To determine the standard consistency of cement, a test is conducted using the Vicat plunger. The standard consistency is achieved when the plunger can penetrate the cement paste to a point 5 to 7mm from the bottom of the Vicat mold during the test.
The procedure for determining the amount of water required to produce a cement paste of standard consistency is as follows: the specified amount of cement and water is mixed together to form a paste. The paste is then placed into the Vicat mold and leveled off.
The Vicat plunger is then brought down onto the surface of the paste and released, allowing it to penetrate the paste. The depth of penetration is measured and recorded. If the penetration depth is not within the range of 5 to 7mm, then the water content is adjusted and the test is repeated until the standard consistency is achieved.
Determination of Standard Consistency of Cement
Apparatus for Standard Consistency
1. Vicat Apparatus
The Vicat apparatus is a device that is used to measure the setting time and consistency of cement. It consists of a frame with a movable rod that has a cap at one end. The other end of the rod has interchangeable attachments, which include a needle for determining the initial setting time, a needle for determining the final setting time, and a plunger for determining the standard consistency.
The initial setting time is the time at which the cement paste starts to lose its plasticity and the needle starts to penetrate the cement paste by a certain depth. The final setting time is the time at which the cement paste completely loses its plasticity and the needle fails to penetrate the cement paste. The standard consistency is the amount of water that should be added to the cement to obtain a cement paste that has a normal consistency.
By using the Vicat apparatus, the setting time and consistency of the cement can be accurately determined. This is important because it allows builders and engineers to determine the appropriate time to start building on the cement and ensures that the cement has the right consistency for the job at hand.
2. Needles
The first needle, used for measuring the initial setting time, has a flat end and a cross-sectional area of 1mm2. It is designed with a specific shape to accurately measure the time it takes for a material to begin to set.
The second needle, used for measuring the final setting time, has a circular shape with a cross-sectional area of 1mm2. It also has a metal attachment with a cutting edge, and the end of the needle extends beyond this edge. This design is necessary to obtain accurate measurements of the time it takes for a material to fully set.
Finally, the plunger used for determining the standard consistency is made of polished brass, is 10 ± 0.05mm in diameter, and has a flat end. It is designed with a projection at the upper end for insertion into the movable rod. This design is important for achieving precise and consistent results when measuring the consistency of a material.
3. Movable Rod
The device consists of a rod that can be moved, and an indicator that moves over a scale attached to a frame. Some models have a dash pot attachment that helps to lower the movable rod slowly. The indicator on the rod is used to measure or indicate a certain value on the scale. This type of device is commonly used in various measuring instruments and can be found in many industries. The addition of the dash pot can make the measurement process more accurate by allowing for slower and more controlled movement of the rod.
4. Graduated Scale
A graduated scale with a length of 40mm is provided, and it has divisions that are 1mm in size.
5. Vicat Mould
The Vicat mould is a frustum of a cone made of foam with specific dimensions. It has an internal diameter of 60+/-0.5mm at the top, 70+/-0.5mm at the bottom, and a height of 40+/-0.5mm.
On the other hand, the split type Vicat mould is an alternative to the single mould. It comprises a split ring with an internal diameter of 80+/-0.1mm and a height of 40+/-0.5mm, accompanied by a non-porous base plate. The split mould also includes a suitable clamping ring to hold it in place.
Procedure for Standard Consistency of Cement
To conduct the Vicat apparatus test for determining the standard consistency of cement, it is important to ensure that the apparatus is placed on a level base. If a dashpot is being used, the movable rod should be set to its highest position and pinned. The top of the dashpot should be unscrewed, and it should be half-filled with suitable oil of viscosity before being screwed back on. The plunger should then be worked a few times.
The plunger used for determining standard consistency should be attached to the movable rod, and worked a few times. Next, 400 gm of cement should be taken in a pan, and a weighed amount of water in a beaker. The water should be added to the cement to make a paste, and a stopwatch should be started at this point.
The Vicat mould should be placed on a non-porous plate, and the cement paste should be filled into it. The mould should be shaken slightly to remove any air bubbles, and the surface of the paste should be smoothed off to make it level with the top of the mould. This will create the test block.
The test block should then be placed under the movable rod bearing the needle. The plunger should be lowered gently to touch the surface of the cement paste, and then quickly released. If a dashpot is being used, the mould filled with cement paste and the non-absorbent plate should be placed on the base plate of the Vicat apparatus. The plunger of the dashpot should be raised and brought in contact with the top cap of the movable bearing rod. The pin holding the movable bearing rod to the surface of the cement paste should then be removed, and the plunger should be quickly released by pushing it down to sink into the paste. This operation should be done immediately after filling the mould.
To determine the amount of water required, trial test specimens should be prepared with varying percentages of water until the plunger penetrates to a point 5 to 7mm from the bottom of the Vicat mould, which is read on the scale. The water required should then be expressed as a 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 =_______
Table
| SL. NO. | QUANTITY OF WATER ADDED (ml) | DEPTH OF PENETRATION (mm) |
The standard consistency of cement can be determined using a specific formula. To do this, the quantity of water needed for 5-7 millimeter penetration is divided by the weight of the cement. This value is then multiplied by 100 to obtain the standard consistency percentage of the cement. This calculation is commonly used in the construction industry to ensure that the cement being used in a particular project is of the correct consistency. By following this formula, builders can ensure that their cement is neither too watery nor too thick, which can impact the structural integrity of the construction project.
Points to be Noted
To ensure accurate results, it is important that the time of gauging when testing cement should fall within a specific timeframe. The duration of this process should not be less than three minutes nor exceed five minutes. Gauging time is the period that transpires between the addition of water to the dry cement until the commencement of filling the mould.
Additionally, the test must be performed at room temperature, specifically at 27 degrees Celsius plus or minus 2 degrees Celsius. It is essential to maintain a stable working environment, and there should be no vibration on the table during the testing process.
Furthermore, to avoid any contamination that may impact the results, the plunger used for testing must be cleaned after every repetition. These measures help to ensure that the cement testing process is as accurate as possible.
Results
Percentage of water content for standard consistency = %