Resources, Conservation and Recycling 58 (2012) 18–24 Contents lists available at SciVerse ScienceDirect Resources, Conservation and Recycling journa l h o me pag e: www.elsevier.com/locate/resconrec Comparative sustainability assessment of warm-mix asphalts: A thermodynamic based hybrid life cycle analysis Omer Tatari a,∗ , Munir Nazzal b , Murat Kucukvar a a Department of Civil, Environmental, and Construction Engineering, University of Central Florida, Orlando, FL 32816, United States b Department of Civil Engineering, Ohio University, Athens, OH 45701, United States a r t i c l e i n f o Article history: Received 9 February 2011 Received in revised form 5 July 2011 Accepted 30 July 2011 Keywords: Life cycle assessment Pavement sustainability System analysis Pavements Uncertainty analysis a b s t r a c t Warm-mix asphalt (WMA) has received considerable attention in the past few years as a potential solution for the reduction of energy consumption and emissions during production and construction of asphalt mixtures. However, many concerns and questions are still unanswered regarding its environmental ben- efits. Although several studies have been conducted to quantify the atmospheric emissions of WMA pavements, the direct and indirect role of ecological resource consumption was generally excluded in these studies. In this study, a thermodynamic based hybrid life cycle assessment model was developed to evaluate the environmental impacts of different types of WMA pavements and compare it to that of a conventional hot mix asphalt (HMA) one. The impacts on the ecosystem were calculated in terms of cumulative mass, energy, industrial exergy, and ecological exergy. Monte Carlo simulation was also conducted to analyze the variability of critical input parameters. The results of this study showed that although the mixing phase is important, it should not be the only phase to evaluate the decreased amount of atmospheric emissions of WMA pavements. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Asphalt pavements play a critical role in transportation infras- tructure in the U.S. More than 92% of roads and highways, which accounts for more than 2.5 million miles, are paved with asphalt materials in the U.S. (National Asphalt Pavement Association, 2009). The rising prices of the asphalt cement materials and increased awareness of environmental impacts of hot mix asphalt (HMA) mixtures due to global warming and climate change are among the main challenges facing the asphalt paving industry. Pro- duction of asphalt mixtures has also significant ecological impacts and alternative ways to mitigate the environmental impacts associ- ated with it generated tremendous interest worldwide. Utilization of warm-mix asphalt (WMA) was one of the five emerging tech- nologies identified to solve some of these problems (Moulthrop et al., 2007). WMA is a generic term for an asphalt mixture mixed and placed at lower than conventional temperatures, 16–55 ◦ C lower than typical HMA (Newcomb, 2005). The use of WMA technologies was developed in Europe with the aim of reduc- ing greenhouse gases produced by the manufacturing industries (Button et al., 2007). While heat is used to reduce asphalt viscos- ity and to dry aggregates during mixing of conventional asphalt mixtures, WMA reduces the asphalt viscosity by including water, ∗ Corresponding author. E-mail address: tatari@ucf.edu (O. Tatari). or special organic or chemical additives in the mixture. The reduc- tion in viscosity allows the asphalt binder to adequately coat the aggregates during mixing. The reduction in mixture viscosity also improves its workability and allows for compaction at lower tem- peratures. The Federal Highway Administration (FHWA) has identified sev- eral additives or processes that may be used in the production of WMA (D’Angelo et al., 2008; Hassan, 2009). Among these addi- tives, Aspha-min ® is a manufactured synthetic zeolite (sodium aluminum silicate), which contains water. Water is released dur- ing mixing, creating a foamed asphalt. As a result, improvement in the mix workability and aggregate coating at lower tempera- tures is realized. Sasobit ® is a wax-type additive of coal gasification that melts in the asphalt binder at high temperatures. As a result, a reduction in the viscosity during mixing is achieved. The melting point of Sasobit ® is approximately 100 ◦ C and is completely soluble in asphalt binder at temperatures in excess of 115 ◦ C. On the other hand, Evotherm TM uses a high-residue emulsion, which results in the improvement of the adhesion of the asphalt to the aggre- gate and the enhancement in mixture workability (Chowdhury and Button, 2008). A reduction in energy requirements associated with the production of this mixture of up to 55% has been reported (Kristjánsdóttir et al., 2007). A number of field trials and studies have been conducted in Europe and the U.S. to evaluate the potential benefits of using of WMA (Barthel et al., 2004; Button et al., 2007; Kvasnak and West, 2009; Nazzal et al., 2010). In general, the results of those 0921-3449/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.resconrec.2011.07.005