Research findings on the use of Rubberized Warm-Mix Asphalt in California

Authors: David Jones, Rongzong Wu, Cathrina Barros, Joseph Peterson



The University of California Pavement Research Center (UCPRC), on behalf of the California Department of Transportation initiated a comprehensive, phased research study into the use of warm-mix asphalt, involving laboratory and accelerated load testing, and full-scale field experiments. The objective of this study was to determine whether warmmix asphalt performs equal to or better than conventional hot-mix asphalt. The third phase of the study covered rubberized asphalt. Caltrans is mandated by law to use rubber recycled from scrap tires in at least 35% of all asphalt placed in the state. Although the benefits of rubberized asphalt are well documented, it has numerous limitations that are often not considered in research, including higher production and placement temperatures that have environmental and health constraints, and restrictions on long hauls and early and late season paving. Observations during rubberized warm-mix experiments indicated an absence of smoke and odour and significantly better workability compared to the hot-mix controls. Similar compaction levels were recorded on hot-mix control and warm-mix sections and on experiments in remote locations, rubberized mixes could be hauled for up to four hours, placed with ease whilst still achieving the required compaction. Equal or better performance has been observed over four years. Based on these research results, Caltrans placed more than one million tons of rubberized warm-mix during the 2011 paving season.


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