Optimal cement paste yield stress for the production of stable cement foams

TL;DR

This study reveals that reducing the yield stress of cement paste, rather than increasing it, enhances the stability of cement foams by improving grain packing and bubble stability, offering a new approach for high-air-content cement foam production.

Contribution

It demonstrates that lower yield stress in cement paste improves foam stability, challenging the conventional focus on high yield stress for stability.

Findings

Lower yield stress enhances foam stability.

Reduced van der Waals forces improve grain packing.

Stable foams achieved without accelerators.

Abstract

Production of morphology-controlled cement foams remains challenging, mainly due to bubble stability issues during cement setting. The use of cement paste with high yield stress is expected to promote stability by damping intrinsic bubble kinetics. Here we show however that for given W/C ratio, fresh foam stability can be achieved instead by decreasing the yield stress of the cement paste. Indeed, in this low apparent yield stress regime, van der Waals attraction between cement grains is reduced and grains are allowed to be efficiently packed by bubbles, providing enhanced mechanical properties. This result is obtained for two distinct additives used at controlled concentrations and without resorting to set accelerators, which highlights the general significance of the underlying stability mechanism. It offers a promising solution to produce stable cement foams at high air content.