Many highway agencies now limit the amount of natural sand in hot mix asphalt (HMA) when used on heavy duty pavements to minimize rutting. This is usually done by generically specifying the maximum allowable percentage of natural sand. Generally, natural sands tend to be rounded whereas manufactured sands tend to be angular. However, there are some natural sands which are subangular rather than rounded. Also, some manufactured or crushed sands can be subrounded rather than completely angular. There is a definite need to quantify the shape and texture of the fine aggregate so that it can be specified on a rational basis rather than generically.

A total of 18 fine aggregates (eight natural sands and ten manufactured sands) of different mineralogical compositions were sampled from various sources in Pennsylvania. Particle shape and texture data was obtained using ASTM D3398, and National Aggregate Association (NAA)‘s two proposed methods. A particle index value of 14 based on ASTM D3398 appears to generally divide the natural sands and manufactured sands, and therefore, can be used for specification purposes. However, the current ASTM D3398 test procedures are too time consuming because each sieve size fraction needs to be tested individually and results combined. Test data obtained in this study indicates that only the major fraction needs to be tested because its particle index has a fairly good correlation with the average particle index. Moreover both NAA’s proposed Methods A and B show very good correlations (R2= 0.97) with the ASTM D3398 method. These methods are straightforward and less time consuming. Equations needed to compute ASTM D3398 weighted average particle index values from NAA Methods’ results are given in the paper.