What is GGBS? Its Advantages and Disadvantages

What is Ground Granulated Blast Furnace Slag (GGBS)?

The ground granulated blast furnace slag (GGBS) is a by-product of iron manufacturing which when added to concrete improves its properties such as workability, strength, and durability.

This material is obtained by the heating of the iron ore, limestone, and coke at a temperature of about 1500^oC. The process is carried out in a blast furnace.

The formation of GGBS is not direct. The by-product of iron manufacturing is molten iron and molten slag. The molten slag consists of silica and alumina, also with a certain amount of oxides.

The slag is later granulated by cooling it. For this, it is allowed to pass through high-pressure water get. This results in the quenching of the particles which result in granules of size lesser than 5mm in diameter.

The main constituents of blast furnace slag are Cao, SiO₂, Al₂O_3, and MgO. These are the minerals that are found in most of the cementitious substances.

The particles are further dried and ground in a rotating ball mill to form a fine powder, known as ground granulated blast furnace slag. Now different methods can be employed to perform the main process called the quenching.

Based on what method is employed, it can be known as palletized slag, foamed or expanded slag, GGBS, or air-cooled blast furnace slag (ACBFS).

The following table is shown the physical properties of GGBS and ordinary Portland cement.

Sr. No	Properties	GGBS	OPC
1	Color	While	Gray
2	Specific Gravity	2.9	3.15
3	Bulk Density	1200 Kg/m³	1470 Kg/m³
4	Fineness	350 m²/kg	205 m²/kg

How to Use Ground Granulated Blast Furnace Slag (GGBS) in Concrete

The blast furnace slag is mainly used in India for manufacturing slag cement. There are two types of methods for making Blast Furnace Slag Cement. In the first method blast furnace slag is interground with the cement clinker along with gypsum. In the second method blast furnace slag is separately ground mix with cement. Also, GGBS can be used as the direct replacement of ordinary Portland cement, on a one-to-one basis by weight. Replacement level varies between 30% to 80% of cement. Typically in India, many RMC companies are used GGBS by adding it to batching plants along with the ordinary Portland cement, aggregates, and water. The ratio of aggregates and water to cementitious material in the mix remains unchanged. The use of GGBS in addition to Portland cement in concrete in Europe is covered in the concrete standard EN 206:2013 and in Indian Standard 12089:1987 gives the specifications for the manufacturing of Portland slag cement.

Application of Ground Granulated Blast Furnace Slag (GGBS)

GGBS is used to make durable concrete structure in combination with ordinary Portland cement and/or the other pozzolanic materials like fly ash, silica fume, usage of GGBS along with OPC in concrete is recommended in BS 6699:1986, ASTM C989:1982, IS 456:2000, and GGBS to OPC in the range of 25%-70% shall be added to manufacture Portland Slag Cement as per Indian Standard 455:1989 GGBS can be used for following structures

All types of residential and commercial and industrial complexes.
Dams and other mass concreting works.
Water retaining structures.
Concrete roads and flyovers.
Ideal for use in marine constructions.
Pre-cast concrete products.
Foundation and piles construction.
Increased flexibility to meet individual requirements in Ready Mix Concrete.

Advantages of Ground Granulated Blast Furnace Slag (GGBS) in Concrete

The incorporation of ground granulated blast furnace slag (GGBS) in concrete manufacture gains many advantages which are mentioned below.

Ground granulated blast furnace slag (GGBS) in concrete increases the strength and durability of the concrete structure.
It reduces voids in concrete hence decreasing permeability.
Ground granulated blast furnace slag (GGBS) gives a workable mix.
It possesses good pumpable and compaction characteristics.
The structure made of ground granulated blast furnace slag (GGBS) constituents helps in increasing sulfate attack resistance.
The penetration of chloride can be decreased.
The heat of hydration is less compared to conventional mixed hydration.
The alkali-silica reaction is resisted highly.
These make the concrete more chemically stable.
Gives a good surface finish and improves aesthetics.
The color is more even and light.
Lower chances of efflorescence.
The maintenance and repair cost of structures is reduced thus increasing the life cycle of concrete structures.
Unlike cement, Ground granulated blast furnace slag (GGBS) does not produce carbon dioxide, sulfur dioxide, or nitrogen oxides.

Disadvantages of Ground Granulated Blast Furnace Slag (GGBS) in Concrete

Additional quality control costs.
Slow and small hydration heat, not suitable in precast factories or during winter concreting.
Faster carbonation rate decreased service life span due to reinforcement corrosion.
Carbonation changes pore structure unfavorably with respect to durability.
Permeability increases at a later age (carbonation).
The pore structure becomes more coarse.
Salt-freeze durability deteriorates.
Inferior workability and cohesion in fresh concrete.

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