The effects of compaction temperature on CRM mixtures made with the SGC and the Marshall compactor Soon-Jae Lee a, * , Serji N. Amirkhanian a , Seung-Zoon Kwon b a Department of Civil Engineering, Clemson University, Clemson, SC 29634-0911, United States b Department of Civil Engineering, Kangwon National University, Samcheok 245-711, Republic of Korea Received 23 January 2007; received in revised form 26 February 2007; accepted 2 March 2007 Available online 20 April 2007 Abstract The compaction temperature of crumb rubber modifier (CRM) asphalt mixes needs to be determined cautiously because the viscosity and the amount of the CRM binder affects the compactability of the mixtures. In this study, a laboratory investigation was carried out on the volumetric properties of CRM mixtures fabricated using the Superpave gyratory compactor (SGC) and the Marshall compactor as a function of compaction temperature. Two CRM binders were incorporated into HMA mixtures. Two other mixtures were produced with the control binder (PG 64-22) and SBS-modified binder (PG 76-22) and used for comparison purposes. The CRM binders were produced using one base binder (PG 64-22) with 10% or 15% ambient CRM (40 mesh) by weight of the binder. For this research, the Superpave and the Marshall mix designs for four different asphalt binders were conducted to determine the optimum asphalt contents (OAC). A total of 128 specimens were manufactured using the SGC and the Marshall compactor at various compaction temperatures (116, 135, 154, and 173 °C). The volumetric properties were obtained and analyzed using the statistical methods. The results from this study indicated that (1) the compaction temperatures used in this study significantly affected the volumetric properties of the CRM mixtures, regardless of the compaction methods (the SGC and the Marshall compactor); (2) the CRM mixtures in both the SGC and the Marshall compactor showed the higher VMA values than the control and SBS-modified mixtures; (3) a general trend of the volumetric properties as a function of compaction temperature and compaction method was found for the CRM mixtures used in this study. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Crumb rubber modifier; Compaction temperature; Volumetric properties 1. Introduction Approximately 300 million scrap tires are annually gen- erated in the United States, and about the same amount is produced in Europe [2]. This is becoming a problem in many Asian countries due to several factors (e.g., lack of landfill space, environmental issues, etc). There are many applica- tions in civil engineering area that this by-product could be utilized to enhance the properties of the existing materi- als. For example, crumb rubber modifier (CRM) can be used to make asphalt pavements that exhibit increased pave- ment life, decreased traffic noise, reduced maintenance costs, and resistance to rutting and cracking [11,10,7]. At present, this application provides a practical way to dispose of millions of scrap tires, a waste issue difficult to solve in many parts of the country and the world. Currently more and more countries have begun using CRM pavements. In general, the compaction temperature influences work- ability, which is related to achieving the proper density of the mixture. The compaction temperature for conventional asphalt mixtures is defined as the range of temperatures where an unaged binder has a kinematic viscosity of 280 ± 30 mm 2 /s [3]. On the other hand, these requirements were determined based on experience with unmodified asphalt binders. Based on the field experience, CRM mixtures are compacted at a higher temperature than unmodified mixtures [2]. Nonethe- less, the properties of the CRM mixtures depending on com- paction temperature is considered to be rather unclear and few studies have been done in this area [8,9]. 0950-0618/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2007.03.003 * Corresponding author. Tel.: +1 864 650 5838. E-mail addresses: soonjae93@gmail.com (S.-J. Lee), kcdoc@clemson. edu (S.N. Amirkhanian), szkwon@kangwon.ac.kr (S.-Z. Kwon). www.elsevier.com/locate/conbuildmat Available online at www.sciencedirect.com Construction and Building Materials 22 (2008) 1122–1128 Construction and Building MATERIALS