What is the consistency of cement?
Consistency of cement refers to the optimum amount of water that is required to initiate the chemical reaction between the cement and water to make it a uniform cement paste.
But the real problem here is, each person may think of a different amount of water as the optimum amount. The amount of water content added to the concrete mix severely affects the strength & durability of the concrete and also we can’t able to compare the strength between the two. To eliminate the differences, a term called standard consistency is created.
What is the standard consistency of cement?
Standard consistency of cement is defined as the consistency which will permit a Vicat’s plunger of 10 mm diameter and 50 mm length to penetrate a depth of 33 – 35mm from the top of the Vicat’s mould.
The standard consistency of cement is sometimes called as Normal consistency of cement.
Why the consistency test of cement is important?
The consistency test of cement is conducted to determine the percentage of water content required for preparing cement pastes of standard consistency for other tests like,
- Setting time tests
- Soundness test
- Compressive strength test
- Tensile strength.
That’s why it is important to perform this test very carefully.
Apparatus used in standard consistency test of cement
The apparatus used in finding the standard consistency of cement are,
1) Vicat’s Apparatus
The Vicat’s apparatus consists of a frame having a movable rod with a cap fitted on one end and for the other either one of the attachments shown below can be fitted.
The rod can be attached with,
- Needle for determining initial setting time
- Needle with annual collar for determining final setting time and
- Plunger for determining standard consistency of cement.
2) Vicat’s Mould
The Vicat’s mould is in the shape of a frustum of a cone having a 60 mm internal diameter at the top and 70 mm internal diameter at the bottom with a height of 40mm.
3) Vicat’s Plunger
It is a cylinder-shaped rod of about 10 mm in diameter and has a length of 40 to 50 mm.
4) Weight balance
It is used to weigh the cement quantity.
5) Stopwatch
Used to measure the time.
Procedure to find the standard consistency test of cement
The following procedure is adopted to find out the consistency of cement.
1) Take about 500 gms of cement and prepare a paste with an approximate weighed quantity of water (say 24 percent by weight of cement) for the first trial.
2) The paste should be thoroughly mixed and should be prepared in a standard manner. The paste should be filled into the Vicat’s mould within 3 – 5 minutes from the addition of water. The stopwatch can be used to calculate the time.
3) After completely filling the mould, shake the mould to expel air and make the top of the mould flat using a trowel.
4) A standard plunger, 10 mm diameter, 50 mm long is attached to the moving rod and brought down to touch the surface of the paste in the mould and quickly released allowing it to sink into the paste by its own weight. Take the reading by noting the depth of penetration of the plunger by seeing it in the scale.
5) Conduct a 2nd trial (say with 26 percent of water) and find out the depth of penetration of the plunger. Don’t forget to clean the plunger in between the trials otherwise it may result in the wrong data.
6) Similarly, conduct trials with higher and higher water/cement ratios till such time the plunger penetrates for a depth of 33-35 mm from the top (or) 5-7mm from the bottom of the Vicat’s mould.
That particular percentage of water that allows the plunger to penetrate only to a depth of 33-35 mm from the top is known as the percentage of water required to produce a cement paste of standard consistency. The percentage is usually denoted as P.
Note that the above test is required to be conducted at a constant temperature (27° ± 2°C) and constant humidity (90%).
Observation table
Standard data
The percentage of water content required to form a paste of standard consistency for other tests is mentioned below.
| S.No | Type of Test | % of the water required |
| 1 | Normal consistency test | 30 – 35% |
| 2 | Initial setting time | 0.85P |
| 3 | Soundness | 0.78P |
| 4 | Compressive strength | P + 3% of water (or) (P/4) + 3% of the combined weight of cement & sand |
| 5 | Tensile strength | (P/5) + 2.5% of the combined weight of cement & sand |
What does 0.85P mean?
0.85 times the water that is required to produce cement paste of standard consistency.
Hope you understand everything you need to know about the standard consistency test of cement. If you have any queries (or) if you find this article helpful, let us know in the comment section.
Read more: 15 Types of cement and their Uses in the construction industry, 5 Types of levels used in leveling.
