An optimized aggregate particle packing density used as a base for concrete mix design provides economic, environmental and technical advantages. The particle packing density can be determined by many methods and predicted by different models. This paper reviews common packing and procedures and compares predictions of three common packing models to each other. It was found that the models tend to show different packing densities and percentage of ingredients for the same mixture. A test setup is proposed to determine the accuracy of each model’s prediction.

The concepts of particle packing and water/paste layer theory are commonly used for basis of concrete mix design models. While particle packing insists on achieving fewer voids in aggregate matrix by adding fine aggregate, water/paste layer theories state that increasing the amount of fines will lead to higher water demand since the specific surface area of particles will increase. In order to calculate the thickness of excess paste, it is essential to quantify the shape of particles. However, there are uncertainties regarding how the various shape parameters would affect the packing and specific surface, mainly because up to now many of the shape parameters are not yet clearly defined and there are no commonly accepted methods for their measurement. In addition, the term “shape” needs to be defined, some research suggest that for obtaining an appropriate shape factor several parameters need to be measured e.g. flakiness, elongation, sphericity, convexity etc. The paper aims to derive a shape factor based on variation of packing from the packing of ideal spheres with the same particle size distribution as the studied aggregate and to apply the shape factor to calculate an approximate specific surface area value.

The packing density of aggregates is of great importance in concrete mix design as obtaining a higher packing density leads to less usage of cement paste which has technical, environmental and economic benefits. It is thus of interest to model particle packing correctly. Hence, in this study, packing densities of seven mixes of aggregate were attained in the laboratory using the loose packing method and were compared to values suggested by three models: 4C, Compressible Packing Model and Modified Toufar Model. Modified Toufar showed 1.72% mean difference from the laboratory values while CPM and 4C had mean differences of 1.79% and 1.84% respectively. In addition, it was found that some of the models are preferable in certain mixtures.