*Setting time of cement is defined as when the cement paste has lost its plasticity and becomes sufficient rigid to withstand an arbitrarily defined pressure when it is said to have set.
*It is divided into two parts
(a) Initial setting time
(b) Final setting time.
(a) Initial Setting Time : It is defined as the time at which the needle in Vicat’s apparatus fails to penetrate the paste by 5 mm to 7mm from bottom (33 to 35 mm from top of the Vicat’s mould is known as initial setting time. For O.P.C. initial setting time should not be less than 30 minutes.
(b) Final Setting Time: At this stage, the cement paste looses its full plasticity. It is defined as the time period elapsing between the time when water added to the cement and the time at which a needle used for testing final setting upon applying gently to the surface of this test block. makes an impression thereon, while the attachment of the needle fails to do so, is known as final setting time of the sample.
For O.P.C. final setting time should not be more than 600 minutes.
