Crushed hydrated fly ash as a construction aggregate

Hydrated fly ash (HFA) is being produced in Texas by first adding water to Class C fly ash and allowing it to hydrate in curing pits for several weeks. HFA typically attain unconfined compressive strengths as high as 15 MPa. Once the HFA gains an acceptable level of strength, it is crushed using specialized equipment to produce an aggregate material with characteristics very similar to those of conventional granular materials such as crushed limestone. In certain regions of Texas, where quality aggregate base materials are in short supply, this synthetic aggregate material has been used in the construction of road bases on an experimental basis. Experience from the use of HFA ash in these different regions has been quite variable. This paper provides an overview of HFA as a construction aggregate, and documents the experience from its use as a road base material.