Objective: To assess the volume of water needed to create a cement paste of standard consistency.
The standard consistency refers to that consistency, which will allow the vicat plunger to break through a to a point 5 to 7mm from the base of the vicat mould or cast when tested as explained below:
- Vicat Apparatus
The vicat apparatus incorporates a frame including a flexible rod with a cap at one stop and at the other stop either one of the following attachment, which can be changed as per the need:
i) Needle for determination of the original setting time
ii) Needle for determination the concluding setting time
iii) Plunger for determination of the standard consistency
Needle for original setting time
The needle must have a cross sectional area of 1mm2. The rear end of the needle should be flat and even
Needle for last setting time
The needle is of round shape having a cross sectional area of 1mm2. The needle has to be fitted with a metal attachment. The end part of the needle projects ahead of the cutting edge of the void metal attachment.
Plunger for standard consistency
It is of polished brass 10 ± 0.05mm in width with a projection at the higher end for inclusion into the mutable rod. The lower end is flat and even.
- Movable Rod
Movable rod transmits an indicator which movements occur above a graduated scale connected to the frame (specific models have a supplementary connection of dash pot, which helps in the lowering of portable rod slowly).
- Graduated Scale
Graduated scale is of 40mm in length and the minimum division of scale is 1mm.
- Vicat mould
Single mould: – The vicat mould or cast is in the foam of a frustum of a cone with the interior width of 60+/-0.5mm at the top, 70 +/- 0.5mm at the base and height 40 +/_ 0.5mm.
18.104.22.168.2 Split type vicat mould:- The split kind of the vicat mould is basically utilized as an substitute to individual mould. This mould incorporates of a split ring including an interior diameter 80+/- 0.1mm and a height 40+/_0.5mm. A non-absorbent foundation plate is given. The split mould is given with a suitable clamping ring.
- Put the vicat apparatus on a flat base (while utilizing the vicat apparatus with dash pot, put the bearing flexible rod to its maximumposition and pin it.) Take the screw off the top of the dash pot. Partially fill the dash pot with any appropriate oil of viscosity and once again screw the top. Adjust the plunger a multiple number of times.
- Connect the plunger for determination of the regular consistency to the flexible rod. Work the plunger a number of times.
Now take the 400 gm of cement and put it in a pan and a measured quantity of water in a vessel.
- Create a paste with the water blended to cement. Start a stopwatch at the moment of mixing cement and water.
- Now put the vicat mould or cast on a non-absorbent plate and put the cement paste in it.
- After totally filling the mould, shudder it gently to exclude the air. Even off the surface of the paste and having it level with the head of the moulder. The cement paste therefore created is the test block.
- Put the test block kept on the non absorbent plate below the flexible rod, bearing the needle.
- Now lower the plunger slowly to tap the facade of the cement paste and rapidly let go; (when vicat apparatus with dash pot is utilized, keep the mould/cast filled with the cement paste and the non porous plate on the bottom plate of the vicat apparatus. Lift the needle of the dash pot, keep it in contact with the top cap of the flexible bearing rod. Now detach the pin holding the flexible bearing rod to the facade of the cement paste and rapidly discharge by closiing down the needle to sink in to the paste). This action shall be done straight away after filling the mould.
- Arrange trial test samples with different proportions of liquid unless the plunger enters through to a point 5 to 7mm from the base of the vicat mould, which is measured on the scale. Express the water needed as proportion by mass 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
= (Quantity of water for 5-7 mm penetration/Weight of cement) X 100
Things to be remembered:
- The time of calculating cannot be lesser than 3 minutes and should not exceed 5 minutes. Measuring time is the time period slipping away from the time of putting water to the dry cement unless beginning to keep it in the mould.
- The test has to be carried out at the room temperature 27oC +/- 2oC
- There cannot be any kind of vibration on the working table.
- The plunger has to be thoroughly cleaned during every recurrence.
Percentage of water content for standard consistency = ….. %