TYPES OF CEMENTS:
* Ordinary
Portland cement
* Rapid
hardening Portland cement
* Low heat
Portland cement
* Portland
Pozzolana cement
* Blast
furnace slag cement
* Sulphate
resisting Portland cement
* Coloured
or White cement
* Quick
setting Cement
*
Hydrophobic Cement
* High
alumina cement
*ORDINARY PORTLAND CEMENT
It should
not be used for construction work exposed to sulphates in the soil.
Ordinary
Portland cement has three grades like 33, 43 & 53 grades
* Rapid hardening Portland cement
for constructing
road pavements, for cold weather concreting and where form
work is to be removed as early as possible. It should not be used for massive concrete structures.
* LOW HEAT PORTLAND CEMENT
contains a
low percentage of tricalcium silicate which hydrates quickly and a
higher
percentage of dicalcium silicate which hydrates slowly. This cement is
widely used
in retaining walls.
* PORTLAND POZZOLANA CEMENT
It is made
by inter-grinding of ordinary Portland cement clinker and
pozzolana.
It is widely used for hydraulic structures such as dams,wiers etc.
* BLAST FURNACE SLAG CEMENT:
It is made by inter grinding of ordinary Portland cement clinker and granulated blast furnace slag. It is cheaper than ordinary Portland cement. It develops low heat of hydration and has less early strength.
* SULPHATE RESISTING PORTLAND CEMENT:
In this cement, the percentage of tricalcium aluminate is kept below 5% and it results in the increase in resisting power against sulphates.
*COLOURED OR WHITE CEMENT:
It is prepared by adding 5 to 15% of a suitable colouring pigment before the cement is finally ground. It is widely used for finishing of floors, external surfaces etc.
* QUICK SETTING CEMENT:
The early settingproperty is brought out by reducing the gypsum content at the time of clinker grinding. It is used mostly in under water construction
*HYDROPHOBIC CEMENT:
Hydrophobic cement is obtained by grinding ordinary Portland cement clinker with water repellant film-forming substance such as oleic acid, and stearic acid. The water-repellant film formed around each grain of cement, reduces the rate of deterioration of the cement during long storage, transport, or under unfavorable conditions.
* HIGH ALUMINA CEMENT:
It contains about 35% of alumina. It sets quickly and attains higher ultimate strength in a short period. It is used for a structure subjected to the action of sea water, chemical plants and furnaces.
TESTING OF CEMENT
1.Fineness test (IS:4031-Part 1-1996 ):
The fineness of cement is tested either by sieve method or Blaine air permeability method.
In the sieve method, the fineness of cement is measured in terms of percentage weight retained on IS sieve number 9 (i.e. 90 micron IS sieve).
According toIndian standards (IS : 269-1967 and 1975), the percentage of residue left after sieving a good
Portland cement through IS sieve number 9, shouldnot exceed 10%.
2.CONSISTENCY TEST ( 4031-4(1988):
This test is conducted to determine the percentage of water required for preparing cement pastes of standard consistency for other tests (e.g. setting time, soundness and compressive strength tests).
This test is performed with the help of Vicat’s apparatus which consists of a plunger having 10 mm diameter and 40 to 50 mm length penetrate to a point 5 to 7 mm from the bottom of the Vicat mould.. In order to make a cement paste of normal consistency, the percentage of water varies from 25 to 35%.
3. SOUNDNESS TEST (IS:4031-PART3-1988)
This test
is carried out to detect the presence of uncombined lime and
magnesia in
cement which causes the expansion of cement. The soundness of
cement is
tested with ‘le Chatelier apparatus. According to Indian standard
specifications, the expansion should not exceed 10 mm for any type of Portland cement
4. INITIAL AND FINAL SETTING TIME TEST
The initial and final setting time test of cement is performed with the help of Vicat apparatus.
The initial setting time of cement shall be the time from the period elapsing between the time when the water is added to the cement and the time at which the needle (1 mm square or 1.13 mm in dia and 40 to 50 mm in length) penetrate to a point 5 mm from the bottom of the Vicat mould.
To perform this test about 400 gm sieved cement is taken and water is added to it @ 0.85 P by weight of cement. Where P is the percentage of water required for normal consistency paste.
The cement shall be considered it finally set while applying final setting time needle gently, no impression is marked on the top surface.
5. COMPRESSIVE STRENGTH TEST
To perform this test 200 gm of cement and 600 gm of standard sand are taken and mixed thoroughly. To this, water is added @ P/4 + 3% when standard sand is used and @ P/4 + 3.5 % when ordinary sand is used. Where P is the percentage of water required for a paste of normal consistency.
It is mixed thoroughly to an even colour. The cube mould of size 7.06 cm is placed on a non-porous base plate and is oiled inside.
The above mortar is put into the cube mould and is compacted for two minutes by the vibration machine.
The top surface is smoothened off by trowel.
Like this mould, six moulds are filled. The prepared cubes are kept at a temperature of 27° ± 2° C for 24 hours.
After this period, mortar cubes are taken out of the moulds and submerged in clean and fresh water for curing.
MANY TYPES OF FIELD TEST OF CEMENT
Date of Manufacturing:
As the strength of cement reduces with age, the date of manufacturing of cement bags should be checked.
* Cement Colour:
The colour of cement should be uniform. It should be typical cement colour i.e. gray colour with a light greenish shade.
* Whether Hard Lumps are formed:
Cement should be free from hard lumps. Such lumps are formed by the absorption of moisture from the atmosphere.
* Temperature inside Cement Bag:
If the hand is plunged into a bag
of cement, it should be cool inside the cement bag. If hydration reaction takes place inside the bag, it will become warm.
* Smoothness Test:
When cement is touched or rubbed in between fingers, it should give a smooth feeling.
If it felt rough, it indicates adulteration with sand.
* Water Sinking Test:
If a small quantity of cement is thrown into the water, it should float some time before finally sinking.
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