To determine the standard or normal consistency of cement, a test is conducted that tells us about the minimum level of water required for cement to react with water and form a paste.
The cement and water react with each other to form a paste that when mixed with other ingredients makes the concrete bond stronger.
In other words, the amount of water added in cement to penetrate the Vicat Plunger up to a depth of 5-7mm from the bottom of the Vicat Mould or 33-35mm from the top of the Vicat mould.
Read the article below to know everything about how the consistency of cement is determined.
Why It is Important to Determine Consistency of Cement?
As soon as the water is mixed with cement, a process called hydration starts. If the addition of water is more than needed, the proportion of water to cement gets affected. This can lead to hampering the strength of cement when it hardens and settles down. On the contrary, less water can also severely affect the strength of cement as the hydration process is incomplete.
What is the Standard Consistency of ordinary Portland Cement?
The ideal proportion of water should be around 25-30% to attain the desired consistency. For example, each 400 gm of cement should be mixed with 120 gm of water to obtain the standard or normal consistency.
The Standard Consistency of Cement Varies!
The most intriguing part about cement is that the amount of water required differs depending upon various factors. We’ve listed down the reason behind the differences in the standard consistency of cement for you to read;
- Fineness of cement
- Weather conditions (amount of humidity)
- Quality of Cement (manufacturing difference)
- The excessive composition of silica
Steps to Calculate Normal Consistency of Cement
As we’ve already discussed that the standard or normal consistency of cement changes from region to region and brand to brand. However, the need for a standardized percentage was felt to determine how much water should be added to achieve the most appropriate mixture. Follow the steps listed below to calculate the standard consistency of cement;
The VICAS Apparatus Test
The test aims at measuring the right amount of water to be mixed with cement for the most suitable mixture. It was developed back in the year 1988.
Apparatus Required: VICAT apparatus, VICAT mould, weighing balance of 1000gm with an accuracy of 1gm and measuring cylinder of 200ml, the plunger of 10mm dia, a glass plate, and a hand trowel.
Procedure:
- Start by taking 400gm of cement in a tray or bowl.
- Now based on the assumption, add 28% water to the cement.
- Mix the paste properly for around 5 minutes. The time taken to obtain the desired mixture of cement is called gauging time.
- Now pour this paste into the VICAT mould and remove any excess paste with the help of a trowel.
- Now place the VICAT mould onto a glass plate and make sure that the plunger touches the surface of the VICAT mould gently.
- Release the plunger gently and wait till it sinks into the test mould.
- Take notes of the penetration of the plunger from the bottom of the mould indicated on the scale.
- Keep repeating the same experiment a couple of times by changing the percentages of water until the reading is in between 5-7mm on the VICAT apparatus scale.
Precautions:
- The entire test must be conducted at room temperature.
- Ensure that the apparatus being used is properly cleaned and free from moisture and dust particles.
- Also, clean the plunger after every penetration.
FAQs on Consistency of Cement
What is the consistency test of cement?
In simple terms, the consistency of cement can be determined through a test that tells about the minimum water required to start the hydration of cement (a chemical reaction between water and cement) and form an ideal cement paste.
Which apparatus is used to determine the consistency of cement?
To determine the consistency of cement, an instrument named Vicat’s apparatus is used.
Which needle is used in the consistency test of cement?
Three different kinds of needles are used: square needle, needle with annular collar, and plunger.