Presentation on theme: " In the most general sense of the word, a cement is a binder, a substance which sets and hardens independently, and can bind other materials together."— Presentation transcript:
In the most general sense of the word, a cement is a binder, a substance which sets and hardens independently, and can bind other materials together. The word "cement" traces to the Romans, who used the term "opus caementicium" to describe masonry which resembled concrete and was made from crushed rock with burnt lime as binder.Romans lime The most important use of cement is the production of mortar and concrete—the bonding of natural or artificial aggregates to form a strong building material which is durable in the face of normal environmental effects.mortar concrete Cements that are used for construction fall into two main categories based on cement properties, hydraulic or non-hydraulic. In addition to the two main cement forms, there are several different forms of hydraulic cement. Of the many varieties of hydraulic cement, the most commonly used cement today is Portland cement.
Hydraulic cement An inorganic material or a mixture of inorganic materials that sets and develops strength by chemical reaction with water by formation of hydrates and is capable of doing so under water. Non-hydraulic cement Non-hydraulic cement is cement which cannot harden while in contact with water, as opposed to hydraulic cement which can. Non-hydraulic cements are created using materials such as non- hydraulic lime and gypsum plasters, and oxychloride, which has liquid properties. After non-hydraulic cement is utilized in construction, it must be kept dry in order to gain strength and hold the structure. When non-hydraulic cement is used in mortars, those mortars can set only by drying out, and therefore gain strength very slowly. Due to the difficulties associated with waiting long periods for setting and drying, non-hydraulic cement is rarely utilized in modern times.
In addition to the two main forms of cement which exist, hydraulic and non- hydraulic, there are also several types of hydraulic cements that can be made and used in construction. The main form of cement used in construction worldwide today is the hydraulic cement called Portland cement. Portland cement is a type of hydraulic cement made by heating a limestone and clay mixture in a kiln and pulverizing the materials. It is a fine, grey or white powder that is made by grinding Portland cement clinker, a limited amount of calcium sulfate which controls the set time, with other minor constituents. Portland cement is the most common type of cement in general usage in many parts of the world. The cement is used as the basic ingredient of concrete, mortar, stucco and most non specialty grout. Invented in the 19th century, Portland cement has become the staple form of cement produced and used worldwide. All references to cement worldwide refer to Portland cement, as it constitutes virtually all cement produced.
The essential raw ingredients of Portland cement are limestone, 75 to 77%, and alumina (A12O3) and silica (SiO2) 20 to 25%. The alumina and silica are commonly found combined as * clay, which is a silicate of aluminum (Al2O32SiO2) + 2H2O.. There are accidental ingredients usually amounting to about 5%, but these must not include over 3% of magnesia (MgO).
Quarrying Two types of materials are necessary for the production of cement: one rich in calcium or calcareous materials such as limestone, chalk, etc., and one that is rich in silica or argillaceous materials such as clay. Extensive quarry drilling and analysis are being undertaken to reduce the variability of the raw material quality. The quality check that starts from the quarry ensures optimization in the utilization of the reserves. Limestone and clay are either scraped or blasted from the quarry and then transported to the crusher. Crushing The crusher is responsible for the primary size reduction of the quarried materials. Boulders as big as 1 meter are being crushed to material sizes less than 80 mm.
Pre-blending The crushed materials pass through an on-line analyzer to determine the pile composition. A stacker is then used to create different piles of materials and to reduce variation in material beds. Raw grinding and blending A belt conveyor transports the pre-blended piles into individual bins where a weighing feeder proportions it according to the type of clinker to be produced. The materials are then ground into the desired fineness by the raw mill equipment. The powdered raw meal is then transported into a continuous blending storage silo where variations are further reduced by mixing using aeration. Finish grinding From the clinker silo, clinker is transferred to the clinker bin. It passes through the weighing feeder, which regulates its flow in proportion with the additive materials. At this stage, gypsum is added to the clinker and then fed to the finish grinding mills. Gypsum serves as a retarder in the too rapid setting or hardening of cement. Either the mixture of clinker and gypsum for Type-1 cement or the mixture of clinker, gypsum and pozzolan material for Type-P cement is pulverized in a closed circuit system in the finish mills to the desired fineness. Cement is now piped to cement silos. Packing and distribution The cement from the cement silos are packed into bags by rotary packers or loaded as bulk and are distributed either
Cement paste setting time is affected by a number of items including: cement fineness, water-cement ratio, chemical content (especially gypsum content) and admixtures. Setting tests are used to characterize how a particular cement paste sets. For construction purposes, the initial set must not be too soon and the final set must not be too late. Additionally, setting times can give some indication of whether or not a cement is undergoing normal hydrationcement finenesschemical contenthydration
Initial set. Occurs when the paste begins to stiffen considerably. Final set. Occurs when the cement has hardened to the point at which it can sustain some load. These particular times are just arbitrary points used to characterize cement, they do not have any fundamental chemical significance Test MethodSet TypeTime Specification Vicat Initial45 minutes Final375 minutes Gillmore Initial60 minutes Final 600 minutes The Vicat needle test is more common and tends to give shorter times than the Gillmore needle test.
The Rapid Hardening Portland Cement's better strength performance is achieved by increasing the refinement of the product. This is the reason that its use is increasing in India. Rapid Hardening Portland Cement is manufactured by fusing together limestone (which has been finely grounded) and shale, at extremely high temperatures to produce cement clinker. To this cement clinker, gypsum is added in small quantities and then finely grounded to produce Rapid Hardening Portland Cement. It is usually manufactured using the dry process technology. Rapid Hardening Portland Cement is used in concrete masonry manufacture, repair work which is urgent, concreting in cold weather, and in pre-cast production of concrete. Rapid Hardening Portland Cement has proved to be a boon in the places where quick repairs are required such as airfield and highway pavements, marine structures, and bridge decks.
The raw materials required for the manufacture of Rapid Hardening Portland Cement are: Limestone I.Shale II.Gypsum III.Coke The major companies producing Rapid Hardening Portland Cement in India are: I.ACC II.Gujarat Ambuja III.J K Cement IV.Grasim Industries V.Indian Cement Ltd.
What is OPC Cement? OPC means Ordinary Portland Cement which contains mixture of Portland clinker and Gypsum ground to a very fine powder. What is PPC Cement? PPC means Portland Pozzolana Cement. It is manufactured by blending a mixture of Ordinary Portland cement and Pozzolana materials such as Fly Ash, in proportions not less than 15% and not more than 35% by weight of cement. The fineness of PPC will be greater than OPC. Difference between OPC and PPC Cement Addition of Pozzolanic material such as fly ash in the cement manufacture by 15% to 35% is the only difference between OPC and PPC. Duration of curing for OPC and PPC Duration for curing is same for both OPC and PPC. But the water cement ratio may be slightly varied. As the cement is attaining full strength at 28 days, concretes made out of both the cements are to be cured for 28 days.
What are the setting time for OPC and PPC? Same for both OPC and PPC. i.e. initial setting time 30 minutes and final setting time 600 Minutes. (10 hours) Preferable constructions by OPC and PPC OPC: OPC is categorized as 33 Grade, 43 Grade and 53 Grade. It is preferably used in Defence Services, Railway Sleeper making and in lean concrete structures. PPC: PPC is having better resistance to Sulphate attack and hence it is preferably used in Sea Shore, Dam constructions and in the earth work concreting to neutralize corrosion effect of soil and water under the earth's crest. Due to higher fineness, mostly it is used in plastering work for smooth finishing.
Ordinary Portland cement (opc) Opc is available in 2 grades (i) 53 grade (ii) 43 grade There is no grade 4 ppc cement Ppc- 1.Nowadays it is used 4 each and every purposes.eg: bridge, buildings construction, road construction, etc 2. Setting time- slow 3. Its strength increases day by day. Therefore there is no complaint about ppc cement. 4. durability more than opc. Opc- 1.It is used 4 building superstructure, dam, road furniture, panels, beam, Commercial Buildings, Industrial Constructions, Multi-storied complexes, Cement concrete, roads, Heavy Duty Floors etc. 2. Setting time faster than ppc 3. Its strength does not increases day by day. What it attend at 28 day, remains the same throughout.. 4. durability not more than ppc.
The rate of all the standard cements available is approximately same. The rate of Opc and ppc is the same. The cost of one bag of cement is Rs 275. dealer ------------------ retailer------------------- consumer Rs 232 +12.50% tax = Rs. 262