One problem associated with using a high-range water reducer in concrete is slump loss. In a study of the behavior of fresh concrete containing conventional water reducers and high-range water reducer, found that with time slump loss is very rapid in spite of the fact that second-generation high-range water reducers are claimed not to suffer as much from the slump loss phenomenon as the first-generation conventional water reducers do. However, slump loss of flowing concrete was found to be less severe, especially for newly developed admixtures based on copolymeric formulations.
The slump loss problem can be overcome by adding the admixture to the concrete just before the concrete is placed.
However, there are disadvantages to such a procedure. The dosage control, for example, might not be adequate, and it requires ancillary equipment such as truck-mounted admixture tanks and dispensers. Adding admixtures at the batch plant, besides dosage control improvement, reduces wear of truck mixers and lessens the tendency to add water onsite. New admixtures now being marketed can be added at the batch plant and can hold the slump above 8 in. (204 mm) for more than 2 hours.
