Physical properties of Ordinary Portland Cement

Cement should be tested for its following properties

1. Fineness

Fineness, or particle size of portland cement affects rate of hydration, which is responsible for the rate of strength gain.  The smaller the particle size, the greater the surface area-to-volume ratio, which means more area available for water-cement reaction per unit volume.  Approximately 95% of cement particles are smaller than 45 micron with the average particle size  about 15 micron. Fineness is measured in terms of surface area per unit mass. Fineness can be tested by Wagner turbidimeter test, Blaine Air-permeability test, 45-micrometer sieve and electronic particle size analyzer.

2. Soundness

Soundness refers to the ability of a hardened cement paste to retain its volume after setting. Lack of soundness is observed in the cement samples containing excessive amounts of hardburnt free lime or magnesia. Autoclave expansion test is used to determine soundness of cement.

3. Consistency

Consistency of a cement paste refers to its ability to flow. Normal consistency pastes are required to be prepared for testing cement specimens. A paste is said to have a normal consistency when the plunger of Vicat apparatus penetrates it by 10±1 mm. the corresponding water-cement ratio is reported.

Initial setting time is the time that elapsed from the instance of adding water untill the pastes ceases to  behave as fluid or plastic. Whereas final setting time referred to the time required for the cement paste to reach certain state of hardness to sustain  some load. Setting time is tested by Vicat apparatus or Gillmore needle.

5. Compressive Strength

Compressive strength of cement is tested by 50 mm mortar cubes made by using standard sand and cured  in a prescribed way. the cubes are tested under a compression testing machine. The strength of cement varies with time, therefore in general it is reported as 3 day, 7 day or 28 day strength. 

6. Heat of hydration

The heat generated during the reaction of cement and water is known as heat of hydration. The factors affecting heat of hydration are C3A, C2S, water-cement ration, fineness of cement and curing temperature. Conduction calorimeter is used to test heat of hydration.

7. Loss on Ignition

A cement sample of known weight is heated between 900 - 1000°C (1650 - 1830°F) until a constant weight is obtained.  The weight loss of the sample due to heating is then determined.  A high loss on ignition (more than 3%) indicates  prehydration and carbonation, which may be due to  inappropriate storage or adulteration.

8. Specific gravity (relative density)

Specific gravity is generally required in mix proportioning for concrete. The particle density (measured by excluding the air between particles) of OPC is found to be in the range of 3.1 to 3.25 Megagram per cubic meter. The relative density of OPC is assumed as 3.15. The density of cement is determined by Le Chatelier apparatus.

9. Bulk Density

The bulk density can be determined by dividing the mass of cement particles and air between particles by the volume of cement sample. Bulk density of OPC ranges from 830 kg/cu.m to 1650 kg/cu.m. This test can be done with the help of two beakers having same amount of cement. The cement in one beaker is slightly vibrated  which shows a decrease in the volume.

Hoover dam