An Investigation into the Use of Ultrasonic Wave Transmission Techniques to Evaluate Air Voids in Asphalt

Air voids and their distribution are very important factors that influence the structural performance of asphalt pavements under traffic loading. Several simple methods exist for the overall (macro) evaluation of air voids in asphalt mixture, however there are very few methods available to assess their micro-distribution within an asphalt matrix. While X-ray methodologies have historically been used by researchers to investigate the complex distribution of air voids in asphalt mixtures, both cost and ease of application do not support their widespread use. The use of non-destructive ultrasonic wave transmission techniques (UWT) is outlined in the paper as an accurate, rapid and economical alternative method. UWT is able to both estimate the total air voids and their distribution within laboratory compacted asphalt samples. Asphalt samples with 14 mm nominal aggregate size manufactured with three types of bitumen; Class 320 (C320), Multigrade (M1000) and a SBS Polymer Modified Bitumen (PMB-A5S) and with different air voids were analysed using UWT techniques. The results have shown that UWT testing has the potential of being a rapid and cost-effective method of estimating total air voids and their distribution in laboratory asphalt mixtures