Advantages of Portland Slag Cement

• Better Workability
• Maximum reduction in Heat of Hydration
• Low risk of Cracking
• Low risk of Shrinkage
• Absorption of surplus lime released out of cement from secondary hydrated mineralogy
• Improved Water Tightness

Impact of using GGBS in concrete

• Reduction in the emission of CO₂ from cement production plants
• Improved durability
• Reduced potential for cracking
• Reduced permeability
• Reduced corrosion repairs cost nearly by 5.0 percent of developed nation’s GDP
• Use of waste or by-products reduces the clinker usage
• Increased benefit to cost ratio and longer service life
• High Impermeability
• Excellent resistance to Chloride Penetration
• Excellent resistance to Sulphate Attacks
• High Flexural and Compressive Strength
• Improved Corrosion Resistance Exhibits very low diffusivity to Chloride ions
• Increased resistance to Alkali-Silica reactions

For any construction activity, use of ingredients like cement, river sand, and aggregates along with water is must to make durable, sustainable, and cost effective constructions, both in the rural and urban societies. Now-a-days, the trend is to use sustainable products like GGBS (Ground granulated blast furnace slag) in Ready Mix Concrete (RMC) production or at site-based batching plants as partial replacement to OPC Cement, and M-sand or slag sand instead of river sands in constructions at infrastructure projects sites as well as at metros and cities where RMC plants are located.

RMC, as a product, is continuously evolving and moving forward by replacing traditional Site Mixed Concrete (SMC) in the Indian urban and infrastructure market place. Many cement and building materials companies in India have launched new eco friendly cements like PPC and PSC instead of OPC Cement, M sand, and Slag sand (instead of natural river sand soil stabilized cement blocks), fly ash blocks (instead of bricks) to make the construction of infrastructure projects eco friendly, both in rural and urban areas in India.

In India, for the last seven to eight years the use of by-products of steel industry like GGBS, slag cement and GBS is gaining momentum as alternative materials for various applications due to products availability and manufacturing of the these products from reputed manufacturing companies and industry houses

The various applications of Steel Industry by-products are as follows:

• GBS or Slag sand in the road construction project as sub base
• Slag sand as partial replacement to river sand in concrete and plastering.
• GGBS (Ground granulated blast furnace slag) as partial replacement to OPC Cement in concrete production at RMC batching plants and Site batching plants.
• Slag aggregates as partial replacement to granite aggregates in concrete.
• Sintered aggregates for light weight Concretes

Use of green products

There is growing interest among infrastructure companies and government of India regarding protection of environment, and to reduce the greenhouse gas emissions after the United Nations Climate Change Conference at Paris during November-December 2015. Worldwide evidence indicates people are concerned about the environment and are changing their behaviour. The use of supplementary cementitious materials (SCMs) like GGBS and Fly Ash in the production of concrete has increased worldwide over the past few decades. These materials can enhance the mechanical and durability properties of concrete and contribute to mitigation of the environmental impact associated with the construction industry. SCMs are used as a partial replacement for Portland cement in concrete, reducing the fraction of Portland cement required to produce concrete with desired performance

Sustainable green products

The Indian infrastructure and the construction industry has started adopting and using many new cement and concrete products which are eco friendly and very cost effective. Following are the by-products of the steel making industry which are being used both in the infrastructure development projects and concrete industry in India.

Eco friendly cements made with using steel industry by products

• Port land slag cement (PSC) Eco friendly Mineral admixture from the steel Industry
• Ground granulated blast furnace slag (GGBS) from steel Industry Eco friendly sands
• Slag Sand Ecofriendly aggregates from the steel industry
• Aggregates

Blended cement is a mixture of port land cement and blast furnace slag (BFS) or a mixture of portland cement and a pozzolana (most commonly fly ash). The use of blended cement in concrete and construction reduce mixing water and bleeding, improves finishability and workability, enhances sulphate resistance, inhibits the alkali-aggregate reaction, and lessens heat evolution during hydration, thus moderating the chances for thermal cracking on cooling

Portland Slag cement is manufactured by either inter-grinding the Portland cement clinker, Gypsum and granulated slag or blending the ground granulated blast furnace slag (GGBS) with Ordinary Portland cement by means of mechanical blenders. “Slag” is a non-metallic product consisting essentially of glass containing silicates and Alumino Silicates of lime. It is the by -product obtained in the manufacture of pig Iron in blast furnaces at around 1400° to 1500°C in the molten form. The granulated slag is obtained by rapidly chilling (Quenching) the molten ash from the furnace by means of water or steam and air. The Blast Furnace Slag, by product of steel industry is an excellent example of resource Conservation and Pollution Management.

GGBS (Slag)

GGBS is obtained by quenching molten iron blast furnace slag in water or stream, to produce a glassy granular product that is then dried and ground into a fine powder. Both are used as a replacement for a portion of the Port land cement. Slag replaces as much as 50 percent in normal concrete (and up to 70 percent in special applications such as mass concrete). Fly ash is usually limited to 20 or 30 percent Ground granulated blast furnace slag (GGBS) is a hydraulic binder, like cement, which has been known and used for more than 150 years. It improves the quality and durability, and performance of concrete, and its production is virtually CO₂-free. Yet its many advantages in producing sustainable, high-quality concrete remain underappreciated and underused. The production of GGBS requires little energy as compared with the huge energy needed for the production of Portland cement.

The replacement of Portland cement with GGBS will lead to significant reduction of carbon dioxide gas emissions. GGBS is, hence, an environ mentally friendly construction material. It can be used to replace as much as 70-80 percent of the Portland cement used in concrete in case of mass concrete applications for reducing temperature differences and to avoid thermal cracking. GGBS concrete has better water impermeability properties as well as improved resistance to corrosion and sulphate attacks. As a result, the service life of a structure is enhanced and the maintenance cost reduced substantially. Durability is essential to the long service life of concrete. In practice, concrete will deteriorate over time. The factors driving this deterioration can be internal (e.g., alkali-silica reaction) or due to external aggressive environments (e.g. sulfate attack, or the effects of chlorides on reinforced concrete). GGBS substantially improves the ability of concrete to resist deterioration from all major threats to long service life. Requiring the use of GGBS is now established best practice where long service lives must be achieved, even in the most aggressive environments. GGBS concrete will even provide better fire resistance. GGBS has got distinctive advantages over Fly ash on many parameters as shown below.

Durability is essential to the long service life of concrete. In practice, concrete will deteriorate over time. The factors driving this deterioration can be internal (e.g., alkali-silica reaction) or due to external aggressive environments (e.g. sulphate attack, or the effects of chlorides on reinforced concrete). GGBS substantially improves the ability of concrete to resist deterioration from all major threats to long service life. Requiring the use of GGBS is now established best practice where long service lives must be achieved, even in the most aggressive environments. GGBS concrete will even provide better fire resistance. GGBS has got distinctive advantages over Fly ash on many parameters as shown below.

Eco friendly Sands from Steel Industries

Eco friendly sands are sands which are alternative to river sand, and being used predominantly today more in urban and semi urban areas. With restrictions on dredging of river sand, there has been a growing need in the construction industry for identification of alternative fine aggregates. Recently, crushed stone or manufactured sand (M-sand) have been used for replacing the natural sand. M-sand is crushed aggregates produced from hard granite stone which is cubically shaped with grounded edges, washed and graded with consistency to be used as a substitute of river sand. The progress in the building material research and identification of role of particle shape and gradation of fine aggregates has triggered the use of manufactured sand in the production of concrete. The complexity of construction and use of high strength concrete in large number of buildings is the prime mover along with the scarcity of river sand in many cities across India. As the natural sand is not replenished at the rate it is being used, the government has begun to promote manufactured sand. Concrete experts vouch that manufactured sand is not only a viable alternative to natural river sand, but is superior in many ways as it does not contain deleterious materials like silt and clay.

Table 1 - Comparison of various parameters of mineral admixtures under study

Quality comparision of River Sand with Slag Sand Testing of Slag sand suitability

Tests have been carried out at National council for cement and building materials for ascertaining the suit ability of Slag sand usage in concrete making

• The experimental investigations carried out on concrete of M20, M30 and M40 grades to evaluate effects of replacing fine aggregate with that of Slag sand at different percentages.
• It is found that the workability of concrete is improved by 20 percent by mixing rock sand and Slag sand in equal proportions (50 percent GBS + 50 percent Rock Sand) due to avail ability of more fine particles in Rock sand
• It is noticed that an increase in strength at an early age (three days) for the 50 percent granulated slag mix and similar strength to the control of at all other ages
• The total substitution of sand by granulated slag caused a decrease in strength at early ages and was almost reaching the control at 28 Days
• The studies concluded that the Compressive strength as well as Flexural strength of concrete improved 4.0 to 6.0 percent
• A positive effect on compressive strength of cement mortar up to 75 percent replacement level of GBS.
• However, with 100 percent replacement, the strength decreases margin ally compared to 100 percent natural sand

Slag sand can be used as an alternative to natural sand up to 75 percent

• The slag sand with similar chemical and physical characteristics is a better replacement for average natural aggregates / rock sand
• The substitution of natural aggregate with slag sand has positive impact on compressive, tensile and flexural strength
• Blasting of rocks and crushing them to produce sand, has serious environ mental implications. Rocks once depleted can never be replenished and do not grow again and hence are not renewable
• Hard rocks are essentially required for high strength and high performance concrete
• The slag sand could be effectively utilized as fine aggregate in all concrete applications as replacement of river sand and is designated as green building material

Use of Slag products in Road projects

Large quantities of natural materials are traditionally used in road construction. Uncontrolled depletion of natural, non-renewable resources leads to environmental destruction and distortion of natural balance. Concurrently, the world faces the problem of management of an increasing quantity of Industrial waste, so that linking the two problems leads to a simple solution: a growing and more diverse application of Industrial by-products such as slag and fly ash in road building and other areas of civil engineering alike. Application of slag as an alternative to standard materials in the world has been known for a number of years, and accordingly numerous research studies have been carried out in that area. Slag is used the most in asphalt mixtures, although its good properties are also used for application in other layers of pavement structure, primarily unbound base courses and embankment. An area of application that has not been studied extensively so far is the application of slag in stabilized mixtures for construction of base courses, which could be of great interest for domestic road construction. Due to very heavy traffic load, cement-bound base courses needs to be designed to increase the bearing capacity.