In this article, we will be discussing Blast Furnace Slag Cement, which is a mixture of Ordinary Portland Cement and fine granulated blast furnace slag. This slag is a by-product of the steel manufacturing process, and its percentage in the cement mixture is below 70%. Ground Granulated Blast Furnace Slag Cement (GGBFS) is a type of slag cement that is made up of fine glassy granules with cementitious properties.
The production process of Blast Furnace Slag Cement involves combining Ordinary Portland Cement with fine granulated blast furnace slag. This slag is obtained during the manufacturing process of steel, and it is added to the cement mixture in a percentage that is less than 70% of the total cement content. GGBFS is produced by grinding the blast furnace slag into fine granules, which results in a cementitious product with unique properties.
The constituents of Blast Furnace Slag Cement are Ordinary Portland Cement and fine granulated blast furnace slag. The slag used in this cement is a by-product of the steel manufacturing process and is often referred to as GGBFS. The percentage of slag used in the mixture is typically below 70% of the total cement content.
Blast Furnace Slag Cement has many properties that make it a popular choice in the construction industry. These properties include low heat of hydration, high ultimate strength, excellent durability, and good resistance to sulfate and chloride attack. GGBFS is also known for its workability and can be used in a variety of applications, including concrete, mortar, and grout.
There are many advantages of using Blast Furnace Slag Cement in construction projects. One of the main advantages is that it is an eco-friendly alternative to traditional cement. Additionally, it has excellent durability, which means that structures built using this cement have a longer lifespan. It is also known to reduce the risk of alkali-silica reaction, which can cause cracks and other forms of damage to concrete structures.
However, there are also some disadvantages of using Blast Furnace Slag Cement. One of the main disadvantages is that it has a slower rate of strength gain compared to Ordinary Portland Cement. This means that structures built using this cement may take longer to achieve their full strength. Additionally, it can be more expensive than traditional cement, which may be a concern for some construction projects.
Manufacture and Constituents of Blast-Furnace Slag Cement
Fig 1: Extraction of molten Slag from Blast Furnace.
GGBFS, which stands for Ground Granulated Blast Furnace Slag, is a by-product obtained during the extraction of iron from its ore using a process called blast furnace. The blast furnace process involves the separation of the slag from the iron ore. Once separated, the slag is cooled down slowly, which leads to the formation of a nonreactive crystalline material known as GGBFS.
The chemical composition of GGBFS is made up of various constituents, which are listed in the table provided. The by-product is often used in the construction industry as a cement replacement material due to its beneficial properties such as high strength, low permeability, and durability. GGBFS is also considered an environmentally friendly material as it reduces the amount of waste generated during the iron extraction process and reduces the amount of carbon dioxide emitted during the production of cement.
Overall, GGBFS is a valuable by-product obtained during the extraction of iron using blast furnace technology. Its usefulness as a cement replacement material makes it an important component in the construction industry, while its environmental benefits make it an attractive alternative to traditional cement materials.
Table 1: Constituents of the Ground Granulated Blast Furnace Slag
| Constituents | % by mass |
| SiO2 | 27-39% |
| Al2O3 | 8- 20% |
| CaO | 38-50% |
| MgO | <10% |
The slag is finely ground to a texture similar to that of cement, after which it is mixed in different proportions depending on the specific requirements of the construction project. The amount of ground granulated blast furnace slag (GGBFS) added can vary, as it is dependent on the type of construction being carried out. Different percentages of GGBFS are used for different types of construction projects.
Table 2: Proportion of slag percentage for different applications.
| Application in Type of Construction | Slag Proportion in % |
| General construction | 20-40 |
| Reduction of heat hydration | 50-80 |
| Structures exposed to chloride attack | 50-81 |
| Structures exposed to sulfate attack | 50-82 |
| Marine structures | 60-80 |
Properties of Blast-Furnace Slag Cement
Table 3: Properties of Blast-Furnace Slag Cement
| Properties | Values |
| Density (g/cm3) | 3.04 |
| Specific Surface Area (cm2/g) | 4050 |
| Setting Time | |
| Initial Setting | 60min |
| Final Setting | 600min |
| Compressive Strength (N/mm2) | |
| 3days | 23.5 |
| 7days | 36.1 |
| 28days | 62.4 |
| Chemical Composition (%) | |
| Magnesium oxide | 2.88 |
| Sulphur tri oxide | 2.19 |
| Ignition loss | 1.47 |
Uses of Blast-Furnace Slag Cement
The material being referred to here is a type of cement that is commonly used in ready mix concrete plants. It is particularly useful for structures that are meant to retain water, such as retaining walls, ports, and tunnels, as it improves impermeability. Additionally, this type of cement is often used in mass concreting works for projects like dams and foundations that require a low heat of hydration. Finally, it is often used in areas that are susceptible to chloride and sulphate attacks, such as sub-structures, bored piles, pre-cast piles, and marine structures.
Fig 2: Use of Slag cement in Sulphate and Chloride attack places.
Advantages of Blast-Furnace Slag Cement
The use of ground granulated blast furnace slag (GGBFS) in concrete results in lower initial strength compared to conventional concrete, but it can achieve equal or higher ultimate strength. This is due to the fine grinding of GGBFS, which allows it to efficiently fill pores and result in high workability and low bleeding.
Moreover, GGBFS has good resistance to sulphate and chloride attack, and the risk of alkali-silica reaction with aggregates is lower. The slow hydration process of GGBFS leads to greater durability and reduced permeability due to its fineness. Additionally, since the hydration process of GGBFS is exothermic, the generation of heat of hydration is slow, making it suitable for use in areas where thermal cracking is anticipated.
The use of GGBFS in concrete also results in a lighter color, as the color of GGBFS is white, compared to conventional cement. Furthermore, the production cost of this cement is lower when compared to ordinary Portland cement (OPC). Additionally, the slow hydration process of GGBFS results in a longer slump retention and initial setting time.
Fig 3: Use of Slag cement in Canal Lining.
Disadvantages of Blast-Furnace Slag Cement
The cement with low initial strength is not suitable for use in reinforced concrete construction because it lacks the necessary strength required for such projects. This type of cement takes a longer time to gain its full strength, making it less ideal for emergency or repair works where time is of the essence. It is crucial to select the right type of cement for each construction project to ensure its safety and durability. Cement with a longer initial setting time may be more appropriate for certain applications, but for reinforced concrete construction, it is essential to choose cement with high initial strength. Similarly, in cases where repairs or emergency works are needed, cement with a faster setting time should be used to avoid any delays or safety issues. Overall, selecting the appropriate type of cement is essential for ensuring the success and safety of any construction project.