Excessive slump loss during concrete pumping is an indicator of what issue?

Excessive slump loss during concrete pumping indicates that the concrete mixture is losing its consistency or workability, which often points to an issue with water absorption or retention in the mix. While inadequate mixing, excess water, and excessive additives can all contribute to problems with concrete workability, the specific context of slump loss during pumping most strongly suggests a lack of proper presoaking of aggregates or insufficient moisture content in the mix.

When aggregates, especially those like lightweight aggregates, are not adequately presoaked, they can absorb water from the mix. This absorption often results in a reduction of the water available for the concrete to maintain its intended slump, leading to difficulties during mixing and pumping. As the concrete is pumped, the mixture can become dryer, resulting in excessive slump loss.

In contrast, too much water typically increases slump, while inadequate mixing results in inconsistent material properties rather than specifically affecting slump. Excessive additives may alter the performance characteristics of the concrete but don’t exclusively lead to excessive slump loss during pumping, especially when considering the role of presoaking. Thus, understanding the nuanced relationship between the moisture content, the condition of aggregates, and concrete performance is crucial to identifying issues like excessive slump loss.