Change is a constant of life and this is an indisputable fact. Some changes are predictable such as the changing of the seasons. Unless you live in San Diego, winter, spring, summer, and fall show up about the same time every year. Some changes are dramatic and come quickly and unexpectedly such as the resignation of Speaker of the House John Boehner. But other changes take quite a while and are very subtle. Such is the case with the change in the perception of fly ash for use in concrete.
Once upon a time the use of fly ash in ready mixed concrete was something to be avoided by ethical producers. In the early years most fly ash use was on very specialized projects such as dam construction and other mass placements. As researchers reported lab findings and results from those specialized applications became known things started to move into more commercial applications. Ready mixed concrete producers started to investigate the potential benefits to be derived from fly ash use. Still, the general perception was that fly ash was a waste to be avoided. Those who opposed fly use warned that you could expect problems entraining air, low compressive strengths, finishing complaints, delayed setting, discoloration, halitosis, cough due to cold, and on and on if you used even modest quantities. Anything that was a problem with a concrete mixture immediately was assigned to the use of fly ash. Even when problems were encountered with mixtures that did not contain fly ash, people were quick to accuse the ready mixed concrete supplier of slipping fly ash in to the concrete and not telling the customer. Fly ash had a real public relations problem.
As time went on, problems with loss on ignition, early compressive strength development, changes in finishing techniques, etc. were investigated and mitigated. The use of fly ash was gradually but steadily expanding. The economic and performance benefits were too powerful to ignore. This “waste” was proving to be pesky. Those producers who were learning to handle this “waste” were gaining significant market advantage. It was becoming hard to defend the traditional thinking that only additional quantities of Portland cement could enhance concrete performance.
An industry was developing to manage and market fly ash. As with all emerging industries companies formed, failed, expanded, and merged as the industry started to grow up.
And it was dawning on the generators that fly ash was of some economic value. Sources that previously gave the “waste” to anyone who would come to the power plant and pick it up started to change their thinking.
There even was a trade association formed to encourage the use of fly ash and other coal combustion products.
Over time the appearance of Class C fly ash, alkali-silica reactivity (ASR) mitigation, high performance concrete mixtures, beneficiation processes to improve ash quality, high volume applications, and other developments helped change the way the market viewed fly ash. No longer was this powder merely a cheap alternative to replace Portland cement. Fly ash was becoming a primary tool to overcome technical challenges.
How things have changed! Today fly ash is regarded as an important part of the answer to challenges faced by architects/engineers and concrete producers. Whether the challenge is ASR mitigation, reducing permeability for enhanced service life, producing high compressive strengths or other challenges the use of fly ash in concrete clearly is regarded as a valuable component. Fly ash is now a respected member of the concrete tool kit. Once upon a time this finely divided residue resulting from the combustion of coal was called a “waste”, even a “hazardous waste” by some. Change indeed!