Influence of clay minerals on the action of PCE superplasticizers - description of the phenomenon and possible solutions.

Clay minerals, which can be contained in aggregates or in limestone meal, reduce the flowability of concretes by absorption (consumption) of water. Superplasticizers also settle on the surfaces of the clay particles and are then no longer available for plasticizing the cement paste. Polycarboxylates in particular can also be incorporated in the chemical structure of the clay mineral montmorillonite (bentonite) and in this way are removed from the cement paste so that their plasticizing action is partially or even entirely lost. The negative effects of clay minerals can be lessened or completely eliminated by using clay-resistant PCE superplasticizers, by supplementary addition of cationic compounds or by "sacrificial substances". [ABSTRACT FROM AUTHOR]