Many types of cements are available in markets with different compositions and for use in
different environmental conditions and specialized applications.A List of such type of cement describe below on which we will discuss in details.

Ordinary Portland cement
Ordinary Portland cement is the most common type of cement in general use around the world. This cement is made by heating limestone (calcium carbonate) with small quantities of other materials (such as clay) to 1450°C in a kiln, in a process known as calcination, whereby a calcium carbonate to form molecule of carbon dioxide is liberated from the calcium oxide,or quicklime, which is then blended with the other materials that have been included in the mix.. The resulting hard substance, called 'clinker', is then ground with a small amount of gypsum into a powder to make 'Ordinary Portland Cement'(often referred to as OPC).
Portland cement is a basic ingredient of concrete, mortar and most non-specialty grout. The most common use for Portland cement is in the production of concrete. Concrete is a composite material consisting of aggregate (gravel and sand), cement, and water. As a construction material, concrete can be cast in almost any shape desired, and once hardened,can become a structural (load bearing) element. Portland cement may be grey or white.



* This type of cement use in construction when there is no exposure to sulphates in the soil or ground water.


 * Lime saturation Factor is limited between i.e. 0.66 to 1.02.
* Free lime-cause the Cement to be unsound.
* Percentage of (AL2O3/Fe2O3) is not less than 0.66.
* Insoluble residue not more than 1.5%.
* Percentage of SO3 limited by 2.5% when C3A < 7% and not more than 3% when C3A >7%.
* Loss of ignition -4%(max)
* Percentage of Mg0-5% (max.)
* Fineness -not less than 2250 cm2/g.

Rapid hardening Portland cement

* It is firmer than Ordinary Portland Cement.
* It contains more C3S are less C2S than the ordinary Portland cement.
* Its 3 days strength is same as 7 days strength of ordinary Portland cement.

Low heat Portland cement

* Heat generated in ordinary Portland cement at the end of 3days 80 cal/gm. While in low heat cement it is about 50cal/gm of cement.
* It has low percentage of C3A and relatively more C2S and less C3S than O.P.Cement.
* Reduce and delay the heat of hydration. British standard ( B S. 1370 : 1974 ) limit the heat of hydration of this cement.

Sulphate resisting Portland cement

* Maximum C3A content by 3.5% and minimum fineness by 2500 cm'/g.
* Firmer than ordinary pot land cement.
* Sulphate forms the sulpha-aluminates which have expensive properties and so causes disintegration of concrete.


* For this cement, the silage as obtained from blast furnace is used.
* The clinkers of cement are ground with about 60 to 65 percent of slag.
* Its strength in early days is less and hence it required longer curing period. It proves to be economical as slag, which is a Waste product, is used in its manufactures.

Pozzolanic cement

* As per Indian standard, the proportions of Pozzolana may be 10 to 25 % by weight.Burnt clay, shale, Fly ash.
* This Cement has higher resistance to chemical agencies and to sea water because of absence of lime.
* It evolves less heat and initial strength is less but final strength is 28 days onward equal to ordinary Portland cement.
* It possesses less resistance to the erosion and weathering action.
* It imparts higher degree of water tightness and it is cheap.


White Portland cement

* Grey colour of O.P. cement is due to presence of Iron Oxide. Hence in White Cement Fe,,O, is limited to 1 %. Sodium Alumina Ferrite (Crinoline) NavAlF6 is added to act as flux in the absence of Iron-Oxide. 
* It is quick drying, possesses high strength and has superior aesthetic values and it also cost lee than ordinary Cement because of specific requirements imposed upon the raw materials and the manufacturing process.
* White Cement are used in Swimming pools, for painting garden furniture, moulding sculptures and statues etc.


Coloured Portland

* The Cement of desired colour may be obtained by mixing mineral pigments with ordinary Cement.
* The amount of colouring material may vary from 5 to 10 percent. If this percentage exceeds 10percent, the strength of cements is affected.
* The iron Oxide in different proportions gives brown, red or yellow colour. The coloured Cement are widely used for finishing of floors, window sill slabs, stair treads etc


Expansive cement

* This type of cement is produced by adding an expanding medium like sulphoaluminate and a stabilising agent to the ordinary cement.
* The expanding cement is used for the construction of water retaining structures and for repairing the damaged concrete surfaces.


High alumina cement

* This cement is produced by grilling clinkers formed by calcining bauxite and lime. It can stand high temper lures.
* If evolves great heat during setting. It is therefore not affected by frost.

Hydration of Cement

 In the anhydrous state, four main types of minerals are normally present: alite, belite celiteand felite. Also present are small amounts of clinker sulfate (sulfates of sodium,potassium and calcium) and gypsum, which was added when the clinker was ground up to produce the familiar grey powder.

Types of Cement, Hydration of Cement, Test on Cement
hydration of cement 

When water is added, the reactions which occur are mostly exothermic, that is, the reactions generate
heat. We can get an indication of the rate at which the minerals are reacting by monitoring the rate at which heat is evolved using a technique called conduction calorimetry.Almost immediately on adding water some of the clinker sulphates and gypsum dissolve producing an alkaline, sulfate-rich, solution.Soon after mixing, the (C3A) phase (the most reactive of the four main clinker minerals) reacts with the water to form an aluminaterich gel (Stage I on the heat evolution curve above). The gel reacts with sulfate in solution to form small rod-like crystals of ettringite. (C3A) reaction is with water is strongly exothermic but does not last long, typically only a few minutes, and is followed by a period of a few hours of relatively low heat evolution. This is called the dormant, or induction period (Stage II).The first part of the dormant period, up to perhaps half-way through, corresponds to when
concrete can be placed. As the dormant period progresses, the paste becomes too stiff to be workable.
At the end of the dormant period, the alite and belite in the cement start to react with the formation of calcium silicate hydrate and calcium hydroxide. This corresponds to the main period of hydration (Stage III), during which time concrete strengths increase. The individual grains react from the surface inwards, and the anhydrous particles become smaller.(C3A) hydration also continues, as fresh crystals become accessible to water.The period of maximum heat evolution occurs typically between about 10 and 20 hours after mixing and then gradually tails off. In a mix containing OPC only, most of the strength gain has occurred within about a month. Where OPC has been partly-replaced by other materials, such as fly ash, strength growth may occur more slowly and continue for several months or even a year.Ferrite reaction also starts quickly as water is added, but then slows down, probably

because a layer of iron hydroxide gel forms, coating the ferrite and acting as a barrier,preventing further reaction.

Products of Hydration
During Hydration process several hydrated compounds are formed most important of which are, Calcium silicate hydrate, calcium hydroxide and calcium aluminium hydrates which is important for strength gain.


Calcium silicate hydrate:
This is not only the most abundant reaction product, occupying about 50% of the paste volume, but it is also responsible for most of the engineering properties of cement paste. It is often abbreviated, using cement chemists' notation, to "C-S-H," the dashes indicating that no strict ratio of SiO2 to CaO is inferred. C-S-H forms a continuous layer that binds together the original cement particles into a cohesive whole which results in its strong bonding capacity. The Si/Ca ratio is somewhat variable but typically approximately 0.45-0.50 in hydrated Portland cement but up to perhaps about 0.6 if slag or fly ash or microsilica is present,depending on the proportions.

Calcium hydroxide:
The other products of hydration of C3S and C2S are calcium hydroxide. In contrast to the CS-H, the calcium hydroxide is a compound with distinctive hexagonal prism morphology. It constitutes 20 to 25 per cent of the volume of solids in the hydrated paste. The lack of durability of concrete is on account of the presence of calcium hydroxide. The calcium hydroxide also reacts with sulphates present in soils or water to form calcium sulphate which further reacts with C3A and cause deterioration of concrete. This is known as sulphate attack.To reduce the quantity of Ca (OH)2 in concrete and to overcome its bad effects by converting it into cementitious product is an advancement in concrete technology.The use of blending materials such as fly ash, silica fume and such other pozzolanic materials are the steps toovercome bad effect of Ca(OH)2 in concrete. However, Ca(OH)2 is alkaline in nature due to which it resists corrosion in steel.

Calcium aluminium hydrates:
These are formed due to hydration of C3A compounds. The hydrated aluminates do Not contribute anything to the strength of concrete. On the other hand, their presence is harmful to the durability of concrete particularly where the concrete is likely to be attacked by sulphates. As it hydrates very fast it may contribute a little to the early strength.



Various tests on cement:
Basically two types of tests are under taken for assessing the quality of cement. These are either field test or lab tests. The current section describes these tests in details.

Field test:
There are four field tests may be carried out to as certain roughly the quality of cement.There are four types of field tests to access the colour, physical property, and strength of the cement as described below.

Colour
* The colour of cement should be uniform.
* It should be typical cement colour i.e. grey colour with a light greenish shade.

Physical properties
* Cement should feel smooth when touched between fingers.
* If hand is inserted in a bag or heap of cement,it should feel cool.

Presence of lumps
* Cement should be free from lumps.
* For a moisture content of about 5 to 8%,this increase of volume may be much as 20 to 40 %,depending upon the grading of sand.

Strength
* A thick paste of cement with water is made on a piece of thick glass and it is kept under water for 24 hours.It should set and not crack.

Laboratory tests:
Six laboratory tests are conducted mainly for assessing the quality of cement. These are: fineness, compressive strength, consistency, setting time, soundness and tensile strength.

Fineness
* This test is carried out to check proper grinding of cement.
* The fineness of cement particles may be determined either by sieve test or permeability apparatus test.
* In sieve test ,the cement weighing 100 gm is taken and it is continuously passed for 15 minutes through standard BIS sieve no. 9.The residue is then weighed and this weight should not be more than 10% of original weight.
* In permeability apparatus test,specific area of cement particles is calculated.This test is better than sieve test.The specific surface acts as a measure of the frequency of particles of average size.
Types of Cement, Hydration of Cement, Test on Cement
Sieve No 9


Compressive strength
* This test is carried out to determine the compressive strength of cement.
* The mortar of cement and sand is prepared in ratio 1:3.
* Water is added to mortar in water cement ratio 0.4.
* The mortar is placed in moulds.The test specimens are in the form of cubes and the moulds are of metals.For 70.6 mm and 76 mm cubes ,the cement required is 185gm and 235 gm respectively.
* Then the mortar is compacted in vibrating machine for 2 minutes and the moulds are placed in a damp cabin for 24 hours.
* The specimens are removed from the moulds and they are submerged in clean water for curing.
* The cubes are then tested in compression testing machine at the end of 3days and 7 days. Thus compressive strength was found out.

Consistency
* The purpose of this test is to determine the percentage of water required for preparing cement pastes for other tests.
* Take 300 gm of cement and add 30 percent by weight or 90 gm of water to it.
* Mix water and cement thoroughly.
* Fill the mould of Vicat apparatus and the gauging time should be 3.75 to 4.25 minutes.
* Vicat apparatus consists of aneedle is attached a movable rod with an indicator attached to it.
* There are three attachments: square needle,plungerand needle with annular collar.
* The plunger is attached to the movable rod.the plunger is gently lowered on the paste in the mould.
* The settlement of plunger is noted.If the penetration is between 5 mm to 7 mm from the bottom of mould,the water added is correct.If not process is repeated with different percentages of water till the desired penetration is obtained.

Setting time
* This test is used to detect the deterioration of cement due to storage.The test is performed to find out initial setting time and final setting time.
* Cement mixed with water and cement paste is filled in the Vicat mould.
* Square needle is attached to moving rod of vicat apparatus.
* The needle is quickly released and it is allowed to penetrate the cement paste.In the beginning the needle penetrates completely.The procedure is repeated at regular intervals till the needle does not penetrate completely.(upto 5mm from bottom).
* Initial setting time =<30min for ordinary Portland cement and 60 min for low heat cement.
* The cement paste is prepared as above and it is filled in the Vicat mould.
* The needle with annular collar is attached to the moving rod of the Vicat apparatus.
* The needle is gently released. The time at which the needle makes an impression on test block and the collar fails to do so is noted.
* Final setting time is the difference between the time at which water was added to cement and time as recorded in previous step,and it is =<10hours.

Soundness
* The purpose of this test is to detect the presence of uncombined lime in the cement.
* The cement paste is prepared.
* The mould is placed and it is filled by cement paste.
* It is covered at top by another glass plate.A small weight is placed at top and the whole assembly is submerged in water for 24 hours.
* The distance between the points of indicator is noted.The mould is again placed in water and heat is applied in such a way that boiling point of water is reached in about 30 minutes. The boiling of water is continued for one hour.
* The mould is removed from water and it is allowed to cool down.
* The distance between the points of indicator is again measured.The difference between the two readings indicates the expansion of cement and it should not exceed 10mm.

Tensile strength
* This test was formerly used to have an indirect indication of compressive strength of cement.
* The mortar of sand and cement is prepared.
* The water is added to the mortar.
* The mortar is placed in briquette moulds.The mould is filled with mortar and then a small heap of mortar is formed at its top.It is beaten down by a standard spatula till water appears on the surface.Same procedure is repeated for the other face of briquette.
* The briquettes are kept in a damp for 24 hours and carefully removed from the moulds.
* The briquettes are tested in a testing machine at the end of 3 and 7 days and average is found out.