Aggregate size and behaviour of self-compacting concrete

One reason why concrete is a successful and commonly used building material is that it can be cast into any structural form required, taking advantage of its fluid behaviour at early ages. However, there is a limit to the fluid behaviour of normal fresh concrete, which cannot, on its own, flow past obstructions, through nooks or into corners. Thorough compaction, using vibration, is normally essential for achieving the required strength and durability of concrete. As concrete is produced and placed at construction sites, under conditions far from ideal, it often ends up with unpleasant results such as rock pockets, sand streaks, and a host of workmanship-related problems. The costs of remediation and making good may be high, or the durability may be compromised. Self-compacting concrete (SCC) may provide a solution to these problems. As the name signifies, it is able to compact itself without any additional vibrations or compactive effort. Consequently the danger of vibration- and noise-related health issues is minimised, and the construction process is safer and more productive. There have been several studies of SCC and the use of admixtures in it. Of these, the partial replacement of sand with ground granulated blastfurnace slag has gained considerable impetus. The main objective of this paper is to investigate the effect of maximum size of aggregate on the fresh and hardened properties of SCC. The behaviour of various mix proportions of SCC was investigated, and the variations in the compressive strength and split tensile strength of standard cubes and cylinders were studied. Ultrasonic pulse velocity was also studied to assess the quality of SCC with different maximum sizes of aggregates.