CEMENT
Cement may be a binder, a substance that sets and hardens and may bind other materials together. cement won't set in wet conditions or underwater, rather it sets because it dries and reacts with CO2 within the air. The reaction leads to hydrates that aren't very water-soluble then are quite durable in water and safe from chemical attack. this enables setting in wet condition or underwater and further protects the hardened material from chemical attack (e.g., Portland cement).
Types of Cements
Many types of cements are available in markets with different compositions and to be used in several environmental conditions and specialized applications. an inventory of some commonly used cement is described during this section:
Ordinary hydraulic cement
Ordinary hydraulic cement is that the commonest sort of cement generally use round the world. This cement is formed by heating limestone (calcium carbonate) with small quantities of other materials (such as clay) to 1450°C during a kiln, during a process referred to as calcination, whereby a molecule of CO2 is liberated from the carbonate to make quicklime , or quicklime, which is then blended with the opposite materials that are included within the mix. The resulting hard substance, called 'clinker', is then ground with alittle amount of gypsum into a powder to form 'Ordinary Portland Cement'(often mentioned as OPC). hydraulic cement may be a basic ingredient of concrete, mortar and most non-specialty grout. the foremost common use for hydraulic cement is within the production of concrete. Concrete may be a material consisting of aggregate (gravel and sand), cement, and water. As a construction material, concrete are often cast in almost any shape desired, and once hardened, can become a structural (load bearing) element. hydraulic cement could also be grey or white.
- this sort of cement use in construction when there's no exposure to sulphates within the soil or spring water .
- Lime saturation Factor is restricted between i.e. 0.66 to 1.02.
- Free lime-cause the Cement to be unsound.
- Percentage of (AL2O3/Fe2O3) isn't but 0.66.
- Insoluble residue less than 1.5%.
- Percentage of SO3 limited by 2.5% when C3A < 7% and less than 3% when C3A >7%.
- Loss of ignition -4%(max)
- Percentage of Mg0-5% (max.)
- Fineness -not but 2250 cm2/g.
Rapid hardening hydraulic cement
• it's firmer than Ordinary hydraulic cement
• It contains more C3S are less C2S than the standard hydraulic cement .
• Its 3 days strength is same as 7 days strength of ordinary hydraulic cement .
Low heat hydraulic cement
• Heat generated in ordinary hydraulic cement at the top of 3days 80 cal/gm. While in low heat cement it's about 50cal/gm of cement.
• it's low percentage of C3A and comparatively more C2S and fewer C3S than O.P. Cement.
• Reduce and delay the warmth of hydration. British standard ( B S. 1370 : 1974 ) limit the warmth of hydration of this cement.
Sulphate resisting hydraulic cement
• Firmer than ordinary pot land cement.
• Sulphate forms the sulpha-aluminates which have expensive properties then causes disintegration of concrete.
Sulphate resisting hydraulic cement
• For this cement, the silage as obtained from furnace is employed.
• Its strength in youth is a smaller amount and hence it required longer curing period. It proves to be economical as slag, which may be a waste , is employed in its manufactures.
Pozzolanic cement
• As per Indian standard, the proportions of Pozzolana could also be 10 to 25 you interested by weight. e.2. Burnt clay, shale, Fly ash.
• This Cement has higher resistance to chemical agencies and to sea water due to absence of lime.
• It evolves less heat and initial strength is a smaller amount but final strength is 28 days onward adequate to ordinary hydraulic cement .
• It possesses less resistance to the erosion and weathering action.
• It imparts higher degree of water tightness and it's cheap.
White hydraulic cement
• Grey colour of O.P. cement is thanks to presence of Iron Oxide. Hence in White Cement Fe,,O, is restricted to I Chronicles . Sodium Alumina Ferrite (Crinoline) NavAlF6 is added to act as flux within the absence of Iron-Oxide. •:
• it's quick drying, possesses high strength and has superior aesthetic values and it also cost lee than ordinary Cement due to specific requirements imposed upon the raw materials and therefore the manufacturing process.
• White Cement are utilized in Swimming pools, for painting garden furniture, moulding sculptures and statues etc.
Coloured Portland
• The Cement of desired colour could also be obtained by mixing mineral pigments with ordinary Cement.
• the quantity of coloring material may vary from 5 to 10 percent. If this percentage exceeds 10percent, the strength of cements is affected.
• The iron Oxide in several proportions gives brown, red or yellow colour.
Expansive cement
• this sort of cement is produced by adding an expanding medium like sulphoaluminate and a stabilising agent to the standard cement.
• The expanding cement is employed for the development of water retaining structures and for repairing the damaged concrete surfaces.
High alumina cement
• This cement is produced by grilling clinkers formed by calcining bauxite and lime. It can stand high temper lures.
• If evolves great heat during setting. it's therefore not suffering from frost.
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