Sound absorption measurement of road surface with in situ technology

•An in situ technology is used to test sound absorption of road surface samples.•Different types of road surfaces are involved in the measurements.•Influences of testing distance, sample size and testing positions are investigated.•Requirements are given for the application of this method in road engineering.

Sound absorption of a road surface is considered one of the most important parameters influencing tire–road noise levels, especially for surfacings with high air voids content. In a recent study, a sound pressure (P)–particle velocity (U) measurement probe was introduced for investigating this property on road surface samples in the laboratory. The device can be applied in situ, thus no reverberant room or impedance tube is required in the test. Measurements were carried out on different types of road surface samples as well as on road sections. Samples considered include cores drilled from road sections, laboratory produced slabs, and a poro-elastic road surface. The influence of the distance between the probe and the testing surface, the influence of sample size, and the testing positions are investigated. To improve the reliability and accuracy of experiments on cores, a test platform was manufactured. According to the analysis of the test results, the in situ technology proved to provide reliable sound absorption results for road surface samples. Requirements are given for the application of this method in road engineering.