[1274] WATER FLOW REDUCTION AND AIR BUBBLE GENERATION MECHANISMS IN NARROW INTERFACES SUCH AS CONCRETE CRACKS
Keywords:Narrow interfaces, Water flow, Self-healing, Air bubbles
Water flow between two parallel plates has been previously studied in fluid mechanics. Based on the same models, Poiseuille's equation has been modified and used to clearly estimate water flow between two parallel surfaces such as concrete cracks. Recent findings in the use of water permeation to evaluate extent of self-healing concrete for a stagnant and penetrating crack have pointed to the blocking effect of large air bubbles. It negated the contribution of the traditionally known self-healing mechanisms during the first few days of water supply. The findings pointed to growth of air bubbles as the main cause of the drastic water flow reduction in the initial stages of water supply. In the follow-up research, water flow reduction has been observed to occur even in the absence of largely visible air bubbles, and within less than 5 hours of water supply. By using equilibrated air saturated water (incapable of growing any large air bubbles) in the current research, water flow reduction was observed to decrease by about 20-30%. This reduction is attributed to micro and nano size air bubbles that are strongly fixed (or trapped in the microstructure) on the surface of concrete. Once formed and fixed there, they cause water flow braking, which is observed in the form of reduced water flows.