How to determine the consistency of cement?

                Consistency Test

Scope:

              This method applies to common cements only. It may not apply to cements types e.g; which have a very short initial setting time.

Principle:

          Cement paste of standard consistency has a specified resistance to penetration by a standard plunger. The water required for such a paste is determined by trail penetrations of pastes with different water contents.

Apparatus:

1. Vicat Apparatus:             

                                                

                
           The plunger shall be of a non-corrodible metal in the form of a right cylinder of at least 4 45 mm effective length and of 1000 mm diameter. The total mass of the moving parts shall be 300g.
               
                 The mould containing the paste under test shall be of hard rubber, plastic or brass. It shall be of cylindrical or preferably truncated conical form 400mm deep and shall have an internal diameter of 75-85mm.
                
                  The base plate should be at least 25 mm thick and larger than the mould.

     


                                     

2. Balance:
Capable of weighing to an accuracy of 1g.

3. Graduated cylinder:
Capable of dispensing to an accuracy of 1 ml.

4. Timer:
Capable of measuring to an accuracy of 1 s.

5. Mixer, Ruler and Distilled water:

Procedure:

1.     Take 500 g of cement and a quantity of water e.g.; 125 g
2.     Mix each batch of paste mechanically using a mixer.
3.     Immediately start the mixer at low speed whilst starting the timing of the mixing stage.
        In addition, record the time to the nearest minute as ”zero time”.
4.     Stop the mixer after 90 s and remove all the paste by a suitable rubber or plastic implement and
        place it in
        a bowl.
5.     Now fill the paste with the mould. Remove any voids in the cement paste by gently tapping
        and level the surface of the paste with a straight edged implement.
6      Adjust the Vicat Apparatus at its zero reading.
7.     Place the mould in the center of Vicat Apparatus under the plunger.
8.     Lower the plunger gently until it is in contact with the cement paste.
9.     Allow the plunger to penetrate and take reading after 30 s of releasing the plunger.
10.   This reading indicates the distance between the bottom face of the plunger and the base plate.

Note:
Zero Time is the point from where initial and final setting times are measured.



Observation and Calculations:

Cement type = Sulfate Resistant


Room conditions:

Temperature = 30 C
Relative Humidity = 80 %
Weight of water sample = 500 g

Trial no. 1:
                Water  = 25 % of the weight of cement
                     = 125 ml
Reading measured by the Vicat apparatus = 20 mm

As the above value is greater than the standard value of 6-8 mm
So, I order to increase the penetration of water we have to increase the water percentage that is used in the cement paste.

Trial no. 2:

           Water =  30 % of the weight of cement
                      = 150 g
Reading measured by the Vicat apparatus = 4 mm

So Standard Consistency of this cement will be 30%.

It is used to determine the soundness of cement.

Limitations:

The room temperature should not be more than 20-22 C otherwise it will not give accurate results.