Initial Setting Time And Final Setting Time Of Concrete

Initial setting time and final setting time of concrete are two important concept regarding its hardness. In this article, you will learn about initial setting time and final setting time of concrete.

Initial Setting Time Of Concrete

The initial setting time of concrete is the time when cement paste begins 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 a 5 mm needle does not make any impression.

In theory, 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 5 mm to 7 mm 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 5 mm attachment does not make any impression.

Final Setting Time Of Concrete

In the process of setting and hardening, the final setting time of concrete is the duration between the point in time when water is mixed with cement to create a paste, and the moment when the paste has entirely lost its plasticity and has obtained enough firmness to resist specific pressure.

During this period, the cement paste undergoes a gradual transformation from a plastic state to a hardened state, and this transition is accompanied by various chemical and physical processes. The final setting time of concrete is an essential parameter that determines the workability, strength, and durability of the concrete.

To determine the final setting time of concrete, the Vicat test is commonly used, which involves measuring the time required for a standard needle to penetrate the concrete mix to a particular depth under specific conditions. Once the concrete has reached its final setting time, it should not be disturbed or manipulated as it may affect the desired properties of the concrete.

Technical Aspects of Concrete Setting Times:

• It is necessary that cement set neither too rapidly nor too slowly. In the first case, there may be insufficient time to transport and place the concrete before it becomes too rigid. In the second case too long a setting period tends to slow up the work unduly, also it might postpone the actual usage of the structure because of adequate strength at the desired age.
• The setting should not be baffled with hardening, which refers to the gain in mechanical strength after a certain degree of resistivity to the penetration of a special attachment pressed into it.
• Setting time is the time needed for the stiffening of cement paste to a defined consistency.
• Indirectly related to the initial chemical reaction of cement with water to create an aluminium-silicate compound.
• The initial setting time is the time when the paste begins losing its plasticity.
• The initial setting time test is crucial for the transportation, placing, and compaction of cement concrete.
• An initial setting time period is needed to delay the process of hydration or hardening.
• The final setting time is the time when the paste entirely loses its plasticity.
• It is the time taken for the cement paste or cement concrete to harden sufficiently and achieve the shape of the mould in which it is cast.
• Determination of final setting time period assists safe removal of scaffolding or form.
• During this period of time, the essential chemical reaction of cement with water is almost completed.

Procedure to Find Setting Time of Cement:

Apparatus Needed:

1. Vicat’s apparatus.
2. Balance.
3. Measuring cylinder.
4. Stopwatch.
5. Glass plate.
6. Enamel tray.
7. Trowel

Test Procedure:

Initial Preparation:

1. Consistency test to be done before starting the test procedure to find out the water needed to give the paste normal consistency (P).
2. Take 400 gm of cement and prepare a clean cement paste with 0.85P of water by weight of cement.
3. Gauge time is kept between 3 to 6 minutes. Begin the stopwatch when the water is added to the cement. Record this time (T1).
4. Fill the Vicat mould, resting on a glass plate, with the cement paste gauged as given below. Fill the mould entirely and smooth off the surface of the paste making it level with the top of the mould. The cement block hence prepared is called a test block.

Test for Initial Setting Time:

1. Place the test block confined in the mould and resting on the non-porous plate, under the rod bearing the needle.
2. Lower the needle gently until it comes in contact with the surface of the test block and speedy release, allowing it to penetrate into the test block.
3. In the starting, the needle completely pierces the test block. Repeat this process i.e. rapidly releasing the needle after every 2 minutes till the needle fails to pierce the block for about 5 mm measured from the bottom of the mould. Note this time as (T2).

Test for Final Setting Time:

1. To find out the final setting time, replace the needle of the Vicat’s apparatus with the needle with an annular attachment.
2. The cement is considered finally set when upon applying the final setting needle gently to the surface of the test block; the needle makes an impression thereon, while the attachment fails to do so. Record this time (T3).

Calculations:

Initial setting time=T2-T1

Final setting time=T3-T1

Where,

T1 = this is the Time at which water is first added to cement

T2 = this is the time when the needle fails to penetrate 5 mm to 7 mm from the bottom of the mould

T3 = this is the Time when the needle makes an impression but the attachment fails to do so.

Standard Specification of Setting Time for Different Type of Cement:

Based upon the admixtures added into the cement in the process of manufacture of cement, the setting time differs for different cement. Standard-setting times are listed in the below table as per IS Codes.

Setting Time for Different Types of Cement:

Cement Type	Initial Setting Time, min (min.)	Final Setting Time, min (max.)
OPC(33)
OPC(43)
OPC(53)
SRC
PPC
RHPC
PSC
High alumina
Super sulphated
Low heat
Masonry cement
IRS-T-40

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