What Is Cement?
Evidence of the use of cement is believed to have been found in the hidden civilization of Mohenjodaro dating back 5000 years. The ancient Greeks used some form of mortar, but it remained for the Romans to develop and use cement.
Cement is a substance that is used in a soft or plastic state which then hardens to make things stick together. It can thus be regarded as a binder, glue, or adhesive which in its hardened state binds aggregate particles
to form a strong, rigid composite. Remember the mixture of cement, sand, stone, and water is referred to as concrete.
There are various substances which can act like cement, but we will be concentrating on the specific types used for concrete within the building and construction industry.
Cement for construction is based on Portland cement and are supplied in powder form (either in bags or bulk) and if mixed with water, will set and develop strength.
Such cement is used extensively in most parts of the world because the raw materials are available in most regions. Also, these cements are relatively cheap and versatile as setting takes place at normal temperature and pressure, and can be used underwater and result in a strong and durable concrete.
Types of Cement.
- OPC Cement
- PPC Cement
- Acid Resistance Cement
- Blast Furnace Cement
- Coloured Cement
- Expanding Cement
- High Alumina Cement
- Hydrophobic Cement
- Low Heat Cement
- Quick Setting Cement
- Rapid Hardening Cement
- Sulphate Resisting Cement
- White Cement
- Artificial Cement
- Air Entraining Cement
- Masonry Cement
- Water Repellent Cement
- Water Proof Cement
1. OPC Cement
Ordinary Portland Cement contains two basic components, namely argillaceous and calcareous. In argillaceous materials, calcareous materials, and in clay predominates, calcium carbonate predominates. Good ordinary cement contains these ingredients.
- Lime (CaO) ———————-62%
- Silica (Sio2) ——————–22%
- Alumina(Al2 u3) —————-5%
- Calcium sulfate (CaSo4)——–4%
- Iron Oxide (Fe2 03)————–3%
- Magnesia (MgO) —————-2%
- Sulphur ————————-1%
- Alkalies ————————-1%
2. Portland Puzzolana Cement (PPC)
It’s manufactured by grinding Portland cement clinker and puzzolana (generally fly ash 10-25percent by mass of PPC) or by intimately and Gradually mixing Portland cement and fine puzzolana.
Puzzolana (burnt clay, shale, or fly ash) doesn’t have cementing value itself but gets the property of combining with lime to make a stable lime-puzzolana compound that has definite cementitious properties.
Free lime within the cement is thus removed. Thus, the resistance to chemical attack raises, which makes it suitable for marine works.
The hardening of Portland puzzolana cement is composed in hydration of Portland cement clinker compounds and after that from the interaction of this puzzolana with calcium hydroxide released through the hardening of clinker.
In the same time, calcium hydroxide is bound to a water-soluble calcium hydrosilicate Based on the reaction
- Ca (OH)2 + Si02 + (n -1) H2O = CaO.SiO2.nH20
With the effect which puzzolana Portland cement acquires greater water-resisting property than ordinary Portland cement
Properties of Portland Puzzolana Cemen
All these have a lower rate of development of strength, but ultimate strength is comparable with ordinary Portland cement
- Compressive Strength
|72 ± 1 hr||16.0 N/Sq.mm|
|168 ± 2 hrs||22.0 N/Sq.mm|
|672 ± 4 hrs||33.0 N/Sq.mm|
The final and the initial setting times are 600 minutes (maximum) and 30 minutes (minimum), respectively.
The drying shrinkage shouldn’t be more than 0.15%, and the fineness should not be less than 300 Sq.m./kg.
Uses of Portland Puzzolana Cemen
- It has low heat evolution and is used in the places of mass concrete such as dams and in places of high temperature.
3. Acid Resistance Cement
This is consists of acid resistance aggregates like quartz, quartzite’s, etc., an additive such as sodium Fluro silicate (Na2SiO6) and an aqueous solution of sodium silicate.
This is used for acid-resistant and heat resistant coating of installations of chemical Industry.
By adding 0.5 percent of unused oil or 2 percent of cereal, its resistance to water is increased and known as water-resistant acid water-resistant cement.
4. Blast Furnace Cement
For this cement slag as obtained from a blast furnace at the manufacture of pig iron and it contains basic components of cement, namely alumina, lime, and silica.
The properties of the cement are more or less the same as those of ordinary cement (OPC in cement) and end up being economical as the slag, that can be a waste product, is used in its manufacture.
5. Coloured Cement
The cement of the desired colour could be obtained by intimately mixing the mineral pigment with ordinary cement.
The amount of coloring can vary from 5 to 10 percent and strength of cement when it exceeds 10 percent. Chromium oxide provides brown, red, or yellow for various proportions.
Coloured cement is used for finishing of floors, external surfaces, artificial marble, granite windows.
6. Expanding Cement:
This type of cement is produced by Incorporating an expanding medium Such as sulpho – aluminate and a stabilizing agent to ordinary cement
Hence this cement expands in which as other cement shrinks. Expanding cement is utilized for the construction of water retaining structures and for repairing damaged concrete surfaces.
7. High Alumina Cement
This cement is produced by the grinding clinkers formed by calcining lime and bauxite.
The entire content shouldn’t be less than 32 percent, and also the ratio by weight of alumina into lime would be between1.30 and 0.85.
8. Hydrophobic Cement
This type of cement includes admixtures, which reduces the wetting capability of cement grains.
The typical hydrophobic admixtures are acidol naphthene soap, oxidized petrolatum, etc. when hydrophobic cement is used, the fire pores in concrete are uniformly dispersed, and so the frost resistance, as well as the water-resistance of this concrete, are substantially increased.
- 2(CaO.AL2.O3.10H2o)+H2O = 2CaO.Al2O3.8H2O + 2Al(OH)2
9. Low Heat Cement
Considerable heat is produced throughout the setting action of cement. To be able to cut the amount of heat, this type of cement is utilized.
It contains a lower percentage of tricalcium aluminates C3A and a higher percentage of dicalcium silicate Cgs. This type of cement is utilized for mass concrete works because of its procedures less compressor strength.
10. Quick Setting Cement
This cement is prepared by adding of a small percentage aluminum sulfate which reduces the percentage of gypsum or retarded for setting action and accelerating the setting action of cement.
Because of this, cement hardness less than 30 minutes, mixing and placing operations needs to be completed. This cement is used to put concrete underwater that was static or running water.
11. Rapid Hardening Cement
This cement has the exact same final and initial setting times as per that of ordinary cement(OPC in cement).
But it attains higher strength in the early days because of
- Burning at very high temperature.
- Increased lime content in the cement composition.
- Very fine grinding.
This cement Initial setting time 30 min, Final setting 10 Hours
This cement compressive strenth 1 day = 16 N/sq.m ,3 day = 27.5 N/sq.m
12. Sulphate Resisting Cement
Inside This cement percentage of tricalcium, aluminates are kept below 5 to 6 percent, and it Contributes to the increase in resisting power against sulfate.
This cement is used for a structure that’s likely to be damaged with a severe alkaline condition like canal linings, culverts, siphons, etc.
13. White Cement
The variety of ordinary cement, and it’s prepared to form such raw materials that are practically free of coloring oxides of Iron, manganese or chromium.
For the burning of this cement, oil fuel is used instead of coal. It is used for floor finish; plasterwork, ornamental works, etc.
14. Artificial Cement
This best variety of Artificial cement is known as ‘Portland Cement’ as it resembles in color to a variety of sandstone, found in abundance in Portland in England. Otherwise, this is known as ‘Normal Settling Cement’ (or Ordinary Cement) portland cement, often called the magic powder is a finely ground material consisting of compounds of lime, silica, alumina, and iron.
When mixed with water, then it forms a paste which hardens and binds the aggregates (sand, gravel, crushed rock, etc.) together to form a hard, durable mass called concrete. Thus, cement is one of the ingredients of concrete.
Artificial cement is manufactured by first burning at a really high temperature that the mixture of calcareous mostly calcium carbonate) and argillaceous ( mainly clay) then grinding the calcined goods, i.e. (clinker) with small amount of gypsum to a fine powder called cement.
Also, read: What Is Bulkage of Sand (Fine Aggregate )
15. Air Entraining Cement
This is produced by adding a number of indigenous air-entraining agents such as resins gues. Sodium salts or sulfates etc. during the grinding of clinker.
This type of cement is to improve the workability with smaller water-cement ratio and also to improve frost resistance of concrete. Vinson resin or vegetable fats and oils and fatty acids are ground with ordinary cement.
These materials have the property to entrain air in the form of fine tiny air bubbles in concrete.
Properties of Air Entraining Cement
- Minute voids are formed while setting of cement which increases resistance against freezing and scaling action of salts. Air entrainment improves workability, and water/cement ratio can be reduced, which in turn reduces shrinkage, etc.
Uses of Air Entraining Cement
- Air entraining cement is used for the same purposes as that of OPC in Cement.
16. Masonry Cement
The Portland cement clinker is mixed and ground intimately with pozzolanic material (flash or calcined clay), or non-pozzolanic (inert) materials (lime-stone, conglomerates, dolomite, granulated slag) and waste materials (carbonated sludge, mine tailings) and gypsum and air-entraining plasticizer in suitable proportions.
Physical requirements of masonry cement are as follows.
- Fineness: Residue on 45-micron IS Sieve, Max, Percent (by wet sieving)
- Setting Time (by Vicat Apparatus):
- Initial, Min——-90min
- Final, Max——-24h
- Le-Chatelier expansion, Max—10mm
- Autoclave expansion, Max——1 percent
- Compressive Strength:
- The average strength of not less than 3 mortar cubes of 50 mm size, composed of 1 part masonry cement and 3 parts standard sand by volume, Min
- 7 days——-2.5MPa
- 28 days—–5MPa
- Air Content: Air content of mortar composed of 1 part masonry cement and 3 parts standard sand by volume, Min
- Water Retention: Flow after suction of mortar composed of 1 part masonry cement and 3 parts standard sand by volume, Min
Also, read: Soundness of Cement Test
17. Water Repellent Cement
It’s also known as hydrophobic cement. A small amount of hydrophobic surfactants like stearic acid, boric add or oleic acid is mixed with the ordinary Portland cement through the grinding of clinker.
These substances are added in amounts of 0.1 to 0.5% of the weight of cement in terms of dry admixtures.
These acids form a thin (monomolecular) film around the cement particles which prevents the entry of atmospheric moisture.
The film breaks down when the concrete is mixed, and the normal hydration takes place.
When concrete is being prepared, hydrophobic admixtures plasticize the mix and contribute to the formation of uniformly distributed fine pores in concrete as it hardens and thus enhances its frost resistance.
Hydrophobic cement also features greater water resistance and water impermeability.
The specific surface of hydrophobic cement should not be less than 350 m2/kg. The average compressive strength should not be less than
|72 ± 1 hr||15.59 N/Sq.mm|
|168 ± 2 hrs||21.57 N/Sq.mm|
|672 ± 4 hrs||30.40 N/Sq.mm|
The weak points of hydrophobic cement are its small strength gain during the initial period because of the hydrophobic films on cement grains which prevent the interaction with water, but its 28-day strength is equal to that of ordinary Portland cement.
Uses: It is most suitable for basements and for making watertight concrete.
18. Water Proof Cement
It is manufactured by adding stearates of Ca and AI and gypsum treated with tannic acid, etc. at the time of grinding.
Properties of Water Proof Cement
- It is resistant to the penetration of water.
Uses of Water Proof Cement
- Water retaining structures like tanks, reservoirs, retaining walls, swimming pools, bridge piers, etc.