We ensure the compressive strength of cement after the compressive strength test at 3, 7 and 28 days of cement mortar cube. We described full procedure of cement mortar cube casting, curing and testing procedure per IS code 4031.
Compressive Strength of Cement
Compressive Strength of Cement Definition
To find compressive strength for any type of cement, we cast 9 mortar cubes with the cement mortar which prepared by mixing a certain proportion of cement, water, and graded sand in a procedure and circumstances. we are describing below.
Why Cement mortar cube required?
- To ensure the compressive strength of cement
- For concrete trial mixes
Apparatus and Tools required for Cement mortar cube casting
- One non-porous plate for mixing cement and graded sand.
- Two numbers of trowel.
- Stopwatch for mixing in a time limit.
- Weighing balance with accuracy 1 gram.
- Standard sand, zone I, zone II and zone III confirming to IS 650-1991.
Let’s see what inside the IS 650
Nothing but just the particle size of standard sand which is
zone-I passed through 2.0 mm and retained on 1.0 mm
zone-II passed through 1.0 mm and retained on 0.5 mm
zone-III passed through 0.5 mm and retained on 90 micron,
- Cement mortar cube Vibration machine confirming to IS 10080-1982
This IS codes 10080 – 1982 showing the manufacturing details of the vibration machine and its speed.
So only the thing we have to remind that it’s speed, which shall be 12000 +/-400 rpm ( round per minute ).
- Poking rod for poking in the mortar while vibration in vibration machine.
- Cube moulds 9 numbers with base plates ( size described below )
- Graduated glass for measure water, with capacity 150 to 200 ml, permissible variation shall be ± 1 ml and graduation lines of the cylinder shall be in circles and numbered.
- Tray for weighing cement and standard sand
- Hand gloves for safety
Cement Mortar Cube Mould Size
The size of mortar cube mould is 70.6 mm * 70.6 mm*70.6 mm.
Cement Mortar Cube Casting IS Code
IS Code for cement mortar cube is IS 4031 part 6.
Precautions before proceeding Cement mortar cube casting
Precautions of Compressive Strength of Cement
- Non-porous plate and trowels shall be clean before starting mixing cement mortar, we should not use trowels and non-porous plate in wet condition, this moisture may affect on compressive strength of cement.
- The temperature of the room where cement mortar mixing and cement mortar cube casting is going to be done shall be 27 +/- 2 degree Centigrade, means between 25 to 29.
- Like temperature, Humidity is also an important factor for cement mortar cube test, humidity shall be 65 +/- 5 percent means between 60 to 70.
- Water temperature for mixing in cement mortar shall be maintained between 25 to 29 centigrade.
- For each cement mortar cube mould, the separate weight of materials and mixing shall be done.
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Procedure of Cement Mortar Cube Casting
- For each cube 800 gram cement and standard sand required in which cement 200 gram and standard sand zone-I 200 gram, zone-II 200 gram, zone-III 200 gram.
cement – 200 gram and standard sand – 600 grams.
so “cement mortar ratio” is 1:3
- Water content shall be calculated as we are showing here
The formula for water content = [(P/4)+3]*8, where p is standard consistency of cement
if standard consistency of cement is 28 percent then
[(28/4) +3]*8 = 80 gram
- Mix cement and standard sand in dry condition first, at least one minute.
- Cement mortar mixing time is 3 to 5 minutes, it will start when you adding water in cement and finish when put the mix in the vibration machine.( important )
- Start the stopwatch and add water in cement simultaneously.
- Mix properly by using both trowels, it’s very important.
- A de-shuttering agent like lubricant oil or grease shall be applied inside the cement mortar cube moulds.
- Empty mould with base plate shall be fixed and tighten in a vibration machine before mixing mortar.
Start Vibration Machine
- After proper mixing, the cement mortar shall be placed in empty cement mortar mould fixed in a vibration machine within the time limit.
- Be ensure about the run time for vibration machine 2 minute means 120 seconds in a vibration machine digital scale before starting the machine.
- After the start vibration machine, temping shall be done 20 times in 8 seconds in cement mortar cube.
- After vibration 120 seconds, cement mortar cube shall be removed from the vibration machine and kept on firm ground or platform.
- Where cement mortar cube shall be placed for 24 hours after casting temperature 25 to 29 centigrade and humidity at least 90 percent shall be maintained.
- After 24 hours, de-mould all 9 cement mortar cubes and put in the water tank.
- Compressive strength test shall be done as follows:
03 cubes for 03 days, 03 cubes or 07 days and 03 cubes for 28 days.
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Cement Mortar Cube Formula of Compressive Strength
Compressive Strength = Applied Load / Surface area = 283 KN / 70.6*70.6 mm2 (load assumed)
= 283*1000 N / 4984.36 mm2 = 56.78 N/mm2
or Shortcut Compressive strength formula = Load / 4.984 ( for only mortar cube compressive strength).
so Compressive strength of cement mortar = 283 / 4.984 = 56.78 N/mm2 or MPa.
Compressive Strength of Cement Mortar Limit
The minumum limit for OPC53
compressive strength of cement required for ordinary portland cement in 3 days – 27 N/mm2 or MPa,
7 days – 37 N/mm2 or MPa
Compressive Strength of Cement after 28 days
28 days – 53 N/mm2 or MPa+
Compressive Strength of OPC 43 Grade Cement
3days – 22
7 days – 33
28 days – 43
Compressive Strength of Cement Mortar 1:3
Always, we cast cement mortar cubes in 1:3 ratio for compressive strength of cement by using vibration machine.
If you are going to test compressive strength for any type of cement then you must follow the same procedure what we described above.
Viva or Interview Questions and Answer
Q.1 What is the size of cube mould to test the compressive strength of cement?
Ans. The size of cube mould is 70.6mm * 70.6mm * 70.6mm.
Q.2 What is the time of vibration to cast the cement mortar cube for compressive strength?
Ans. The time of vibration is 120 seconds or 2 minutes.
Q.3 What is the time of mixing cement mortar with water before casting the mortar cubes?
Ans. The time of mixing cement mortar with water is between 3 to 5 minutes.
Q.4 What is the RPM of cement mortar cube casting vibration machine?
Ans. The RPM of cement mortar cube casting vibration machine is 12000 +/- 400.
Q.5 What is the formula of water for cement mortar cube?
Ans. The formula of water for cement mortar cube is [( p/4 ) + 3] * 8, where p is consistency.
If normal or standard consistency is 28 then
[ (28/4) + 3]*8 = [ 7 + 3 ] * 8 = 80 gram.
Q.6 What is the IS code for cement mortar cube casting and testing?
Ans. The IS code for cement mortar cube casting and testing is IS 4031 part 6.
Q.7 How to calculate compressive strength for a cement mortar cube?
Ans. Compressive strength = Applied Ultimate Load / Area ( on which load applied)
suppose the applied ultimate load is 200 KN
the area on which load applied is 70.6mm * 70.6mm = 4984.36 mm2
compressive strength = Load ( N )/ Area (mm2)
= 200 * 1000 N / 4984.36 mm2
= 200000 / 4984.36
= 40.13 N/mm2
Q.8 What is the compressive strength minimum limit for OPC mortar cube?
Ans. Compressive strength minimum limit for OPC
OPC 33 – 33 N/mm2
OPC 43 – 43 N/mm2
OPC 53 – 53 N/mm2
Any other Question? Just ask in comment. We are waiting.
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