What difficulties arise in the use of aggregates which absorb water How theyovercome (a) in the laboratory and (b) on the job?

Answer 1

When using aggregates that absorb water, several difficulties can arise. These difficulties include:

1. Increased water demand: Aggregates that absorb water can increase the water demand in a concrete mix. This can lead to challenges in achieving the desired water-cement ratio and can affect the strength and durability of the concrete.

2. Reduced workability: The absorption of water by aggregates can reduce the workability of the concrete, making it more difficult to place and finish. This can result in issues such as segregation, poor compaction, and difficulty in achieving the desired surface finish.

To overcome these difficulties, the following approaches can be taken:

(a) In the laboratory:

• Pre-wetting aggregates: One way to overcome the increased water demand and reduced workability is to pre-wet the aggregates before mixing them with cement and other ingredients. This ensures that the absorbed water in the aggregates is taken into account during the mix design process. It helps maintain the desired water-cement ratio and improves workability.

• Adjusting mix proportions: The mix proportions can be adjusted by considering the absorption characteristics of the aggregates. By accounting for the water absorption capacity of the aggregates, the required water content can be determined to achieve the desired consistency and workability.

(b) On the job:

Proper storage and handling: Aggregates should be stored in covered areas or protected from rainwater to prevent additional water absorption. Proper handling practices during transportation and on-site storage can help minimize the absorption of water by aggregates.

Moisture control: On-site, measures can be taken to control moisture levels. For example, if the aggregates are excessively dry, they can be sprayed with water to ensure they have the right moisture content before mixing. Conversely, if the aggregates are already saturated, adjustments can be made to the mix design to compensate for the absorbed water.

By implementing these strategies, the difficulties associated with the use of aggregates that absorb water can be mitigated, ensuring better concrete performance both in the laboratory and on the job.