Some hold the opinion that the best gradation curve is the one passing exactly in the middle of the space between the upper and lower gradation limits. To a certain extent in some cases this may be true; however, in the majority of cases it is not. The shape of a design gradation curve exerts a significant impact on mix properties. For example, by looking at its shape, one may determine if the mix is more or less coarse or has the probability of being overfilled with mastic. Therefore the shape of a design gradation curve is not an unimportant question.
The subsequent phases of design will be discussed later, starting with the coarse aggregate fraction, going through the sand fraction, and ending with the filler content. A familiarity with the basic rules of designing aggregate mixes, including the algorithm and calculations, is assumed. To brush up on these rules, refer to a basic text, such as The Asphalt Handbook (MS-4), a publication of Asphalt Institute.
