The Benefits of Slag Cement: This blog will discuss the overall benefits and uses.
What is Slag?
Slag is a byproduct of steel production that has been used as an ingredient in Portland Cement in concrete for more than 100 years. Slag cement is a hydraulic binder, which means that it hardens when water is added. A hydraulic binder also hydrates with carbonation reactions and reacts with acids to produce solid products that provide the strength of concrete.
Slag cement is granulated blast-furnace slag (GGBFS) that has been finely ground. It may be combined with Portland cement or hydrated lime to produce blended cements. Slag cement can be added to concrete at the concrete plant or at the jobsite.
Slag cement is a hydraulic cement formed when granulated blast furnace slag (GGBFS) is ground to suitable fineness and is used to replace a portion of portland cement. It is a recovered industrial by-product of an iron blast furnace. Molten slag diverted from the iron blast furnace is rapidly chilled, producing glassy granules that yield desired reactive cementitious characteristics when ground into hydraulic cement. Slag cement can contribute to achieving LEED points to help your project attain this globally-recognized sustainability certification.
Slag cement has been used in concrete projects in the United States for over a century. Its use continues to grow in popularity as more construction professionals discover its unique performance benefits and environmental advantages.
Slag Cement Benefits
In comparison to portland cement, supplementary cementitious materials like slag cement have been shown to offer increased strength, improved durability and enhanced chemical resistance.
Specific benefits include:
Improved Finishability – Slag cement contributes smoothness and workability properties that make it easier for contractors to achieve high quality finishes. The material also assists in controlling bleeding, segregation and finishing operations while increasing workability and slump retention properties.
Increased Strength – Slag cement provides strength at an earlier age than portland cement while providing equivalent
Slag cement is a hydraulic cement formed when granulated blast furnace slag (GGBFS) is ground to suitable fineness and is used to replace a portion of portland cement. It is a recovered industrial by-product of an iron blast furnace. Molten slag diverted from the iron blast furnace is rapidly chilled, producing glassy granules that yield desired reactive cementitious properties when ground into cement fineness.
Benefits include:
– Lower Carbon Footprint – Slag Cement reduces the carbon footprint of concrete and concrete products by up to 15%.
– Increased Durability and Sustainability – Slag Cement improves many performance characteristics and enhances the long term durability of concrete.
– Better Concrete Economy – The performance and durability benefits of slag cement generally allow designers to reduce the total amount of cementitious materials needed in a mix design. This can result in a lower overall cost for the concrete product or structure.
One of the most sustainable building materials used in construction today is slag cement. Slag cement, often called ground granulated blast-furnace slag (GGBFS), is a glassy granular material formed when molten iron blast furnace slag (a byproduct of iron and steel making) is rapidly chilled as by immersion in water.
Slag cement is a recovered industrial by-product of an iron blast furnace. Molten slag diverted from the iron blast furnace is rapidly chilled, producing glassy granules that yield desired reactive cementitious properties when ground into powder. The grounds are commonly blended with Portland cement to produce a consistent, performance-enhancing product.
Slag cement requires nearly 90% less energy to produce than Portland cement. According to the Slag Cement Association, substituting 50% slag cement for Portland cement reduces greenhouse gas emissions by more than 40% and lowers the embodied energy of concrete by more than 30%.
Slag cement, or ground granulated blast-furnace slag (GGBFS), has been used in concrete projects in the United States for over a century. Earlier usage of slag cement in Europe and elsewhere demonstrates that long-term performance is enhanced in many ways. The use of slag cement to replace a portion of portland cement in a concrete mixture is known as “blending.” Slag cement is a recovered byproduct of the iron manufacturing process and can be used to replace a portion of portland cement in concrete mix design. The use of slag cement has demonstrated long-term performance enhancements allowing designers to reduce the environmental footprint of concrete while ensuring improved performance and increased sustainability.
The primary difference between GGBFS and portland cement is that fly ash requires more water for hydration than does GGBFS, which can result in higher early strength gain. In fact, ASTM C989 permits the addition of up to 50 percent slag cement by weight to produce moderate heat Type IS mixtures.
Slag cement acts as a supplementary cementitious material (SCM). An SCM reduces permeability; improves resistance to chemical attack; improves resistance to sulfate attack; reduces alkali-silica reactivity; improves abrasion
Slag cement replaces a portion of the Portland cement in concrete. This replacement can range from 5 to 70 percent slag cement, with typical use at 25 to 40 percent.
Slag cement is environmentally friendly. Slag is an industrial by-product of an iron blast furnace. Its production diverts this waste material from landfills and reduces demand for primary raw materials such as limestone, clay and sand. The production of slag cement produces less carbon dioxide than Portland cement, by up to 50% according to some estimates.
Slag cement can provide a more workable initial mix that requires less water to achieve the target slump. This can reduce shrinkage cracking potential and improve long-term durability. Slag is ground finer than Portland cement, which means it has more surface area for chemical reactions that retard the setting time in the initial mix, providing longer finishing times.
Slag’s coarse texture makes it ideal as a partial replacement in concrete mixes because it increases workability while improving strength characteristics, impermeability and resistance to deicing salts and other chemicals.
Slag’s slow hydration rate also provides more time for structural elements such as columns and beams to be poured, finished and cured before generating the expansive internal forces that can result in cracking.
Slag cement, often called ground granulated blast-furnace slag (GGBFS), is one of the most consistent cementitious materials used in concrete. It is actually a byproduct of iron production. When the iron is processed using a blast furnace, slag and iron both collect at the bottom of the furnace. The molten slag must first be separated from the molten iron. The process of rapidly chilling (quenching) the molten slag induces a chemical reaction that causes it to form granules of glassy material. This material is ground into a fine powder to produce GGBFS for use as a cementitious material in concrete.
Because of its pozzolanic properties, GGBFS can be added to concrete mixtures as an individual ingredient or in conjunction with portland cement to create blended cements. In order for GGBFS to react correctly, it must be finely ground and have proper particle size distribution characteristics.
Slag cement has been used successfully in virtually all concrete applications (i.e., pavements, bridges, buildings, hydraulic structures and portland cement concretes). Slag also provides benefits when used as an ingredient in other construction materials such as:
Portland-slag cement
Blended hydraulic c