Setting Time of Cement
Using Vicat Apparatus the percentage of water required for producing a cement paste can be determined. The apparatus consist of a Vicat plunger having 10 mm diameter and 50 mm length to penetrate a depth around 33 to 35 mm from the top of the mould. Take 500gms of cement and prepare a paste with a water around 24 percentage by the weight of the cement. See that the paste is prepared and filled in mould with in 3 to 5 minutes.
A Vicat Plunger of 10 mm diameter which is 50 mm long is attached is attached and brought down to touch the surface of the paste in that block and quickly release the needle in such a way that it sink into the cement paste by its own weight. Conduct similar number of trials by increasing the water percentage so that the penetration depth is in the range of 33 to 35 mm.The percentage of water required for making cement paste can be calculated by this method. Usually the test is conducted with a constant temperature of 27° ± 2°. In practice while you use a cement material for construction there should be a elapsing time for transporting and placing the cement mixture, so we need to find the initial setting time and final setting time.
A Vicat Plunger of 10 mm diameter which is 50 mm long is attached is attached and brought down to touch the surface of the paste in that block and quickly release the needle in such a way that it sink into the cement paste by its own weight. Conduct similar number of trials by increasing the water percentage so that the penetration depth is in the range of 33 to 35 mm.The percentage of water required for making cement paste can be calculated by this method. Usually the test is conducted with a constant temperature of 27° ± 2°. In practice while you use a cement material for construction there should be a elapsing time for transporting and placing the cement mixture, so we need to find the initial setting time and final setting time.
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| Vicat Apparatus |
The Initial setting time can be found by using a Vicat Apparatus, take around 500 gm of cement sample and mix it with 0.85 times the water percentage required to produce a cement paste. Start the stop watch from the moment you add water to the cement. A needle with 1mm sq. used in the test apparatus, after filling the cement paste release the needle to penetrate inside the cement paste. Repeat it untill the needle penetrate only to a depth of 33 to 35 mm. The period between the time from adding water to the penetration range is called the initial setting time. This is the stage were the cement starts loosing its plasticity.
The Final setting time can be done by same manner by replacing the needle with 5 mm diameter, the procedure is repeated until the paste attain its hardness that the needle does not penetrate more that 0.5 mm. Generally the Initial setting time should be less than 30 minutes ( for mixing and handling of the materials) and the final setting time should not be more than 10 hours.
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| Automated Vicat apparatus |
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