Frequently Asked Questions

General Questions

Frequently Asked Questions

Separation Technologies answers important questions regarding their innovative methodology:

There are a number of reasons fly ash isn’t used in all concrete. Prior to ProAsh® beneficiation there were most often the issues of inconsistent product quality and availability. Just when the concrete producer needed it most the utility ran out of quality product.

Today the biggest issues are strength gain and set times. Though ultimate strengths of a fly ash concrete are greater than a reference without it, fly ash concrete gains early strength a little slower than reference mixtures without it. Form stripping can be somewhat delayed if the slower strength gain is not balanced with admixtures.

And, even though properly proportioned fly ash concrete can generally be finished more easily, If the mixture is not set balanced with accelerators in cooler weather finishers might take longer to put the final finish on the concrete.

While beneficiated ash done with the ProAsh® process is one of the most consistent components in the concrete mixture it cannot eliminate all air entrainment variables. The largest potential air concern involving fly ash prior to ProAsh® was from precipitator managed ash fluctuations in LOI. Load to load variation left load to load variables for the concrete producer to manage.

There are however many other variables involving air entrainment in concrete using fly ash. They can range in scope from the type of air entrainment used to the fine to coarse aggregate ratio in the mixture, to the FM of the fine aggregate, the SE in the coarse aggregate, ambient temperature, even to the type of other
chemical admixtures used or even the sequence of loading and mixing of the concrete.

In the performance of concrete mixtures there is no substitute for experience. If you are working with the same components from the same sources with which you always work the best air entrainment for HVFA mixtures is the one with which you have the most experience. Of course for concretes with critical performance needs trial mixes should always be run.