An empirical approach for the optimisation of aggregate combinations for self-compacting concrete

The fresh and hardened properties of self-compacting concrete (SCC) depend on number of factors such as paste composition, paste content, aggregate content, aggregate gradation etc. In the present investigation, the influence of the packing density of aggregates on the properties of SCC was evaluated. Experiments were conducted to measure the packing density for different combinations of aggregates precisely. A ternary packing diagram (TPD) was developed based on the packing density of measured and interpolated data. Considering the limitations in generalising the TPD and the difficulty involved in adopting mathematical models for aggregates, an attempt was made to establish a simple method for the selection of the combination of aggregates resulting in maximum packing density from the particle size distribution of aggregates (represented by the Coefficient of uniformity-C (u)). Further, studies were extended to investigate the effect of aggregate packing density on fresh and hardened SCC properties. The results indicate that for a constant paste volume and paste composition, with increase in packing density of aggregates, the fresh properties and the compressive strength of SCC were improved positively. An attempt was also made to identify the influence of 10 different proportions of aggregates having the same packing density on the properties of SCC. The results indicate that at the same aggregate packing density, the fresh concrete properties were influenced significantly by the choice of the aggregate combination, while there was little or no influence on the hardened properties. Furthermore, the experimental data obtained was used for supplementary validation of the existing model (compressible packing model) for predicting the packing density and the fresh behaviour of SCC