Use of Ash in Concrete

Fly ash, one of the residues produced in coal fired plants, has long been known to be usable as a cement substitute in concrete. Fly ash brings a number of performance enhancements to concrete, such as better durability and easier placement. It is also more cost-effective than cement. Engineers and Contractors would welcome higher ash contents.

Despite its positive attributes, the use of ash has been limited due to rapidly deteriorating performance at high substitution levels. Ash proportions in excess of as little as 20% of cement significantly impact early strength development. This is critical, since weaker concrete at early construction stages slows down building schedules or affect manufacturing productivity, which is not acceptable in today’s marketplace.

A number of technologies have been developed to treat ash so as to enable a higher substitution level of cement, including a variety of chemical, mechanical or thermal treatment methods. However, these methods are generally unattractive to the market, as they either offer incomplete or costly solutions, or require large amounts of upfront capital investment. It is no surprise, then, that their success has been very limited, with treated ash being more costly and more complicated to use than cement.

More than 500 million tons of ash are still being disposed of every year.