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 procedure is usually accomplished 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 that 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. Fine aggregates (8 natural and 10 manufactured sands) of different mineralogical compositions were sampled from various sources in pennsylvania. Particle shape and texture data were obtained using astm d3398, and two proposed methods of the national aggregate association (naa). On the basis of astm d3398, a particle index value of 14 appears to divide the natural and manufactured sands, and therefore, can be used for specification purposes. However, because each sieve size fraction needs to be tested individually and results combined, the current astm d3398 test procedures are too time consuming. However, test data indicate that only the major fraction needs to be tested becauseits particle index has a fairly good correlation with the average particle index. Moreover, both naa proposed methods a and b show goodcorrelations (r-squared equals 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 two naa methods are described. This paper appears in transportation research record no. 1301, Factors affecting properties and performance of pavements and bridges 1991.
Abstract