When is the slump test useful in detecting changes in the concrete?

Q. When is the slump test useful in detecting changes in the concrete?

A. When the aggregates and cement content remain unchanged, the slump test gives a good measure of changes in consistency. Where the materials are being accurately measured, a change in the slump as the work proceeds indicates either a change in the grading of the aggregates or a change in water content or air content of the concrete. The slump test under these conditions can be a good basis for control. The use of water-reducing admixtures, however, makes it difficult to determine if the changes in consistency are due to a change in the mixing water content or the effects of the admixture.

References: SP-1(02); ACI 238.1R-08; ASTM C143

Topics in Concrete: Concrete Fundamentals; Testing of Concrete