The difference between white Portland cement and slag cement is not in their material composition or in their use but in their color. Both materials are composed of calcium, silicon, aluminum and iron.
White Portland Cement
White Portland cement is used for making architectural concrete exposed to the elements because it has a high resistance to sulfates and chlorides. Slag cement is often confused with fly ash, another material used for similar purposes. Fly ash is a byproduct of burning coal in an electric power plant. Slag cement is a byproduct of the production of pig iron from iron ore during the smelting process.
Slag Cement
Slag cement contains components that produce beneficial chemical reaction with water and concrete aggregates, enhancing concrete’s strength, durability and thermal performance. The rate at which slag cement reacts varies depending on the type of portland cement used, but overall its reaction rate tends to be slower than portland cement. Its slower reaction rate means that slag cement takes longer to reach its full potential strength compared with portland cement. Slag also reduces heat generated during hydration and lowers the risk of cracks in large or mass concrete pours.
Well, it is worth noting that white cement and white Portland cement are not the same thing.
White portland cement is made from raw materials containing little or no iron or manganese, the substances that give conventional cement its gray color. So the secret of the whiteness is the raw material selection. Raw materials high in alumina, silica, and sulfate are used, and the finished product is produced by shortening the burning process and halting oxidation.
Slag cement is a more generic term and most often refers to a secondary cementitious material (SCM) — most commonly 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 molten slag is then either air-cooled or water-quenched, depending on how it will be processed further. The water quenching results in a granular product known as granulated blast furnace slag. The less common air-cooled slag is formed into large balls or dense cubes for use as an SCM with portland cement in concrete applications.
White Portland Cement
White Portland cement is typically used for decorative or architectural concrete. It has lower heat of hydration and higher sulfate resistance than gray cement, but is more expensive. White cement is used in combination with white aggregates to produce white concrete for prestige construction projects and decorative work. White cement is specified to ensure clean, bright, consistent colors, including light pastels.
Slag Cement
Slag Cement (Ground Granulated Blast Furnace Slag) – The principal constituents of blast furnace slag are silicates and alumino-silicates of calcium. When ground to a fine powder, granulated blast furnace slag has pozzolanic properties, which enables it to blend with and enhance the performance of portland cement. Slag cement provides durability, increased strength and improved finish. When added to concrete mix designs, slag cement acts as a partial replacement for portland cement and uses less energy in production than portland cement. It also helps conserve natural resources by using industrial byproducts.
The manufacturing of Portland cement involves mining, crushing and grinding raw materials (limestone, clay and iron ore) into a fine powder, which is heated to form a clinker. In the kiln, the clinker is heated to form a grey granule-like material called cement.
Slag cement is made by grinding of blast furnace slag granules that are formed in a molten state through rapid cooling. The granules range in size from fine grains to coarse gravel. The resulting material is ground into a fine powder similar in appearance to Portland cement. Both SCMs have similar chemical compositions but differ significantly in their fineness or particle size distribution and the amount of each added to concrete (pounds per cubic yard).
The two SCMs can be used independently or together in combination amounts ranging from 0% to 100% replacement for Portland cement. Slag cements typically contain between 50% and 70% slag by mass, and are commonly referred to as Type IS (Slag Cement). White cements typically contain less than 5% of other ingredients by mass and are commonly referred to as Type IP (Portland-Pozzolan Cement).
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.
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 iron is usually recycled while the slag is accumulated and then transported to processing plants where it’s ground into a fine powder called GGBFS.
When used in concrete, slag increases the workability and decreases the water demand without affecting strength. It also improves pumpability, reduces bleeding, and can help mitigate alkali-silica reactivity when incorporated into concrete mixtures. Slag also contributes to long term strength by continuing to react years after the concrete has been placed.
Slag cement can be added to concrete in the concrete manufacturer’s batching plant, along with other components, or directly at job sites via cement slurry during placement operations.
The two main types of cement in the early part of the twentieth century were natural cement and portland cement. Natural cements are made primarily from limestone, marl or chalk and shale or clay. As the names imply, portland cement is not a brand name, but the generic term for the type of cement used in virtually all concrete, just as stainless is a type of steel and sterling a type of silver. The name “portland” comes from its similarity to a high quality building stone quarried on the Isle of Portland in England. Its originators were attempting to develop a hydraulic cement that would harden under water and resist sulfate attack, which was one of the major problems with natural cements.
Portland cements are hydraulic cements composed primarily of hydraulic calcium silicates. More than 30 raw materials are known to be used in the manufacture of portland cement, and these materials can be divided into four distinct categories: calcareous, argillaceous, gypsum-containing, and miscellaneous. Calcareous materials provide lime (CaO), which combines with silica (SiO2), alumina (Al2O3), and ferrous oxide (Fe2O3) to form tricalcium silicate (3CaO
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