Evaluation of Reclaimed Asphalt Pavement Aggregate in Road Bases and Subbases

Abstract

Recycling of pavement materials has become a viable alternative to be considered in road maintenance and rehabilitation. Conservation of resources, preservation of the environment, and retention of existing highway geometrics are some of the benefits obtained by reusing pavement materials. In the United States of America, more than 50 million tons (45.36 million Mg) of asphalt paving material are milled annually; recycling into new asphalt paving mixtures is the predominant application. However, large quantities of reclaimed asphalt pavement (RAP) aggregate remain unutilized and further uses should be explored. In the Sultanate of Oman, recycling of pavement materials is not practiced; this study presents a first attempt at evaluating RAP aggregate. The reuse of RAP aggregate could be economically attractive in Oman because certain regions of the country experience virgin aggregate shortage. Furthermore, rehabilitation of the road network would provide a valuable resource to be considered in highway construction. A laboratory evaluation of RAP and RAP-virgin aggregate mixtures as road base and subbase materials is described here. Physical, compaction, and California bearing ratio tests were conducted on the following RAP/virgin aggregate blends: 100/0, 80/20, 60/40, 40/60, 20/80, and 0/100 percent. Initial results indicate that RAP could be expected to replace virgin aggregate in the pavement subbase structure with satisfactory results if the RAP material were mixed with virgin aggregate. Best results were obtained for the 60/40, 40/60, 20/80, and 0/100 percent RAP/virgin aggregate blends. Higher dry density and CBR values are obtained as virgin aggregate content is increased. Based on a comparison with standard paving materials used in the Sultanate of Oman roads, the stabilized RAP material appears to be able to function as well as a conventional subbase material. However, only minimal use of RAP (about 10 percent) can be expected in road bases.