Calculating normal consistency of cement is calculated using a Vicat apparatus. Mix a cement paste, fill a mold with the paste, place the mold under the Vicat apparatus, let the Vicat plunger penetrate the paste, and measure the penetration depth.
When using cement as a binding material in construction projects, the paste should not be too dry or too liquid. This is where the normal/ standard consistency test of cement comes in!
The standard consistency test of cement determines the amount of water to add when mixing cement paste. This ensures you don’t add too much or too little water and cause the cement to lose its strength after hardening.
But how do you calculate the normal consistency of cement? This article will answer this question. We’ll look at the tools required for the consistency of the cement test, the test procedure, precautions to take, and more.
At the end of this article, you’ll be one step closer to making a proper water-cement ratio that gives excellent workability and strength of cement paste for your construction projects.
How to Calculate the Normal Consistency of Cement
Understanding cement consistency is crucial for calculating the normal consistency of cement.
The hydration process, which involves the chemical reaction between cement and water, is fundamental to understanding cement consistency.
Using a Vicat Apparatus test helps calculate the normal consistency of cement.
“The consistency of cement test involves preparing a mix of cement paste, allowing the moving part of the Vicat apparatus to penetrate the paste, and then checking the depth of penetration to see whether it’s within the standard range (corresponding to the water-cement ratio that gives excellent workability, strength, and durability of concrete).”
Tools required to calculate the normal consistency of cement
To calculate the normal consistency of cement, you’ll need the following tools:
- Vicat apparatus: Vicat Apparatus features the plunger used for plunger penetration into the cement specimen and a measuring gauge for reading off the penetration.
- Vicat mold: Vicat mold holds the cement paste for penetration with the Vicat plunger.
- Weighing balance: Weighing balance is used to measure the quantity of cement for the test.
- Measuring cylinder: Measuring cylinder is used to measure the amount of water.
- Glass plate: The Glass plate is a non-porous resting plate for the Vicat mold.
- Gauging trowel: Gauging trowel is used to level the cement paste surface with the top of the mold.
- Stopwatch: Stopwatch is for timing the gauging time (the time taken to obtain a paste when mixing cement and water).
- Tray: For mixing the cement specimen to obtain a paste
You may also like: Test Cement With Superior Products
Test Procedures for Calculating Normal Consistency of Cement
The step-by-step procedure for carrying out a normal consistency test of cement using the Vicat Apparatus is as follows:
- Step 1: Take 400 grams of dry cement sample, and put it in a mixing tray.
- Step 2: Start by assuming a consistency of 28%. So add 28% of water (by the weight of cement) to the cement. That is, add 112 grams of water.
- Step 3: Mix the cement and water gently but thoroughly for 3 to 5 minutes to get a cement paste.
- Step 4: Place the mold on a non-porous glass plate.
- Step 5: Use the cement paste to fill the mold. Use a trowel to trim off excess cement paste from the mold’s surface, making the paste level with the mold’s top.
- Step 6: Place the glass plate and Vicat mold under the moving rod of the Vicat apparatus.
- Step 7: Lower the Vicat apparatus plunger gently until its tip just touches the surface of the cement paste.
- Step 8: Quickly release the plunger, allowing it to penetrate the cement paste freely.
- Step 9: Use the Vicat apparatus scale to record the plunger’s penetration depth. The setting time of the cement can be influenced by the water content and the composition of the cement.
Using the Vicat Apparatus Plunger
The normal/ standard consistency of cement is the quantity of water that needs to be added to cement for the Vicat Apparatus plunger to penetrate the cement paste up to a depth of 33 – 35mm from the top (or 5 – 7mm from the bottom).
So repeat the same experiment, changing percentages of water until the plunger penetrates the paste up to a depth of 33 – 55mm from the top or 5 – 7mm from the bottom.
Increase water quantity by 1-2% for each subsequent trial run. Report your observations in a table as follows:
Read also: Consistency of Concrete: How It’s Measured, Why It’s Important, and Relation to Workability
Precautions to Take When Calculating the Normal Consistency of Cement
To obtain reliable results when calculating the standard or normal consistency of cement, you should take the following precautions:
- Perform the test under standard conditions. Maintain a room temperature of 27±2°C and a relative humidity of 65±5%.
-
Place the Vicat apparatus on a level surface.
- The working table should be stable so the Vicat apparatus is free of vibrations or other disturbances.
- The gauging time should be between 3 to 5 minutes – it should not be less than 3 minutes or greater than 5 minutes.
- Mix the cement sample thoroughly to get a homogenous paste.
- Prepare cement paste using clean (distilled) water.
- Clean the mold properly before filling it with the cement paste.
- After completely filling the mold, ensure the cement paste is level with the top of the mold.
- The plunger should be vertical in the cement paste.
- Clean the Vicat plunger thoroughly before every penetration.
Why Calculate the Consistency of Cement?
Calculating the standard consistency of cement determines the proper cement-water ratio. This ratio ensures the cement paste has excellent workability and that the cement remains strong and durable after hardening. Therefore, adding water to cement is crucial for it to be effective as a binding material in construction projects.
The initial setting time is crucial for understanding when the cement starts to lose its plasticity, while the final setting time indicates when the cement has completely solidified and developed its initial mechanical strength. These setting times are important for determining the useful properties and structural strength of the concrete, as well as for knowing when molds can be safely removed.
When water is added to cement, a hydration reaction begins. The active compounds in cement form chemical bonds with water molecules to become hydrates which interlock and harden to give cement its strength.
However, adding too little or too much water leads to an array of quality problems; ultimately, cement loses strength after hardening.
What if Too Much Water is Added?
When you add too much water, the excess water will not participate in the hydration process but remain in the mixture. When exposed to the atmosphere, the excess water evaporates, leaving voids in the concrete after hardening.
The voids make the concrete porous. It also causes the concrete to lose strength. The lower tensile strength causes a tendency towards high shrinkage, resulting in cracking.
Adding too little water is also not the solution. With too little water, cement does not hydrate properly, as some of the cement components will have no water molecules to bond with.
The incomplete hydration reaction causes less compressive strength. The mix dries out too quickly, causing cracks on the surface.
With too little water and too much water being problematic and causing the cement to lose strength, finding the perfect water-cement ratio is critical. This is where the standard consistency test comes in.
The test helps you determine the right quantity of water to add to cement for the mix to be perfectly workable and the cement work to be strong and durable.
Factors Affecting the Calculating Normal Consistency of Cement
The standard consistency of cement does not remain the same. Instead, certain factors cause it to vary. For example, the standard consistency of ordinary Portland cement varies between 25% to 35%.
The factors that cause the standard calculating normal consistency of cement to vary include:
- Weather conditions
- The composition of silica in the cement
- The cement fineness, which refers to the particle size distribution of the cement
- The company that produces the cement
Takeaway: Determine the perfect cement-water ratio for strong and durable cement works
The standard consistency of cement test helps determine the ideal cement-water ratio. This ensures a workable mix and strong cement after hardening. The workability of the cement mix is crucial for easy application and molding into the desired shape.
Using a Vicat apparatus is an easy way to conduct this test. It helps determine the right amount of water to add to cement.
You should have no problem performing this test if you follow the test procedures and precautions outlined above.
However, you will also need a top-quality Vicat Apparatus guaranteed to give accurate readings. This is where Certified MTP comes in!
We offer a wide range of construction materials testing equipment guaranteed to give accurate readings.
We are the ultimate plug for lab supplies and testing equipment for cement testing, concrete testing, aggregate testing, asphalt testing, and soil testing.
Our Standard Vicat Apparatus is everything you’ll need to calculating normal consistency of cement and set times of hydraulic cement, mortar, and gout. Ready to get strong and durable cement works? Get the Standard Vicat Apparatus today!
