Estimation of Initial and Final Setting Time of Cement

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We all know cement is a binder, a substance used for construction that bonds with other materials that set and binds them together. For initiating the process of binding, cement is first mixed with water, then the hydration process starts and in due course, the cement paste is formed.

In this article, a brief description is given about the initial setting time and the final setting time of cement. However, in the construction industry cement contractors and suppliers will often discuss about the initial and final setting time of cement. But this setting time of cement, always depends upon the quality of cement procured during construction.

It is known to everyone that cement does not set too quickly or too slowly. Therefore, one should understand if the initial setting time is too fast, the cement will start to set while it is being transported, and before getting poured. Again if the final setting time takes too long, the concrete structure will not have the durability and strength to support the weight of additional construction.

In this context, we should also note that the setting time should not be confused with the cement hardening time. The setting of cement can be explained as when the cement paste starts to reach consistency by losing its workability and plasticity whereas the hardening of cement simply means the solidifying and strengthening of materials.

Initial Setting Time of Cement

Initial Setting Time of Cement can be simply explained as the time in between the addition of water in cement and when the reaction happens and the cement starts losing its plasticity. This is the perfect moment where you can mold the cement and give it the desired shape.

This particular initial setting time is very important to know for cement contractors and also suppliers as it ascertains how much time is needed for transportation, placing, and compaction of concrete.

Final Setting Time of Cement

Final Setting Time of Cement is that time period between the time water is added to the cement and the time at which 1mm needle makes an impression on the paste in the mould but 5mm attachment does not create any impression.
The final setting time also reveals the contractors when the cement will completely lose its plasticity and be able to support its own shape and weight without formwork. This particular time is the earliest time at which scaffolding and formwork can be removed.

How to Test the Initial Setting Time of Cement

Both Initial Setting Time and final setting time can be determined with a simple experiment using Vicat Apparatus

Apparatus Required

Vicat's Apparatus

Measuring Cylinder

Balance

Stop Watch

Glass Plate

Enamel Tray

Trowel

Procedure

For the Initial Setting Time Of Cement

1. Consistency Test can be done before initiating the test procedure to find out the water required to give the paste normal consistency (P).
2. Let us take 300 gms of cement-free from lumps to measure the initial setting time.
3. Then add 0.85P of water to the cement.

Amount of Water = 300 * 0.85 * 30/100

=76.5 ml

1. Now 76.5 ml of water is added to 300 gm of cement and blended well. The time is recorded as T1
2. The mixture is placed and leveled well in Vicat mold within 3 - 5 minutes of adding water to the cement and placed under Vicat apparatus.
3. 1mm2 needle is used to find the initial setting time of cement.
4. At first, the needle is placed in such a way that it touches the surface of the mold and then it is allowed to fall freely.
5. The test is repeated again for 2 minutes till the needle penetrates 5 to 7 mm from the bottom of the mould. The time is then recorded. Note this time as T2
6. Initial setting time is then calculated using the formulae

Initial Setting Time = T2 - T1

For Final Setting Time of Cement

1. For determining the final setting time, replace the needle of the Vicat's apparatus with the needle with an annular attachment.
2. In here the cement is finally set when upon applying the final setting of the needle gently to the surface of the test block; the needle makes an impression thereon while the attachment fails to do so. Now lets us record the time as T3.
3. Applying the formulae, we can determine the final setting time

Final Setting time = T3 -T1

Where,

T1 =Time at which water is first added to cement

T2 = When the needle penetrates 5 to 7 mm from the bottom of the mould
T3 =Time when the needle makes an impression but the attachment fails to do so.

Precautions Taken for the test

Certain precautions must be adopted before taking the initial and Final setting time for the cement test. The precautions are mentioned below:

1. The needle must be cleaned after every use
2. The mold must be slightly removed so that the penetration must not be at the same place
3. The experiment should be conducted in such a place where there is no external vibrations
4. The room temperature must be between 27 degrees to 29 degrees where this experiment is carried out.
5. The hydration must be maintained between 60 to 70%