Water is an important ingredient of concrete as it actively participates in the chemical reaction with cement. Since it helps to form the strength giving cement gel; the quantity and quality of water required to look into very carefully. Here quality of water has been discuss. In practice, very often great control on properties of cement and aggregate exercised. But the control on the quality of water is often neglect. Since quality of water affects the strength. So it is necessary for us to go into the purity and quality of water.

Read more about – Water quality parameters

Qualities of Water

A popular suitability of water for mixing concrete is that, if water is fit for drinking; it is fit for making concrete. This does not appear to be a true statement for all conditions. Some waters containing a small amount of sugar would be suitable for drinking but not for mixing concrete. Conversely water suitable for making concrete may not necessarily fit for drinking. Few specifications require that if the water not obtained from source that has proved satisfactory; the strength of concrete/mortar made with questionable water should then compared with similar concrete/mortar made with pure water.

Strength

Some specification also accept water for making concrete if the pH value of water lies between 6 and 8. Also the water is free from organic matter. Instead of depending upon pH value and other chemical composition; the best course to find out whether a particular source of water is suitable for concrete making or not; is to make concrete with this water and compare its 7 days’ and 28 days’ strength with cubes made with distilled water. If the compressive strength is upto 90 percent, the source of water may be accepted.

This criteria may safely adopted in places like coastal area of marshy area. Or in other places where the available water is brackish in nature and of doubtful quality. However, it is logical to know what harm the impurities in water do to the concrete. And what degree of impurity is permissible is mixing concrete and curing concrete.

Chemicals

Carbonates and bi-carbonates of sodium and potassium effect the setting time of cement. While sodium carbonate may cause quick setting, the bi-carbonates may either accelerate or retard the setting. The other higher concentrations of these salts will materially reduce the concrete strength. If some of these salts exceeds 1000 ppm, tests for setting time and 28 days strength should be carried out. In lower concentrations they may be accepted.

Brackish water contains chlorides and sulphates. When chloride does not exceed 10,000 ppm and sulphate does not exceed 3,000 ppm; the water is harmless, but water with even higher salt content has been used satisfactorily.

Salts of Manganese, Tin, Zinc, Copper and Lead cause a marked reduction in strength of concrete. Sodium iodate, sodium phosphate, and sodium borate reduce the initial strength of concrete to an extra-ordinarily high degree. Another salt that is detrimental to concrete is sodium sulphide and even a sulphide content of 100 ppm warrants testing.

Characteristics

Silts and suspended particles are undesirable as they interfere with setting, hardening and bond characteristics. A turbidity limit of 2,000 ppm has been suggested. Following table shows the tolerable concentration of some impurities in mixing water.

The initial setting time of the test block made with a cement and the water proposed to be used shall not differ by +-30 minutes from the initial setting time of the test block made with same cement and distilled water.

Guidelines

The following guidelines should also be taken into consideration regarding the quality of water.

• To neutralize 100 ml sample of water using phenoplhaline as an indicator, it should not require more than 5 ml of 0.02 normal NaOH.
• To neutralize 100 ml of sample of water, using mixed indicator, it should not require more than 25 ml of 0.02 normal H2SO4.
• Permissible limits for solids is as given below in table.

Algae in mixing water may cause a marked reduction in strength of concrete either by combining with cement to reduce the bond or by causing large amount of air entrainment in concrete. Algae which are present on the surface of the aggregate have the same effect as in that of mixing water.

Use of Sea Water for Mixing Concrete

Sea water has a salinity of about 3.5 percent. In that about 78% is sodium chloride and 15% is chloride and sulphate of magnesium. Sea water also contain small quantities of sodium and potassium salts. This can react with reactive aggregates in the same manner as alkalies in cement. Therefore sea water should not used even for PCC if aggregates are_known to be potentially alkali reactive. Its reported that the use of sea water for mixing concrete does not appreciably reduce the strength of concrete; although it may lead to corrosion of reinforcement in certain cases.

Researches

Research workers are unanimous in their opinion, that sea water can be used in un-reinforced concrete or mass concrete. Sea water slightly accelerates the early strength of concrete. But it reduces the 28 days strength of concrete by about 10 to 15 percent. However, this loss of strength could be made up by redesigning the mix. Water containing large quantities of chlorides in sea water may cause efflorescence and persistent
dampness. When the appearance of concrete is important sea water may be avoided. The use of sea water is also not advisable for plastering purpose-which is subsequently going to be painted.

Divergent opinion exists on the question of corrosion of reinforcement due to the use of sea water. Some research workers cautioned about the risk of corrosion of reinforcement particularly in tropical climatic regions; whereas some research workers did not find the risk of corrosion due to the use of sea water. Experiments have_shown that corrosion of reinforcement occurred when concrete was_made with pure water and immersed in pure water. When the concrete was comparatively porous, whereas, no corrosion of reinforcement was_found when sea water was_used for mixing. Also the specimen was_immersed in salt water when the concrete was dense and enough cover to reinforcement was_given.

Conclusion of research

From this it is_concluded that factor for corrosion is; not the use of sea water or the quality of water where the concrete is placed. The factors effecting corrosion is permeability of concrete and lack of cover. However, since these factors cannot be adequately taken care of always at the site of work. It may be wise that sea water be_avoided for making reinforced concrete. For economical or other passing reasons, if sea water cannot be avoided for making reinforced concrete; particular precautions should be take to make the concrete dense. This_is done by using low water/cement ratio and to give an adequate cover of at least 7.5 cm. The use of sea water must be_avoided in prestressed concrete work. Because of stress corrosion and undue loss of cross section of small diameter wires.

The latest IS 456 : 2000 prohibits use of sea-water for mixing and curing of reinforced concrete and prestressed concrete work. This specification permits the use of Sea Water for mixing and curing of plain cement concrete (PCC) under unavoidable situation.

It is pertinent at this point to consider the suitability of water for curing. Water that contains impurities which caused staining, is objectionable for curing concrete members whose look is important. The most common cause of staining is usually high concentration of iron or organic matter in the water. Water that contains more than 0.08 ppm. Of iron may be avoided for curing if the appearance of concrete is important. Similarly the use of sea water may also avoided in such cases. In other cases, the water, normally fit for mixing can also used for curing.

How treatment of waste water is done?

Testing of cement can be brought under two categories –

1. Field testing
2. Laboratory testing

Read more about types of cement.

1. Field testing of cement

It is sufficient to subject the cement to field tests when it is used for minor works. The following are the field tests:

• Open the bag and take a good look at the cement. There should not be any visible lumps. The colour of the cement should normally be greenish grey.
• Thrust your hand into the cement bag. It must give you a cool feeling. There should not be any lump inside.
• Take a pinch of cement and feel-between the fingers. It should give a smooth and not a gritty feeling.
• Take a handful of cement and throw it on a bucket full of water, the particles should float for some time before they sink.
• Take about 100 grams of cement and a small quantity of water and make a stiff paste. From the stiff paste, pat a cake with sharp edges. Put it on a glass plate and slowly take it under water in a bucket. See that the shape of the cake is not disturbed while taking it down to the bottom of the bucket. After 24 hours the cake should retain its original shape and at the same time it should also set and attain some strength.

2. Laboratory for testing of cement

• Fineness test
• Setting time test
• Consistency test
• Strength test
• Soundness test
• Heat of hydration test
• Chemical composition test

(i) Fineness Test

The fineness of cement has an important bearing on the rate of hydration and hence on the rate of gain of strength and also on the rate of evolution of heat. Finer cement offers a greater surface area for hydration and hence faster the development of strength. The fineness of grinding has increased over the years. But now it is stabilized. This is considered most important among all testing of cement.

Fineness of cement is tested in two ways –

(a) By sieving

(b) By determination of specific surface by air-permeability apparatus

(a) Sieve Test

Weigh correctly 100 grams of cement and take it on a standard IS Sieve No. 9 (90 microns). Break down the air-set lumps in the sample with fingers. Continuously sieve the sample giving circular and vertical motion for a period of 15 minutes. Mechanical sieving devices may also be used. Weigh the residue left on the sieve. This weight shall not exceed 10% for ordinary cement. Sieve test is rarely used.

(b) Air Permeability Method

Testing of cement covers the procedure for determining the fineness of cement as represented by specific surface expressed as total surface area in sq. cm/gm. of cement. It is also expressed in m2/kg.

The apparatus can be used for measuring the specific surface of cement. The principle is based on the relation between the flow of air through the cement bed and the surface area of the particles comprising the cement bed. From this the surface area per unit weight of the body material can be related to the permeability of a bed of a given porosity. The cement bed in the permeability cell is 1 cm, high and 2.5 cm. in diameter.

Specific surface Sw is calculated from the following formula

Knowing the density of cement the weight required to make a cement bed of porosity of 0.475 can be calculated. This quantity of cement is placed in the permeability cell in a standard manner. Slowly pass on air through the cement bed at a constant velocity.

Adjust the rate of air flow until the flow-meter shows a difference in level of 30-50 cm. Read the difference in level (h1) of the manometer and the difference in level (h2) of the flow-meter. Repeat these observations to ensure that steady conditions have been obtained as shown by a constant value of h1/h2.

Fineness can also be measured by Blain Air Permeability apparatus. This method is more commonly employed in India.

(ii) Standard Consistency Test

For finding out initial setting time, final setting time and soundness of cement, and strength a parameter known as standard consistency has to be used. It is pertinent at this stage to describe the procedure of conducting standard consistency test. The standard consistency of a cement paste is defined as that consistency which will permit a Vicat plunger having 10 mm diameter and 50 mm length to penetrate to a depth of 33-35 mm from the top of the mould. The appartus is called Vicat Appartus. This appartus is used to find out the percentage of water required to produce a cement paste of standard consistency. The standard consistency of the cement paste is some time called normal consistency (CPNC).

The following procedures is adopted to find out standard consistency.

Take about 500 gms of cement and prepare a paste with a weighed quantity of water (say 24 per cent by weight of cement) for the first trial. The paste must be prepared in a standard manner and filled into the Vicat mould within 3-5 minutes. After completely filling the mould, shake the mould to expel air. A standard plunger, 10 mm diameter, 50 mm long is attached and brought down to touch the surface of the paste in the test block and quickly released allowing it to sink into the paste by its own weight. Take the reading by noting the depth of penetration of the plunger.

Conduct a 2nd trial (say with 25 per cent of water) and find out the depth of penetration of plunger. Similarly, conduct trials with higher and higher water/cement ratios till such time the plunger penetrates for a depth of 33-35 mm from the top. That particular percentage of water which allows the plunger to penetrate only to a depth of 33-35 mm from the top is known as the percentage of water required to produce a cement paste of standard consistency This percentage is usually denoted as ‘P. The test is reguired to be conducted in a constant temperature (27° ± 2°C) and constant humidity (90%).

(iii) Setting Time Test

An arbitrary division has been made for the setting time of cement as initial setting tine and final setting time. It is difficult to draw a rigid line between these two arbitrary divisions.

For convenience/ initial setting time is regarded as the time elapsed between the moment that the water is added to the cement, to the time that the paste starts losing its plasticity The final setting time is the time elapsed between the moment the water is added to the cement, and the time when the paste has completely lost its plasticity and has attained sufficient-firmness to resist certain definite pressure.

In actual construction dealing with cement paste, mortar or concrete certain time is required for mixing, transporting, placing, compacting and finishing. During this time cement paste, mortar, or concrete should be in plastic condition. The time interval for which the cement products remain in plastic condition is known as the initial setting time.

Normally minimum of 30 minutes is given for mixing and handling operations.

The constituents and fineness of cement is maintained in such a way that the concrete remains in plastic condition for certain minimum time. Once the concrete is placed in the final position, compacted and finished, it should lose its plasticity in the earliest possible time so that it is least vulnerable to damages from external destructive agencies. This time should not be more than 10 hours which is often referred to as final setting time.

The Vicat Apparatus is used for setting time test also. The following procedure is adopted. Take 500 gm. of cement sample and gauge it with 0.85 times the water required to produce cement paste of standard consistency (0.85 P). The paste shall be gauged and filled into the Vicat mould in specified manner within 3-5 minutes. Start the stop watch the moment water is added to the cement. The temperature of water and that of the test room, at the time of gauging shall be within 27°C + 2°C.

(a) Initial Setting Time

Lower the needle (C) gently and bring it in contact with the surface of the test block and quickly release. Allow it to penetrate into the test block. In the beginning, the needle will completely pierce through the test block. But after some time when the paste starts losing its plasticity, the needle may penetrate only to a depth of 33-35 mm from the top. The period elapsing between the time when water is added to the cement and the time at which the needle penetrates the test block to a depth equal to 33-35 mm from the top is taken as initial setting time.

(b) Final Setting Time

Replace the needle (C) of the Vicat apparatus by a circular attachment (F). The cement shall be considered as finally set when, upon, lowering the attachment gently cover the surface of the test block, the centre needle makes an impression, while the circular cutting edge of the attachment fails to do so. In other words the paste has attained such hardness that the centre needle does not pierce through the paste more than 0.5 mm.

(iv) Strength Test

The compressive strength of hardened cement is the most important of all the properties. Therefore, it is not surprising that the cement is always tested for its strength at the laboratory before the cement is used in important works. Strength tests are not made on neat cement paste because of difficulties during the testing of cement of excessive shrinkage and subsequent cracking of neat cement.

Strength of cement is indirectly found on cement sand mortar in specific proportions. The standard sand is used for finding the strength of cement. It shall conform to IS 650-1991. Take 555 gms of standard sand (Ennore sand), 185 gms of cement (i.e. ratio of cement to sand is (1:3) in a non-porous enamel tray and mix them with a trowel for one minute, then add water of quantity P/4 + 3.0 per cent of combined weight of cement and sand and mix the three ingredients thoroughly until the mixture is of uniform colour. The time of mixing should not be less than 3 minutes nor more than 4 minutes.

Immediately after mixing, the mortar is filled into a cube mould of size 7.06 cm. The area of the face of the cube will be equal to 50 sq cm. Compact the mortar either by hand compaction in a standard specified manner or on the vibrating equipment (12000 RPM) for 2 minutes.

Moulding of 70.7 mm Mortar Cube Vibrating Machine

Keep the compacted cube in the mould at a temperature of 27°C + 2°C and at least 90 per cent relative humidity for 24 hours. Where the facility of standard temperature and humidity room is not available, therefore cube may be kept under wet gunny bag to simulate 90 per cent relative humidity. After 24 hours the cubes are removed from the mould and immersed in clean fresh water until taken out for testing of cement.

Three cubes are thus tested for compressive strength at the periods. The periods being reckoned from the completion of vibration. The compressive strength shall be the average of the strengths of thus three cubes for each period respectively.

(v) Soundness Test

It is very important that the cement after setting shall not undergo any appreciable change of volume. Certain cements have been found to undergo a large expansion after setting causing disruption of the set and hardened mass. This will cause serious difficulties for the durability of structures when such cement is used. The testing of soundness of cement to ensure that the cement does not show any appreciable subsequent expansion is of prime importance.

The unsoundness in cement is due to the presence of excess of lime than that could be combined with acidic oxide at the kiln. This is also due to inadequate burning or insufficiency in fineness of grinding or thorough mixing of raw materials. It is also likely that too high a proportion of magnesium content or calcium sulphate content may cause unsoundness in cement.

For this reason the magnesia content allowed in cement is limited to 6 per cent, It can be recalled that, to prevent flash set, calcium sulphate is added to the clinker while grinding. The quantity of gypsum added will vary from to 5 per cent depending upon C3A content. If the addition of gypsum is more than that could be combined with C3A, excess of gypsum will remain in the cement in free state. This excess of gypsum leads to an expansion and consequent disruption of the set cement paste.

(vi) Heat of Hydration

The reaction of cement with water is exothermic. The reaction liberates a considerable quantity of heat. This can be easily observed if a cement is gauged with water and placed in a thermos flask. Much attention has been paid to the heat evolved during the hydration of cement in the interior of mass concrete dams. It is estimated that about 120 calories of heat is also generated in the hydration of 1 gm. of cement. From this it can be assessed the total quantum of heat produced in a conservative system such as the interior of a mass concrete dam. A temperature rise of about 50°C has been observed. This unduly high temperature developed at the interior of a concrete dam causes serious expansion of the body of the dam and also with the subsequent cooling considerable shrinkage takes place resulting in serious cracking of concrete.

The use of lean mix, use of pozzolanic cement, artificial cooling of constituent materials and incorporation of pipe system in the body of the dam as the concrete work progresses for circulating cold brine solution through the pipe system to absorb the heat, are some of the methods adopted to offset the heat generation in the body of dams due to heat of hydration of cement.

Testing for heat of hydration is essentially required to be carried out for low heat cement only. Testing of cement is thus carried out over a few days by vaccum flask methods, or over a longer period in an adiabatic calorimeter. When tested in a standard manner the heat of hydration of low heat Portland cement shall not be more than 65 cal/gm. at 7 days and 75 cal/g, at 28 days.

(vii) Chemical Composition Test

A fairly detailed discussion has been given earlier regarding the chemical composition of cement. Both oxide composition and compound composition of cement have been discussed. At this stage it is sufficient to give the limits of chemical requirements.

Ratio of percentage of lime to percentage of silica, alumina and iron oxide, when calculated by the formulae

(Cao – 0.7 SO3) : (2.8 SiO2 + 1.2 Al2O3 + 0.65 Fe2O3 : Not greater than 1.02 and not less than 0.66.

The above is called lime saturation factor percent.

1. Ordinary Portland Cement
2. Rapid Hardening Cement
3. Extra Rapid Hardening Cement
4. Sulphate Resisting Cement
5. Portland Slag Cement
6. Quick Setting Cement
7. Super Sulphated Cement
8. Low Heat Cement
9. Portland Pozzolana Cement
10. Air-Entraining Cement
11. Coloured Cement (White Cement)
12. Hydrophobic cement
13. Masonry Cement
14. Expansive Cement
15. IRS-T 40 Special Grade Cement
16. Oil-Well Cement
17. Rediset Cement
18. High Alumina Cement
19. Refractory Concrete
20. 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