A Study of Packing Effects in Self-Consolidating Mortar Systems with and without Pozzolanic Mineral Admixtures

Abstract

The classical idea of particle packing is based on Apollonian concept, in which the smaller particles fit into the interstices left by the large particles. Well defined grading with an ideal size distribution of aggregate will decrease the voids in the concrete and hence paste demand. Crushed aggregate particles are irregular in shape and pack more poorly together than naturally formed gravel. Aggregate voids demand paste to fill empty spaces or porosity. In order to reduce volume of paste in the matrix, improvement in packing density of constituent materials and use of mineral powder as partial replacement looks like a possible solution. Performance of concrete is greatly affected by the packing density and corresponding particle size distribution of aggregates. Better packing yields improvement in many properties of concrete like strength, modulus of elasticity, creep, shrinkage etc. Packing is not an intrinsic characteristic of aggregates since it depends on the size, shape and surface morphology of the particles. The closeness of packing of very large volumes of particles of uniform shape and size is independent of the size of the particles. However, well/continuous grading with proper amount of each size results in aggregate blends with high packing and in concrete with low paste demand. By optimizing aggregate grading curve, cement content can be reduced. Better particle packing reduces binder demand thus results in low water/cement or powder ratio. Resultantly, concrete formulation is less expensive/environment friendly and will have less durability problems caused by the paste such as heat generation, porosity, and drying shrinkage etc. Pozzolanic mineral admixtures have particle sizes even finer than cement grain. Therefore, once used in cementitious system will contribute to improve packing density. Particle packing models of Thompson & Fuller, Andreasen & Andersen and Funk & Dinger (Modified Andresean) have been studied in detail and theoretical and experimental investigation have been made to study the concept of particle packing in self-consolidating mortar systems. It was found that proportion of binder in overall schema of solid particle be considered for design of Self Consolidating Cementitious Systems i.e binder-aggregate ratio. Present research will be performed utilizing locally available materials and pozzolanic mineral admixtures imported from Germany. The research results will benefit our construction industry in terms of producing more durable and economical concrete.