Compressive Strength of Cement
Hello friends, today in this post you will learn the Compressive Strength of Cement with calculations & detailed stepwise procedure.
So, don't skip to read the post completely. After reading the post, you will completely understand the simple tests of the Compression test on concrete cubes.
So, let's start with these amazing topics...
Compressive Strength test of Cement and How to find it?
For any general construction work, Compressive strength is the important basic data to be considered while selecting the cement.
Compressive Strength of Cement:
Compressive strength is the property of a material or structure to resist compression.
The Compressive strength of a material is determined by the ability of the material to resist failure in the form of cracks and fissures.
In this test, we will record the impact force applied on both faces of the specimen made with Cement.
As well as the maximum compression that cement specimen bears without failure recorded.
In a simple Technical way, the compressive strength of cement means :
The ability of cement specimen to withstand or be capable of compressive stress when tested under a Compressive Testing Machine [CTM] at 28 days.
Apparatus required for these Test are :
Procedure:
- After that, we have to add water & mix for 3 minutes until the paste is of uniform colour. The quantity of water mixed with the cement, and the sand mixture should be
- (P/4 + 3) % where P is the percentage of water required to produce the Standard consistency
- The apparatus should be clean & room temperature should be maintained for this test should be 27 ± 2°C.
- Now, we have to Mix the cement & sand with the trowel for about 1 min on Non–porous plate. Cement should be free from lumps.
- Clean the mould and apply oil to moulds for easy removal of mortar cube after drying.
- Now pour the mortar in steel mould. Tamp the cube with rod for 20 times in 8 sec to eliminate the entrained air.
- You can also use vibrator instead of a rod. The vibrator is played for the period of 2 mins with the speed 12000±400 vibrations /minute.
- After completing the vibration, now remove the mould from the vibration machine & place it in room temperature for 24 hrs.
- After setting of mortar cube in 24 hours, we have to open the steel mould from mortar cube.
- Now we have to Keep the test specimens submerged underwater for 7, 14 or 28 days and for every 7 days the water is changed.
Test the three cubes, one at the 7th day, the other at the 14th day & another on the 28th day.
After that, these mortar cubes are placed in the space between the bearing surfaces of the Compressive strength machine.
During testing, care to be taken that The loading must be applied axially on the specimen without any shock & increased at the rate of 35 N/mm2/min. till the specimen collapses.
Due to the constant application of load on the face of the cube, the mortar cube starts cracking and fails at a point.
We have to note down the reading from the Compressive testing machine where the specimen starts failing.
The formula for calculating the Compressive strength of cement is
The maximum load carried by the mortar specimen which means the load point on CTM at which the specimen starts breaking is divided by the surface area (contact area).
Example:
Assume the test specimen tested on 28 days and max compression load at which the specimen starts breaking is 165KN.
As per above fig, Surface are is 50 Sq.cm = 5000mm2
1 KN = 1000N = 165 x 1000 = 165000
As per formula,
Compressive strength of cement = 165000/5000 = 33N/mm2
Hence, the Grade of cement is 33 Grade .
Observations:
Important notes :
As per the IS recommendation, at least 3 cubes to be tested on 7 days, 14 days, 28 days.
Ater that we have to take the average of the three cubes are rounded to nearest 0.5N/mm2 . Do not consider the specimen which differs more than 10% of the average value of compressive strength.
Results:
The average Compressive strength of cement cube at 7 days _________N/mm2
The average Compressive strength of cement cube at 14 days ________N/mm2
The average Compressive strength of cement cube at 28 days________N/mm2 .
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