Types of Cement and their Usage
Ordinary Portland cement
This is widely used for general construction purpose and most of the specifications on concrete construction are oriented to this, very rarely a false set may occur because of insufficient cooling of the cement in cement mills, there by causing the gypsum to loose water. Upon mixing with water, the hymidydrate form of gypsum takes up the water and sets immediately. (When “False set” occurs , mixing carried out once again to regain the workability)
Ordinary Portland cement shouldn’t be mixed with High alumina cement, rather these two should not come in contact with each other, since “Flash set” may occur, where by the mix sets within a very short time. Though this property is used for emergency repairs, use of high alumina cement is a specialist job and will not be a part of routine application.
Rapid hardening Portland cement
This gives higher early strengths and is there fore suitable for prestressed concrete and pre cast concrete works. The so called super fine cement is also classified as rapid hardening cement. Another variation known as extra rapid hardening cement contains calcium chloride. This extra rapid hardening cement is not produced in India, but if it is made available in works abroad, particular note should be taken regarding the possible presence of calcium chloride in extra rapid hardening cement. Most specification prohibit the use of calcium chloride in prestressed works and now there is a trend towards avoiding calcium chloride even in ordinary works, if the concrete contains reinforcements or embedded metal fixtures and fasteners, because of the corrosion risk.
Portland slag cement
The slag obtained during the manufacture of iron and steel has a composition similar to that of cement clinker. This fact is used in manufacturing Portland slag cement which is obtained by inter- grinding a mixture of Portland cement clinker and granulated slag with addition of gypsum. The resultant product has properties similar to those of ordinary Portland cement and therefore can be used whenever ordinary Portland cement is used. Some times Portland slag cement is specified for works where durability problems arise because of sulphates or marine environments, sewers work, structures involving large mass concrete such as dams, retaining walls, and bridge abutments and for structure exposed to sulphate-bearing soils such as foundations and roads. However in prestressed concrete works the slag content of the cement should not be more than 50 %.
Portland pozzolana cement
This is a blend of ordinary Portland cement and a suitable pozzolans, say fly-ash or burnt clay pozzolana. It can be generally used whenever ordinary Portland cement is usable under normal condition.
Increased impermeability, lower heat of hydration, lower drying shrinkage, reduced alkali-aggregate expansion and improved resistance to aggressive chemical, resistance to sulphate attack and sea- water are some of the advantages of using Portland pozzolana cement.
However, the addition of pozzolana does not contribute to strengths at early ages and probably for this reason pozzolana cement is not recommended for prestressed concrete works, For the same reason, demoulding may have to be delayed in precasting yards. Certain water reducing admixtures, especially those containing lignosulphonates are also retarders and therefore should not be uses with pozzolana cement without adequate trials.
High strength ordinary portland cement
This cement is intended for specialized works such as prestressed concrete and some item of precast concrete requiring consistently high strengths concrete. No special precautions required in using this cement.
Hydrophobic Cement
This type is specified when prolonged storage of cement under unfavorable condition is anticipated. It is obtained by inter grinding ordinary portland cement with hydrophobic (water repelling) agents such as oleic acid or stearic acid. Hydrophobic cement should not be confused with water proofing cements. With hydrophobic cements, a longer mixing period will be necessary in order to remove the coating of hydrophobic agent over the cement grain.
Sulphate Resisting Cement
This in other words known as low C3A cement. The tri-calcium aluminate content in the cement is restricted to 5 % maximum and tetra calcium alumino ferrote to 25 %. This cement is used in structures in contact with sub soil and ground water sulphates and should not be used for concrete likely to be exposed to acids.
Super Sulphated Cement
Though an Indian standard specification is available this type is not produced in India, but may nevertheless be specified , for instance, in works abroad. It is recommended for use where concrete is likely to be attacked by sulphates. It is a product of granulated blast furnace slag , calcium sulphate (gypsum) and a small quantity of portland cement clinker. This cement has chemical resistance to most of the aggressive conditions encountered in construction industry and to the attack of sulphates in particular.
Precaution
• According to IS 6909 use of Super Sulphated cement is permitted in tropical conditions, provided the prevailing temperature is below 40 0 C .
• Generally Super Sulphated cement should not be used for steam cured products. If accelerated curing is to be adopted along with use of super Sulphated cement the curing temperature should be restricted to say 50 Degree Centigrade.
• Super Sulphated cement should not be mixed with any other type of cement.
• Special care is required in the storage of supersulphated cement since it will deteriorate rapidly in poor storage conditions. The rate of strength development of concrete made with super Sulphated cement is considerable reduced at low temperature. Unless adequately cured, the surface of super Sulphated cement concrete is liable to become friable and dusty. It should be
kept moist atleast four days after placing .
High Alumina Cement
This is usually used when durability under extreme sulphate or acid attack is desirable and when very early development of strength is required or for emergency repair work. In tropical countries, high alumina cement should be used with extreme care and caution. Use of high alumina cement for general construction purposes has gone out of vogue. Proper specification and full instructions must be insisted upon before taking up responsibility for execution. When used with crushed bricks it makes a good refractory concrete. High alumina cement is not recommended for structural use.
Low Heat Portland Cement
The chemical constituents proportioned in such a way that the heat liberated due to hydration is reduced, making the cement particularly suitable for use in massive structures, such as dams, bridge abutments, and retaining walls. Its rate of gain of strength is how ever slower than that of ordinary Portland cement hence it requires longer curing period.
Besides these other types of cements like oil well cement, white and colored cement, shrinkage compensated cement for grouting applications, acid resisting cement are available. These cements are produced by some cement manufactures based on the requirements only and not on regular basis.
Ordinary Portland cement
This is widely used for general construction purpose and most of the specifications on concrete construction are oriented to this, very rarely a false set may occur because of insufficient cooling of the cement in cement mills, there by causing the gypsum to loose water. Upon mixing with water, the hymidydrate form of gypsum takes up the water and sets immediately. (When “False set” occurs , mixing carried out once again to regain the workability)
Ordinary Portland cement shouldn’t be mixed with High alumina cement, rather these two should not come in contact with each other, since “Flash set” may occur, where by the mix sets within a very short time. Though this property is used for emergency repairs, use of high alumina cement is a specialist job and will not be a part of routine application.
Rapid hardening Portland cement
This gives higher early strengths and is there fore suitable for prestressed concrete and pre cast concrete works. The so called super fine cement is also classified as rapid hardening cement. Another variation known as extra rapid hardening cement contains calcium chloride. This extra rapid hardening cement is not produced in India, but if it is made available in works abroad, particular note should be taken regarding the possible presence of calcium chloride in extra rapid hardening cement. Most specification prohibit the use of calcium chloride in prestressed works and now there is a trend towards avoiding calcium chloride even in ordinary works, if the concrete contains reinforcements or embedded metal fixtures and fasteners, because of the corrosion risk.
Portland slag cement
The slag obtained during the manufacture of iron and steel has a composition similar to that of cement clinker. This fact is used in manufacturing Portland slag cement which is obtained by inter- grinding a mixture of Portland cement clinker and granulated slag with addition of gypsum. The resultant product has properties similar to those of ordinary Portland cement and therefore can be used whenever ordinary Portland cement is used. Some times Portland slag cement is specified for works where durability problems arise because of sulphates or marine environments, sewers work, structures involving large mass concrete such as dams, retaining walls, and bridge abutments and for structure exposed to sulphate-bearing soils such as foundations and roads. However in prestressed concrete works the slag content of the cement should not be more than 50 %.
Portland pozzolana cement
This is a blend of ordinary Portland cement and a suitable pozzolans, say fly-ash or burnt clay pozzolana. It can be generally used whenever ordinary Portland cement is usable under normal condition.
Increased impermeability, lower heat of hydration, lower drying shrinkage, reduced alkali-aggregate expansion and improved resistance to aggressive chemical, resistance to sulphate attack and sea- water are some of the advantages of using Portland pozzolana cement.
However, the addition of pozzolana does not contribute to strengths at early ages and probably for this reason pozzolana cement is not recommended for prestressed concrete works, For the same reason, demoulding may have to be delayed in precasting yards. Certain water reducing admixtures, especially those containing lignosulphonates are also retarders and therefore should not be uses with pozzolana cement without adequate trials.
High strength ordinary portland cement
This cement is intended for specialized works such as prestressed concrete and some item of precast concrete requiring consistently high strengths concrete. No special precautions required in using this cement.
Hydrophobic Cement
This type is specified when prolonged storage of cement under unfavorable condition is anticipated. It is obtained by inter grinding ordinary portland cement with hydrophobic (water repelling) agents such as oleic acid or stearic acid. Hydrophobic cement should not be confused with water proofing cements. With hydrophobic cements, a longer mixing period will be necessary in order to remove the coating of hydrophobic agent over the cement grain.
Sulphate Resisting Cement
This in other words known as low C3A cement. The tri-calcium aluminate content in the cement is restricted to 5 % maximum and tetra calcium alumino ferrote to 25 %. This cement is used in structures in contact with sub soil and ground water sulphates and should not be used for concrete likely to be exposed to acids.
Super Sulphated Cement
Though an Indian standard specification is available this type is not produced in India, but may nevertheless be specified , for instance, in works abroad. It is recommended for use where concrete is likely to be attacked by sulphates. It is a product of granulated blast furnace slag , calcium sulphate (gypsum) and a small quantity of portland cement clinker. This cement has chemical resistance to most of the aggressive conditions encountered in construction industry and to the attack of sulphates in particular.
Precaution
• According to IS 6909 use of Super Sulphated cement is permitted in tropical conditions, provided the prevailing temperature is below 40 0 C .
• Generally Super Sulphated cement should not be used for steam cured products. If accelerated curing is to be adopted along with use of super Sulphated cement the curing temperature should be restricted to say 50 Degree Centigrade.
• Super Sulphated cement should not be mixed with any other type of cement.
• Special care is required in the storage of supersulphated cement since it will deteriorate rapidly in poor storage conditions. The rate of strength development of concrete made with super Sulphated cement is considerable reduced at low temperature. Unless adequately cured, the surface of super Sulphated cement concrete is liable to become friable and dusty. It should be
kept moist atleast four days after placing .
High Alumina Cement
This is usually used when durability under extreme sulphate or acid attack is desirable and when very early development of strength is required or for emergency repair work. In tropical countries, high alumina cement should be used with extreme care and caution. Use of high alumina cement for general construction purposes has gone out of vogue. Proper specification and full instructions must be insisted upon before taking up responsibility for execution. When used with crushed bricks it makes a good refractory concrete. High alumina cement is not recommended for structural use.
Low Heat Portland Cement
The chemical constituents proportioned in such a way that the heat liberated due to hydration is reduced, making the cement particularly suitable for use in massive structures, such as dams, bridge abutments, and retaining walls. Its rate of gain of strength is how ever slower than that of ordinary Portland cement hence it requires longer curing period.
Besides these other types of cements like oil well cement, white and colored cement, shrinkage compensated cement for grouting applications, acid resisting cement are available. These cements are produced by some cement manufactures based on the requirements only and not on regular basis.
