Yielding of complex liquid foams

Roussel

Pitois

2019

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.

Section: Time Evolution Of Rheological Propertiessupporting

confidence: 67%

“…The yield stress of foams made with a yield stress fluid (characterized by a yield stress value τ y,int ) has been shown to be described by equation 4, provided that τ y,int R/γ < 0.5 [19].…”

Section: Early Age Rheological Propertiesmentioning

confidence: 99%

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

Roussel

Pitois

2019

“…The interstitial yield stress τ y,int is the effective stress that the bubbles must overcome to deform. It can be obtained from the macroscopic cement foam yield stress τ y,f oam (Φ), as measured for this purpose, using the following equation [19]:…”

Section: Effect Of Bingham Capillary Numbermentioning

confidence: 99%

Stability criterion for fresh cement foams

Aimedieu

Scheel

et al. 2019

We prepare and study cement foam samples with well-controlled structure, i.e. containing monodisperse bubbles. We observe that the foam structure often changes before cement setting and identify ripening as the major destabilization mechanism at stake. Drainage plays only a minor role in cement foam destabilization except when bubble size is large. Then we show that a single stability criterion can be defined, for a large range of cement foams with different formulations. This criterion involves the bubble radius and the yield stress of the cement paste such as confined by and between the bubbles, at a given characteristic time after sample preparation.

“…In the case of mortar sprayed on a vertical support, yield stress dictates the maximum thickness of the layer [3]. Among cementitious materials, aerated materials raise growing interest.…”

Section: Introductionmentioning

confidence: 99%

Yield stress of aerated cement paste

Roussel

Pitois

2020

Yield stress of aerated cement paste is studied. Samples are prepared by mixing aqueous foam with cement paste, which allows controlling bubble size, gas volume fraction and yield stress of the cement paste. Two distinct behaviors are observed depending on the surfactant used to prepare the precursor aqueous foam: (i) For a surfactant with low adsorption ability with respect to cement grains, bubbles tend to decrease the yield stress of the paste with magnitude governed by the Bingham capillary number, which accounts for bubble deformability. (ii) For a surfactant with high adsorption ability, bubbles increase significantly the yield stress. This behavior is shown to result from the surfactant-induced hydrophobization of the cement grains, which adsorb at the surface of the bubbles and tend to rigidify them. Within this regime, the effect of air incorporation is comparable to the effect of added solid particles.