Proposed Compaction Procedure for Dry Process Crumb Rubber Modified Asphalt Mixtures Using Air Void Content and Expansion Ratio

Abstract

The dry process for crumb rubber modified (CRM) asphalt mixtures is characterized by a simple construction process that results in greater environmental benefits than the wet process does. However, the difficulties of compaction in the dry process often lead to unstable pavement performance; therefore, its application is highly restricted. This research aims to investigate the compaction procedure for dry process CRM asphalt mixtures using air void content and expansion ratio as the principal indices for evaluation. To evaluate the key factors affecting compaction, a series of CRM mixtures were prepared and compacted at four different crumb rubber contents by total aggregate volume of 3.0 %, 5.5 %, 8.0 %, and 10 %. First, with the air void ratio as the target indicator, the crumb rubber content, compaction temperature, and compaction method were evaluated to determine the appropriate compaction procedure. Second, the variations in height and expansion ratio of the CRM asphalt mixture specimens with different crumb rubber contents were analyzed in order to calculate the expansion ratio. The results indicated that generally the height and expansion ratio increase as the crumb rubber content of the CRM asphalt mixtures increases. Furthermore, it was found that when the crumb rubber addition was 5.5 % of the bulk volume of minerals, the volume stability of the mixture was improved, and this value is recommended for dry process CRM asphalt mixtures.