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.

Workability in the fresh state is one of the most important factors in design and production of concrete and can be related to the water demand of the mixture, which in addition to other factors is a function of the particle shape of aggregates and binders and their specific surface area. While it is known that the shape of fine particles has a significant effect on the water demand, there are uncertainties regarding how the various shape parameters would affect the specific surface area, mainly because up to now many of the shape parameters have not yet been clearly defined and there are no commonly accepted methods for their measurement and/or estimation. In this research, the actual particle shapes were replaced with regular convex polyhedrons to calculate the total specific surface area using the size distribution curves of the samples. The obtained results indicate that while, in some cases, the assumption of a spherical particle shape leads to an acceptable estimation of the specific surface area when compared with Blaine test results, the specific surface area of powders with more angular particles could be calculated more accurately with the assumption of a polyhedron shape rather than a sphere.

The specific surface area (SSA) of constituents in a concrete mixture has a significant effect on its workability in fresh state. Excess layer theories relate the SSA to the flow behaviour of mixtures and can be used as part of an approach to mix design. However, measurement of SSA is complex and includes several issues, and thus is commonly replaced by mathematical estimation of the parameter. The mathematical approximation of surface area is based on the assumption of a spherical shape for the particles, which leads to failure of taking into account the effect of shape and the square–cube law. The article explores the possibility of replacing the assumption of a spherical shape with that of Platonic solids as the representative shape to account for the angularity of aggregates. The calculation was conducted based on information on the particle size distribution (PSD) obtained from dry sieving method. A calculated surface area on the assumption of a dodecahedron shape for natural aggregates and a cubical shape for crushed aggregates showed good agreement with SSA measurements conducted by X-ray microtomography. Furthermore, the effect of changes in PSD on the accuracy of the approach was also studied. It was found that the estimated value of SSA was improved in comparison with the traditional way of calculation on the assumption of a spherical shape.

Mortars can be studied as mixtures of solid and flowable phases. The volume of the flowable phase required for deformation depends on the solid phase surface area according to excess layer theories. This paper examines the relation between the specific surface area of constituents in mortars and their flow. The flowable phase volume was divided by the solid phase surface area to obtain the layer thickness surrounding the surface of the particles. The results suggested that the amount of water and paste needed to ensure flow could be estimated from the packing density and specific surface area of the particles.

Mortar and concrete can be divided into two phases of solids and water where water fills the voids between the grains and also coats the surface of particles. The current study investigates the influence of the thickness of coating water on flow spread of mortars and concretes. The article aims at correlating consistency of concretes to consistency of mortars. It was found that the flow behavior of granular mixtures can be directly related to the average water film thickness that envelops the particles. The concept was tested on mortar and concrete mixtures with different cement types, aggregate grading, aggregate shape, fineness and proportioning; proving water film thickness to be the most critical parameter affecting the flow. The results of the study indicate the possibility of predicting the flowability of mixtures by knowing the enveloping water film thickness. In addition, the relation between flowability of mixtures measured in different sizes of slump cone is explored to enable translating flow of mortars measured in mini-slump cone to flow of concrete obtained from Abram’s cone.

Packing density of particles is regarded as a key factor affecting workability of cementitious mixtures. While the value can be easily measured, and several models exist for estimating the parameter, no generally accepted definition exist for the optimal packing. Current study aims at exploring the concept of optimal packing in mortars and paste using particle packing and excess water layer theories. A semiempirical method is used for calculating water demand of mixtures based on their specific surface area. The approach allows for estimating optimal packing considering water demand and water to cement ratio of mixtures in addition to packing density.