Yielding and flow of foamed metakaolin pastes

We perform an experimental study of the rheology of a foamed non-reactive particulate paste. The paste is a concentrated suspension of metakaolin, a material commonly used in the production of ceramics and in the construction industry. Most manufacturing processes of porous ceramics or foamed building materials require the preparation and handling of a foamed slurry. The slurry is a concentrated particulate paste, which has a non-Newtonian rheology. In particular, a minimum stress is necessary to make it flow: it is a yield stress fluid. We systematically investigate the influence of bubble addition on the workability of our metakaolin slurry by dispersing bubbles of known radius at a chosen volume fraction in the surfactant-laden metakaolin paste. We perform rheometry measurements to characterize the minimum stress required for the foamed materials to flow (yield stress), and the dissipation occurring during flow. We show that the yield stress of the foamed samples is equal to that of the metakaolin paste, and that dissipation during flow increases quadratically with the bubble volume fraction. We show that this behaviour can be well understood from the recent results of Ducloué et al. [7]. This agreement suggests that the results we present here on foamed metakaolin samples may apply to a broader class of foamed particulate pastes.

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