How A Slag Cement is different and What to Expect

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Slag cements are different from other types of cements. They are a unique category of cement made by grinding together Portland cement clinker and granulated blast furnace slag.

Slag is an industrial waste product from the production of iron and steel in a blast furnace. Slag is rich in silica, alumina, lime, and other compounds that are often valuable minerals. The principal constituents of slag are calcium, magnesium, aluminum, and iron oxides.

Blended cements can also be made by adding fly ash or other pozzolans to an existing cement such as Type I/II or Type III. However, the pozzolanic reactivity of these materials is often limited by their calcium content which may reduce the benefit obtained through addition of these materials to the concrete mixture. Furthermore, Type I/II and Type III cements can often contribute to significant amounts of alkali silica reaction (ASR) expansion when used in combination with some aggregates. In contrast, slag cement is more reactive than fly ash due to its lower calcium oxide content and lower insoluble residue content. Slag cement’s high reactivity enables it to reduce alkali-silica reactivity expansion compared to Portland cement or blended cements containing fly

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 fine powder.

Slag cements are just one type of supplementary cementitious material (SCM). SCMs can be added at the concrete plant or at the jobsite. The general rule of thumb is to use slag cements as part of a blended cement, not on their own. Blended cements have better performance characteristics than portland cement alone; they produce more durable, lower permeability concrete at a lower cost than if only portland cement was used.

The first thing anyone should know about slag cements is that they are not to be used exclusively as your primary binder. Most specifications require that fly ash and/or slag cements be used in combination with portland cement, up to a maximum replacement level of 50% of the total cementitious content. If you take nothing else away from this blog, then please remember that

A 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 to fineness.

In general, slag cements require more time to achieve comparable strengths when compared to ordinary portland cement (OPC). This increase in setting time can be mitigated by the use of accelerators (commonly calcium chloride) or by the use of a retarding admixture (commonly lignosulfonate).

A: Slag cement is used to enhance the performance of concrete. A common use is as a partial replacement for Portland cement.

A: Compared to portland cements, slag cements have lower CO2 production. They also have lower heat of hydration, which means they create less cracking in hot weather and larger pours. Slag cements also have increased resistance to chemical attack and sulfate attack and are more durable in marine environments.

A: Slag cements can be produced by intergrinding or blending portland cement and granulated blast furnace slag, or by blending portland cement with ground granulated blast furnace slag.

A: 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 durability.

Concrete is a mixture of sand, gravel and cement. The cement paste contains a variety of chemical compounds which act as binders, that allow the aggregate to chemically and physically bond together. The paste also acts as a lubricant for the aggregate to flow together, making it easier for the concrete to be placed and molded.

Slag cement does not contribute to concrete shrinkage because it has no free lime. Free lime makes the concrete shrink when it dries out. Low shrinkage can mean less cracking and drying shrinkage in concrete pavements, structures and flatwork.

In addition, slag cement enhances the performance of concrete by improving workability and durability. It also reduces permeability, which limits migration of aggressive ions through the concrete structure. Slag cement has been used in almost every type of construction project imaginable including highways, bridges, marine structures, mass transit systems, schools, airports and commercial projects such as office buildings and parking garages.

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 produces glassy, sand-Type granules, which are then ground into a fine powder to produce GGBFS.

The use of GGBFS as a partial Portland cement replacement takes advantage of the energy invested in its manufacture and its subsequent energy saving effect on concrete’s heat of hydration when used at levels of 40% or more by mass of total cementitious material.

The use of GGBFS has been shown to improve concrete’s resistance to sulfate attack, alkali-silica reaction (ASR), freeze/thaw conditions and corrosion while providing reduced permeability and an improved finishability.

A common misconception concerning slag cement is that it contains harmful levels of heavy metals. Slag cement has in fact been proven to contain no known or suspected carcinogens or respiratory

A general purpose cement is a special blend of Portland cements, sand and other materials to produce a workable mix when mixed with water. It can be used for concrete and mortar work in most situations where normal structural concrete is used.

Applications of General Purpose Cement:

Brick, block and stone laying.

Pointing, rendering and plastering.

Floor screeds, steps and paving.

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