Yielding and flow of foamed metakaolin pastes

TL;DR

This study investigates the rheological behavior of foamed metakaolin pastes, revealing that bubble volume fraction influences flow dissipation but not yield stress, with implications for manufacturing processes involving foamed ceramics.

Contribution

It provides the first detailed rheological analysis of foamed metakaolin pastes, highlighting the relationship between bubble content and flow properties.

Findings

Yield stress remains unchanged with bubble addition.

Dissipation during flow increases quadratically with bubble volume fraction.

Coupling between bubble surface tension and paste rheology explains observed behavior.

Abstract

Metakaolin is a broadly used industrial raw material, with applications in the production of ceramics and geopolymers, and the partial replacement of Portland cement. The early stages of the manufacturing of some of these materials require the preparation and processing of a foamed metakaolin-based slurry. In this study, we propose to investigate the rheology of a foamed metakaolin-based fresh paste by performing well-controlled experiments. We work with a non-reactive metakaolin paste containing surfactant, in which we disperse bubbles of known radius at a chosen volume fraction. 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 the one of the metakaolin paste, and that dissipation during flow increases quadratically with the bubble volume fraction. Comparison with yielding and flow of model foamed yield stress fluids allows us to understand these results in terms of coupling between the bubbles' surface tension and the metakaolin paste's rheology.