Effect of production and sample preparation methods on aggregate shape parameters

The performance of hot mix asphalt (HMA) greatly depends upon the aggregate shape characteristics, namely angularity, two-dimensional (2D) form, texture and sphericity. This paper presents the effect of plant production and sample preparation methods on the shape characteristics of coarse aggregate (CA) and fine aggregate (FA). Six different types of aggregates, namely original aggregate (OA), plant mix (PM) aggregate and aggregate retrieved from specimens compacted at four different air voids [6% (AV6), 8% (AV8), 10% (AV10) and 12% (AV12)] were used. Each type of aggregate was divided into two different sizes: coarse and fine. The sizes of CAs were passing a 19 mm sieve and retained on a 12.5 mm sieve (CA12), and passing a 9.5 mm sieve and retained on a 4.75 mm sieve (CA4). Similarly, the sizes of FAs were passing a 4.75 mm sieve and retained on a 2.36 mm sieve (FA8), and passing a 2.36 mm sieve and retained on a 1.18 mm sieve (FA16). The Aggregate Image Measurement System was used to measure the shape characteristics of each size of aggregate. A statistical method called analysis of variance was used to compare the mean of shape parameters. The analyses of the results indicate that the texture and 2D form of CA particles change significantly when they undergo different processes of HMA production and sample preparation. No significant difference was observed in angularity and sphericity for all types of CAs. Similarly, no significant changes were observed in FA shape parameters. The effect of aggregate size on the shape parameters is also discussed. It is expected that the present study would develop a better understanding of HMA mixture behaviour in light of aggregate properties pertaining to aggregate shape.