Speed of sound in gypsum slurries with foaming agent and expected spanwise spreading

This work aims at spanwise spreading of gypsum slurry with foaming agent on a moving belt under a rotating roller, a common practice in modern industry. Prediction of the spreading magnitude is intrinsically related to compressibility of gypsum slurry with foaming agent. Such a compressibility is characterized by measuring the speed of sound in foamed gypsum slurries. To facilitate experimental measurements of the speed of sound in such three-phase media, a novel theoretical model is proposed and developed here. Compression of three-phase gypsum slurries is conducted in a syringe. That allows one to measure the pressure–density dependence, which can be recast into the speed of sound. Thus, the slurry compressibility was found as a function of the components content, which in turn, sheds light on a predicted/expected spanwise spreading on a belt. The experimental results revealed that three-phase suspensions (slurries of solid gypsum stucco particles suspended in water with added foaming agent) can entrap and hold a significant amount of atmospheric air during mixing process at the preparation stage. It was shown that even a tiny content of the entrapped air can cause such a significant compressibility that the speed of sound would be diminished by an order of magnitude compared to that of air and about two orders of magnitude compared to that of water. Accordingly, air content could significantly affect the spanwise spreading magnitude predicted in the incompressible approximation. Graphical Abstract