What is Ground Granulated Blast Furnace Slag (GGBS)
The ground granulated blast furnace slag (GGBS) is the waste slag produced when smelting pig iron in steel plants. In the process of blast furnace ironmaking, in addition to iron ore and dye (coke), an appropriate amount of limestone and dolomite should be added as a flux in order to reduce the melting temperature. The calcium oxide and magnesium oxide obtained from their decomposition in the blast furnace and waste ore in iron ore, as well as the ash in coke are melted in phases to form a melt with silicate and aluminate as the main components. After quenching and granulation, the slag will be ground in the grinding station to become GGBS powders.
The ground granulated blast furnace slag (GGBS) is mainly amorphous vitreous structure and contains a small number of crystalline minerals. Due to the large content of glass in slag, the structure is in a high-energy state, unstable and has great potential activity, so it needs to be ground to give full play to its potential activity. It is a kind of high-quality concrete admixture.
The Main Application of GGBS
The ground granulated blast furnace slag (GGBS) is usually added to cement as an admixture to produce blast furnace slag cement. The GGBS powder can significantly improve the comprehensive properties of concrete and cement products by replacing the amount of cement in them for various purposes.
Advantages of Slag Cement
The advantages of adding slag powder to cement mainly include:
1) It can greatly improve the strength of cement concrete and prepare ultra-high-strength cement concrete;
2) It can effectively inhibit the alkali-aggregate reaction performance of cement concrete and improve the durability of cement concrete;
3) It can effectively improve the anti seawater erosion performance of cement concrete, especially suitable for anti seawater engineering;
4) It can significantly reduce the bleeding of cement concrete and improve the workability of concrete;
5) It can significantly improve the compactness and impermeability of cement concrete.
Influence of Components in Slag on Cement
The chemical composition of slag produced by different steel plants varies greatly, and the slag discharged by the same steel plant in different periods is also sometimes different. It is necessary to test the chemical composition of slag by batch before applying them to cement production. The influence of oxides in slag on cement quality is as follows:
1) Calcium Oxide (CaO)
Calcium oxide is an alkaline oxide and is the main component of slag, accounting for about 40%. It is synthesized into active minerals in slag, such as dicalcium silicate. Calcium oxide is the main factor determining the activity of slag. Therefore, the higher its content, the greater the activity of slag.
2) Alumina (Al2O3)
Alumina is an acidic oxide and a good active component in slag. It forms minerals such as aluminate or calcium aluminosilicate in slag and forms glass after water quenching in the molten state. The content of alumina in slag is generally 5% ~ 15%, and some are as high as 30%; The higher its content, the greater the activity of slag, and the more suitable it is to be added to cement.
3) Silicon Oxide (SiO2)
Silicon oxide is a kind of slightly acidic oxide, and its content in slag is high, generally 30% ~ 40%. Compared with calcium oxide and alumina, its content is too much, resulting in the formation of low activity and low calcium minerals, and even the existence of free silica, which reduces the activity of slag.
4) Magnesium Oxide (MgO)
The activity of magnesium oxide is lower than that of calcium oxide. Its content in slag generally fluctuates between 1% ~ 18%. It is a stable compound or glass in slag and will not produce poor stability. Magnesia can increase the fluidity of molten minerals and help to improve the granulation quality and activity of slag. Therefore, magnesium oxide is generally regarded as the active component of slag.
5) Manganese Oxide (MnO)
Manganese oxide is harmless to the stability of cement, but it has a certain effect on the activity of slag. Its content should generally be limited to 1% ~ 3%. If it exceeds 4% ~ 5%, the activity of slag will decrease significantly. The content of alumina in ferromanganese granulated blast furnace slag can be relaxed to 15%, which is because the content of alumina in ferromanganese slag is high and the content of silicon oxide is low.
6) Sulphur (S)
The high sulfur content in slag will lead to the loss of cement strength. However, calcium sulfide reacts with water to form calcium hydroxide, which plays an alkaline excitation role. The existence of manganese oxide not only makes sulfide form harmful manganese sulfide, but also reduces the content of calcium sulfide accordingly.
7) Titanium Dioxide (TiO2)
Titanium in slag exists in the form of ilmenite, which will reduce the activity of slag. China’s national standards stipulate that the content of titanium dioxide in slag shall not exceed 10%.
8) Ferric Oxide (Fe2O3) and Ferrous Oxide (FeO)
The content of ferric oxide and ferrous oxide in slag is very small, generally, 1% ~ 3%, which has little effect on the activity of slag.