The consistency of cement mortar is its ability to flow. The consistency test on cement is performed to determine the water necessary for attaining standard consistency or normal consistency.
Cement is the most important and highly recognized binding material used in construction. Cement is an integral part of all types of construction ranging from huge skyscrapers, bridges, tunnels, etc to small residential buildings. For industrial structures like power plants, refineries, steel plants, cement plants, bridges, roads, etc. cement is the main component. Cement, when mixed with sand and aggregates, forms concrete and with sand makes mortar. The serviceability, strength, and durability of a structure are closely related to cement used in various works.
Cement tests – Categories
Cement is one of the oldest and most used binding materials and an integral ingredient used in the construction sector. The quality, serviceability, and stability of a structure are directly related to the quality of cement used in it. Hence it is required to analyse the quality of cement before using it for works. The tests for determining cement quality are split into two major categories.
- Laboratory test
- Field tests for cement
Field tests on Cement
The quality of cement is determined using some simple field tests. These tests do not require any sophisticated types of equipment and professional skills and get the results very quickly. By conducting these simple tests and analyzing the results we will get an idea about the cement quality and can immediately decide on accepting or rejecting it.
Following are the common field tests conducted to ensure the quality of cement.
These are first look tests and quality of cement is ensured by its smoothness to touch, the colour of cement, etc.
- Checking manufacturing date
- Visual checking of lumps
- Feel test
- Heat of cement
- Water float test
- Setting test
These basic tests give an approximate characteristic of cement. These are easy and quick but not accurate, however help in concluding the acceptance of cement for works.
Also read : Field tests for cement
Laboratory tests for Cement
The laboratory tests are conducted to define the physical and chemical properties of cement. It is not possible to check all the cement properties at the site. The main laboratory tests conducted on cement is as follows.
- Fineness Test
- Compressive Strength Test
- Consistency Test on cement
- Setting time
- Soundness Test
- Tensile strength Test
- Heat of hydration
Lab tests require time. But it provides accurate results. In this article we are going to describe about Consistency test on cement.
Significance of Consistency test on Cement
The strength of concrete depends on the quality of cement. In order to achieve good strength, the mortar should be consistent. The standard consistency of cement is when the Vicat plunger penetrates to a point 5 to 7 mm from the bottom of the Vicat mould. This is a trial and error method.The consistency test determines the water necessary for attaining standard consistency or normal consistency. The consistency of cement is necessary to conduct other tests like compressive strength, setting time determination etc. Because consistency gives the quantity of water in cement paste. The hydration of cement occurs in presence of water. Also, the consistency depends on the composition and fineness of the cement. Excess use of water makes cement brittle after hardening. The lower water-cement ratio affects the rate of hydration which in turn affects its strength. That is why determination of consistency is essential.
Relevant IS code for consistency test on cement
- IS 4031 (Part 4)-1988
- ASTM C 187
- BS EN 196-3:2005
Apparatus used for consistency test on cement
The Vicat apparatus is used to determine the consistency of cement. It consists of a plunger, a movable rod weighing 300 g, graduated scale, non-porous plate, split mould and Vicat mould. The diameter of the plunger is 10mm and the length is 50mm. The graduate scale measures the depth of penetration. The Vicat mould is a cone frustum with 80 mm diameter. The test should be conducted at a standard temperature of 27 C. The humidity should be 65%. A stop clock is used to measure the time from the addition of water to the drying of cement. As per IS code, the time of gauging is not less than 3 minutes, nor more than 5 min.
Procedure of consistency test for cement
- The first step is the preparation of cement paste. For this take 400 gm of cement in a tray.
- Add water of about 28% by weight of cement. Start the stopwatch at the time of adding water.
- Now thoroughly mix the cement paste. Place the mould above the non-porous plate and fill the paste into the Vicat mould.
- Remove the excess cement paste using a trowel and slightly tap the mould to remove the entrapped air.
- Attach the standard plunger in the Vicat apparatus. After placing the mould lower the plunger till it gently touches the surface.
- Then release the plunger quickly and measure the depth of penetration from the bottom.
- Repeat the procedure by increasing the water content until the plunger penetrates up to 5mm to 7mm.
- Then calculate the standard consistency.
The standard consistency is expressed in terms of the percentage of the quantity of added water to the weight of cement. The consistency of cement ranges from 26% to 33%.
Standard consistency = ( Quantity of water added / Weight of cement) x 100
We should take certain precautions before starting the test so that to obtain accurate results.
- Clean the Vicat mould properly and grease the inside surface
- Take immense care while attaching the plunger. Make sure it is vertical.
- Place the apparatus on a levelled surface.
- Maintain the standard temperature and humidity throughout the test.
Finding out standard consistency of cement is essential because the amount of water added in cement affect the setting time of cement, Less water added than this standard consistency would not complete chemical reaction thus resulting in the reduction concrete of strength and more water would increase water-cement ratio and so would reduce its strength.