This method, also called the method of iteration, is known chiefly by those who have practiced ready-mix concrete design in a laboratory. It is a laborious procedure because numerous tests need to be conducted (so now it is rarely used). It involves selection of consecutive aggregate fractions so that smaller particles can fit in among bigger ones with no increase in the mix volume (i. e., so that no larger particles are shoved aside by smaller ones).
We start by fixing the proportion of the coarsest aggregate (N1) with a finer fraction (N2). Having found such proportions for which we have a minimum of air voids with an unchanged volume of the mix, we mark the acquired mixture as aggregate N1,2. Then we start establishing the proportion of the aggregate N1,2 with the finer aggregate N3, and so on. The process involves making consecutive batches of aggregate and determining air voids for each mix. Its comprehensive description has been explained in the publication by Sliwitiski (1999).
Despite the completely different primary purpose of this method, it seems that nothing stands in the way of making use of its principles for determining a suitable gradation of an SMA aggregate mix.
