This is the second installment in our four-part blog series examining where the industry stands today in capturing the value of supplementary cementitious materials (SCMs). Since the benefits of SCMs scale directly to how much portland cement is replaced, having a reliable supply is critical for success. Heidelberg Materials has taken a comprehensive approach to increasing SCM supply, both by opening and upgrading facilities and by developing new technologies that boost output. The result is enhanced access to SCMs, supporting stronger performance in your concrete and greater sustainability on your projects!

Installments of this series were first published as the article "What’s Up with SCMs?” in the NRMCA’s Concrete InFocus magazine, Winter, 2025.

Slag cement comes from the production of primary iron processed in a blast furnace. Iron ore and process additions are heated to nearly 1500 degrees Centigrade to form two components: iron and molten slag. Molten slag can be granulated by quenching it with water. The quenching process creates glassy granules, which are then ground into the fine cementitious powder known as ground granulated blast-furnace slag (GGBFS), or slag cement.

According to Nick Brimley, Director of Membership and Marketing for the Slag Cement Association (SCA), shipments from SCA members represent over 95% of all slag cement used in U.S. concrete. “Since 2019, U.S. shipments each year have been greater than 3.7 million metric tons, with some years nearing 4 million metric tons. Furthermore, several of our member companies announced expanded production in 2023 and 2024,” said Brimley.

For SCA member Heidelberg Materials, that means operating more than five slag grinding plants. In 2023, the company opened its reconfigured Port Canaveral plant after a $24-25m project to increase its slag cement output by 25 per cent. The expansion added 200,000 tons of capacity to support construction projects throughout Florida and beyond.

"Over the past thirty years, slag cement has become commonly used. The engineering community and concrete companies' quality control departments are fully aware of the benefits it brings to concrete. So, we routinely see slag substitutions occurring at 40 to 70 percent, or in some geotechnical applications, up to 90 percent," said Jorge Armenteros, Vice President, Cement Sales, Heidelberg Materials Florida.

High replacement rates of slag cement—above 70 percent –are also beneficial for mass concrete pours, such as dams and large foundations. By reducing the heat of hydration, slag cement minimizes the risk of thermal cracking. Typical concrete mixtures for mat foundations in Florida use a 70-80 percent replacement of slag cement for portland cement.

Heidelberg Materials converted its cement plant in Speed, Indiana, to a slag grinding facility in 2024 to serve the fast-growing Midwest market. The projected volume of slag produced at the Speed plant is more than 400,000 tonnes annually. [In November 2025, the company acquired Walan Specialty Construction, a slag grinding plant located in Wilmington in Delaware.] Other Heidelberg Materials slag grinding facilities are in Cape Canaveral, Florida and Camden, New Jersey, with additional locations to come online in the coming years.

Contact Heidelberg Materials today to learn more…

Look for Part 3 of our series, “Fly Ash Reclamation,” or click here to read Part 1, “The Benefits of SCMs.”