Wednesday, 10 April 2019

TYPES OF CEMENTS

Ordinary Portland Cement ( OPC ) :
·                                     o   OPC is used in general concrete construction where there is no exposure to sulphates in oil or in groundwater.
o   Initial and final setting time are 30 minutes and 10 hours.

Rapid Hardening cement :
·       Contains high percentage of C2S  to the extent about 56%
·       3 days strength is equivalent to 7 days strength of OPC.
·       Initial and Final setting times are as same as  OPC.
Advantages :
·       Sets rapidly requires a short period of curing.
·       Early removal of formwork.
Extra rapid hardening cement :
·       Imparts strength about 25% higher than that of rapid hardening cement.
·       It is obtained by inter-grinding calcium chloride ( CaCl2) with  rapid hardening of Portland cement .
Low Heat cement:
·       Contains lower % of C3A of about 5% and higher% of C2S about 46%.
·       Initial setting time is about an hour and final setting time is about 10 hours.
·       Mainly used for mass concrete works.
Hydrophobic  Cement :
·       Contains admixtures which decrease the wetting ability of cement grains.
·       Frost resistance and water resistance of concrete can be increased by using this type of cement.
·       Example of hydrophobic admixtures includes oleric acid, oxidized petroleum naphthalene, soap etc.
Quick setting cement :
·       Produced  by adding small percentage of aluminum sulphates and finely grinding the cement
·       Setting action starts within 5 minutes after addition of water and within 30 minutes it hardens.
·       Used to lay concrete under water.
Expanding cement :
·       Produced by adding an expanding medium like sulpho-aluminate and a stabilizing agent to OPC.
·       Used for repairing damaged concrete surfaces and for construction of water retaining structures.
High Alumina  cement :
·       Produced by grinding clinkers formed by calcined bauxite and lime.
·       Initial setting time is more than 3 and half hours and final setting time is about 5 hours.
·       Acid resistant  but high heat of hydration.
Pozzolana cement :
·       Pozzolana is a silicacious material which has  no cementitious properties when it is used alone  but in the presence of cement it posses cementitious  properties.
·       Pozzolana material should be between 10-30%
·       Fly ash , blast furnace slag , silica fume are examples for artificial pozzolana and burnt clay pumicite examples for natural pozzolana materials.
·       Used to prepare mass concrete of lean mix and marine works sewage works and for laying concrete under water.
White cement and coloured cement:
·       Used for finishing plastering and architectural and ornamental works.
·       Colouring agent such as ron oxide, cobalt maganese dioxide etc. are added to white cement to obtain red and yellow blue and black  colour cements.

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