Asked by : Shekhar , Construction-Construction Management M/s Gammon India Ltd,Mumbai
Industry : Cement
Activity: Question posted: 07 20 2008 22:20:54 +0000, 12 answers, 17483 views, last activity 02 15 2014 11:45:38 +0000
OPC is available in grades 33,43 and 53.Why these grades are in figures 33,43 & 53 why not in roundoff figures like 30/35,40/45,50/55 ? I want basic reason for the same.
I am sorry to say that all the answers given here give very good understanding about classification of cement based upon its 28 days' compressive strength but none of them are answer to the question in question. The question is that why 33,43,53 why not 30/35 and so on (like bitumen).
I have no scientific answer to it but I think so that as BS follows 32.5, 42.5 and 52.5, we have just rounded it off and copied. Since we are commonwealth country and our reference codes at very begining were BS codes so it might also have come from there with typical "Indian" modification.
This is what they call "adapted to Indian conditions."
33, 43 and 53 are 28 days mortar cube compressive strength results in N/sq mm (MPa) of cement tested at a proportion of 1:3 (1 part cement and 3 part standard sand. The strength depends on the fineness and chemical composition of the cement. Now days, 33 grade cement is discontinued. On testing cement of reputed brand, one can find an average strength of 52 and 58 MPa for 43 and 53 grade cement respectively. (against a required of 43 and 53 MPa). However OPC is almost not available in retail market and for procurement in a project, the requisition should be given well in advance. PPC is readily available.
Ordinary Portland cement is produced by grinding Clinker with Gypsum. 33,43,53 is minimum 28 days strength to be achived as per BIS for that particular grade.
Ex: 33 denotes OPC 33 GRADE cement the strength of should not be less than 33 Mpa (330Kgs/cm2) Vice versa for 43 Grade OPC 43 Mpa and 53 Mpa for 53 Grade OPC
With all the Tech Details We Have Seen in Disscussion is Correct.But The Next part is that We Have to Judge the Grade of Cement Depending On Site & Type of Structure viewing Curing Process.If It is Raft or Pile Foundation we would Prefer 33 Grade As in foundation we do not have Sufficient Curing Process Or No Full Proof Controle.If Mass concreting is There Then we would use 33 Grade as heat of Hydration will be less in 33 Grade.Heigher Grade Requires More Curing So We will use it where we could Insure Proper Curing.Otherwise Crack will develope.In summerwe could use 33 grade & In Winter Or Rainning Season We could use 53 G.
The grades indicates the minimum compressive strength after 28 days of the mortar cubes. ( Mortar cubes are casted with the cement to be tested for strength with the BIS approved Standard Sand with water as per consistency test)
for eg:- 33 grade indicates minimum 33 MPa or 330 Kg/ cm2 i.e. 100%strength achieved after 28 days . Similarly 43 & 53 grades can be defined.
But today. The production of OPC is almost stoped maximum of cement companys in the country&manufacture PPC which is not early strength i.e not achieved 100% strength after 28 days.