What is slag and why is it used in construction

Although slag may seem like an odd choice for building materials, it has long been recognized as a valuable resource. Slag is essentially a waste product from the processing of metals like steel and iron. Slag, the material left over after these metals are removed from their ores, has a variety of uses, especially in the building sector.

Slag’s durability is one of the key justifications for its use in building. Concrete can be made by processing it into aggregates and mixing them with cement. When compared to conventional concrete made with natural aggregates, this concrete is frequently stronger and more resilient to deterioration. Slag-based concrete is therefore perfect for demanding construction projects like roads, bridges, and buildings.

Utilizing slag has positive environmental effects as well. By reusing slag, less natural resources need to be quarried, protecting natural areas and lowering the carbon footprint of building projects. Slag can be made into a useful component by adding it to construction materials, which also aids in the efficient management of industrial waste.

The versatility of Slag doesn’t stop there. It can also be used as a base material for new roads, giving them a sturdy base that improves their performance and lifespan. Slag’s many uses are further demonstrated by the fact that it can enhance soil quality in agricultural applications.

What is slag

Slag is an artificial, non-metallic silicate that develops on the surfaces of different metals when:

• smelting of raw materials;
• processing of intermediate products;
• refining of liquid alloys.

Additionally, as raw materials are extracted to extract fluxes, construction slags are formed during the reduction of ore in the production process.

When discussing the chemical makeup of metallurgical waste, there are various categories of this material to consider:

• Basic (CaO, MgO and FeO). In this case, the material contains up to 50% calcium oxide and about 10% alumina.
• Acidic (SiO2 and TiO2) with a calcium oxide content of no more than 42% and alumina up to 15%.
• Neutral (Al2O3 and ZnO) in which there is about 45% calcium oxide.

Particles of silicon, aluminum, magnesium, manganese, sulfur, and other elements are also present in the waste. The characteristics of the slag vary based on their volume.

Scope and properties of slag

Speaking about what slag is, it is worth mentioning the scope of application of this material. Most often, granulated slag of different diameters is used in construction:

• Larger granules are used in the manufacture of cinder blocks, which are characterized by wear resistance, lighter weight and increased heat and moisture insulation. Large granulated slag is also used in the construction of foundations (as a substrate), strengthening embankments, and processing the edges of reservoirs.
• From slag of a finer fraction you can make an additive for concrete or asphalt.
• Dust and the finest particles are used as additives in the production of paving slabs and mineral wool.
• Crumbs are added to construction mixtures to increase the strength characteristics of the compositions. Crumbs are also used to fill voids in walls.

Recycled materials come in a wide variety of colors, from rich black to white. Pearlescent or lilac-colored materials are frequently encountered.

Slag’s density varies according to the constituents that make up its composition.

Accordingly, these values will vary between 800 and 3,200 kg per cubic meter if we measure this indicator in "cubes."

The mass of the raw material, or its specific gravity, ranges from 2.5 to 3.6 g/cm^3. The indicators of natural rocks are essentially the same. It is important to keep in mind, though, that the kind of raw material used can affect the specific gravity of slag:

• For slag concrete, this indicator will be about 2-2.4 t/m 3 .
• The specific gravity of lump slag ranges from 2.1 to 2.8 t/m 3 .
• If secondary raw materials in the form of crushed stone are used, the weight of the material will be the smallest from 1.05 to 1.6 t/m 3 .

Furthermore, the type of secondary raw material influences its properties. In modern metallurgy, slag can be classified into four categories: chemical, fuel, non-ferrous, and black.

Non-ferrous metallurgy slags

This category’s secondary raw materials are less common because of their high cost and labor-intensive manufacturing. Non-ferrous raw materials have a higher specific gravity and a higher content of ferrous oxide, which can reach 40% by volume, in contrast to ferrous metallurgy slags. These materials also contain rare and valuable metals.

The construction industry occasionally uses non-ferrous metallurgy waste, which is created during the smelting of copper and nickel. Secondary raw materials used in copper smelting are solid and have a black color. Its water absorption ranges from 0.1-0.6% while its density varies from 3,300 to 3,800 kg/m3.

The properties and indicators of nickel raw materials are the same as those of waste from copper smelting.

These kinds of slags are rarely used to make construction materials; instead, they are occasionally utilized to make cast products or mineral wool. Slags from blast furnaces are more frequently found on the production line.

Because of its strength, durability, and environmentally beneficial qualities, slag—a byproduct of the steel industry—is being utilized more and more in construction. It can make concrete mixes more economical and environmentally friendly by taking the place of conventional materials like cement and gravel. Its use provides sturdy building materials that adhere to industry standards while assisting in waste reduction and minimizing the environmental impact of construction projects.

Ferrous metallurgy slags (blast furnace)

This kind of raw material comes in three varieties:

• Granulated blast furnace slag, which is obtained by cooling cast iron during its smelting. As a rule, the resulting granulated slag is used as a substitute for more expensive mineral additives.
• Non-granulated blast furnace slag. It is mined in the process of air cooling of metallurgical waste, its crushing and subsequent screening. The resulting material is most often used as a filler for asphalt concrete in the construction of road surfaces. In addition, non-granulated raw materials have found application in the agricultural sector, where waste is used to deoxidize the soil.
• Slag pumice is distinguished by the fact that it does not have binding properties. Therefore, this raw material is often used as insulation, soundproofing material and in the production of cinder blocks and other products from porous and lightweight concrete.

The characteristics of blast furnace slag include stability, reactivity, and a high resistance to grinding. Granulated slag is divided into three grades based on its hydraulic properties:

• Grade 1. In such material, the content of aluminum oxide is allowed to be at least 8%, magnesium no more than 15%, titanium no more than 4% and manganese no more than 2%.
• 2nd grade. Aluminum oxide – 7.5%, magnesium – 15%, titanium – 4%, manganese – 3%.
• 3rd grade. Aluminum oxide – no more than 7.2%, magnesium – 15%, titanium – 4%, manganese – 4%.

Fuel slags

These days, ash slags, another name for coal slags, are also commonly used in industrial construction. These raw materials have a higher FeO content and a lower CaO content than blast furnace slag. Enhanced alkalinity is another characteristic of coal slag.

Granulated slag, or "ash slag," is identified by its dark hue. The divalent iron in the raw material is what gives it this color. Depending on the amount of oxide present, slag can be brown, white, olive, or green in color. The raw material is crushed to create slag sand; in this instance, the material will have a gray color.

When different fuels are burned, ash and slag are produced, and based on the type of fuel used, one can calculate how much secondary raw material is present:

• in brown coal the slag content is up to 15%;
• in hard coal – from 3 to 40%;
• in anthracite – up to 30%;
• in oil shale – from 50 to 80%;
• in firewood – about 0.5-1.5%;
• in fuel oil – no more than 0.2%.

But it’s important to think about whether coal slag is dangerous. It is not advised to use this material as a filler for concrete walls or to arrange screeds for residential buildings due to the fact that it contains radioactive materials.

Chemical slags (electrothermophosphorus)

Granulated slags are byproducts of the electrothermal method used to produce phosphorus. Up to 98% of these secondary raw materials are made of glass. CaO and Si02 form the material’s foundation. Chemical waste also includes waste paper particles, rags, rubber crumb, polymeric materials, related petroleum products, and a host of other materials. Because of this, building rarely uses these slags.

The most prevalent kind of slag is secondary raw material from blast furnaces. This material does, however, have some drawbacks in addition to its many benefits.

Slag is a byproduct of the steel industry that is frequently wasted but has a lot of usefulness in building. Because of its special qualities, it’s a material that works well in a variety of settings.

One of the main benefits of slag is its strength and durability, making it ideal for use in concrete and road construction. It enhances the stability and longevity of structures, providing a sustainable and cost-effective alternative to traditional materials.

Slag is also used to recycle waste products from the steel industry, which lessens its impact on the environment. This promotes a more environmentally friendly approach to building and infrastructure projects by minimizing the use of landfills and conserving natural resources.

Slag is a valuable resource that helps to create stronger, more durable, and environmentally friendly construction practices, so it’s more than just a byproduct. Slag is an excellent way to utilize industrial byproducts efficiently while enhancing sustainability and performance in building projects.

Video on the topic

Residents of “Podsolnukhy”: instead of crushed stone, they use slag and mud when building a road

If life is in shambles?) Radiation background of the material.

Slag formation and its properties. Kyzylbayev E.TO.

"Blast furnace slag" Chemical composition.

What happened to the slag wall in 7 years.

About slag concrete and formwork

BUILDERS ARE SHOCKED! INSULATION WHICH HAS NO EQUALS!