Practical approach for designing flexible pavements using recycled roadway materials as base course

Resilient modulus and plastic deformation of two recycled base course materials, recycled pavement material (RPM) and road surface gravel (RSG) and natural aggregate (Class 5), were investigated using a large-scale model experiment (LSME) and laboratory bench-scale resilient modulus (BSRM) tests. The RPM and RSG were tested alone and with 10% by weight Class C fly ash. The LSME tests indicate that the summary resilient modulus (SRM) of the unbound base course materials increases with increasing thickness of the base course and RPM and RSG exhibit significantly higher rate of plastic deformation (i.e. three to four times) than Class 5 aggregate. Stabilisation of the recycled materials by fly ash reduces the required thickness of the base course up to 30% when designed in accordance with the AASHTO 1993 design guide. The SRM and plastic deformation from LSME tests were used in the Mechanistic-Empirical Pavement Design Guide (MEPDG) to predict the lifetime expectancy of a pavement with a base course consisting of recycled materials alone and with fly ash stabilisation. Stabilisation of recycled materials used as base course can reduce the required thickness of the base course up to 30% or increase the service life of pavements by more than 20%.