4.6 : זמן התקשות הצמנט

The setting time of cement is the time taken for the cement paste to change from a plastic state to a rigid state, and it is determined using a Vicat apparatus.

Initially, water is added to the cement, and a paste of the required consistency is prepared, which is then filled in the mold.

A needle with a diameter of 0.04 inches is then lowered into the cement paste at regular time intervals until it penetrates a specified distance from the bottom of the mold. The time taken from adding water to this instance gives the initial setting time of cement. 

Subsequently, a needle with an annular attachment is lowered into the cement paste at specific time intervals until the attachment fails to leave a mark on the paste's surface. The time elapsed from adding water to this instance gives the final setting time of cement.

Lastly, according to American standards, the initial setting time of Portland cement should not be less than 60 minutes, and the final setting time should not exceed ten hours.