Utilizing Waste as a Valuable Resource

Fly ash, a byproduct of coal combustion in electric power plants, is comprised of very fine particles captured from exhaust gases through emission-control systems. It shares similar properties with volcanic ash and is classified as a pozzolan.

Referred to as a supplementary cementing material (SCM) when incorporated into concrete mixes, fly ash has been a prevalent addition to concrete formulations since the 1930s. It can be used either independently to supplement cement or in combination with other SCMs in blended cements.

Fly ash typically requires minimal processing and can be directly supplied from power plants to ready mixed concrete producers, where it is combined with conventional ingredients such as cement, aggregates, and water. Concrete containing fly ash finds application in various construction projects.

Over half of all concrete production involves some utilization of fly ash as a partial substitute for cement. Builders commonly employ concrete mixes containing 40 percent fly ash, with replacement ratios reaching up to 70 percent for certain construction purposes.

Connecting Environmental Advantages to Performance

Fly ash transcends being merely a filler; its benefits extend to both environmental preservation and performance enhancement. It contributes to the strength and durability of concrete, while also fostering sustainable construction practices by conserving natural resources and reducing energy consumption and emissions.

Each ton of fly ash used to replace portland cement results in approximately one ton of carbon dioxide emissions saved and prevents around 0.882 tonnes of greenhouse gas emissions. The widespread utilization of fly ash in North America is equivalent to removing over 2.5 million cars from the road annually.

Furthermore, when specified and applied appropriately in concrete, fly ash can:

• Enhance resistance to sulfate attack
• Improve resistance to Alkali Aggregate Reactivity (AAR)
• Decrease permeability
• Minimize shrinkage and thermal cracking
• Lower the heat of hydration compared to pure cement
• Enhance workability and pumpability
• Increase strength at 56 days