In a report prepared by the Virginia Highway and Transportation Research Council (VHTRC) and summarized by Halstead (1986), several restraints relating to the use of fly ash concrete for construction of highways and other highway structures were discussed. These restraints include the following: 

• Special precautions may be necessary to ensure that the proper amount of entrained air is present.
• Not all fly ashes have sufficient pozzolanic activity to provide good results in concrete.
• Suitable fly ashes are not always available near the construction site, and transportation costs may nullify any cost advantage.
• Mix proportions might have to be modified for any chance in the fly ash composition.

Since the cement-fly ash reaction is influenced by the properties of the cement, it is important for the executing agency not only to test and approve each fly ash source but also to investigate the properties of the specific fly ash-cement combination to be used for each project.