Utilization of Steel Slag in Sustainable Construction

Last Updated on March 16, 2024 by Admin

Steel slag has been used as a cement substitute in concrete for sustainable development in the building industry. Steel slag is a byproduct of the steel industry with a wide range of chemical components and low cementitious characteristics. The massive amount of SS produced by steel mills throughout the world is a major motivator for recycling this by-product of steel manufacturing.

Recycling SS, on the other hand, could be beneficial if the materials used are durable and keep qualities that meet acceptable specifications after a lengthy period of time. Steel slag, which is utilized as aggregate or as supplementary cementing materials in cement and concrete production, has a considerable positive influence on the environment due to its long-term strength and durability. Because of its vast production, which will cause environmental concerns if disposed of directly, large-scale usage of SS is critical for sustainable growth.

What is Steel Slag?

Steel slag is an unavoidable by-product of iron and steel production, consisting primarily of metal oxides and silicon dioxide (silicate). Iron and Steel Slag, on the other hand, is nonmetallic and does not contain any dangerous compounds. Slag is an environmentally sustainable alternative construction material with improved product attributes.

The slag produced is referred to as High Sulphur slag, LD slag (Steel Furnace slag – SFS), LF slag, or Electric Arc Furnace (EAF) slag depending on the stage or type of steelmaking process. Steel slag, particularly LD and EAF Slag, is widely utilized for a variety of purposes in many nations throughout the world, including the United States, the European Union, Brazil, Australia, and China.

Steel slag has a high density, high strength, a lot of pits on the surface, a lot of wear resistance, and it has a gel property. As a result, steel slag can be utilized to make cement and steel slag bricks that contain little or no clinker, concrete aggregate, and other building components. Steel slag contains a lot of active elements including 3CaOSiO2 and 2CaOSiO2, which are similar to the major ingredients in Portland cement clinker.

Steel slag can thus be mixed in a certain proportion with cement clinkers to produce steel slag cement, steel slag Portland cement, steel slag white cement, and other products in the cement industry. Shan et al. exploited the premise that steel slag and blast furnace slag can activate each other to enhance hydration to boost the strength of the cement by adding a 25% steel slag and 25% blast furnace powder as an additive.

Primary characteristics & applications of Iron and steel slag

Iron and steel slag is now used in a variety of fields where its particular properties can be put to good use. Iron and steel slag is widely regarded as a recycled material that can lessen environmental impacts due to its resource-conservation and energy-saving effects as a result of increased environmental consciousness.

Air-cooled blast furnace slag

When this slag combines with water, it hardens and develops a hydraulic feature that gives it increased strength over time. It is utilized as road base course material in the same way that gravel is because of its high load-bearing capacity. This slag includes no clay or organic contaminants, thus there is no risk of alkali-aggregate reaction. As a result, it is used in the same way as natural aggregate as a concrete aggregate.

Granulated blast furnace slag

This slag has a hydraulic property, similar to air-cooled blast furnace slag, and there is no risk of alkali-aggregate reaction. This slag is employed in products like Portland blast furnace slag cement because of the significant latent hydraulic characteristic that develops from fine grinding. When crushed granulated blast furnace slag is mixed with cement, it creates Portland blast furnace slag cement, which has the same qualities as conventional (Portland) cement.

The benefits of this blast furnace slag cement, such as increased strength over time, low heating speed when reacting with water, and high chemical durability, are put to good use in a variety of industries, including port and harbor building and other significant civil engineering projects.

Steelmaking slag

Steelmaking slag is utilized as a road base course material because of its hydraulic properties and large bearing capacity. Because of its high particle density and hardness, this slag is employed as an aggregate in asphalt concrete because of its higher wear resistance. It is also utilized as a material for civil engineering projects and as a ground improvement material due to its high angle of shearing resistance, high particle density, and large weight per unit volume (i.e., material for sand compaction piles).

Iron and steel slag products

Iron and steel slag products are manufactured and quality controlled for a wide range of applications. In Japan, iron and steel slag products are used as construction materials for roads, ports, airports, and other infrastructure, as well as an environmental material for restoring or improving marine, soil, and other habitats.

Cement

Slag products made of iron and steel are utilized in a number of applications where their distinctive properties are put to good use. The cement industry accounts for the majority of the demand for these goods. Cement uses about 40% of iron and steel slag products and 60% of blast furnace slag. The majority of these materials are utilized in Portland blast furnace slag cement as a raw ingredient. The following are the characteristics of Portland blast furnace slag cement.

• It has great resistance to seawater and chemicals, as well as the potential to increase durability.
• The chloride ion diffusion coefficient is low (resists rebar corrosion).
• It has the ability to decrease the alkali-aggregate reaction.
• It becomes stronger over time.
• When employed in ground improvement, it produces negligible hexavalent chrome elution

This product is also being utilized more frequently in construction projects. Portland blast furnace slag cement is appropriate for use in piles, foundations, underground beams, and continuous walls due to its generally large material cross-sections, simplicity of ensuring concrete cure time, and relatively large cover it provides.

Concrete Aggregate

Iron and steel slag aggregate is an industrial product that is produced under strict quality control and is free of biological impurities, clay, shells, and other similar things. The chemical composition is fully uniform for both fine and coarse particles.

Furthermore, this aggregate is free of reactive silica, which is one of the main causes of chemical reactions in alkali aggregates. It has a lower environmental impact, conserves valuable natural resources needed to maintain ecosystems, and can minimize the amount of energy used in mining, stone crushing, and other activities.

The two types of a concrete aggregate are made from iron and steel slag as a starting material. Coarse aggregate is a mechanically stabilized aggregate made by cooling molten slag slowly after it has been extracted from a blast furnace or an electric arc furnace. Fine aggregate is a mechanically stabilized aggregate made by rapidly cooling molten slag after it is evacuated from the furnace with water, air, or other means.

There are a number of advantages to iron and steel slag aggregates, including the lack of biological contaminants, clay, shells, or other particles that can impact concrete durability; low variation in quality; and no expansion due to alkali-aggregate reaction.

Moreover, under oven-dry conditions, the density of electric arc furnace oxidizing slag aggregate is around 3.6 g/cm3, which is higher than other aggregates. This property is useful in applications like radiation shielding concrete and heavy-duty concrete

Roads

Crushing and mechanical stabilization of blast furnace slag and steelmaking slag for use as paving material produce iron and steel slag for road construction. Steelmaking slag is utilized as an aggregate in asphalt mixtures, and these two types of slag are employed in base course materials that are made from them alone or in a mixture.

The hydraulically and mechanically stabilized slag HMS-25, which is used as a base course material for iron and steel slag, hardens over time. This hardening property can be exploited to make a thinner pavement than regular crushed stone (mechanically stabilized crushed stone).

The material is praised for its ease of use, with benefits such as the ability to reopen the road to traffic immediately after work is completed and the capacity to continue compacting the base course even if it rains. Steelmaking slag is utilized as an aggregate in asphalt mixtures in addition to being used as a base course material due to its outstanding hardness and wear resistance.

Civil Engineering works

Granulated slag is lighter than natural sand (11–16 kN/m3 wet unit weight), has a high angle of shearing resistance (35°C or higher), and has the hydraulic property of hardening with time. It also has the same water permeability as high-quality sand, if not better.

Steelmaking slag can be handled as a granular material in the same way as natural road base course material due to its characteristics. It has better soil mechanics than natural base course material, such as a higher bulk density and a bigger internal friction angle. Because it contains lime, however, it has features such as expansion and high alkali dissolution.

Granulated slag is utilized in a variety of civil engineering applications, including coastal protection backfill, earth covering for soft ground correction, road subgrade, and embankments. Sand-like granulated slag has physical and mechanical properties similar to natural sand, such as being lighter and having a greater angle of shearing resistance. It also possesses a hydraulic feature that causes it to hydrate and solidify over time, providing excellent liquefaction resistance in the case of an earthquake.

The lightweight and high angle of shearing resistance of granulated slag as a coastline protection backfill material can be employed to good advantage, considerably decreasing active earth pressure on the front sheet piles and allowing the sheet pile cross-section to be lowered. It will not liquefy in an earthquake once fully solidified, hence no extra liquefaction countermeasures are required.

The lightweight of granulated slag as earth covering for correcting soft ground decreases the risk of lateral soil flow and the amount of consolidation settlement. It has greater trafficability since it is also resistant to the impacts of water. Granulated slag subgrades are lightweight and ideal for soft soils.
They do not distort significantly under traffic loads and have adequate bearing capacity. The hydraulic feature of this subgrade gives it advantages as a road structure, such as no loss of strength due to penetrating water even under repeated traffic loads. It has good durability in addition to cost-effectiveness and workability.

When granulated slag is utilized in embankments, it can provide design advantages due to its lightweight and a large angle of shearing resistance when embankments are built on soft ground.

Ground Improvement

Granulated blast furnace slag is utilized in some sand mats because it is lower in weight than natural materials. Steelmaking slag also takes on shapes with multiple edges and rough surfaces, resembling natural crushed stone or sand in appearance.

Steelmaking slag for ground improvement has a higher unit mass and better angle of shearing resistance than natural sand, and it has been discovered that these geotechnical properties can be employed to lower ground improvement costs.

Although the pH of the water eluted from steelmaking slag is typically high, when slag is used as an SCP filler material, it is contained inside the casing pipe and has essentially little interaction with seawater.

Indian Infrastructure and utilization of iron and steel slag

Steel slag output is currently over 12 million tonnes per year. However, as steel output rises, slag production is likely to expand dramatically as well. In comparison to other countries, most slag produced in India, particularly steel slag, is wasted; however, due to a lack of land, this is progressively becoming a problem; slag utilization is currently in the trial phase.

Steel slag, on the other hand, can be put to a variety of positive purposes with the right legislative assistance.

• Using steel slag instead of natural aggregates reduces the environmental impact of quarrying and prevents deforestation.
• When used in the asphalt layer, steel slag improves road safety by providing improved skid resistance. When employed in the road construction process, steel slag provides economies of scale, answering India’s expanding infrastructure needs.
• In locations such as Eastern India, steel slag can be utilized as a soil neutralizer for severely acidic soils; its usage as a fertilizer is also well-established.
• When used as rail ballast, steel slag has a longer life and durability than natural aggregates, reducing maintenance expenses.
• Steel slag is widely utilized in landfills around the world, and it is a feasible alternative in India.

Way Forward

So, because the focus of government policy is increasingly on improving housing, roads, and other infrastructure, the only way forward is to expand the resource base. The government must, as soon as possible:

• Use slag as an aggregate in infrastructure and construction projects;
• Including slag in standards and regulations will help to alleviate the resource shortage. Though BIS has started the process, it has a long list of requirements, including supporting data, study reports, and R&D.
  Treat steel slag as a co-product of the steel-making process rather than a by-product.
  Assign carbon credits to (slag) users that can be shared with the steel sector.
• Identify collaborative research possibilities to uncover regions where varying quantities and quality of slag can be used, as well as f. Establish a mission mode approach with all stakeholders to identify optimal steel slag use prospects in the Indian infrastructure sector.

Conclusion

Steel slag’s complex composition and structure determine the diversity of its characteristics, allowing it to be used in a variety of fields, including cement, concrete aggregate, road paving, fertilizer production, and so on, with some success. However, steel slag’s application in these areas is limited due to some negative factors. Steel slag’s catalytic efficacy might be improved, opening up a new avenue for steel slag resource exploitation.

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