The standard consistency of cement is that consistency, which permit the vicat plunger to penetrate to a point 5 to 7mm from the bottom of the vicat mould when tested. Procedure to determine the quantity of water required to produce a cement paste of standard consistency is described below.
Determination of Standard Consistency of Cement
Apparatus for Standard Consistency
1. Vicat Apparatus
The vicat apparatus consists of a frame having a movable rod with a cap at one end and at the other end any one of the following attachment, which are interchangeable:
- Needle for determining the initial setting time
- Needle for determining the final setting time
- Plunger for determining the standard consistency
Needle for Initial Setting Time
The needle is having a cross sectional area of 1mm2. The end of the needle is flat.
Needle for FInal Setting Time
The needle is circular having a cross sectional area of 1mm2. The needle is fitted with a metal attachment. The end of the needle projects beyond the cutting edge of the hollowed out metal attachment.
Plunger for Standard Consistency
It is of polished brass 10 ± 0.05mm in diameter with a projection at the upper end for insertion into the movable rod. The lower end is flat.
3. Movable Rod
Movable rod carries an indicator which moves over a graduated scale attached to the frame (certain models have an additional attachment of dash pot, which facilitates lowering of movable rod slowly).
4. Graduated Scale
Graduated scale is 40mm in length and the smallest division of scale is 1mm.
5. Vicat Mould
The vicat mould is in the foam of a frustum of a cone having an internal diameter of 60+/-0.5mm at the top, 70 +/- 0.5mm at the bottom and height 40 +/_ 0.5mm.
Split type vicat mould
The split type vicat mould is used as an alternative to single mould. This mould consist of a split ring having an internal diameter 80+/- 0.1mm and a height 40+/_0.5mm. A non-porous base plate is provided. The split mould is provided with a suitable clamping ring.
Procedure for Standard Consistency of Cement
- Keep the vicat apparatus on a level base (when using vicat apparatus with dashpot, keep the bearing movable rod to its highest position and pin it.) Unscrew the top of the dashpot. Half fill the dashpot with any suitable oil of viscosity and screw the top. Work the plunger a number of times.
- Attach the plunger for determining standard consistency to the movable rod. Work the plunger a number of times.
- Take 400 gm of cement in a pan and a weighed quantity of water in a beaker.
- Prepare a paste with the water added to cement. Start a stopwatch at the time of adding water to cement.
- Keep the vicat mould on a non porous plate and fill the cement paste in it.
- After completely filling the mould, shake it slightly to expel the air. Smooth off the surface of the paste making it level with the top of the moulder. The cement paste thus prepared is the test block.
- Place the test block resting on the non porous plate under the movable rod, bearing the needle.
- Lower the plunger gently to touch the surface of the cement paste and quickly release; (when vicat apparatus with dashpot is used, place the mould filled with cement paste and the non absorbent plate on the base plate of the vicat apparatus. Raise the plunger of the dash pot, bring it in contact with the top cap of the movable bearing rod.
- Remove the pin holding the movable bearing rod to the surface of the cement paste and quickly release by pushing down the plunger to sink in to the paste). This operation shall be done immediately after filling the mould.
- Prepare trial test specimens with varying percentages of water until plunger penetrates to a point 5 to 7mm from the bottom of the vicat mould, which is read on the scale. Express the water required as percentage by weight of the dry cement.
Observations and Calculations
- Weight of cement taken (g) = _________
- Initial percentage of water added to cement = __________
- Quantity of water added to cement =_______
|SL. NO.||QUANTITY OF WATER ADDED|
|DEPTH OF PENETRATION|
Standard Consistency of Cement = (Quantity of water for 5-7 mm penetration/Weight of cement) X 100
Points to be Noted
- The time of gauging should not be less than 3 minutes and not more than 5 minutes. Gauging time is the time elapsing from the time of adding water to the dry cement until commencing to fill the mould.
- The test should be conducted at room temperature 27oC +/- 2oC
- There should be no vibration on the working table.
- The plunger should be cleaned during every repetition.
Percentage of water content for standard consistency = %