Many strategies to increase the workability of concrete either have a negative effect on performance, or come at an important cost for the concrete producer or contractor. Entraining air can be a strategy to enhance workability of concrete, but it should be kept in mind that air is compressible and the workability under pressure may be different than the workability in atmospheric conditions. This paper shows the theoretical concepts of the behavior of air bubbles under shear and under pressure, highlighting the differences between both conditions. Full-scale pumping tests on air-entrained and nonairentrained concrete have further shown that the pressure loss in 100 mm pipes is approximately equal for both concrete mixtures, while the pressure loss was different in the 125 mm pipes. Based on these results, it is argued that a pressure of 5 bar may eliminate the positive effects of air on workability. This would correspond to a hydrostatic pressure under a concrete column of approximately 20 m, which is not exceptional for deep foundations.
Subjects: Workability, air-content, pressure
Author: Dimitri Feys
Publisher: DFI, EFFC