Critical size of entrained air to stability of air volume in mortar of self-compacting concrete at fresh stage

Abstract

The objective of this paper is to determine the critical size of air bubbles, which harmfully affects the stability of air in mortar of self-compacting concrete (SCC). Mortar samples produced by different type of mixing procedures and mixing time with various dosage of air-entraining agent (AE) were tested. Air diameter distribution of these mortar samples was measured at fresh stage with air-void analyzer (AVA). With AVA machine, size of air bubble measured is considered as the chord length, which is assumed to be 2/3 of the diameter of air bubble (according to ASTM C 457). It was assumed that air bubbles with over the critical size were easily to escape either by collapsing or floating upward. It was found that instability in volume of air in fresh mortar of SCC was caused mainly by the existence of air bubbles with chord length of over 1000 μm and partially by 500 to 1000 μm due to unification between air bubbles with chord length of less than 1000 μm.