Objective:-
- This test is conducted to determine the compressive strength of cement mortar cube casting.
The reference is :-
- IS: 4031, (Part-6) Method of physical test for hydraulic cement, Determination of compressive strength, Compressive strength hydraulic cement.
- IS: 3535, Method of sampling of cement.
- S:650 Specification for standard sand for testing cement.I
- S:10086, Specification for Gauging Trowel.
- IS: 10080, Specification of apparatus for measuring the change in length of hardened cement paste, mortar and concrete.
Testing Equipment:-
- Vibration machine should conform to IS: 10080
- Poking rod (made of rubber) t
- Three types of standard Ennore sand conforming to IS: 650.
- Cube mould of size 70.6 mm, conforming to IS: 10080.
- Gauging trowel.
- weight balance.
- Graduated cylindrical glass jar.
- Compression Testing Machine 500 kN
- The ingredients for each cube are to be mixed separately and the quantities of cement, standard sand and water are given below.
- a) Cement : 200 grams
- b).Standard sand 600g (200g of each grade)
- I) Where P is the % of water required to make a paste of standard consistency.
- ii) Place the cement and sand mixer on a non-porous plate and mix it well with a gauging trowel for a minute.
- iii) Then mix the above mentioned quantity of water with cement to make a uniform mortar.
- iv) Mixing time should not be less than 3 minutes and the time taken to obtain uniform colour should not be more than four minutes.
Number of samples:-
- Three samples are required for each treatment period of 3, and 7, and 28 days.
Sample Mold:-
- I) When assembling ready-to-use molds, the joints should be coated with a thin layer of petroleum jelly. Apply a thin layer of oil to the inside surface of the mold .
- ii) Then place the mould on the table of the vibration machine and hold it firmly by means of suitable clamps.
- iii) Place a suitable sized hopper on the top of the mould to prevent the mortar from spilling out during vibration.
- iv) Immediately after mixing, place the mortar in cube in a vibrating machine and layer it and press it 20 times in about 8 seconds through poking rod to remove trapped air and honeycomb.
- v) The duration of vibration should not be less than 2 minutes and the specified speed should be 12000 ± 400 times per minute.
- vi) At the end of vibration, remove the mould and then smooth the top surface of the specimen with a trowel.
Treatment of the sample:-
- Keep the filled mould in a humid chamber for 24 days .
- At the end of that period remove the specimen from the mould and immediately immerse it in clean fresh water and keep it there until the test is done.
- Curing tank Of the cement specimen should be cleaned & changed the water at 7 days intervals.
TESTNG OF THE CEMENT CUBE:-
- Test three cubes for compressive strength for each period Of curing Of 3.7 & 28 days.
- Bearing surface of testing machine should wiped clean & the loose materials from the surface of specimens also removed.
- Cube specimens should be placed in such_manner that the load shall be applied to opposite sides as it cast.
- The axis of the specimens should be carefully aligned with the center of the thrust.
- The pace rate is to be set to 2.9 kN/Sec for cube. Record the maximum load applied to the specimen.
CALCULATIONS :-
- The measured compressive strength of the specimen P/A ( Kg/cm2, N/mm2 or MPa)
- a). P = Max load applied to the specimen during the test,
- Jb). A = Cross sectional area Of the specimen,
- Average Of three values is taken as representative Of the batch .
- Individual variation should not be more than ± 15 % of the Average.
ACCEPTANCE CRITERIA:-
- For compressive strength Of cement (OPC -43)
- At 3 days it should not be less than 23 (MPa).
- At 7 days it should not be less than 33 (MPa).
- At 28 days it should not be less than 43 (MPa).
SPECIFICATIONS:-
- The property specification requires testing to be performed on laboratory-prepared mortar to demonstrate compliance with a specified minimum compressive strength, minimum water retention and maximum air content. This information is required for submittals, so is performed prior to construction.