At the ASCC Finishing Committee meeting in September, one topic of discussion was maintaining the proper air content in concrete for slabs. Two things that may affect air content were discussed: pumping concrete and high-range water reducers made from polycarboxylates.
Polycarboxylate technology for high-range water reducers (superplasticizer) has been available for more than 20 years. Several concrete contractors attending the Finishing Committee meeting have experienced high air contents when using this admixture despite assurances from the manufacturers that this is not a problem. The committee is hoping to conduct a survey to determine if this is a common problem and if anyone has a solution. If you have experienced this problem, send me an email and I’ll get it to the committee.
The American Concrete Pumping Association is supporting research conducted by Tyler Ley at Oklahoma State University into entrained air content after pumping. Conventional wisdom is that pumping reduces air content, but Ley’s research seems to show that isn’t necessarily the case. Rather, his theory is that the air dissolves into the concrete during pumping but the bubbles reform after the pressure is released. However, he is still gathering data to confirm this. “Because we’re challenging an existing belief, we need to prove beyond a doubt that air entrainment returns after pumping and before setting,” Ley says. “We’d like to enlist contractors in the field to help us collect that data—taking measurements and hardened air void analysis on concrete both before and after pumping. If we can establish a pattern in the results, in different parts of the country and in different situations, we’ll know we can make solid recommendations on how to better design concrete mixtures to make them easier to pump and place.” To contact Dr. Ley, click here. To learn more about his research, click here.