or thermo- against major distresses. chemical conversion, they say. Biochemical conversions such ���Laboratory testing evaluated the rutting performance, as anaerobic digestion and fermentation typically involve large moisture resistance, fracture performance, and low temperafacility footprints and long processing time, on orders of days ture resistance of the produced mixtures using the Hamburg or months, and pose potential threats to surface or ground waters. ���However, thermochemical conversions, including pyrolysis, gasification and hydrothermal liquefaction, feature more compact facility size and faster reaction (usually in order of minutes) when compared to biochemical conversions,��� they write. The bio-binder considered in this study was produced by fast pyrolysis of biomass, say Mohammed, Elseifi, Cooper, Challa and Naidoo. During fast pyrolysis, biomass is heated rapidly in a high temperature environment (Fig. 1). The resulting product is a mixture of liquid fuel (bio-oil), combustible gases, Fig.1: Biomass pyrolysis for production of bio-binder. and solid char. Bio-oils produced by fast pyrolysis have many industrial uses, which include: combustible fuel, liquid smoke, preservative, loaded-wheel tester, the modified Lottman test, the semibase for chemicals and resins, binder for combustible fuel circular bending test, and the TSRST [thermal stress restrained starter and briquettes for boilers, or an adhesive. specimen test].��� ���The binding properties of the material are desirable for Based on the results of the experimental program, the reuse in asphalt pavements,��� they say. ���Typically, [in practice] searchers conclude: bio-binders are a combination of petroleum asphalt cement ��� With respect to rutting performance, mixtures modified with and bio-oils. Bio-binders are used to reduce the demand for [this] green asphalt have shown similar or improved perforpetroleum-based bituminous binder in three ways: direct mance when compared to the conventional mixes. replacement (100 percent replacement), an extender (25 to ��� The mean rut depths of the mixtures containing PG 64-22 75 percent replacement), or a modifier (<10 percent replaceand PG 76-22 [binders] were significantly improved with ment). Applications of bio-binder range from asphalt paving the addition of bio-binder. In addition, all the mixtures did to roofing shingles to sealants. not experience tertiary flow or passed the stripping inflec���Several research studies have evaluated the viability of biotion point, indicating moisture susceptibility. binders in asphalt pavements,��� they say. ���However, in many of ��� All mixtures, except for two, including one without an antithese cases the bio-binder was evaluated in minimal proporstripping agent, exceeded the 80 percent tensile strength tions (<10 percent). In addition, much of the research evaluratio. An anti-stripping agent was used for only one mixture ated manure, oak tree and switch grass feed stock. There is a comparison, 64-22. After the addition of the anti-stripping need for a comprehensive laboratory evaluation of mixtures agent, the tensile strength ratio of those two mixes exceeded Photo courtesy of Mohammed, Elseifi, Cooper, Challa and Naidoo RoadScience 20 April 2013 Better Roads RoadScience_BR0413.indd 20 4/1/13 3:24 PM