Understanding the role of particle packing characteristics in rheo-physical properties of cementitious suspensions: A literature review

Interest for enhancing particle packing of the solid skeleton in concrete stems efforts to reduce the content of cementitious materials and water/admixture demand, thus decreasing cost and environmental impact as well as improving material performance. Solid particles in cementitious suspensions can be classified as non-colloidal particles, such as aggregates, where only mechanical interactions exist; and colloidal particles, such as cementitious materials, where particle surface forces predominate over gravitational-shear forces, thus particles tend to agglomerate. This paper intends to review advances in knowledge on the effect of packing characteristics of colloidal and non-colloidal particles on rheo-physical properties of cementitious suspensions. Focus is placed on solid particle sizes ranging from 10−2 μm (representing cementitious materials) to 104 μm (representing coarse aggregate). The effect of the volume fraction and particle packing of solids (both colloidal and non-colloidal particles) on rheology and stability characteristics of cementitious suspensions is discussed. The rheological properties of cementitious suspension are primarily dominated by the relative solid packing fraction (ϕ/ϕm). There exists a critical transition volume fraction (ϕc) of granular skeleton so-called percolation volume fraction beyond which direct frictional contacts among particles begin to dominate the rheological properties. Therefore, in order to design fluid concretes, the aggregate volume fraction should be kept below the critical transition value as well as the rheological properties of suspending fluid medium should be properly adjusted to secure adequate stability of aggregates. The optimization of particle packing of granular skeleton can improve the particle lattice effect, and consequently enhance the stability characteristics of concrete.