Engineered cold in-place recycling project: Blue Earth County State Aid Highway 20, Minnesota

Abstract

Cold in-place recycling (CIR) has been effective at rehabilitating aged pavements, but it has lacked well-defined engineering parameters, and success has been inconsistent. To rehabilitate a County State Aid Highway in Blue Earth County, Minnesota, both conventional CIR and a new engineered process were used. The new process includes selection guidelines, a sampling protocol, a new mix design protocol including performance testing of laboratory-prepared samples, a quality control and quality assurance plan, and an asphalt emulsion with a new chemistry designed for quicker early strength, higher residual binder content, and longer durability. The performance testing includes a new raveling test, thermal cracking testing, strength tests, and moisture susceptibility testing. The design included laboratory crushing of the reclaimed asphalt concrete into three gradations. Mix designs were done on each of the gradations so that when the actual gradation was determined in the field the correct job mix formula could be selected. The samples prepared by the new CIR process exhibited superior performance by raveling, thermal cracking, and moisture susceptibility testing. Field stiffness testing showed quicker early strength, which would enable the quicker return of traffic. Falling weight deflectometer testing showed higher moduli for the new CIR process. Although the initial costs are about 10% higher, the higher binder content and the reliability of the engineered process are expected to give lower overall life-cycle costs. The costs were significantly lower than those for the new Superpave® mix. The project also evaluates several surface treatments. The project will continue to be monitored with time to determine the long-term performance and relative cost benefits.