Comparison of Unconfined‐ and Confined‐Creep Tests for Hot Mix Asphalt

Abstract

Both unconfined‐ and confined‐creep tests have been widely used to evaluate and characterize rutting potential in hot mix asphalt (HMA). However, no reference has been made suggesting that either the unconfined‐creep test or the confined‐creep test is better than the other. The unconfined and confined creep of a dense graded laboratory mix were measured at the conditions at which rutting is most likely to occur in HMA pavements. The relationship between sample air voids and the unconfined, as well as the confined, creep were evaluated in the laboratory and compared to the relationship between in‐place air voids and HMA rutting under traffic. In addition, the effect of mix preparation and specimen height on confined and unconfined creep were also evaluated. The creep test (unconfined‐or confined‐) that produced the test results most consistent to HMA rutting has the higher probability of evaluating the rutting performance of HMA, and is therefore recommended as the preferred method for conducting the creep test. The confined‐creep test was found to be more representative of in‐place performance.