1374383 - Laboratory Studies on Resilient Modulus of Foamed Asphalt Mix and Virgin Aggregate Used in Base Course Layers

The continuous demand for virgin aggregates in construction of new roads and maintenance and rehabilitation of in-service pavements, and the ever-increasing demand to reduce the disposal of construction waste, is making agencies to look for ways to recycle construction materials. Foamed asphalt base course (FA) mix, which is typically produced by stabilizing Reclaimed Asphalt Pavement (RAP) with foamed (expanded) asphalt, is a material that can help in reducing the use of virgin aggregate in base layers in construction projects. A fundamental property used to characterize unbound pavement materials is the material’s Resilient Modulus (Mr). Resilient modulus is also one of the primary input parameters for base course materials in the mechanistic-empirical (M-E) method of designing pavements. The purpose of this study was to determine the stiffness of foamed asphalt and virgin aggregate base course materials using the repeated load triaxial resilient modulus test and estimating the parameters of a resilient modulus model used in M-E pavement design. Both materials were compacted at three different density levels (98%, 100%, and 102% of maximum dry density) and tests were performed in accordance with the AASHTO T307 procedure, except that the number of conditioning and testing cycles were reduced to prevent potential damage of the FA specimens, which appeared to have more brittle behavior after curing in the oven for two days at 40C. To maintain consistency, the same conditioning and testing protocol was followed to test virgin aggregate. From the results it was observed that: (1) Mr of both materials increased with increases in density, (2) the coefficient K2, the exponent for the bulk stress term, was found to be positive for both material types, indicating that an increase in the bulk stress results in an increase in the material stiffness, (3) the coefficient K3, the exponent for the shear stress term, was negative for the foamed asphalt mix but positive for the virgin aggregate, suggesting that an increase in shear stress decreases the stiffness of the foamed asphalt but increased stiffness of virgin aggregate. The resilient modulus of the foamed asphalt mix was found to be between 1.8 and 5.0 times that of the virgin aggregate depending on density level and bulk stress, indicating suitability of foamed asphalt mix as a base course material in lieu of virgin aggregate, at least in the as-compacted state.