13.4 : Design Example: Managing Concrete Workability

This example deals with managing the workability of concrete for a raft foundation project under hot weather conditions. Workability is crucial for ensuring the concrete is easy to place, compact, and finish. In this scenario, a slump test — a common method to measure the workability of fresh concrete — initially indicated low workability. This was attributed to the rapid water loss from the concrete mix, exacerbated by the high temperatures causing the course aggregates to heat up.

To address the issue, the site engineer decided to cool down the aggregates by wetting them, which slightly improved the workability but still did not achieve the desired slump value. Recognizing that evaporation due to the hot sun was a significant factor reducing workability, a further solution was implemented by adding sugar to the mix. Sugar acts as a retarder in concrete, slowing down the setting time. This adjustment finally resulted in achieving the desired slump value in the subsequent tests.

This example illustrates the challenges of concrete workability in adverse weather conditions and highlights innovative solutions like temperature management of materials and chemical modification of the mix to maintain quality and workability during construction. Such adjustments are essential to ensure the structural integrity and durability of the concrete foundation.