Types of Cement
- Ordinary Portland Cement
- Rapid Hardening Cement
- Extra Rapid Hardening Cement
- Sulphate Resisting Cement
- Portland Slag Cement
- Quick Setting Cement
- Super Sulphated Cement
- Low Heat Cement
- Portland Pozzolana Cement
- Air-Entraining Cement
- Coloured Cement (White Cement)
- Hydrophobic cement
- Masonry Cement
- Expansive Cement
- IRS-T 40 Special Grade Cement
- Oil-Well Cement
- Rediset Cement
- High Alumina Cement
- Refractory Concrete
- Very High Strength Cement
1. Ordinary Portland Cement
Ordinary Portland cement (OPC) is by far the most important types of cement. Prior to 1987, there was only one grade of OPC which was governed by IS 269-1976. After 1987 higher grade cements were introduced in India. The OPC was classified into three grades, namely 33 grade, 43 grade and 53 grade depending upon the strength of the cement at 28 days when tested as per IS 4031-1988. If the 28 days strength is not less than 33 N/mm2, it is called 33 grade cement, if the strength is not less than 43 N/mm2, it is called 43 grade cement, and if the strength is not less than 53 N/mm2, it is called 53 grade cement. But the actual strength obtained by these types of cement at the factory are much higher than the BIS specifications.
It has been possible to upgrade the qualities of cement by using high quality limestone, modern equipments, closer on line control of constituents, maintaining better particle size distribution, finer grinding and better packing. Generally use of high grade cements offer many advantages for making stronger concrete. Although they are little costlier than low grade cement, they offer 10-20% savings in cement consumption and also they offer many other hidden benefits. One of the most important benefits is the faster rate of development of strength. In the modern construction activities, higher grade cements have become so popular that 33 grade cement is almost out of the market.
2. Rapid Hardening Cement (IS 8041-1990)
This cement is similar to ordinary Portland cement. As the name indicates it develops strength rapidly and as such it may be more appropriate to call it as high early strength cement. It is pointed out that rapid hardening cement which develops higher rate of development of strength should not be confused with quick-setting cement which only sets quickly. Rapid hardening cement develops at the age of three days, the same strength as that is expected of ordinary Portland cement at seven days.
The rapid rate of development of strength is attributed to the higher fineness of grinding (specific surface not less than 3250 sq. cm per gram) and higher C3S and lower C2S content.
The use of rapid heading cement is recommended in the following situations-
- In pre-fabricated concrete construction.
- Where formwork is required to be removed early for re-use elsewhere.
- Road repair works.
- In cold weather concrete where the rapid rate of development of strength reduce the vulnerability of concrete to the frost damage.
3. Extra Rapid Hardening Cement
Extra rapid hardening cement is obtained by intergrinding calcium chloride with rapid hardening Portland cement. The normal addition of calcium chloride should not exceed 2 percent by weight of the rapid hardening cement. It is necessary that the concrete made by using extra rapid hardening cement should be transported, placed and compacted and finished within about 20 minutes. It is also necessary that this cement should not be stored for most than a month.
Extra rapid hardening cement accelerates the setting and hardening process. A large quantity of heat is evolved in a very short time after placing. The acceleration of setting, hardening and evolution of this large quantity of heat in the early period of hydration makes the cement very suitable for concreting in cold weather. The strength of extra rapid hardening cement is about 25 percent higher than that of rapid hardening cement at one or two days and 10-20 percent higher at 7 days. The gain of strength will disappear with age and at 90 days the strength of extra rapid hardening cement or the ordinary portland cement may be nearly the same.
4. Sulphate Resisting Cement (IS 12330-1988)
Ordinary Portland cement is susceptible to the attack of sulphates, in particular to the action of magnesium sulphate. Sulphates react both with the free calcium hydroxide in set cement to form calcium sulphate and with hydrate of calcium aluminate to form calcium sulphoaluminate, the volume of which is approximately 227% of the volume of the original aluminates. Their expansion within the frame work of hadened cement paste results in cracks and subsequent disruption. Solid sulphate do not attack the cement compound. Sulphates in solution permeate into hardened concrete and attack calcium hydroxide, hydrated calcium aluminate and even hydrated silicates.
The above is known as sulphate attack. Sulphate attack is greatly accelerated if accompanied by alternate wetting and drying which normally takes place in marine structures in the zone of tidal variations.
To remedy the sulphate attack, the use of cement with low C3A content is found to be effective. Such cement with low C3A and comparatively low C4AF content is known as Sulphate Resisting Cement. In other words, this cement has a high silicate content. The specification generally limits the C3A content to 5 percent.
5. Portland Slag Cement (PSC) (IS 455-1989)
Portland slag cement is obtained by mixing Portland cement clinker, gypsum and granulated blast furnace slag in suitable proportions and grinding the mixture to get a thorough and intimate mixture between the constituents. It may also manufactured by separately grinding Portland cement clinker, gypsum and ground granulated blast furnace slag and later mixing them intimately. The resultant product is a cement which has physical properties similar to those of ordinary Portland cement.
In addition, it has low heat of hydration and is relatively better resistant to chlorides, soils and water containing excessive amount of sulphates or alkali metals, alumina and iron, as well as, to acidic waters, and therefore, this can be used for marine works with advantage.
6. Quick Setting Cement
This cement as the name indicates sets very early. The early setting property thus brought out by reducing the gypsum content at the time of clinker grinding. This cement required to mixed, placed and compacted very early. It is used mostly in under water construction where pumping is involved. Use of quick setting cement in such conditions reduces the pumping time and makes it economical. Quick setting cement may also find its use in some typical grouting operations.
7. Super Sulphated Cement (IS 6909-1990)
Super sulphated cement, manufactured by grinding together a mixture of 80-85 percent granulated slag. 10-15 per cent hard burnt gypsum, and about 5 per cent Portland cement clinker. The product thus ground finer than that of Portland cement. Specific surface must not be less than 4000 cm2 per gm. The super-sulphated cement is extensively use in Belgium, where it is termed as “ciment metallurgique sursulfate“. In France, it is termed as “ciment sursulfate“.
This cement is rather more sensitive to deterioration during storage than Portland cement. Super-sulphated cement has a low heat of hydration of about 40-45 calories/gm at 7 days and 45-50 at 28 days. This cement has high sulphate resistance. Because of this property this types of cement, therefore particularly recommended for use in foundation, where chemically aggressive conditions exist.
As super-sulphated cement has more resistance than Portland blast furnace slag cement to attack by sea water, it also used in the marine works. Other areas where super-sulphated cement thus recommended include the fabrication of reinforced concrete pipes which are likely to bury in sulphate bearing soils. The substitution of granulated slag is responsible for better resistance to sulphate attack.
Super-sulphated cement, like high alumina cement, combines with more water on hydration than Portland cements. Wet curing for not less than 3 days after casting is essential as the premature drying out results in an undesirable or powdery surface layer. When we use super sulphated cement the water/cement ratio should not be less than 0.5. A mix leaner than about 1:6 also not recommended.
8. Low Heat Cement (IS 12600-1989)
Its well known that hydration of cement is an exothermic action which produces large quantity of heat during hydration. Formation of cracks in large body of concrete due to heat of hydration has focused the attention of the concrete technologists to produce a kind of cement which produces less heat or the same amount of heat, at a low rate during the hydration process. Cement having this property was; developed in U.S.A. during 1930 for use in mass concrete construction, such as dams, where temperature rise by the heat of hydration can become excessively large.
A low-heat evolution thus achieved by reducing the contents of C3S and C3A which are the compounds evolving the maximum heat of hydration and increasing C2S. A reduction of temperature will retard the chemical action of hardening and so further restrict the rate of evolution of heat. The rate of evolution of heat will, therefore, be less and evolution of heat will extend over a longer period. Therefore, the feature of low-heat cement is a slow rate of gain of strength. But the ultimate strength of low-heat cement is the same as that of ordinary Portland cement. As per the Indian Standard Specification the heat of hydration of low-heat Portland cement shall be as follows –
- 7 days – not more than 65 calories per gm.
- 28 days – not more than 75 calories per gm.
9. Portland Pozzolana Cement (IS 1489-1991)
The history of pozzolanic material goes back to Roman’s time. However a brief description is below.
Portland Pozzolana cement (PPC), manufactured by the inter-grinding of OPC clinker with 10 to 25 per cent of pozzolanic material (as per the latest amendment, it is 15 to 35%). A pozzolanic material is essentially a silicious or aluminous material which while in itself possessing no cementitious properties, which will, in finely divided form and in the presence of water react with calcium hydro-oxide, liberated in the hydration process, at ordinary temperature, to form compounds possessing cementitious properties. The pozzolanic materials generally used for manufacture of PPC are calcined clay (IS 1489 part 2 of 1991) or fly ash (IS 1489 part 1 of 1991).
Fly ash is a waste material; generated in the thermal power station, when powdered coal used as a fuel. These are collect’d in the electrostatic precipitator. (It is termed as pulverized fuel ash in UK). It may be recalled that calcium silicates produce considerable quantities of calcium hydroxide, which is by and large a useless material from the point of view of strength or durability. If such useless mass could converted into a useful cementitious product, it considerably improves quality of concrete. The use of fly ash performs such a role.
10. Air-Entraining Cement
Air-entraining cement, not covered by Indian Standard so far. This cement thus made by mixing a small amount of an air entraining agent with ordinary Portland cement clinker at the time of grinding. The following types of air-entraining agents could be used in this cement –
- Alkali salts of wood resins.
- Synthetic detergents of the alkyl-aryl sulphonate types of cement.
- Calcium lignosulphate derived from the sulphite process in paper making.
- Calcium salts of glues and other proteins obtained in the treatment of animal hides.
11. Coloured Cement (White Cement) (IS 8042-1989)
For manufacturing various coloured cements either white cement or grey Portland cement therefore used as a base. The use of white cement as a base is costly. with the use of grey cement only red or brown cement can be produced.
Coloured cement consists of Portland cement with 5-10 per cent of pigment. The pigment cannot be satisfactorily distributed throughout the cement by mixing, and hence, it is usual to grind the cement and pigment together. The properties required of a pigment to used for coloured cement are the durability of colour under exposure to light and weather a fine state of division, a chemical composition such that the pigment neither effected by the cement nor detrimental to it, and the absence of soluble salts.
The process of manufacture of white Portland cement is nearly same as OPC. As the raw materials, particularity the kind of limestone required for manufacturing white cement is only available around Jodhpur in Rajasthan, two famous brands of white cement namely Birla
White and J.K. White Cements are manufactured near Jodhpur. The raw materials used are high purity limestone (96% CaCoz and less than 0.07% iron oxide). The other raw materials are china clay with iron content of about 0.72 to 0.8%, silica sand, flourspar as flux and selenite as retarder. The fuels used are refined furnace oil (RFO) or gas. Sea shells and coral can also be used as raw materials for production of white cement.
12. Hydrophobic cement (IS 8043-1991)
Hydrophobic cement, obtained by grinding ordinary Portland cement clinker with water repellant film-forming substance such as oleic acid, and stearic acid. The water-repellant film formed around each grain of cement, reduces the rate of deterioration of the cement during long storage, transport, or under unfavourable conditions. The film thus broken out when the cement and aggregate mixed together at the mixer exposing the cement particles for normal hydration. The film forming water-repellant material will entrain certain amount of air in the body of the concrete which incidentally will improve the workability of concrete.
In India certain places such as Assam, Shillong etc., get plenty of rainfall in the rainy season have high humidity in other seasons. Transportation and storage of cement in such places cause deterioration in the quality of cement. In such far off places with poor communication system, cement perforce requires to store for long time. Ordinary cement gets deteriorated and loses some if its strength, whereas the hydrophobic cement which does not lose strength is an answer for such situations. The properties of hydrophobic cement is nearly the same as that ordinary Portland cement except that it entrains a small quantity of air bubbles.
13. Masonry Cement (IS 3466 : 1988)
Ordinary cement mortar, though good when compared to lime mortar with respect to strength and setting properties, is inferior to lime mortar with respect to workability, water retentivity, shrinkage property and extensibility.
Masonry cement is a types of cement which, particularly made with such combination of materials, which when used for making mortar, incorporates all the good properties of lime mortar and discards all the not so ideal properties of cement mortar. This types of cement is mostly use, as the name indicates, for masonry construction. It contains certain amount of air-entraining agent and mineral admixtures to improve the plasticity and water retentivity.
14. Expansive Cement
Concrete made with ordinary Portland cement shrinks while setting due to loss of free water. Concrete also shrinks continuously for long time. This is termed as drying shrinkage. Cement used for grouting anchor bolts or grouting machine foundations or the cement used in grouting the prestress concrete ducts, if shrinks, the purpose for which the grout used will to some extent defeat. There has been a search for such types of cement which will not shrink while hardening and thereafter. As a matter of fact, a slight expansion with time will prove to be advantageous for grouting purpose. This types of cement which suffers no overall change in volume on drying is termed as expansive cement. Cement of this types has developed by using an expanding agent and a stabilizer very carefully. Proper material and controlled proportioning are necessary.in order to obtain the desired expansion.
Generally, about 8-20 parts of the sulphoaluminate clinker, mixed with 100 parts of the Portland cement and 15 parts of the stabilizer. Since expansion takes place only so long as concrete is moist, curing must be carefully controlled. The use of expanding cement requires
skill and experience.
15. IRS-T 40 Special Grade Cement
IRS-T 40 Special Grade Cement is manufactured as per specifications laid down by ministry of railways under IRS-T 40:1985. Its very finely ground cement with high C3S content . Designed to develop high early strength required for manufacture of concrete sleepers for Indian Railways.
16. Oil-Well Cement (IS 8229-1986)
Oil-wells, drilled through stratified sedimentary rocks through a great depth in search of oil, that if oil either struck, oil or gas may escape through the space between the steel casing and rock formation. Cement slurry thus used to seal off the annular space between steel casing and rock strata and also to seal off any other fissures or cavities in the sedimentary rock layer. The cement slurry has to pump into position, at considerable depth where the prevailing temperature may be upto 175°C. The pressure required may go upto 1300 kg/cm2.
The slurry should remain sufficiently mobile to be able to flow under these conditions for periods upto several hours and then hardened fairly rapidly. It may also have to resist corrosive conditions from sulphur gases or waters containing dissolved salts. The types of cement suitable for the above conditions is termed as Oil-well cement. The desired properties of Oil-well cement can obtained in two ways: by adjusting the compound composition of cement or by adding retarders to ordinary Portland cement. Many admixtures have been patent as retarders. The commonest agents are starches or cellulose products or acids.
17. Rediset Cement
Acclerating the setting and hardening of concrete by the use of admixtures is a common knowledge. Calcium chloride, lignosulfonates, and cellulose products form the base of some of admixtures. The limitations on the use of admixtures and the factors influencing the end properties; also fairly well known.
High alumina cement, though good for early strengths, shows retrogression of strength when exposed to hot and humid conditions. A new product was need for use in the precast concrete industry, for rapid repairs of concrete roads and pavements, and slip-forming.
In brief, for all jobs where the time and strength relationship was important. In the PCA laboratories of USA, investigations were conduct for developing a cement which could yield high strengths in a matter of hours, without showing any retrogression. Regset cement was the result of investigation. Associated Cement Company of India have developed an equivalent cement by name REDISET Cement.
18. High Alumina Cement (IS 6452 : 1989)
High alumina cement obtained by fusing or sintering a mixture; in suitable proportions, of alumina and calcareous materials and grinding the resultant product to a fine powder. The raw materials used for the manufacture of high alumina cement are limestone and bauxite. These raw materials with the required proportion of coke were charge into the furnace. The furnace, fired with pulverized coal or oil with a hot air blast. The fusion takes place at a temperature of about 1550-1600°C. The cement maintained in a liquid state in the furnace.
Afterwards the molten cement run into moulds and cooled. These castings are termed as pigs. After cooling the cement mass resembles a dark, fine gey compact rock resembling the structure and hardness of basalt rock. The pigs of fused cement, after cooling, thus crushed. And then ground in tube mills to a fineness of about 3000 sq. cm/gm.
19. Refractory Concrete
An important use of high alumina cement is for making refractory concrete to withstand high temperatures in conjunction with aggregate; having heat resisting properties. It is interesting to note that high alumina cement concrete loses considerable strength only when subjected to humid condition and high temperature. Desiccated high alumina cement concrete on subjecting to the high temperature; will undergo a little amount of conversion and will still have a satisfactory residual strength. On complete desiccation the resistance of alumina cement to dry heat is so high; that the concrete made with this cement considered as one of the refractory materials. At a very high temperature alumina cement concrete exhibits good ceramic bond; instead of hydraulic bond as usual with other cement concrete.
20. Very High Strength types of Cement
Various types of Very High Strength cement are as follows –
- Macro defect free cements
- Densely packed system
- Pressure densification and warm pressing
- High early strength cement
- Pyrament cement
- Magnesium Phosphate cement