Success for slag in the southeast

The properties of ground granulated blast furnace slag (GGBFS), known commonly as slag cement, make it useful in many applications. Particularly important is slag’s ability to reduce the environmental footprint of concrete. In fact, supplementary cementitious materials (SCMs), and especially slag cement, are currently the most effective lever a producer can use to lower the carbon footprint of concrete. Among its benefits, slag offers improved workability, easier placement and finishability, higher long-term compressive and flexural strengths, reduced permeability, mitigation of alkali-silica reaction, greater durability and resilience, and lighter colour than ordinary portland cement (OPC). Given its benefits, the market for slag is expanding. To meet this demand, in 2023 Heidelberg Materials North America added capacity to its facility in Cape Canaveral, Florida.

Commissioned in 2004, the Port Canaveral Slag Plant and Terminal is currently the newest slag grinding plant in North America. The recent addition of a roller press, coming less than 20 years after the plant was opened, has increased grinding capacity by more than 25% and ensures the facility’s position as a state-of-the-art provider of slag in the region. Highlighting the Cape Canaveral plant’s significance, this year’s Slag Cement School, an event hosted by the Slag Cement Association (SCA), was held in Cape Canaveral on 22 – 23 May, 2023, and featured a tour of the plant and its expansion.

As part of its original design, the Cape Canaveral plant was intended to eventually accommodate the installation of a roller press. This set the stage for the plant’s expansion at such a time where market demand would make that expansion desirable. The hydraulic roller press is a highly energy-efficient system that provides additional comminution (grinding) of feed particles and results in finer materials being fed into the plant’s ball mill (a grinder that reduces particle size using impact as the mill’s cylinders turn and steel balls act as the grinding media). Previously, material was routed directly from the flash drier to the ball mill. With the expansion, raw materials are diverted after drying to be crushed in the roller press, which subjects the feed material to very high pressures between its counter-rotating rollers to achieve a semi-finish grind. The pressure forms microcracks in the feed particles, resulting in a very fine particle size. With significantly smaller particles arriving at the ball mill, efficiency of the overall process is improved and energy usage is reduced.

The market for slag expands

The push in recent years to make concrete more sustainable has resulted in the widespread adoption of slag in admixtures.

"In the nearly 20 years since I led the opening of this plant, the market for slag has remained strong, despite the economic downturn of the late 2000s. This is attributable to the strength and corrosion resistance slag lends to concrete – an especially important consideration in our coastal areas,” said Neil Hodgson, Director, Cement Operations – Florida, Heidelberg Materials.

One contributor to corrosion in concrete is the alkali-silica reaction (ASR), a chemical reaction between the alkalis in portland cement and certain types of silica minerals present in some aggregates. The reaction results in a hygroscopic gel that absorbs moisture and swells, thereby potentially causing expansion and cracking and leaving the concrete more susceptible to corrosion damage from moisture and chloride ingress. The use of slag cement reduces the potential for ASR because it binds a greater proportion of the alkalis and reduces the amount of alkalis in the system that are available for reaction with the aggregates.

Enjoyed what you've read so far? Read the full article and the rest of the July issue of World Cement by registering today for free!

Read the article online at: https://www.worldcement.com/special-reports/10072023/success-for-slag-in-the-southeast/