More than 20 billion tons of concrete is produced globally each year—and its use is expected to expand rapidly to meet ever-increasing infrastructure needs. Here in North America, the ready-mix concrete market is likewise projected to grow strongly—at a compounded annual growth rate of 5.35 percent over the next five years.

The challenge with this tremendous growth in the use of concrete is the greenhouse gas emissions that are produced by the manufacture of portland cement—one of several constituents in concrete. And while cement comprises only 10-15 percent of a typical concrete mix, it accounts for almost 90 percent of concrete’s carbon-dioxide emissions.

Cement manufacturing releases greenhouse gas emissions to the atmosphere from the combustion of fuels required to fire the cement kiln, as well as from the generation of carbon dioxide when limestone—a principal component of cement—is heated. Reducing the volume of cement in concrete is thus critical to lowering the carbon emissions associated with concrete production.

The most efficient method for lowering concrete’s greenhouse gas emissions is to replace a portion of the portland cement used in its production with fly ash. For each ton of fly ash used in place of portland cement, a reduction of slightly less than one ton of carbon dioxide is achieved.

Fly ash does not require the energy-intensive kilning associated with portland cement manufacturing. Use of fly ash also reduces the need for the energy-intensive operations required to mine and process the virgin materials it replaces—and the emissions associated with those operations.

As coal plant retirements continue across the U.S.—reducing the availability of fresh fly ash—harvesting of previously disposed ash can provide a reliable supply of high-quality ash that meets applicable standards for its use in concrete. Moreover, a 2023 life-cycle study conducted by the Electric Power Research Institute concluded that the use of harvested ash to replace cement in concrete produces environmental benefits under every process evaluated (screening, grinding, drying, and/or carbon removal).**

*Mordor Intelligence, 2024. “North America Ready-Mix Concrete Market Size & Share Analysis - Growth Trends & Forecasts (2024-2029).”

**EPRI, 2023. “Harvested Coal Ash Used as a Cement Replacement in Concrete: Life-Cycle Impacts.”