An aggregate grading that yields maximum solid density and maximum particle interlock is highly desirable for both bound mixtures, such as asphalt concrete and plain and reinforced concrete, and for unbound mixtures such as those used in base courses. Maximum particle interlock leads to high strength. Whereas minimum voids in a certain material composition is conducive to high strength and low compression. Aggregate grading may be obtained, for instance, from the ASTM, which is based on experience or may be designed according to Lees' method. In the present work five different types of aggregates were used, each with a variety of chosen grading. It was found that Lees' method produced the lowest porosity of all types of aggregates as well as for the various employed gradings. Lees' rational method of aggregate grading, however, is a very lengthy and time-consuming procedure. Therefore, programming of Lees' method is an essential step to make such an excellent method available to practicing engineers. A program named `RATMIX' was developed and has incorporated 58 design graphs of the Lees' method. RATMIX is a comprehensive program for Lees' rational method; it conducts interpolation for intermediate points within the design graphs as well as between graphs of different properties.
Keywords: Aggregate grading; Maximum density; Rational method; ASTM; Fuller's method; Lees' method; Computer program
Lees' rational method  is a dynamic method of aggregate grading. It is used to design aggregate gradings to obtain maximum solid volume density and maximum particle interlock, for a given compactive effort. This method may also be used to design aggregate gradings of specified or prescribed voids content, i.e. other than the minimum voids or maximum density. The aggregate grading with desirable voids may be used for free draining `friction courses' for high speed skid resistance, and also for providing sufficient volume of voids in the aggregate mix to accommodate a minimum quantity of binder for fatigue resistance and durability.
The classical methods of aggregate grading, such as the ASTM (C33) and the Fuller, are based on experience and are independent of the factors that influence packing of aggregates. Lees' rational method  on the contrary, takes into account and recognizes the importance of the factors that influence packing, namely variation in the aggregate shape, size, and texture, compactive effort, and the boundary conditions, such as thickness of section to be laid.
Lees' rational method  of aggregate grading design may be used for unbound materials, such as base courses as well as for bound mixtures, such as asphalt concrete mixtures and plain and reinforced portland concrete. For unbound materials the two most important needed properties are minimum voids (maximum solid density) for minimum compression, and maximum particle interlock for maximum strength.
Durability is the most important property for asphalt concrete pavements. Durability is the resistance of asphalt pavements to the action of temperature and temperature changes, action of air and water, and the action of traffic. Abdullah et al.  have shown that Lees' rational method of aggregate grading ...