Ordinary Portland Cement Physical Properites

  Ordinary Portland Cement Physical Properites:-

   

     (a) Rate of setting:The chemical reaction in cement starts sometime after the water is mixed.  The cement then slowly starts to harden.  The time from the time of watering to its freezing is called the initial setting time.  But the time taken for it to completely solidify is called the final setting time.

   Initial and final setting time of ordinary partland cement is 30 minutes.  and 10 hours.

 (b) Fineness: The finer the grain of cement, the higher its strength and firmness and the higher its soundness.  

     The 100 gm sample was placed in an I.S.  When running through a 90 micron sieve, more than 90% of the sample will come out through that sieve.  

(C) Heat of Hydration: The chemical reaction that takes place between water and cement is called hydration.  During this process a lot of heat is generated from the mixture and this is called heat of hydration during the reaction. 

      No more than 65 calories per gram of cement will be emitted after 7 days of mixing and 75 calories after 28 days.

(d) Soundness: It is not recommended to have lime or magnesium in cement free state. When water is added for their presence, it expands and as a result cracks form in the solidified cement structure. 

 The magnitude of this expansion will not exceed 10mm when tested with a La-Chatelier device or 0.5% when tested with an autoclave device. 

Soundness or firmness is the non-expansion of cement.

 (e) Compressive strength:-1: 3 ratio of sand in a pressure instrument should be tested to get the following results - 

after 3 days - not less than 160 kg / square cm or 16N / square mm * (or 16 M Pa), 

after 7 days - Not less than 220 kg / square cm or 22 N / square mm or 22 M Pa. 

 (f) Tensile strength: A specific briquette of spices made with cement sand in the ratio of 1: 3 is tested on a tenuile strength measuring instrument and the following results should be obtained in . 

after 3 days - not less than 20 kg / square cm or 2N / square mm * (or 2 M Pa), 

 After 7 days 25 Kg / sq cm or 2.5 N / sq mm or 2 Pa.