TESTING OF CEMENT

LECTURE 3

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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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