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 For Precast and Block, Slag Makes Sense News

Cromwell Racks 1s.jpg

Type IS blended cement combines portland and slag cements into a single product form.  For concrete producers with limited silo capacity, blended cement allows them to achieve benefits of using slag cement in concrete—like greater strength and durability—without multiple silos.  A Type IS blend performs similarly to a Type I portland cement and conforms to ASTM C595, “Standard Specification for Blended Hydraulic Cements.”
Family business refines products with blended cement and gains “green” customers
Lael Libera started using a blended slag/portland cement in his concrete products to achieve a number of benefits: greater strength, less cracking, better color. Now Libera’s company, Cromwell Concrete Products, is one of the only producers in New England using slag cement in concrete masonry units, and his business is thriving because of it.

Boosting quality in block, and opening doors with precast
The company has used a blended portland-blast furnace slag cement (Type IS, 65% portland, 35% slag) for about two and a half years. One of the biggest benefits of incorporating the blended product is a reduction in cracking during block processing: Libera says there are fewer cracks than with a straight portland cement mix.

Rich Sullivan, territory manager for supplier Lehigh Northeast, says that “the material is filling the mold better, and is more consolidated.” While some cracking is normal during concrete block production, Libera’s blocks routinely go through the processing machinery without cracking. The slag cement is also allowing Libera to produce lighter-colored blocks with smoother finishes, as well as great-looking split-face blocks.

Cromwell Racks 2s.JPGBecause of the company’s success with slag cement in block, Libera says it was natural to try it in precast applications. “We do architectural work—coping, wall caps, and window sills—so the smoother the finish, the better,” says Libera. Strength is also boosted by at least 10% at 28 days, he says. Additionally, slag cement cuts down on turnaround time: when the weather is right, the company does a lot of its placement outside, and the sun on the forms can break down the release agent—but with a blended product, the lower portland cement content helps reduce sticking to the form and makes for easier cleanup.

Going green
The company initially embraced slag cement for one reason, but now has many more. “We started using a blended cement with the block to make a better product. Now it’s turning into a requirement with the precast—more and more jobs are requiring the use of a byproduct,” he says. The firm supplies block for many schools, including Wesleyan University, and architects are specifying “green” products that include recycled content and byproducts.

Cromwell Split Face s.JPG“When you use a byproduct, that’s a good thing,” explains Libera. “You’re getting a better product, using less cement and less natural resources that create cement, and using up a byproduct that you wouldn’t have had a use for before.”

Jan Prusinski, executive director of the Slag Cement Association, says that, “using slag cement in block and precast is an ideal way to increase the environmental sustainability of a structure.”  SCA offers a new publication, the LEED-NC™ 2.1 Guide: Using Slag Cement in Sustainable Construction, that “shows how slag can help achieve green building certification using the U.S. Green Building Council’s LEED green building rating system.” (Click here to download the publication).

Cromwell Concrete Products is even using blended cement in work for the Connecticut Department of Transportation (DOT), which requires concrete to include incorporated byproducts. Libera says the material’s lighter color and cleaner finish are ideal for curbing and barrier projects where high visibility is an important safety attribute.

Cromwell Precast s.jpgMore in Store for the Future
Libera says his experience with slag cement has opened up more possibilities. Soon the company will add a new silo for unblended slag cement, to achieve greater control of mix designs.  Also, they plan to use slag cement as they develop self-consolidating concrete (SCC) mixtures; slag cement adds “fines” to SCC which is an important paramater in SCC proportioning a successful SCC mixture.







 Cromwell Concrete Products


 Lehigh Cement Company


LEED-NC™ 2.1 Guide: Using Slag Cement in Sustainable Construction 

Click here to download

 SCIC #18: Producing Concrete Block with Slag Cement

Click here to download

SCIC #16: Producing Precast and Prestressed Concrete with Slag Cement

 Click here to download