Properties of Ordinary hydraulic cement
(i) Chemical properties: Portland cement consists of the next chemical compounds:
(a) Tricalcium silicate 3 CaO.SiO2 (C3S) 40%
(b) Dicalcium silicate 2CaO.SiO2 (C2S) 30%
(c) Tricalcium aluminate 3CaO.Al2O3 (C3A) 11%
(d) Tetracalcium aluminate 4CaO.Al2O3.Fe2O3 (C3AF) 11%
There could even be small quantities of impurities present like quicklime (CaO) and periclase (MgO). When water is added to cement, C3A is that the primary to react and cause initial set. It generates large amount of warmth. C3S hydrates early and develops strength within the first 28 days. It also generates heat. C2S is that the next to hydrate. It hydrates slowly and is responsible for the increase in ultimate strength. C4AF is a relatively inactive compound.
(ii) Physical properties:
The following physical properties should be checked before selecting a Portland cement for the engineering works. IS 269–1967 specifies the tactic of testing and prescribes the limits:
(a) Fineness (b) Setting time
(c) Soundness (d) Crushing strength.
(a) Fineness:
It is measured in terms of the percentage of weight retained after sieving the cement through 90-micron sieve or by area of cement in square centimeters per gram of cement. consistent with IS code specification weight retained on the sieve should not be quite 10 percent. In terms of the specific surface should not be but 2250 cm2/gm.
(b) Setting time:
A period of half-hour as a minimum setting time for the initial setting and a maximum period of 600 minutes as maximum setting time is specified by IS code, provided the tests are conducted as per the procedure prescribed by IS 269-1967.
(c) Soundness:
Once the concrete has hardened it is necessary to form sure that no volumetric changes take place. The cement is claimed to be unsound if it exhibits volumetric instability after hardening. IS code recommends test with Le Chateliermould for testing this property. At the highest of the test, the indicator of le Chatelier mold shouldn't expand by quite 10 mm.
(a) Crushing strength:
For this mortar, cubes are made with standard sand and tested in a compression testing machine as per the specification of IS code. The minimum strength specified is 16 N/mm2 after 3 days and 22 N/mm2 after 7 days of curing.
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