Aggregate gradation theory, design and its impact on asphalt pavement performance: a review

Gradation is one of the crucially important features of aggregate blend. The objective of this paper is to present a review on the theory and design method of aggregate gradation, followed by its effect on asphalt pavement performance. The results indicate that, (i) Theory of maximum density curve, particle interfering theory and fractal theory are the main theories for aggregate gradation. (ii) The gradation design of asphalt mixture has two types by aggregate morphology-continuous and gap gradation, or three types by air voids of mixture-dense, open and semi-open gradation. However, the only constant principle of aggregate gradation design is to strictly follow the requirements of pavement performance. (iii) Aggregate gradation significantly influences almost all of the pavement performances. The performance-based design method for asphalt mixture should pay more attention on aggregate gradation. (iv) The variability of aggregate gradation cannot be eliminated due to its objective existence from aggregate production in quarry to mixture compaction in field. Several effective control measures are summarized to limit gradation variability under an acceptable range. (v) The latest developments and the trend for gradation analysis are numerical simulation based on virtual reconstruction, image-based modelling and computer-generated modelling.