We're involved in a project in which heavily reinforced concrete columns are being repaired with preplaced-aggregate concrete. One material specification calls for the grout to contain a "fluidifier." Are grout fluidifiers simply superplasticizers or are they some other type of admixture?
ACI 212 "Chemical Admixtures for Concrete" does not consider grout fluidifiers to be superplasticizers, but lists them under the general heading of "Grouting admixtures." Grout fluidifiers usually contain water-reducing admixtures to increase flowability; a suspending agent to minimize bleeding; and an aluminum powder expansive agent to prevent bleedwater from collecting under the coarse aggregates. They also retard the set of the grout, increasing the time available for pumping the grout.