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Testing Cement
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TESTING OF CEMENT
LECTURE 3
Motivational Quote of the Day "Trust yourself. You know more than you think you do.
Benjamin Spock
Why do we have to conduct the tests?
To ensure the quality of cement
To determine the properties of cementChemical propertiesPhysical propertiesTest should be conducted according to the relevant standardMS 522 Pt. 1, 2, 3 OPCBS 12
Tests of Cement
Chemical compositionFinenessSetting timeSoundnessStrength
CHEMICAL COMPOSITION
To determine the amount of C3S, C2S, C3A, C4AF
Conducted at the cement factory
For research work need to be conducted
FINENESS
Rate of hydration depends on the fineness of cement
Specific surface (m2/kg)
Can be determined by the air permeability Lea and Nurse or Blaine methods
SETTING TIME
Describing the stiffening of cement paste OR the change from fluid to a rigid state
Cement paste = cement + water
Setting is mainly caused hydration of C3A and C3S together with C2S
Accompanied by increase in temperature (heat)
Type of Setting
Initial set corresponds to rapid rise of temperature
Final set corresponds to the peak temperature/strength
False set sometimes occurs within a few minutes of mixing with water, no heat is evolved, concrete can be remixed
Cont.
Flash set caused by the rapid reaction between C3A and water
Prevented by the addition of gypsum
Setting Time
For OPC and RHPC:Initial setting time not less than 45 minutesFinal setting time Not more than 600 minutes
Setting time is affected by: temperature and relative humidity
SOUNDNESS
It is important that the cement paste, after setting, does not undergo a large change in volume i.e. expansion
Expansion may occur due to reactions of free lime, magnesia, and calcium sulphate
Cement exhibits expansion is classified as unsound
Can be determined by Le Chattelier test
STRENGTH - compressionStrength test is not made on neat cementTwo methods:Mortar test Concrete test
Mortar TestMortar = cement + sand = waterMass of water = 10% of the mass of the dry materialsSand standard sand, one size, spherical shapeCube size of 71 mmMaterials are mixed and compacted using vibrating table
Steel Mould
Testing of Sample
Cont.
After 24 hours demould the mortar cubes and cure in water until the day of test
Average of three samples
According to MS 522: Pt. 1OPC 23 MPa at 3 days41 MPa at 28 days
RHPC 29 MPa at 3 days46 MPa at 28 days
Curing Tank
CONCRETE CUBE
Concrete = cement + aggregates + water
W/C ratio : 0.6, 0.55, 0.45
Cube size of 100 mm
Preparation procedures are the same as mortar testOPC 11.5 MPa at 3 days 26 MPa at 28 daysRHPC 18 MPa at 3 days33 MPa at 28 days
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