AASHTO R 91:2018 Standard Practice for Determining Aggregate Source Shape Values from Digital Image Analysis Shape Properties.
Shape, angularity, and surface texture of aggregates have been shown to directly affect the engineering properties of highway construction materials such as hot mix asphalt concrete, portland cement concrete, and unbound aggregate layers. This standard is used to characterize the combined shape values for an aggregate source from the individual particle shape properties determined by digital image analysis from T 381. The aggregate shape characterization includes gradient angularity, Form 2D, sphcricity, texture, and flat and elongated values.
Note 2—The National Cooperative Highway Research Program Report 555 provides background information relevant to characterizing aggregate shape, texture, and angularity.
4.2. This practice may be used to characterize the shape characteristics of single-source aggregate materials and multiple-source aggregate material blends.
Determine the aggregate sample grading according to T 27 and the amount finer than 75 irn according to T 11.
5.2. Determine the aggregate sample specific gravities according to T 84 and T 85.
5.3. Determine the material sample shape values for Form 2D, gradient angularity, sphericity, form ratios (F&E, For E), and texture according to T 381.
6.1. The material sample is typically characterized by individual evaluation of material retained on each sieve size, passing the next larger sieve. For the purpose of calculating the combined shape values, consider any sizes that contain inadequate percent retained mass to achieve niinimum particle count to have the same shape value as the average of the next larger or the next smaller size, whichever is present.
6.2. Calculate the percent retained for the aggregate sample on each sieve using the T 27 results.AASHTO R 91 pddf download.