Indirect tension relaxation test to evaluate the effect of the addition of RAP to HMA mixes

A total of 160 different hot mix asphalt (HMA) combinations of binders, aggregates, and reclaimed asphalt pavement (RAP) were compacted and tested using indirect tension stress relaxation at two temperatures (5 and 22 degrees C). Two relaxation characteristics from a power law fit through the data were used to define the effect of RAP on the HMA binder-related properties: the initial modulus at 1 s (regression constant) and the curvature coefficient (regression exponent). The results showed there is a nonlinear relationship between both the initial modulus and the curvature coefficient and the percent RAP from 0 to 100% RAP. A linear relationship can only be obtained between the properties and the percent RAP between 0 and 50%. There is little change in either the initial modulus or curvature coefficient for HMA mixes with 50 or more RAP. When three tests per sample are averaged, the coefficient of variation is 18 and 7% for the initial modulus and curvature coefficient, respectively.