what is cement? : Cement is the most used construction material in the world that has both adhesive and cohesive properties due to which it can make bonding and bind particles of solid matter into a compact durable solid mass. It is obtained by mixing limestone and clay, burning them, and grinding to a fine powder. Here we discuss different types of Cement.
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.
The cement manufacturing process is given here in detail: manufacturing of cement.
Types of cement :
Followings are the 19 types of cement:
- Ordinary Portland cement
- Portland pozzolana cement
- Rapid hardening Portland cement
- Extra rapid hardening cement
- Portland slag cement
- Hydrophobic Portland cement
- Low heat Portland cement
- Sulphate resisting Portland cement
- Quick setting Cement
- High alumina cement,
- Supersulphated cement
- Masonry cement
- Oil well cement
- White Portland cement
- Colored cement
- Water-proof cement
- Expansive cement
- Sand cement, and
- Air-entraining Portland cement.
In this list, 9 to 19 are special-purpose cement.
Ordinary Portland Cement
This cement is also called 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
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.
PPC cement is suitable for the following conditions: For waterfront structure or for marine structure as in dams, bridge piers and thick foundation where mass concrete is used, also used for sanitation system like Sewers.
The history behind PPC: 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 one of the Siliceous material, therefore, it has no cementitious properties or less binding property but in the finely divided form with the presence of water can react with calcium hydroxide at a suitable temperature to form compounds having sufficient binding properties. Other natural volcanic materials having pozzolanic properties like diatomaceous earth, calcined clay, and fly ash.
Advantages of PPC (Portland Pozzolana cement )
- The production is economical because costly clinker is replaced by cheaper.
- This cement reduces the permeability so, suitable for hydraulic structure. But it requires very fast curing is tedious.
- It produces a very slow rate of the heat of hydration and also reduces the heat.
- The particle size of PPC is smaller than OPC, so it improves the pore size distribution and also reduces micro-cracks.
- PPC mortar is more volume than OPC mortar.
- The Ultimate long term Strength of PPC is more than OPC if enough curing for pozzolanic action.
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.
Extra rapid hardening cement:
Extra rapid hardening cement is a proper modification of rapid hardening cement. It is manufacture by inter grinding Calcium Chloride with rapid hardening portland cement. Normally, calcium chloride with 2 percentage by weight of rapid hardening cement is mixed. Since Extra rapid hardening cement is very sensitive, concrete should be transported, placed, compacted, and finished within 20 minutes after mixing. After the addition of water, a very huge amount of heat is evolved within a short period of time along with hydration. So, this type of cement is perfect for concreting in cold weather.
Properties of Extra Rapid hardening cement:
- At the age of one or two days strength of Extra rapid hardening cement is 25% more than rapid hardening cement, and only 0-20 % higher at 7 days but at 90 days both cement have nearly the same strength.
- The use of Extra rapid hardening cement in pre-stressed concrete is prohibited.
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.
Sulphate Resisting Cement:
Since ordinary Portland cement is susceptible to attack of sulfate, sulfate resisting Cement is developed to use where the soil is infected with sulfates.
Due to the attack of sulphate in O.P.C. cement, there are chances of expansion within the framework of concrete and there are cracks and subsequent disruption.
Many research found that to reduce sulphate attack, cement with low C3A content better results. Sulphates resisting cement has a high silicate content that is with low C3A and low C4AF.
Under the following conditions sulphate resisting cement is used:
- When concreting is done for Marine structure in the zone of tidal variations.
- Where foundation soil is infected with Sulphate.
- In marshy soil or sulphate bearing soil.
- Concrete construction used for sewerage treatment, etc.
Quick setting Cement:
Quick setting cement sets very fast. This cement is used for aggressive foundation conditions like where pumping is needed or submersible land area.
In quick setting cement, the quick setting property is achieved by reducing the Gypsum content at the time of clinker grinding. Quick setting cement is also used in some typical grouting operations.
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 super sulphated cement must be used only under special circumstances.
Masonry 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
Oil-well cement is a special purpose cement for sealing the space between steel casing and sedimentary rock strata by pumping slurry in the oil-well which is drilled for the search of oil. This cement prevents the escape of oil or gas from the oil-well. This cement also prevents from sulphur gases or water containing dissolved salts. This all properties of oil-well cement is obtained by adding the compound composition of cement with retarder agents like starches or cellulose products or acids.
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 type of cement.
Coloured cement is made by adding colour carrying pigment with a Portland cement clinker. The dose of pigment is 5-10 percentage of Portland cement. For achieving various colors, either white cement or grey Portland cement is used as a base material. The white Portland cement is manufactured as same as OPC.
Expansive cement is a type of cement that shows no change in volume on drying. This type of cement also not shrink while hardening or after that. This type of cement has been developed by using an expansive agent and stabilizer.
Generally, sulphoaluminated clinker is mixed with Portland cement with stabilizer. This cement is used for grouting anchor bolts or grouting machine foundations, grouting the prestressed concrete ducts where volume change is very sensitive for stability.
Air entraining cement is manufacture by adding an air-entraining agent in power or in liquid form with OPC cement clinker. There are other external materials added are animal and vegetable fats, oil and another acid with a certain wetting agent like aluminum powder, hydrogen peroxide, etc. by introducing air-entraining agent frost resisting characteristics of hardened concrete is increased. Workability, segregation, and bleeding property of concrete is improved by using this cement.
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