TYPES OF CEMENT
Cement of unique characteristics for desired performances in a given environment are being manufactured by changing the chemical composition of O P C or by using additives or by using different raw materials. some of the cements available in the market re as follows.
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| TYPES OF CEMENT |
Rapid Hardening Portland Cement (IS: 8041)
Has high lime content and can be obtained by increasing the content but is normally obtained from o p c clinker by finer grinding (3250 cm 2/g)> The basis of applications of rapid hardening cement (RHC) is hardening properties and heat emission rather than setting rate. This permits addition of a little more gypsum during manufacture to control the rate of setting. RHC attains same strength in one day which an ordinary cement may attain in 3 days. However ,it is subjected to large shrinkage and water requirement for workability is more. The cost of rapid hardening cement is about 10% more than ordinary cement. concrete made with RH C can be safely exposed to frost, since it matures more quickly.
Properties: Initial setting time 30 minutes ( minimum)
Final setting time 10 hours (maximum)
Compressive strength
1 day 16.0 N/ mm2
3 day 27.5 N/mm2
Uses: It is suitable for repair of roads and bridges and when load is applied in a short period of time .
High Alumina Cement (IS: 6452)
This is not of portal cement and is manufactured by fusing 40 per cent bauxite, 40 per cent lime, 15 per cent oxide with a little of farric should and silica, magnesia, etc. at a very high temperature. The alumina content should not be less than 32% . The resultant product is ground finely. The main cement ingredient is mono calcium aluminate CA which interacts with water and forms di calcium oc tahydrate hydroaluminate and aluminium oxide hydrate >
2(CaO.AL2O3.10H2O) + H2O = 2CaO.Al2O3.8H2O+2AL(OH)2
The dicalcium hydroaluminate gel consolidates and the hydration products crystallise. the rate of consolidation and crystallisation is high leading to a rapid gain of strength . since C3A is not present , the cement has good sulphate resistance.
Properties: It is not quick setting: initial setting time is 30 minutes, even up to 2 hours . the setting time should not exceed 600 minutes. It attain strength in 24 hours and has highly early strength. high heat of hydration and resistance to chemical attack. Compressive strength after one day is 30.0 n/mm2 and after 3 days it is 35.0 n/mm2. after setting and hardening . there is no free hydrated lime as in the case of ordinary portland cement. The fineness of the cement should not be less than 2250 cm2/g The cement not have expansion more than (5 mm ).
Uses: It is resistant to the action of fire, sea water, acidic water and sulphates and is used as refractory concrete in industries and is used widely for precasting . It should not be used in places where temperature exceeds (18 C .)
Super sulphated portland cement (IS: 6909)
Manufactured by intergrinding or intimately blending a mixture of granulated blast furnace slag not less than 70 per cent . calcium sulphate and small quantity of 33 grade portland cement. in this cement tricalcium aluminate which is susceptible to sulphate is limited to less than 3.5 per cent Sulphate resisting cement may also be produced by the addition of extra iron and oxide before firing this combines with alumina which would otherwise form C3A, instead forming C4 A F which is not affected by sulphates. It is used only in places wuth temperature below 40 C.
Water resistance of concrete form supersulphate portland cement is higher thatn that of commom portland cements because of the absence of free calcium oxide hydrate. In supersulphate portland cements the latter is bound by long into calcium hydroaluminates of low solubility and calcium hydro silicates of low basicity , whereas concrete form portland cement carry a large amount of free calcium oxide hydrate which may wash out and thus weaken them. Supersulphate from portland cement due to the fact that hydrosilicates of low basicity show greater tendency to deformation form humidity fluctuations and resist the combined action of water and frost less effectively.
Properties: It has low heat of hydration and is resistant to chemical attacks and is particular to sulphate. Compressive strength should be as follows:
72+ 1 hour 15 N/ mm2
168+ 2 hours 22 N /mm2
672+ 4 hours 30 N/ mm2
It should have a fineness of 4000 cm2/ g. the expansion of cement is limited to 5 mm . The initial setting time of the cement should not be less than 30 minutes. and the final setting time should not be more than 600 minutes.
Uses: Supersulphated portland cement is used for similar purpose as common portland cement. But owing to its higher water- resisting properties. it should be preferred in hydraulic engineering installations and also in consideration intented for services in moist media, R C C pipes in ground water. concrete structures in sulphate bearing soils,sewers carrying industrial effluents, concrete exposed to concentrated of weak mineral acids are some of the examples of this cement, This cement should not be used in constructions exposed to frequent freezing and having or moistening and drying conditions.
Sulphate resisting portland cement ( IS: 12330)
In this cement the amount of tricalcium aluminate is restricted to on acceptably . It should not be mistaken for super sulphated cement it is manufactured by grinding and intimately mixing together calcareous and argillaceous and/ or other silica, alumina ans iron oxide bearing materials. The materials are burnt to clinkering temperature . The resultant clinker ground to produce the cement. no material is added after burning except gypsum nd not more than one per cent of air- entraining agents are added.
Properties:The specific surface of the cement should not be less than 2250 cm2/g. The expansion of cement is limited to 10 mm and 0.8 percent, when tested by Le-chatelier method and autoclave test, respectively. The setting times are same as hat for ordinary Portland cement. The compresssive strength of the cubes should be a follows.
72+_1 hour \<10 N/mm2
168+_2 hours \<16 N/mm2
672+_4 hours \<33 N/mm2
It should have a fineness of 400 m2/kg . The expansion of cement is limited to 5 mm. The initial setting time of the cement should not be less than 30 mm and the final setting time should not be more than 600 mm.
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