Compaction-interaction packing model: regarding the effect of fillers in concrete mixture design

For the design of defined-performance concrete, predicting the material properties of concrete becomes more and more important. To be able to select the right type of fillers and control the water demand in such mixtures, an extension to the compressible packing model was developed to optimize the particle packing of aggregates as well as powders in concrete. Modelling mixtures with particles smaller than 125 μm requires advanced interaction equations, taking due account of surface forces like van der Waals forces, electrical double layer forces and steric forces. In this paper the equations for the newly developed compaction-interaction packing model are presented, including the additional effects of agglomerating particles on the wall and loosening effect. Calculated packing densities are related to the results of compressive strength experiments on 50 mortar mixtures. Higher packing densities leave less space for voids to be filled with water, which reduces the water demand and increases the strength of concrete mixtures. This is shown by the cement spacing concept. The relation between the cement spacing factor and strength can be used as a tool to predict concrete strength in defined-performance concrete mixtures.