Effect of Production Variance on Air Void Content of Airfield Asphalt Mixtures in Australia

In Australia, thin (50-80 mm) asphalt is widely used as the primary type of surfacing for airfield pavements. The function of the asphalt surface is to provide a flexible, waterproof, durable, and skid-resistant wearing layer on top of the pavement structure. During production of airfield asphalt, variable constituents result in variations in the air void content of the mixture. Monte Carlo simulation was used to generate datasets, based on actual airfield asphalt production data, to determine the variance of air voids, and the effect that the different production variances had on the resulting air void content. It was found that the coarse aggregate (gravel) fraction gradings had the greatest influence on the air voids in the mixture, followed by the fine aggregate gradations and the bituminous binder content. It is recommended that the tolerances for production (Marshall) air voids in the current Australian airport asphalt specification be revised from a tolerance that is tied to the mixture design, to a fixed range. This will also allow the specification to be tightened, to a range that is still practically achievable, and that has been recommended previously.