18-Types of Cement ,and its Properties

18-Types of cement ,and its Properties

18-Types of Cement ,and its Properties

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(g) 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 setcement 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 C3 A 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.

Tetracalcium Alumino Ferrite (C3AF) varies in Normal Portland Cement between to 6 to 12%. Since it is often not feasible to reduce the Al2O3 content of the raw material, Fe2O3 may be added to the mix so that the C4AF content increases at the expense of C3A. IS code limits the total content of C4AF and C3A, as follows

                             2C3A + C4AF should not exceed 25%.

In many of its physical properties, sulphate resisting cement is similar to ordinary Portland cement. The use of sulphate resisting cement is recommended under the following conditions:

(a ) Concrete to be used in marine condition;
(b ) Concrete to be used in foundation and basement, where soil is infested with sulphates;
(c ) Concrete used for fabrication of pipes which are likely to be buried in marshy region or sulphate bearing soils;
(d ) Concrete to be used in the construction of sewage treatment works.

(h) Low Heat Cement – IS 12600: 1989

It is well known that hydration of cement is an exothermic action which produces large quantity of heat during hydration. This aspect has been discussed in detail in Chapter 1. Formation of cracks in large body of concrete due to heat of hydration has focussed 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 is 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.
The specific surface of low heat cement as found out by air-permeability method is not less than 3200 sq. cm/gm. The 7 days strength of low heat cement is not less than 16 MPa in contrast to 22 MPa in the case of ordinary Portland cement. Other properties, such as setting time and soundness are same as that of ordinary Portland cement.

(i) Rediset Cement – IS 8229: 1986

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 are 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 needed 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 conducted 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.

Properties of “Rediset”

(i ) The cement allows a handling time of just about 8 to 10 minutes

(ii ) The strength pattern is similar to that of ordinary Portland cement mortar or concrete after one day or 3 days. What is achieved with “REDISET” in 3 to 6 hours can be achieved with normal concrete only after 7 days.
(iii ) “REDISET” releases a lot of heat which is advantageous in winter concreting but excess heat liberation is detrimental to mass concrete.
(iv ) The rate of shrinkage is fast but the total shrinkage is similar to that of ordinary Portland cement concrete.
(v) The sulphate resistance, is however, very poor.

Applications

(a ) very-high-early (3 to 4 hours) strength concrete and mortar,
(b) patch repairs and emergency repairs,
(c ) quick release of forms in the precast concrete products industry,
(d ) palletisation of iron ore dust,
(e ) slip-formed concrete construction,
(f ) construction between tides.

(j) High Alumina Cement – IS 6452: 1989

High alumina cement is 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 charged into the furnace. The furnace is fired with pulverised coal or oil with a hot air blast. The fusion takes place at a temperature of about 1550-1600°C. The cement is maintained in a liquid state in the furnace. Afterwards the molten cement is run into moulds and cooled. These castings are known as pigs. After cooling the cement mass resembles a dark, fine gey compact rock resembling the structure and hardeness of basalt rock.

The pigs of fused cement, after cooling are crushed and then ground in tube mills to a finess of about 3000 sq. cm/gm.

(k) Portland Pozzolana Cement – IS 1489 -1991

Portland Pozzolana cement (PPC) is manufactured by the intergrinding 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 hydroxide, 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 I of 1991). Fly ash is a waste material, generated in the thermal power station, when powdered coal is used as a fuel. These are collected in the electrostatic precipitator.

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 be converted into a useful cementitious product, it considerably improves quality of concrete. The use of fly ash performs such a role.

Calcium hydroxide + Pozzolana + water → C – S – H (gel)

Advantages of PPC

(a ) In PPC, costly clinker is replaced by cheaper pozzolanic material - Hence economical.

(b ) Soluble calcium hydroxide is converted into insoluble cementitious products resulting in improvement of permeability. Hence it offers, alround durability characteristics, particularly in hydraulic structures and marine              construction.

(c) PPC consumes calcium hydroxide and does not produce calcium hydroxide as much as that of OPC.

(d) It generates reduced heat of hydration and that too at a low rate.

(e) PPC being finer than OPC and also due to pozzolanic action, it improves the pore size distribution and also reduces the microcracks at the transition zone.

(f ) Reduction in permeability of PPC offers many other alround advantages.

(g) As the fly ash is finer and of lower density, the bulk volume of 50 kg bag is slightly more than OPC. Therefore, PPC gives more volume of mortar than OPC.

(h) The long term strength of PPC beyond a couple of months is higher than OPC if enough moisture is available for continued pozzolanic action.

Application

Portland pozzolana cement can be used in all situations where OPC is used except where high early strength is of special requirement. As PPC needs enough moisture for sustained pozzolanic activity, a little longer curing is desirable. Use of PPC would be particularly suitable for the following situations:

(a ) For hydraulic structures;

(b) For mass concrete structures like dam, bridge piers and thick foundation;

(c ) For marine structures;

(d ) For sewers and sewage disposal works etc.

(l) Air Entraining Cement – IS 1489

Air-entraining cement is not covered by Indian Standard so far. This cement is 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:

(a) Alkali salts of wood resins.
(b) Synthetic detergents of the alkyl-aryl sulphonate type.
(c ) Calcium lignosulphate derived from the sulphite process in paper making
(d) Calcium salts of glues and other proteins obtained in the treatment of animal hides.
     
These agents in powder, or in liquid forms are added to the extent of 0.025–0.1 percent by weight of cement clinker. There are other additives including animal and vegetable fats, oil and their acids could be used. Wetting agents, aluminium powder, hydrogen peroxide could also be used. Air-entraining cement will produce at the time of mixing, tough, tiny, discrete non-coalesceing air bubbles in the body of the concrete which will modify the properties of plastic concrete with respect to workability, segregation and bleeding. It will
modify the properties of hardened concrete with respect to its resistance to frost action. Air entraining agent can also be added at the time of mixing ordinary Portland cement with rest of the ingredients. More about this will be dealt under the chapter “Admixtures.”

(m) Oil Well Cement – IS 8229: 1986

Oil-wells are drilled through stratified sedimentary rocks through a great depth in search of oil. It is likely that if oil is struck, oil or gas may escape through the space between the steel casing and rock formation. Cement slurry is 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 be pumped 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 type of cement suitable for the above conditions is known as Oil-well cement. The desired properties of Oil-well

cement can be obtained in two ways: by adjusting the compound composition of cement or by adding retarders to ordinary Portland cement. Many admixtures have been patented as retarders. The commonest agents are starches or cellulose products or acids. These retarding agents prevent quick setting and retains the slurry in mobile condition to facilitate penetration

to all fissures and cavities. Sometimes workability agents are also added to this cement to increase the mobility.

(n ) Coloured Cement: White Cement – IS 8042: 1989

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 be 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 is 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% CaCo3 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.

The properties of white cement is nearly same as OPC. Generally white cement is ground finer than grey cement. Whiteness of white cement as measured by ISI scale shall not be less than 70%. Whiteness can also be measured by Hunters Scale. The value as measured by Hunters scale is generally 90%. The strength of white cement is much higher than what is

stated in IS code 8042 of 1989

(o) Hydrophobic Cement – IS 8043: 1991

Hydrophobic cement is 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 is broken out when the cement and aggregate are 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 had have high humidity in other seasons. The 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 be stored 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. The hydrophobic cement is made actually from ordinary Portland cement clinker. After grinding, the cement particle is sprayed in one direction and film forming materials such as oleic acid, or stearic acid, or pentachlorophenol, or calcium oleate are sprayed from another direction such that every particle of cement is coated with a very fine film of this water repellant material which protects

them from the bad effect of moisture during storage and transporation. The cost of this cement is nominally higher than ordinary Portland cement.

(p) 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, waterretentivity,

shrinkage property and extensibility.

Masonry cement is a type of cement which is 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 kind of cement is mostly used, 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.

(q) Expansive Cement – IS 3466: 1988

Concrete made with ordinary Portland cement shrinks while setting due to loss of free water. Concrete also shrinks continuously for long time. This is known 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 is used will be to some extent defeated. There has been a search for such type 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 type of cement which suffers no overall change in volume on drying is known as expansive cement. Cement of this type has been 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 are 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.

One type of expansive cement is known as shrinkage compensating cement. This cement when used in concrete, with restrained expansion, induces compressive stresses which approximately offset the tensile stress induced by shrinkage. Another similar type of cement is known as Self Stressing cement. This cement when used in concrete induces significant compressive stresses after the drying shrinkage has occurred. The induced compressive stresses

not only compensate the shrinkage but also give some sort of prestressing effects in the tensile zone of a flexural member.

(r ) Concrete Sleeper grade Cement – IRS-T 40: 1985

IRS-T-40 special grade cement is manufactured as per specification laid

down by ministry of Railways under IRST40: 1985. It is a very finely ground

cement with high C3S content designed to develop high early strength required

for manufacture of concrete sleeper for Indian Railways. This cement can also be used with advantage for other applications where high early strength concrete is required. This cement can be used for prestressed concrete elements, high rise