Abstract
In order to improve the stability of air bubbles in fresh concrete, it is of great significance to have a better understanding of the mechanisms and main influencing factors of bubble stability. In the present review, the formation and collapse process of air bubbles in fresh concrete are essentially detailed; and the advances of major influencing factors of bubble stability are summarized. The results show that the surface tension of air–liquid interface exerts a huge impact on bubble stability by reducing surface free energy and Plateau drainage, as well as increasing the Gibbs surface elasticity. However, surface tension may not be the only determinant of bubble stability. Both the strength of bubble film and the diffusion rate of air through the membrane may also dominate bubble stability. The application of nano-silica is a current trend and plays a key role in ameliorating bubble stability. The foam stability could be increased by 6 times when the mass fraction of nano-particle reached 1.5%.
Highlights
Concrete’s freeze-thaw damage [1] leads to premature cracking and other deterioration of concrete [2], which have seriously impaired the service life of concrete, and is one of the primary problems that affect the durability of concrete [3,4,5,6,7,8]
The higher the membrane strength, the more stable the air bubbles entrained by air-entraining agent (AEA), and the greater durability of concrete
The surface viscosity is an important factor affecting the process of liquid film drainage
Summary
Concrete’s freeze-thaw damage [1] leads to premature cracking and other deterioration of concrete [2], which have seriously impaired the service life of concrete, and is one of the primary problems that affect the durability of concrete [3,4,5,6,7,8]. It has been reported that assuring appropriate number, spacing, and distribution of tiny entrained air bubbles in concrete can significantly affect the mechanical properties of concrete [24,25,26,27,28] and is critical for solving the destruction of freeze-thaw cycles [14,29,30] This is because the distance the freezing water travels to the nearest air void is shortened [31]. Formation and Collapse of Air in Bubbles in Concrete only causes the liquid to produce vortex and take in air, and makes the larger bubbles in fresh
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