Cost-effectiveness of using geotextiles in flexible pavements S.-H. Yang 1 and I. L. Al-Qadi 2 1 Graduate Research Assistant, Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, 205 N. Mathews, MC-250, Urbana, IL 61801, USA, Telephone: +1 217 265 0427, Telefax: +1 217 333 1924, E-mail: yang20@uiuc.edu 2 Founder Professorof Engineering, Illinois Center for Transportation, Director, University of Illinois at Urbana-Champaign, 205 N. Mathews, MC-250, Urbana, IL 61801, USA, Telephone: +1 217 265 0427, Telefax: +1 217 333 1924, E-mail: alqadi@uiuc.edu Received 30 January 2006, revised 8 September 2006, accepted 18 November 2006 ABSTRACT: Using geotextiles in secondary roads to stabilize and reinforce weak subgrades has been a well-accepted practice over the past 30 years. However, from an economics point of view, a complete life-cycle cost analysis, which includes not only costs to agencies but also costs to users of the road, is urgently needed to assess the benefits of using geotextiles in secondary road flexible pavements. This paper presents a cost analysis process that includes costs for the initial construction, each rehabilitation, work-zone queue delays, moving delays, accidents, and fuel consumption. Two of the most practical design methods, developed by Al-Qadi and Perkins, were adopted to quantify the cost–benefits provided by geotextiles when incorporated in secondary road flexible pavements. Although both methods showed significant traffic benefit ratio (TBR) at very low California Bearing Ratio (CBR), the benefits suggested by Perkins diminished as the CBR became greater than 2%. This study also shows that, when user costs are considered, a greater TBR value may not result in the most effective life-cycle cost. Hence, for an optimum secondary road flexible pavement design with geotextile incorporated in the system, a life-cycle cost analysis that includes user cost must be performed. KEYWORDS: Geosynthetics, Geotextiles, Pavements, Service life, Life cycle, Cost analysis, Traffic benefit ratio REFERENCE: Yang, S.-H. & Al-Qadi, I. L. (2007). Cost-effectiveness of using geotextiles in flexible pavements. Geosynthetics International, 14, No. 1, 2–12 1. INTRODUCTION The application of geosynthetics by the transportation industry, including roadway, airport, railroad, and water- way agencies, has received considerable attention over the past three decades. In particular, the uses of geosynthetics in flexible pavements have significantly increased over time. However, using fabricated material to enhance pavement performance is not a new idea. For example, in the 1920s the state of South Carolina used a cotton textile to stabilize the underlying materials on a road that had a low bearing capacity subgrade soil (Beckham and Mills 1935). However, because of their susceptibility to degrada- tion, cotton fibers have since been replaced by synthetic polymers, which can resist harsh conditions better. Currently, geotextiles are being used to enhance pave- ment performance over soft subgrades by providing separation between the base aggregate layer and the natural subgrade. Since the usefulness of geosynthetic materials in pavements has been recognized (Tsai and Holtz 1998), the next question to answer is whether or not the practice is cost-effective. Thus a detailed life-cycle cost analysis (LCCA) is needed to quantify the benefit– cost ratio of geosynthetics application in pavements. Such an analysis should include the initial construction, main- tenance, and user costs. LCCA is a useful economic tool in considering certain transportation investment decisions. In the 1986 American Association of State Highway and Transportation Officials (AASHTO) Guide for the Design of Pavement Structures, the use of LCCA was encouraged, and a process was introduced to evaluate the cost- effectiveness of alternative pavement designs (AASHTO 1986). This paper presents an approach for evaluating the benefits of using geotextiles in flexible pavements. Two models, introduced by Al-Qadi and colleagues (Al-Qadi et al. 1997; Al-Qadi and Bhutta 1999; Loulizi et al. 1999), Perkins (2001), and Perkins and Edens (2002, 2003) for incorporating geosynthetics in pavement designs were utilized in this evaluation. The approach considers, in Geosynthetics International, 2007, 14, No. 1 2 1072-6349 # 2007 Thomas Telford Ltd