What are the Properties of Ordinary Portland Cement?
Properties of Ordinary Portland Cement
|Portland cement consists of the following chemical compounds:|
|Tricalcium silicate 3 CaO.SiO2 (C3S) 40%|
|Dicalcium silicate 2CaO.SiO2 (C2S) 30%|
|Tricalcium aluminate 3CaO.Al2O3 (C3A) 11%|
|Tetra calcium aluminate 4CaO.Al2O3.Fe2O3 (C3AF) 11%|
- Portland cement; There may be small quantities of impurifies present such as calcium oxide (Ca O) and magnesium oxide (MgO).
- When water is added to cement, C3A is the first to react and cause the initial set. It generates a great amount of heat. C3S hydrates early and develops strength in the first 28 days. It also generates heat. C2S is the next to hydrate. It hydrates slowly and is responsible for an increase in ultimate strength. C4AF is comparatively inactive compound.
- The following physical properties are should be checked before selecting one of the Portland cement for all civil engineering works. The IS 269 to1967 specifies the method of lab testing and prescribes the limits.
- Setting time
- Crushing strength.
- It is measured in terms of percentage of weight retained after sieving the cement through 90-micron sieve or by the surface area of cement in square centimetres per gramme of cement. According to the IS, code specification weight is retained on the sieve should not be more than 10 per cent in this test method. In these terms of the specific surface area should not be less than 2250 cm2/gm.
- A period of 30 minutes as the minimum setting time for initial setting and a maximum period of 600 minutes as maximum setting time is specified by IS code, provided these type tests are conducted as per the testing procedure prescribed by IS code 269-1967.
- Once the concrete has hardened it was necessary to ensure that no volumetric changes take the concrete place. This type of testing methods cement is said to be unsound (no sound) if it exhibits volumetric (volume calculation) instability after hardening. Civil IS code recommending test with Le Chatelet mould for testing this property. At the end of the test, the indicator of Le Chatelet mould should not expand by more than 10 mm.
- For this mortar, cubes are made with a standard sand and tested in compression testing machine as per the specification of IS code. The minimum strength of the cement specified is 16 N/mm2 after that 3 days and 22 N/mm2 after 7 days of the curing process.