Types of cement:- Cement is an adhesive and cohesive material that is capable of bonding together particles of solid matter into a compact durable mass. It is obtained by mixing limestone and clay, burning them and grinding to fine powder.
In other words, Cement is one of the most widely used material that has cohesive and adhesive properties in the presence of water. Such blocks of cement are called hydraulic cement. This type consist primarily of silicates and aluminates of lime obtained from limestone and clay. This mixture is round, blended, fused in a kiln at about 1400 C, and a product called clinker is obtained. The clinker is cooled and ground to get cement. Such cement combines chemically with water to form a hardened mass.
The hydraulic cement is usually known as Portland cement because of its resemblance upon hardening to the Portland stone found near Dorset, England. Thus the name was first used by Joseph Aspdin of Leeds, England in 1824 in his patent.
Different types of cement, properties, and uses
- Ordinary Portland cement
- Portland pozzolana cement,
- Rapid hardening Portland cement,
- Portland slag cement,
- Hydrophobic Portland cement
- Low heat Portland cement and
- Sulphate resisting Portland cement
Besides these, there are few special-purpose types of cement such as:
- High alumina cement,
- Supersulphated cement,
- Masonry cement,
- Oil well cement,
- White Portland cement,
- Colored cement,
- Water-proof cement,
- Expanding cement,
- Sand cement, and
- Air-entraining Portland cement.
Ordinary Portland Cement
This cement is the basic Portland cement and is best suited for use in general concrete construction where there is no exposure to sulphates in the soil or in groundwater.
This cement is obviously produced in the maximum quantity than other cements. It is produced by grinding Portland clinker with the possible addition of a small quantity of gypsum, water or both and not more than 1 % of air-entraining agents. This very useful types of cement.
The clinker of Portland consists of calcium silicate and is obtained by heating to incipient fusion a predetermined and homogeneous mixture of materials mainly containing 59% – 64% lime (CaO) and 19% – 24% silica (SiO2) with 3% – 6% of alumina (Al2O3) and 1% – 4% iron oxide (Fe2O3).
The setting and hardening of cement after the addition of water to it is due to the dissolution and reaction of the constituents.
The calcium aluminate is the first to set and harden, then comes calcium trisilicate (3CaO.2SiO2.3H2O) which is responsible for the early gain in strength during the first 48 hours. Calcium disilicate reacts slowly and contributes to the strength at a later stage usually from 14 to 28 days.
Typical chemical reactions are as follows:
3CaO.Al2O3 + 6H20 → 3CaO.Al2O3.6H2O
(3CaO.SiO2) + 6H2O → 3 CaO.2SiO2.3H2O + 3Ca(OH)2
3 (2CaO.SiO2) + 6 H2O → 3CaO.2SiO2.3H2O + 3 Ca(OH)2
Types of Ordinary Portland cement
- 33 grade ordinary Portland cement,
- 43-grade ordinary portland cement,
- 53 grade ordinary Portland cement,
Portland pozzolana cement
The Romans and Greeks knew that certain volcanic materials if finely ground and mixed with lime and sand could be used as building mortars of good strength. The Roman builders used the red or purple volcanic tuff found near the Bay of Naples, notably in the neighborhood of Pozzuoli. This was a good building material and became known as pozzolana, a name that is now frequently used to describe a range of materials both natural and artificial. The main use of pozzolana is to replace a proportion of cement in a mix and this can result in a significant economy particularly if the materials are locally available.
The pozzolana is essentially a siliceous material which while in itself possesses little or no cementitious properties will, in finely divided form and in the presence of water react with calcium hydroxide at suitable temperature to form compounds possessing cementitious properties. The term includes natural volcanic materials having pozzolanic properties such as diatomaceous earth, calcined clay and fly ash.
Portland pozzolana cement is prepared either by grinding clinker and pozzolana or by blending Portland cement and fine pozzolana. The proportion of pozzolana may vary between 10% to 25% by weight of cement.
Rapid hardening Portland cement
The cement is manufactured by intimately mixing together calcareous and argillaceous and/or other silica, alumina or iron oxide bearing materials.
This cement has the same chemical composition as the ordinary Portland cement but is more finely ground. Its 24 hours strength is nearly equal to that attained by ordinary portland cement after 3 days. The use of this cement permits early removal of shuttering thus directly affecting saving in time and money.
It is generally used in road work and bridge construction where the time factor is very important.
Portland slag cement
In Portland slag cement a Blast furnace slag is a non-metallic product consisting essentially of glass containing silicates and aluminosilicates of lime and other bases and is developed simultaneously with iron in a blast furnace or electric pig iron furnace. Ground granulated slag is obtained by further processing the molten slag by rapidly chilling or quenching it with water or steam and air.
This cement is prepared by intimately grinding Portland cement clinker and ground granulated blast furnace (GGBF) slag with the addition of gypsum and permitted additives. and the proportion of slag should not be less than 25% and not more than 65% of Portland slag cement. The slag contains oxides of lime, alumina, and silica and easily replaces clay or shale used in the manufacture of ordinary Portland cement.
Portland slag cement can be used for all purposes for which ordinary Portland cement is used.
However, the former has certain advantages: it has lower heat evolution and is more durable.
Thus, it can be used in mass concrete structures such as retaining walls, foundation, and dams.
Hydrophobic cement is prepared from ordinary Portland cement clinker by adding certain water repellent chemicals during the grinding process. A water repellent coating is formed over each particle of cement that prevents water or moisture from the air being absorbed by the cement. This film is broken during the mixing of concrete and the normal hydration process takes place in the same manner as with the ordinary Portland cement.
This cement is ideal for storage for longer periods in extremely wet climatic conditions. The hydrophobic agents can be oleic acid, stearic acid, naphthenic acid, etc. This cement is different from waterproofing cement.
High alumina cement
This cement is obtained by grinding high alumina clinker consisting of monocalcium aluminates. High alumina cement clinker is obtained by complete or partial fusion of a predetermined mixture of materials mainly containing alumina (Al203) and lime (CaO) with a smaller proportion of iron oxides, silica (Si02) and other oxides. High early strength, the high heat of hydration and very high durability against chemical attack are the characteristics of high alumina cement. It is black in colour. Its rapid hardening properties are due to a higher percentage of calcium aluminate in place of calcium silicate as found in ordinary Portland cement.
The rapid development of heat of this cement is of great advantage when concreting is to be done in freezing weather. Its use in hot weather, however, is very limited due to increased porosity, hence reduction in strength.
It is a hydraulic cement having sulphuric anhydride (SO3) content less than 5% and made by inter grinding mixture of at least 7% granulated blast furnace slag, calcium sulfate and a little amount of lime or Portland clinker. This cement is used in very serious conditions such as marine works, mass concrete jobs to resist the attack of aggressive waters, reinforced concrete pipes in groundwaters, concrete construction in sulphate bearing soils, and in chemical works exposed to the high concentration of sulphates of weak solutions of mineral acid. It can also be used for the underside of bridges over railways and for sewer pipes.
High alumina cement and supersulphated cement must be used only under special circumstances.
This cement is obtained by intergrading a mixture of Portland cement clinker with inert materials (non-pozzolanic), such as limestone.
Conglomerates, dolomite, limestone and gypsum, and air-entraining plasticizer in suitable proportions. Masonry cement is slow hardening, has high workability and high water retentivity that makes it especially suitable for masonry work.
Oil well cement
At the condition of high pressure and temperature in sealing water and gas pockets, and setting casing during the drilling and repairing of oil wells Hydraulic cement is suitable to use , often contains retarders to meet the requirements of such use in addition to coarser grinding and/or reduced tricalcium aluminate (C3A) content of clinker.
Slurries of such cement have to remain pumpable at high-temperature and pressures for a sufficient length of time then harden very rapidly.So this is a very useful types of cement.
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