Road Materials and Pavement Design iFirst, 2012, 1–18 Practical approach for designing flexible pavements using recycled roadway materials as base course Ali Ebrahimi*, Brian R. Kootstra, Tuncer B. Edil and Craig H. Benson University of Wisconsin-Madison, Madison, Wisconsin, USA Resilient modulus and plastic deformation of two recycled base course materials, recycled pavement material (RPM) and road surface gravel (RSG) and natural aggregate (Class 5), were investigated using a large-scale model experiment (LSME) and laboratory bench-scale resilient modulus (BSRM) tests. The RPM and RSG were tested alone and with 10% by weight Class C fly ash. The LSME tests indicate that the summary resilient modulus (SRM) of the unbound base course materials increases with increasing thickness of the base course and RPM and RSG exhibit significantly higher rate of plastic deformation (i.e. three to four times) than Class 5 aggregate. Stabilisation of the recycled materials by fly ash reduces the required thickness of the base course up to 30% when designed in accordance with the AASHTO 1993 design guide. The SRM and plastic deformation from LSME tests were used in the Mechanistic-Empirical Pavement Design Guide (MEPDG) to predict the lifetime expectancy of a pavement with a base course consisting of recycled materials alone and with fly ash stabilisation. Stabilisation of recycled materials used as base course can reduce the required thickness of the base course up to 30% or increase the service life of pavements by more than 20%. Keywords: pavement design; MEPDG; recycled roadway materials; base course 1. Introduction Recycling existing pavement materials during rehabilitation and reconstruction of roads provides a more sustainable alternative to conventional methods such as full removal and replacement of the pavement materials. Existing deteriorated asphalt surface can be pulverised and mixed with the underlying materials to form a new recycled base layer known as recycled pavement material (RPM). The depth of pulverisation typically ranges from 100 to 300 mm and includes some or all of the existing base course and even part of the underlying subgrade (Epps, 1990). Similarly, when upgrading unpaved gravel roads to a roadway with a paved surface, the existing road surface gravel (RSG) can be recycled to form a base or sub-base. In situ recycling of roadway materials is cost effective and environmentally friendly, resulting in reduced energy consumption, greenhouse gas emissions and waste material disposal (Lee, Edil, Tinjum, & Benson, 2010; Wen & Edil, 2009). However, the asphalt binder in RPM and fines in RSG may adversely affect the strength, stiffness, and plastic deformation of recycled materials used as base course (Cooley, 2005; Kim, Labuz, & Dai, 2007; Kootstra, Ebrahimi, Edil, & Benson, 2010; Mohammad, Herath, Rasoulian, & Zhongjie, 2006; Taha, 2003). One method to enhance the performance of these recycled roadway materials is chemical stabilisation with binders like cement, asphalt emulsion, lime, cement kiln dust or fly ash. *Corresponding author. Email: aebrahimi@geosyntec.com ISSN 1468-0629 print/ISSN 2164-7402 online © 2012 Taylor & Francis http://dx.doi.org/10.1080/14680629.2012.695234 http://www.tandfonline.com Downloaded by [Ali Ebrahimi] at 06:11 02 July 2012