The initial setting time of concrete is the time when cement paste starts hardening while the final setting time is the time when cement paste has hardened sufficiently in such a way that a 1 mm needle makes an impression on the paste in the mould but 5 mm needle does not make any impression.
Theoretically, the Initial setting time of concrete is the time period between the addition of water to cement till the time at 1 mm square section needle fails to penetrate the cement paste, placed in the Vicat’s mould 5mm to 7mm from the bottom of the mould.
The final setting time is the time period between the time water is added to cement and the time at which 1 mm needle makes an impression on the paste in the mould but a 5 mm attachment does not make any impression.
Let’s discuss some of the important facts about setting the time of concrete.
- It is essential that cement is set neither too rapidly nor too slowly. It should have sufficient time till the pouring of concrete, and concrete should be set within a reasonable time to develop its strength.
- Setting should not be confused with hardening, which refers to the gain in mechanical strength after a certain degree of resistance to the penetration of a special attachment pressed into it.
- Setting time is the time required for the stiffening of cement paste to a defined consistency and also Initial setting time is the time when the paste starts losing its plasticity.
- Initial setting time duration is required to delay the process of hydration or hardening.
- Final setting time is the time when the paste completely loses its plasticity. It is the time taken for the cement paste or cement concrete to harden sufficiently and attain the shape of the mould in which it is cast.
The followings are some of the signs of concrete setting
- Low slump of the concrete
- Low workability of concrete
- Showing the plastic nature of the concrete
- Resistance to the movement
- Difficulty in vibrating
If these kinds of behaviour are identified, the condition of the concrete shall be checked and make sure there is no issue.
Above mentions issues could even rise from loss of workability of concrete due to the low water content or use of high range water reducing admixtures and spend some time before concreting.