Concrete specifiers and producers continue to use record amounts of slag cement in their product. Consumption of both forms of the product — finely ground hydraulic cement stored in dedicated silos or as a blended cement combined with portland cement — has exceeded the previous year's levels for the past five years. Use of slag cement shipped as a separate product increased 17 percent in 2001 over 2000 levels, for a total of 2.26 million metric tons, more than double the shipments in 1996. Use of blast-furnace slag blended cement increased 43 percent to 560,000 metric tons in 2001.

Few companies in North America have been as aggressive in increasing their slag cement production capacity as Holcim Ltd., through facilities operated by Holcim (US) Inc. and St. Lawrence Cement. Concrete fortified with Holcim's GranCem slag product — a ground granulated blast furnace slag — can resist 13,000 lb. of pressure per square inch or more and experience reduced levels of calcium hydroxide for improved resistance to sulfates and alkali-silica reaction. Perhaps most importantly to the environmentally aware cement industry, slag cement reduces the waste stream by utilizing byproducts of iron and steel production. Without slag cement production, this material would simply be sent to landfills.

One of the most recent grinding operations to open in North America is St. Lawrence's Camden, N.J. plant. Since its April 2001 commissioning, the Camden operation has secured GranCem acceptance among specifying authorities throughout a market area roughly bounded by Maine, Virginia, Buffalo and Pittsburgh.

Along with its partners in Holcim, St. Lawrence embarked on a two-year promotional campaign among engineers, contractors, architects, concrete producers, and departments of transportation to create awareness of GranCem's potential in high performance concrete and heat of hydration conditions for which fly ash might have been viewed as the only option. Although Lehigh and Lafarge have some slag cement distribution in the Northeast, the market's overall lack of capacity resulted in limited acceptance in areas such as New England and the state of New York (excluding New York City). St. Lawrence officials hosted tours of the Camden plant for specifiers and producers; discussed optimal mixes for particular jobs; developed trial mixes in independent labs or in the field; proposed mix designs; and conducted sampling and follow-up testing after the projects were completed.

Jerry Dooley, St. Lawrence's architectural and engineering marketing manager for New York metro, notes, “The Port Authority of New York and New Jersey has readily adopted slag cement specs for pavement and structures, with early work including Kennedy Airport and the Holland Tunnel.”

According to St. Lawrence, the New York State DOT has been pleased with the results of slag cement concrete and the availability of a consistent supply. The latter is owed to long term arrangement wherein raw slag is shipped for grinding in Camden from a plant in Italy. Approximately 500,000 metric tons of slag granules are expected to arrive and be processed this year.

In the case of Camden, Dooley adds, the vertical roller mill is supplied by Germany's Krupp Polysius and is said to be the most energy efficient of its grinding type for slag granules and is the largest vertical roller mill in the world.