Compressive strength of cement test
Aim :-
To determine the compressive strength of cement .
Objective :-
The compressive strength of hardened cement is the most important of all the properties. Therefore, it is not surprising that the cement is always tested for its strength at the laboratory before the cement is used in important works. Strength tests are not made on neat cement paste because of difficulties of excessive shrinkage and subsequent cracking of neat cement.
Apparatus :-
- Sand
- Vibration Machine
- Cube Mould ( 70.6 mm size cube )
- Compression Testing Machine
- weight machine
- Graduated Glass Cylinders
- Trowel to mix
- Non-porous plate
- water
References :-
IS 4031(Part 6):1988 Methods of Physical Tests for Hydraulic Cement- Determination of Compressive Strength of Hydraulic Cement other than Masonry Cement (First revision).
Procedure :-
- Clean the apparatus with the dry cloth and ensure that the room temperature for conducting this test should be 27 ± 2°C.
- Mix the cement and sand with the trowel for the period of 1 min on Non – porous plate. Ensure that the cement should not have any lumps in it
- Now add water and mix for 3 minutes until the paste is of uniform color . The quantity of water mixed with the cement, the sand mixture should be
(P/4 + 3) % where P is the percentage of water required to produce the standard consistency. - Clean the mould with the dry cloth and apply the mould oil for easy removal of mortar cube after drying.
- Now pour the mortar in steel cube mould. Prod the mortar for 20 times in 8 sec with the help of rod 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 to eliminate the entrained air in mortar mix.
- Once the vibration completes, immediately remove the mould from the vibration machine and place it in room temperature for 24 hrs.
- Once mortar cube sets, After 24 hours dismantle the steel mould from mortar cube.
- Keep the test specimens submerged underwater for the stipulated time. This process is called curing.
- As mentioned the specimen must be kept in water for 7 or 14 or 28 days and for every 7 days the water is changed.
- Test the three cubes, one at 7th day, other at 14th day and another at 28th day.
- Testing specimens (mortar cubes) are placed in the space between bearing surfaces of the Compressive strength machine.
- Care must be taken to prevent the existence of any loose material or grit on the metal plates of machine or specimen block.
- The loading must be applied axially on specimen without any shock and increased at the rate of 35 N/mm2 /min. till the specimen collapse.
- Due to the constant application of load on the face of the cube, the mortar cube starts cracking and fails at a point.
- Note down the reading from Compressive testing machine where the specimen starts failing.
Observation table :-
| S.No. | Days | Surface area of cube (mm2) | Max Load (N) | Compressive Strength N/mm2 | Average Compressive Strength N/mm2 |
|---|---|---|---|---|---|
| 1 | 7 days | ||||
| 2 | 14 days | ||||
| 3 | 28 days | ||||
Calculation
The measured compressive strength of the cubes shall be calculated by dividing the maximum load applied to the cubes during the test by the cross-sectional area, calculated from the mean dimensions of the section and shall be expressed to the nearest 0.5 N/mm2. In determining the compressive strength, do not consider specimens that are manifestly faulty, or that give strengths differing by more than 10 percent from the average value of all the test specimens. After discarding specimens or strength values, if less than two strength values are left for determining the compressive strength at any given period, a retest shall be made.
Formula :-
compressive strength of concrete = max load / surface area of cube
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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