Types of Cement
Portland Pozzolana Cement
The history of pozzolanic material goes back to Roman’ s time.
The descriptions and details of pozzolanic material will be dealt separately under the chapter ‘Admixtures’.
However a brief description is given below. Portland Pozzolana cement (PPC) is manufactured by the intergrinding of OPC clinker with 10 to 25 per cent of pozzolanic material (as per the latest amendment, it is 15 to 35%).
Air-Entraining Cement
Air-entraining cement is not covered by Indian Standard so far. This cement is made by mixing a small amount of an air-entraining agent with ordinary Portland cement clinker at the time of grinding. The following types of air-entraining agents could be used:
- Alkali salts of wood resins.
- Synthetic detergents of the alkyl-aryl sulphonate type.
- Calcium lignosulphate derived from the sulphite process in paper making.
- Calcium salts of glues and other proteins obtained in the treatment of animal hides.
Coloured Cement (White Cement )
For manufacturing various coloured cements either white cement or grey Portland cement is used as a base.
The use of white cement as a base is costly. With the use of grey cement only red or brown cement can be produced.
Coloured cement consists of Portland cement with 5-10 per cent of pigment. The pigment cannot be satisfactorily distributed throughout the cement by mixing, and hence, it is usual to grind the cement and pigment together.
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 unfavourable conditions.
The film is broken out when the cement and aggregate are mixed together at the mixer exposing the cement particles for normal hydration
Masonry Cement
Ordinary cement mortar, though good when compared to lime mortar with respect to strength and setting properties, is inferior to lime mortar with respect to workability, water- retentivity, shrinkage property and extensibility.
Masonry cement is a type of cement which is particularly made with such combination of materials, which when used for making mortar, incorporates all the good properties of lime mortar and discards all the not so ideal properties of cement mortar.
Expansive Cement
Concrete made with ordinary Portland cement shrinks while setting due to loss of free water. Concrete also shrinks continuously for long time.
This is known as drying shrinkage. Cement used for grouting anchor bolts or grouting machine foundations or the cement used in grouting the prestress concrete ducts, if shrinks, the purpose for which the grout is used will be to some extent defeated.
There has been a search for such type of cement which will not shrink while hardening and thereafter
Oil-Well Cement
Oil-wells are drilled through stratified sedimentary rocks through a great depth in search of oil. It is likely that if oil is struck, oil or gas may escape through the space between the steel casing and rock formation.
Cement slurry is used to seal off the annular space between steel casing and rock strata and also to seal off any other fissures or cavities in the sedimentary rock layer.
The cement slurry has to be pumped into position, at considerable depth where the prevailing temperature may be upto 175°C. The pressure required may go upto 1300 kg/cm
Rediset Cement
Acclerating the setting and hardening of concrete by the use of admixtures is a common knowledge. Calcium chloride, lignosulfonates, and cellulose products form the base of some of admixtures.
The limitations on the use of admixtures and the factors influencing the end properties are also fairly well known.
High alumina cement, though good for early strengths, shows retrogression of strength when exposed to hot and humid conditions
High Alumina Cement
High alumina cement is obtained by fusing or sintering a mixture, in suitable proportions, of alumina and calcareous materials and grinding the resultant product to a fine powder.
The raw materials used for the manufacture of high alumina cement are limestone and bauxite.
These raw materials with the required proportion of coke were charged into the furnace. The furnace is fired with pulverised coal or oil with a hot air blast.
The fusion takes place at a temperature of about 1550-1600°C. The cement is maintained in a liquid state in the furnace.
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