Cement is the most popular building material throughout the world, especially in India it is used in almost every project. So It is necessary to know some properties of cement before we actually place it at the site. So, In this article, we will try to discuss the initial and final setting time of cement.
What is setting time?
When water is mixed with cement, it forms a paste that can be molded into any shape due to its plasticity. But after some time the cement will lose its plasticity and starts setting, this entire cycle is known as setting time. In simple terms, It is the time required for cement to lose its plasticity is known as setting time.
Setting time is categorized into the Initial setting time and final setting time of cement.
what is Initial and final setting time of cement?
These two properties of cement are very useful in deciding the time required for transportation, placing, and compaction of cement concrete.
Initial setting time of cement: It is the time required for the cement to be able to mold into any desired shape is known as initial setting time.
Final setting time of cement: It is the time at which cement starts hardening and completely loses its plasticity is known as final setting time.
Factors Affecting setting time of cement?
- The mineral composition of cement is the major factor affecting the setting and hardening of the cement.
- The amount of gypsum in the cement is also a major factor affecting the setting time, if the gypsum present in the cement is more then it retards the setting time and vice versa.
- Cement’s fineness: The finer the particles are, the quicker the setting time will be.
- The Impact of curing conditions
- The Impact of curing age
- water content required for mixing also affects the setting time of cement.
- Admixtures are used to retard and accelerate the setting time of the cement.
Calculation of Initial and final setting time of cement
We can calculate the initial and final setting time of cement As Per IS: 4031 (Part 5) – 1988. For finding the setting time of cement, we use the VICAT apparatus and it is conducted in the laboratory. Both the initial and final setting times of the cement indicate the quality of cement.
- VICAT’s apparatus
- Measuring cylinder
- Glass plate
- Enamel tray
- A consistency test has to be done on the cement to know the water content required for normal consistency (P) of cement.
- Now take 400g of cement and make a paste using 0.85P of water by weight of cement.
- Generally, gauge time is kept for 3-4 minutes, now start the stopwatch at the instant when we add water into the cement and note the time as T1.
- Fill the VICAT mold while resisting on a glass plate, with the cement paste gauged above. Fill the mold completely and smooth off the top surface. The cement block thus prepared is known as the “Test block” which is used for calculating both the Initial and Final setting time of cement.
Initial Setting time of cement:
- Place the VICAT mold or Test block on the glass plate, under the rod bearing the needle.
- Now gently lower the needle to touch the surface of the mold and quickly release the needle allowing it to penetrate into the mold.
- In the beginning, the needle fully penetrated into the mold, for every 2 minutes repeat the procedure until the needle fails to penetrate about 5mm from the bottom of the mold, note the time as T2.
Final setting time of cement:
- For finding the final setting time of cement, replace the needle or plunder with the annular attachment and conduct the experiment.
- The cement is finally set when the needle is applied gently on the mold and makes an impression but attachment fails to do so, note the time as T3
Precautions for test conducted on setting time
- The needle has to be cleaned after every penetration.
- The mold must be moved slightly for every repetition so that the penetration would not happen at the same place.
- The experiment should be conducted at a location where there is no disturbance due to external vibration or noise.
- The mold must be remained undisturbed from the initial setting time to the final setting time.
- The experiment should be conducted at a room temperature ranging from 27° – 29° c
For calculating the Initial and final setting time of cement we require T1, T2, T3 from the above procedure;
Initial setting time= T2-T1
Final setting time= T3-T1
T1 is the time at which water is added to the cement
T2 is the time at which the needle fails to penetrate about 5mm from the bottom
T3 is the time at which the needle makes an impression on the mold but attachment fails to do so.
Standard specifications of setting time of different types of cement
Depending upon the various admixtures added during the manufacturing of cement, the setting time differs for different types of cement, so they will have different initial and final setting times. Standard-setting times of various types of cement are tabulated below;
|Cement Type||Initial setting time (minutes)||Final setting time (minutes)|
- It is essential that cement should not set too rapidly or too slowly, In the first case the time is insufficient to transport and place the cement concrete whereas in the second case the cement takes a longer time to get strengthen which increases the project completion time.
- Setting time is the time required for the cement to lose its total plasticity.
- Initial setting time is the time available to mold the cement into any shape.
- Initial setting time test is very important for transportation, placing, and compaction of cement concrete.
- The final setting time is the time when cement loses its total plasticity and becomes harder.
- The final setting time test is very important to know the safe removal time of scaffolding or formwork.