Volume 6, Issue 3 (March 2009)
Adhesion Development of Organic and Silicone Sealants on Wet and Dry Concrete
Reliability of a sealed joint is directly related to the durability of its adhesion to the substrate. The presence of moisture on the surface of porous substrates caused by changing weather conditions prior to the application of sealants, such as the wetting of concrete by rainfall, can lead to poor sealed joint durability due to adhesion loss. In an attempt to better understand this mechanism, a method of testing adhesion of sealants on wet concrete has been developed and the effect of changes in surface conditions on sealant adhesion has been evaluated during the various drying phases identified for concrete. In the first 2 h of drying, a significant reduction of the pH at the surface is observed, which is mirrored with a reduction of the surface humidity. Both of these properties seem to have reached their plateau value within that timeframe, but in the following hours of the drying process the concrete continues to lose weight through water evaporation. Sealants based on different chemistries have been applied at various stages of the drying process (t = 0, 0.33, 2, 8, 24, 56 h) showing that the critical time period affecting the development of adhesion is within the first 2 h of concrete drying. This indicates that the alkalinity, surface moisture, on both, are the major factors responsible for the poor adhesion obtained on wet porous substrates and this is also the same for adhesion development of a primer on the substrate. The different sealant technologies evaluated in this program were silicones, urethanes, acrylics, silyl-terminated polyether, and silyl-terminated polyurethanes. In terms of adhesion development on wet concrete, the results highlight that the differences are more related to formulation within a sealant family than to the binder chemistry itself.