Confined E * testing on poroelastic road surface mixtures

In Europe, poroelastic road surface (PERS) material is being tested to a level at which it can be applied on different types of roads as a noise-reducing pavement. Traffic noise reductions of around 10–12 dB have been achieved using PERS in comparison to a conventional dense asphalt concrete. The PERS material is designed as an open-graded mix to have at least 20% air voids by volume. The objective of this research study was to evaluate the effect of six different confinement levels on the E * dynamic modulus testing of PERS mixtures. The major aim of utilising confinement on PERS materials was specifically to simulate and assess field performance characteristics of those mixes in the laboratory. Furthermore, the choice for confinement is essential in order to obtain realistic test results for a porous or open-graded aggregate structure of the PERS mix. AASHTO TP 62-07 was utilised for dynamic modulus E * testing; for confined tests, a lateral air pressure was provided that simulated confining effect on the samples. Confined tests were conducted only on the two variants of the PERS mixtures that had about 50% or greater amount of aggregates by volume of the mix. Moduli (E *) and phase angle (φ) master curves were established using the test results. For both mixes, at all temperatures and frequencies, the samples tested at the highest confinement level had the highest E * (a two-fold increase) compared with unconfined tests. Additionally, the samples tested confined had relatively small variations in φ between the different confinement pressures; but were higher than the unconfined test results. Based on the evaluation of the different confinement levels, this study also recommended that 138 kPa be considered a reasonable minimum confinement level for the PERS mixes for any future testing purposes. Overall, confined tests on the PERS variants were able to distinguish material parameters reasonably well within (for different confinements) the same mix, and between the different mixtures with varying mix designs. This study is anticipated to provide a basis for the selection of an appropriate confinement level for the PERS mixtures to correlate field test results in future.