TYPES OF CEMENTS
The demands made on the cement industry from time to time by the engineers, builders, and users of cement for specialized jobs, and efforts of cement technologists led to the development of different types of cement with special properties.
VARIETIES AND GRADES
India is at present producing different varieties of cement-like Ordinary Portland Cement (OPC), Portland Pozzolana Cement (PPC), Portland Blast Furnace Slag Cement (PBFS), Rapid Setting Cement, Oil Well Cement, White Cement, etc. It is also producing High Compressive Strength Cement like Grade 43 (43 MPa after 28 days) and Grade 53 (53 MPa after 28 days) to meet the special requirements of the India market like prestressed railway concrete sleepers.
Cement produced in India conforms to Indian Standard Specifications issued by Bureau of Indian Standard (BIS) the national body for the formulation and regulation of India Standards. The Indian Standard Specifications for the different varieties and grades of cement produced in India are given below.
INDIAN STANDARD SPECIFICATIONS
Ordinary Portland Cement – 33 Grade High Strength Ordinary Portland Cement – 43 Grade – 53 Grade Portland Pozzolana Cement Portland Blast Furnace Slag Cement High Alumina Cement for Structural Use Rapid Hardening Portland Cement Oil Well Cement Sulphate Resisting Portland Cement Low Heat Portland Cement White Portland Cement Super Sulphate Cement Hydrophobic Cement Manonry Cement | IS : 269 – 1989 IS : 8112 – 1989 IS : 12269 – 1987 IS : 1483 – 1991 IS : 455 – 1989 IS : 6452 – 1989 IS : 8041 – 1990 IS : 8229 – 1986 IS : 12330 – 1988 IS : 12600 – 1989 IS : 8042 – 1989 IS : 6909 – 1990 IS : 8043 – 1991 IS : 3466 – 1967 |
PROPERTIES OF CEMENT
PHYSICAL PROPERTIES
The following factors are examined to appraise the physical properties of cement :
- Fineness
- Sieve Residue
- Specific Surface
- Setting time
- Soundness
- Compressive strength
- Heat of hydration
Fineness
Sieve Residue: The quantity of cement depends to a great extent on the fineness of grinding. Finely ground cement has a higher initial strength than coarsely ground cement.
Specific Surface: The specific surface of cement in Cm2/gm is calculated from the air permeability of a bed of cement, its porosity, the density of the cement, and the viscosity of air. The measure of permeability is the time is taken for a certain quantity of air to flow through the bed under specified conditions. The air permeability method according to Blain is mostly used in the cement industry.
Setting Time
Cement sets and gives concrete sufficient strength within a reasonable time, obviously, in order to allow sufficient time for applying the mortar or placing the concrete, cement must not set too quickly. It is also important that after mixing, the setting should be complete within a reasonable period. The setting times, initial and final set are specified in Indian standard specification.
Soundness
Soundness is understood as the ability of the cement to maintain a constant volume, thus a cement is to be rated as sound if, after it has hardened, it remains tree from expansion effects which may crack, loosen and destroy the hardened paste.
Strength Requirements
Depending upon its class and type, a cement should attain the compressive strengths required at one, three, seven, and twenty-eight days, which are not less than the minimum specified in various cement standards. Because of varying test methods applicable, different cement standards are not entirely comparable. In general, a lower water-cement ratio and a higher content of cement resulting in higher strength.
Heat of Hydration
Ordinary Portland Cement during the first four weeks of hardening liberates heat of hydration to the extent of about 90 cal/gm. Where great masses of concrete are involved as in large hydraulic structures there is always a risk of expansion and shrinkage cracks arising from the thermal stresses created by the heat of hydration and by the dissipation of the same. Low heat Portland cement liberates only 70 cal/gm. During the same period and can be used without fear of such troubles.
CHEMICAL PROPERTIES
The various chemical characteristics which have an influence on the quality of cement are:
| Lime Saturation Factor (LSF) Alumina Modulus (A/F) Insoluble Residue (IR) Loss on Ignition (LOI) Magnesia (Mgo) Sulphate as SO3 Mineral Composition (C3S, C2S, C3A, C4AF) Free Lime (CaO f) Alkalies (as Na2O equivalent) Chloride (Cl) |
ORDINARY PORTLAND CEMENT (OPC)
Ordinary Portland Cement is made by heating a mixture of limestone and clay or other materials of similar composition and sufficient reactivity ultimately to a temperature of 1450o C. Partial unification occurs and nodules of clinker are produced. The clinker is mixed with some percent of gypsum and finely ground to make the cement.
This cement develops a high strength in its early stages and continues to grow stronger with the passage of time.
Used for all types of construction from sidewall to high rise buildings, bridges, roads, etc.
Grades 43 & 53 are used where greater strength is required e.g. for the manufacture of prestressed concrete, railway sleepers, precast products, and high strength concrete.
IRS-T-40 – Special grade cement developed for use in concrete sleepers to meet the requirements of Indian Railways, has higher fineness (3700 cm2/g), and seven days compressive strength comparable to grade 53 (375 Kg/cm2).
| Conforms to : IS : 269 – 1989 : Grade 33 IS : 8112 – 1989 : Grade 43 IS : 12269 – 1987 : Grade 53 |
LOW HEAT PORTLAND CEMENT
Where great masses of concrete are involved as in large dams, there is always a risk of expansion cracks arising from the thermal stresses created by the heat of hydration. Low Heat Portland Cement liberates only 70 cal/gm during the 28 days of hardening (as against 90 cal/gm from OPC) and can be gainfully used without fear of the above troubles.
| Conforms to IS : 12600 – 1989 |
PORTLAND POZZOLANA CEMENT (PPC)
Portland Pozzolana Cement (PPC) is manufactured by grinding together Portland Cement clinker and Pozzolana with the addition of gypsum or by intimately and uniformly blending Portland Cement. Fly ash, calcined clays are generally used as Pozzolana for the manufacture of Portland Pozzolana Cement.
PPC provides improved workability, less segregation, and bleeding, has increased water tightness, and reduced the tendency of lime to separate. Further, there is the prevention of damage due to alkali reaction in concrete made from PPC and an increase in the durability of structure in sulfate-containing waters. It has a low heat of hydration.
The study on the incidence of corrosion of steel reinforcement in PPC concrete indicates that under normal and semi-industrial environments. The PPC may not induce corrosion of steel reinforcement in PPC concretes. But may cause considerable corrosion of steel under the marine and industrial environments due to failing in pH (alkalinity) of these concretes. The incidence of corrosion in PPC concrete can, however, be brought at par to OPC concrete, by providing 10 mm or more cover thickness or using more cement i.e. rich concrete.
PPC is used in construction of dams, dykes, sewage pipes, etc.
| Conforms to IS : 1489 – 1991 |
RAPID HARDENING PORTLAND CEMENT
Highly early strength Portland Cement/Rapid Hardening Portland Cement was developed to meet the demands for speed in modern construction.
Special Properties: This cement develops a high early strength at every stage which continues to increase with the passage of time; expansion or shrinkage during hardening is very small; develops high strength even in cold weather.
This helps reduce construction period.
| Conforms to : IS : 8041 – 1990 |
PORTLAND BLAST FURNACE SLAG CEMENT (PBFS)
PBFS Cement is a mixture of finely ground granulated blast furnace slag and Portland cement clinker with a calcium sulfate activator. PBFS cement is suitable for mass concrete structures. The slag constituent shall be not less than 25% or more than 65% of the Portland slag cement as per B.I.S.
PBFS cement has the ability to combine with lime to form stable compounds, which help prevent leaching of lime as efflorescence, whenever water seepage takes place. PBFS reduces alkali-aggregate reaction. It is better resistant to solid and water containing excessive amounts of sulfates of alkali metals, alumina, and iron as well as too acidic waters.
PBFS Cement is used in the construction of bridges, seaports where saline water comes into constant contact with the foundations. PBFS is also used in the preparation of channels, through which the washings of acids, salts, sulfur, etc. flow.
| Conforms to : IS : 455 – 1989 |
WHITE CEMENT
White cement is essentially a cement that incorporates the requirements of ordinary Portland cement but only it is pure white in color. Its compressive strength shall not be less than 90 percent of that specified for 33 grade ordinary Portland cement. It is manufactured from raw materials nearly iron-free such as calcite, chalk, and china clay, Fe2O3, Mn2O3, and Cr2O3 should not exceed 0.4%, 0.35%, and 0.01% respectively in the raw mix. Higher burning temperatures than usual are essential for achieving the desired clinkering. Fuel oil is used for burning the raw mix in place of coal. Grinding of the clinker is carried out in mills containing porcelain balls and lined with a flint lining plate.
White cement is used for tiles, terrazzo, artistic decorations, floors, decorative concrete, etc. generally meant for non-structural use.
| Conforms to : IS : 8042 – 1989 |
SUPER SULPHATED CEMENT
Super sulfated cement is a product of a finely ground mixture of granulated blast furnace slag, calcium sulfate and a small amount of ordinary Portland cement or clinker, or any other source of time. The dry granulated blast furnace slag component of the mixture shall not be less than 70% by weight.
Super sulfated cement is used in a variety of aggressive conditions i.e. saline soils, marine works, mass concrete jobs to resist the attack by aggressive waters, reinforced concrete pipes in groundwater, concrete construction in sulfate bearing soils, and in chemical works under conditions involving exposure to high concentrations of sulfates or weak solutions of mineral acids. It has also been used for the underside of bridges over railway lines and for concrete sewers carrying industrial affluents. Its heat of hydration is low as compared to OPC.
| Conforms to : IS : 6909 – 1990 |
SULPHATE RESISTING CEMENT
Concrete made using ordinary Portland cement cured at ordinary temperature, is susceptible to attack by sulfate solutions which can cause it to expand and disintegrate. Some groundwaters as well as seawater contain enough sulfate and pose a serious problem. The severity of the attack depends primarily on the C3A content, and Sulphate Resisting Cements contain reduced properties of C3A or none at all. Rapid cooling of clinker as it leaves the kiln, improves the sulfate resistance, either because it causes less C3A to be formed or because it affects the size or perfection of the crystals.
The resistance of concrete to sulfate attack may be improved in the following ways :
- Sulfate resisting cement (C3A less than 5%) should be used where concentrations are greater than 0.2% of water-soluble sulfates in the soil or 1000 ppm sulfate in the water are present and the structure is exposed to less than 25 to 30o C. for most of its life. When the concentrations are 0.1 to 0.2% of water-soluble sulfates in the soil or 150 to 1000 ppm sulfates in the water, OPC can be used. When sulfate concentrations are low and/or the temperature to which the structure is exposed for the majority of its life is above 25 to 30o C, the sulfate attack is of low intensity.
- The water-cement ratio should not exceed 0.50 and the concrete should have increased minimum cement content. Concrete should be vibrated and cured thoroughly.
- Substitution of 15 to 30% and even 65% of cement by weight, by an active pozzolanic material, may be very effective (e.g. Finely powdered blast-furnace slag from steel mills or fly ash from thermal powerhouses.)
Sulfate Resisting Cement is used mainly in marine structures.
| Conforms to : IS : 12330 – 1988 |
OIL WELL CEMENTS
Oil well cement is used by the petroleum industry for cementing gas and oil wells at high temperatures at pressures. Slurries of such cement have to remain pumpable at these elevated temperatures and pressures for a sufficient length of time and then harden fairly rapidly. The two principal uses of oil well cement are- to cement the steel casing to the walls of the well and to seal the porous formations which contain either gas/water that is flowing into oil-bearing formations. With current technology, oil wells are typically up to 6000 meters deep. The temperature of the rock at the bottom of the well at that depth is 100 – 250oC. the pressure experienced by the slurry during pumping is equal to the hydrostatic load plus the pumping pressure and maybe as much as 150 MPa.
Indian Standard Specification for Oil-Well cement IS: 8229 – 1986 covers nine classes of Oil-Well cement used for the purpose of securing Oil-Well pipe casing with the surrounding earth and rocks i.e. – classes A, B, C, D, E, F, G, H, J.
HIGH ALUMINA CEMENT
High Alumina Cement is mainly a refractory cement but in some cold areas, this cement may find use as a structural material taking advantage of high heat of hydration and high early strength development. Mortars of concrete made with aluminous cement and a refractory, or heat resistance aggregate (Such as crushed firebrick), do not crack or spall during repeated firings to white heat and these could be safely quenched in water without loss of stability.
These properties have since led to the widespread use of such mixtures as “Castable refractories”, for furnace or kiln construction and repairs.
This cement is not to e used for structural purposes.
| Conforms to : IS : 6452 – 1989 |
HYDROPHOBIC CEMENT
In some parts of the country, where humidity is high, cement may form lumps and deteriorate in strength on prolonged storage. By the use of hydrophobic agents, it is claimed that deterioration of cement on prolonged storage is arrested. Resistance to moisture penetration by hydrophobic cement is noteworthy.
| Conforms to : IS : 8043 – 1991 |
MASONRY CEMENT
Masonry cement is a product obtained by intergrading a mixture of Portland cement clinker with inert materials such as limestone dolomite and gypsum and an air-entraining plasticizer in suitable proportions. Masonry cement possesses greater plasticity and water retentivity that the OPC.
Masonry cement is used in mortar for brick, stone, and concrete block masonry, as well as for rendering and plastering work. Because of a smoothness, cohesiveness, and strongness, properties yet workable mortar when mixed with fine aggregates, masonry cement is considered superior to lime mortar, lime cement mortar or straight cement mortar.
However, masonry cement is not intended for use in structural concrete, flooring and foundation work, or for reinforced and prestressed concrete work.
| Conforms to : IS : 3466 – 1967 (Revised) |
