The ground granulated blast furnace slag (GGBFS) 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 iron ore, limestone and coke at a temperature about 1500 degree Celsius. The process is carried out in a blast furnace.
The formation of GGBFS is not direct. The by-product of iron manufacturing is a molten slag and molten iron. The molten slag consists of alumina and silica, also with the certain amount of oxides.
This slag is later granulated by cooling it. For this, it is allowed to pass through a high-pressure water get. This result in quenching of the particles which results in granules of size lesser than 5mm in diameter.
The main constituents of blast furnace slag are CaO, SiO2, Al2O3 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 cement. Now different methods can be employed to perform the main process called as the quenching.
Based on what method is employed, it can be known as palletized slag, foamed or expanded slag, GGBFS or air-cooled blast furnace slag (ACBFS).
- Composition of Ground Granulated Blast Furnace Slag (GGBFS)
- Physical Properties of Ground Granulated Blast Furnace Slag (GGBFS)
- Particle Size Distribution of Ground Granulated Blast Furnace Slag
- Using GGBFS cement
- Advantages of GGBFS in concrete
Composition of Ground Granulated Blast Furnace Slag (GGBFS)The difference in mineralogical composition in GGBFS compared to Portland cement is shown in the table below.
Physical Properties of Ground Granulated Blast Furnace Slag (GGBFS)Ground granulated blast furnace slag have a color nearly white in appearance. The figure below shows GGBFS and ordinary Portland cement, to clearly show the color difference between them. Hence the use of GGBFS in concrete manufacture would give a light and brighter color to concrete unlike the dark grey color of ordinary cement concrete structures. This is an added advantage of GGBFS in terms of aesthetics. The typical properties of GGBS are given in Table-2.
Table 2. Physical properties of GGBFS (As per Tasong et.al)
|Physical Form||Off white powder|
|Bulk density (kg/m3)||1200|
|Specific surface (m2/kg)||425 - 470|
Particle Size Distribution of Ground Granulated Blast Furnace SlagIt is observed that the particle size of GGBFS varies with the grinding techniques used during its manufacture. It is also observed that the product from ball mill has wide particles and narrow particles for the one grounded in airflow mill. Those grounded in vibro-mill have spherical shaped particles.
Using GGBFS cementIn the concrete manufacturing plant, the GGBFS can be added along with the Portland cement, water and aggregates. The normal ratio of the mixture remains the same. The studies show that the GGBFS can be replaced from 30 to 85 % of the cement weight. Most of the instances we replace 40 to 50%.
Advantages of GGBFS in concreteThe incorporation of ground granulated blast furnace slag in concrete manufacture gains many advantages which are mentioned below:
- GGBFS in concrete increases the strength and durability of the concrete structure.
- It reduces voids in concrete hence reducing permeability
- GGBFS gives a workable mix.
- It possesses good pumpable and compaction characteristics
- The structure made of GGBFS constituents help in increasing sulphate attack resistance.
- The penetration of chloride can be decreased.
- The heat of hydration is less compared to conventional mix hydration.
- The alkali-silica reaction is resisted highly.
- These make the concrete more chemically stable
- Gives good surface finish and improves aesthetics
- The color is more even and light.
- Lower chances of efflorescence
- The maintenance and repair cost of structures are reduced thus increasing the life cycle of concrete structures.
- Unlike cement, GGBFS does not produce carbon dioxide, sulphur dioxide or nitrogen oxides.