Exp 2 Setting Time of Cement

Experiment No. 2:

Standard test method for the determination of the initial and final setting time of the hydraulic cement by Vicat needle apparatus.

Scope & Significance:

• This test method is used to determine the time of setting of the hydraulic cement by VICAT needle apparatus.
• The knowledge of the setting time of the cement is always helpful in deciding the time duration to mix, transport, place and compact the concrete effectively.
• We always prefer a larger initial setting time so that we can mix, transport and place the concrete easily. According to ASTM specifications, the initial setting time shall not be less than 45 min but in the field we prefer an initial setting time not less than 90 min.
• A smaller value of the final setting time is always preferred in order to avoid large expenditures on the formwork. According to most of the specifications, the final setting time shall not be greater than 10hrs and shall not be less than ( 90 + 1.2 x (initial setting time) ) min.

i.e.     ( 90 + 1.2 x (initial setting time) ) min < final setting time < 10hrs

Related  Theory:

Setting

In the setting process very little chemical reaction takes place. It only includes the shape acquisition due to evaporation of water. During the setting process the cement remains in the fluid or the semi-fluid state and there is very little or no gain in strength. Finer the cement particles more will be the hydration and therefore it will lead to quick settlement.

Hardening

Hardening is the rate of gain of strength due to the chemical reaction. It also refers to the strength of the concrete after a specified interval of time.

Initial setting time

The time elapsed between the initial contact of cement and water and the time when a 1mm² cross-section needle gives a reading between 4-7mm from the bottom in a standard Vicat apparatus is known as initial setting time of that particular cement paste.

Final setting time

It is the time elapsed between the initial contact of cement and water and the time when the smaller needle (1mm² cross-section and 0.5mm deep) completely penetrates into the paste and the outer metal attachment of 5mm diameter does not leave an impression on the cement paste.

Apparatus:

• VICAT apparatus
• Needle of 1mm² cross-section and 50mm length (for initial setting time)
• Plunger with 1mm smaller needle and 5mm outer diameter (for final setting time)
• Flat trowel
• Reference Masses and Devices for Determining Mass
• Spatula
• Graduated cylinders

Test Specifications:

Needle  Sizes

1-   For Initial Setting Time

1mm x 1mm cross-section

50mm length

2-   For Final Setting Time

1mm² cross-section and 1mm deep inner needle

5mm diameter outer metal attachment

Mixing Water

Portable water is satisfactory for the routine tests.

Temperature & Humidity

The temperature of the air in the vicinity should be between 23±3 °C. The temperature of the mixing water should be 23±2 °C. The relative humidity of the laboratory should not be less than 50%.

Amount of cement

Amount of cement required for the test according to various specifications are mentioned below.

BS  = 500gm   ,    ASTM = 650gm

Procedure:

Prepare a cement paste of standard consistency and put it in the ring of the Vicat apparatus within the allowable time of 4±1/4 min. Clear and level any extra paste by means of a trowel.

1-   Initial Setting Time

Determine the penetration of the 1-mm needle at the start. If a penetration reading of 4-7mm is obtained then note down the time as the initial setting time otherwise keep checking the penetration reading after every 10min thereafter until a penetration reading of 4-7 mm is obtained which will be the initial setting time of the cement.Make each penetration test at least 5 mm away from any previous penetration and at least 10 mm away from the inner side of the mold.

2-   Final Setting Time

Now fix the final setting time plunger in which the smaller needle has the diameter of 1mm and the diameter of the outer needle is 5mm. Drop the rod of the Vicat apparatus and note down the time when the smaller 0.5 mm diameter needle completely penetrates into the paste and the outer needle leaves no impression on the cement surface.

Observations & Results

Brand of Cement S.R.MAPPLE LEAF

Time of  Starting the experiment = 9:25 am

Time at taking initial setting reading = 10:45 am

Time at taking final setting reading = 1:50 pm

Initial Setting Time = …1 hour 20 minutes….

Final Setting Time  = …4 hours 25 minutes….

Comments:

After Performing the experiment we have concluded the results that the initial setting time of cement is 1 hr 20 mins and final setting time of cement paste is  4 hrs & 25 mins. The minimum initial setting time is 45 minutes and maximum final setting time is 10 hrs. As the Initial and Final setting time is coming in between the prescribed range , it means that the experiment is performed accurately. The requirements of temperature and humidity were not taken into account in the lab. Usually in fields a larger initial setting time is preferred so that we can mix, transport and place the concrete easily as some times concrete mixers have to transport concrete to some places which are not very close to the concrete plant and in the same time a smaller value of the final setting time is always preferred in order to avoid large expenditures on the form work or shuttering as it plays a vital role in the economy of a construction project.

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