In India, Bureau of Indian Standards (BIS) has broadly classified cement into three categories:
- Ordinary Portland Cement (OPC) 33, 43, 53 grade
- Blended Cement – Portland Pozzolana Cement (PPC) and Portland Slag Cement (PSC)
- Special Cement – White cement, Sulphate Resisting Portland Cement (SRC), Quick setting Cement, Oil well Cement, etc.
The two principal raw materials used for manufacturing the Portland cement are calcareous materials such as limestone, chalk or marl and argillaceous materials such as clay and shale.
OPC – Ordinary Portland Cement is common cement that can be used for all types of general works. It’s more suitable where very high early strength is required such as tall chimneys, pre stressed concrete girders, large diameter concrete pipes. OPC generates lot of heat and its resistance to harmful salts is very low.
Grade of cement is nothing but its compressive strength at 28 days. Higher the grade higher will be its compressive strength.
Blended cements are aiming to impart durability (long life) to structures apart from giving compressive strength. Blended cements have more technical benefits in comparison to OPC such as improved workability, cohesion, lower heat of hydration, better resistance to aggressive environment and harmful salts, higher ultimate strength.
Bureau of Indian Standards (BIS) has specified two types of blended cements –PPC and PSC. PPC means Portland Pozzolana Cement wherein Fly ash – a by-product from thermal power plants is used. PSC means Portland Slag Cement wherein Slag – a by-product from steel plant is used.
GGBS (also known as GGBS or GGBFS) is manufactured from blast furnace slag, a by-product from the manufacture of iron. It is obtained by quenching molten iron blast furnace slag immediately in water or stream, to produce a glassy granular product that is then dried and ground into a fine powder (GGBS). It is an excellent binder to produce high performance cement and concrete.
The production technologies of GGBS are mainly the following three:
- The traditional ball mill
- High Pressure Roller Press
- Vertical Roller Mill
As compared to the traditional ball mill, the GGBS produced from the modern vertical mill has the following characteristics:
- High fineness, good particle size distribution, the GGBS activeness could be fully developed
- High activity index, small variation in the quality
- The product has low energy consumption, high production efficiency
The stability of raw material: The raw material for GGBS, raw slag, is usually obtained from the predetermined steel plant, which ensures the stability of the raw material.
The stability of the chemical compositions: Due to the stringent quality control in producing iron and steel, the steel plant imposes strict control in the usage ratio of all materials in the iron production process. Therefore, the stability of the chemical compositions of its by-product – raw slag is under control.
With the use of the state-of-art vertical mill installed by JSW to process raw slag, the fineness of GGBS can be controlled, and therefore consistency in quality is attainable.
PFA that is collected using average techniques usually does not have the above-mentioned characteristics, and therefore presents a higher fluctuation in quality.
As per IS 455-1989, 25-70% of slag can be mixed. Higher the dosage of slag better the benefits are.
When water is mixed with cement, the paste formed remains plastic for a certain time. During this period, it is possible to mould it into any desired shape. As the reaction between water and cement continues, the paste loses its plasticity. This early period in the hardening of cement is referred to as Setting of cement. The BIS has specified the Initial Setting time should not be less than 30 minutes and Final Setting time should not exceed 600 minutes.
No. Setting time of concrete and cement are different. The setting time of concrete / mortar is not only dependent on setting time of cement but also depends on mix proportion, ambient temperature, wind velocity and amount of water in the mix.
The construction / working practice is same irrespective of cement.
PSC has the advantages both in the fresh and hardened properties of concrete.
- Improved workability and cohesiveness of the mix.
- Reduced heat of hydration and thermal cracks.
- Reduced plastic shrinkage cracks.
- Smooth surface finish.
- Increased resistance to chlorides, sulphates, carbon dioxide and such other harmful salts.
- Higher ultimate compressive and flexural strength.
- Higher impermeability.
- Increased resistance to Alkali – silica reaction
- Durable and Sustainable Construction.
Production of slag cement creates a value-added product from a material—blast furnace slag.It also reduces air emissions at steel plants through the granulation process. Use of slag cement in concrete reduces the environmental impact of concrete by:
- Replacing the Portland cement by Slag helps in reducing CO2 emissions and in conserving non-renewable resources of lime stone.
- Reducing energy consumption, since a ton of slag cement requires nearly 90% less energy to produce than a ton of Portland cement.
- Reducing the amount of virgin material extracted to make concrete.
- Reducing the “urban heat island” effect by making concrete lighter in color thus reflecting more light and cooling structures and pavements with exposed concrete.