Dewar’s particle packing model incorporates the interaction diagram of Powers and offers significant advantages for industrial application due to its manageability which is related to the limited number of required input parameters compared to other particle packing models. Moreover, Dewar demonstrated that applying the interaction diagram in concrete mix design is an effective method for optimizing material use in concrete. The basic concept is that when two materials are mixed, the voids ratio of the combined aggregate mixtures is calculated taking into account particle interference. The change in voids ratio with varying fine fraction is graphically represented in an interaction diagram, consisting of six key points, of which four change points. These change points are determined by empirical factors, amongst others. Experimental voids ratio diagrams of combined monosized sieved aggregate fractions are used to determine the applied empirical factors to validate/update the Dewar’s particle packing theory. From the experimental interaction diagrams, it is assumed that the wall effect is greater than the model predictions for the materials used in this study. It was found that by adapting the empirical factor kint, used to calculate the notional width factor Z, a better agreement between experimental results and the model can be obtained, which should be further verified in future research.