Lecture-3: Lime stone desirable Characteristics for Cement Manufacture | Cement chemistry by Dr. K. Mohan.
Dr K Mohan is an internationally renowned and an acclaimed cement scientist. He is a former Director General of National Council for Cement and Building Materials (NCCBM).
He holds a Ph.D. degree in Cement Chemistry from University of Aberdeen, Scotland, U.K.
Desirable Characteristics of Limestone for Cement Manufacture:
• The average size of calcite crystal should preferably be less than 0.25 mm.
• Limestone should have low moisture content less than 5%.
• Limestone should have low compressive strength less than 1000 kg cm2.
• Presence of coarse grains of quartz and siliceous veins is undesirable.
Categorisation of Limestone:
• Based on NCBs norms, the limestone can be categorized to different grades based on the chemical composition of limestone.
-----------------------------------------------------------------------------------------------------------------
Limestone (%) CaO(%) SiO2(%)
High grade limestone 48 - 52 6 - 8
Cement grade limestone 44 - 48 8 - 12
Marginal grade limestone 40 - 44 12 - 16
Low grade limestone 36 - 40 16 - 20
--------------------------------------------------------------------------------------------------------------
Now I will discuss about argillaceous and corrective materials.
Argillaceous Materials
• Argillaceous materials are natural earthy substances.
• Argillaceous materials are:
• Clay (75-85% clay, 15 - 25% CaCO3)
• Shale (95-100% clay, 0- 5% CaCO3)
• Calcareous marl (25-35% clay, 65- 75% CaCO3)
• Marl (35-65% clay, 35- 65% CaCO3)
• Marly clay (75-85% clay, 15- 25% CaCO3)
• Clay and shale are mainly used in cement manufacture.
• They are source of silica (SiO2) and alumina (Al2O3).
• Clays are chemically hydrous aluminosilicates, like kaolinite Al2O3.2SiO2.2H2O and montmorillonite Al2O3.4SiO2.H2O+nH2O.
• The order of reactivity of silica bearing materials is:
Quartz - chalcedony - opal -cristobalite and tridymite - silica from feldspar - silica from mica - silica from clay minerals - silica from glassy slags.
Corrective Materials:
• If it is not possible to obtain the desired chemical composition of raw mix just with the calcareous and argillaceous materials components, it will be necessary to add relatively small quantity of corrective materials to the mix.
• Corrective materials are added to compensate for the deficiency of SiO2, Al2O3 and Fe2O3.
• Some of the limestone may not require any argillaceous materials but may need only a small quantity of corrective materials.
• To compensate for the deficiency of silica (SiO2) sand, sandstone and high silica clay are used as corrective materials.
• To compensate for the deficiency of alumina (Al2O3) bauxite is used as corrective materials.
• To compensate for the deficiency of iron oxide (Fe2O3) iron oxide is used as corrective materials.
• To compensate for the deficiency ofSiO2 and Fe2O3 laterite is used as corrective materials.
• To compensate for the deficiency of Al2O3 and SiO2 aluminous laterite is used as corrective materials.
• Sometimes more than one corrective materials is used to get the desired chemical composition of raw mix.
Usage of various wastes as cement raw materials:
• Use of industrial and agricultural wastes in the production of cement is gaining ground.
• The degree of their usefulness as a substitute raw material primarily depends on economic considerations as well as their chemical composition.
• These materials can be categorised in three categories:
• Materials replacing calcareous components
• Materials replacing siliceous components
• Materials replacing argillaceous components
• They replace partially or fully the above components of the raw mix based upon their chemical composition and compatibility with the replacing materials.
Materials replacing calcareous components
• Marginal grade limestone
• Cement kiln dust
• Carbonate sludge
• Carbide sludge
• Blast furnace slag
• Oil shale residue
• Phosphorous furnace slag
Materials replacing siliceous components
• Foundry sand
• Sand washings
• Rice husk ash
• Ore rejects and mineral tailings
Materials replacing argillaceous components
• Catalyst fines
• Fly ash
• High carbon fly ash
• Bottom ash / Pond ash
• Red mud
• Basalt rock
#Cementchemistry #Limestone #LimestoneCharacteristics #cementmanufacturingprocess #Cementplant
Негізгі бет Lime stone desirable Characteristics for Cement Manufacture | Cement chemistry
Пікірлер: 5