Collapse of fresh foam concrete: Mechanisms and influencing parameters

This study assesses the influence of rheology and density on the collapse behaviour of mechanically foamed fresh aerated concrete. The collapse mechanism was studied under two conditions of varying interstitial paste's rheology and varying foam content. Adequate yield stress in the interstitial cement paste (critical yield stress) is crucial to achieve stability, below which the foam concrete displays partial or complete collapse. However, higher yield stresses may affect the hardened properties, thus an optimum range is important. Besides, this critical yield stress decreases with the foam content, leading to enhanced stability at lower densities. The critical yield stress to prevent collapse was then experimentally determined and compared against the yield stresses required to prevent the rising of bubbles (buoyancy) and the flow of interstitial paste through the foam network (drainage). This comparison showed that the experimentally determined critical yield stress to prevent foam collapse agrees well with the drainage-based stability criteria.