India Section

Dear all,
My client asked me for an advice on setting up a Quality Control Laboratory. I went for a field visit as a part of feasibility survey and when i was studying the costs, I found a scrupulous employee who explained me in detail what they are doing. For M40 concrete in the design they are rejecting any sample with strength lower than M52 (Verified the records and found to be genuine). This will give extra burden to the budget plan. 
My question is, is this kind of practice encouraged or discourage and please give me your reasoning?

------------------------------
Venkata Prem Kumar Janapala S.M.ASCE
Project Advisor
Vinukonda
------------------------------

According to IS:10262 (2009),
f'_ck = f_ck + 1.65s

where,

f'_ck = Target Mean Compressive strength at 28 days in N/mm2 
f_ck = Characteristic Compressive strength at 28 days in N/mm2 (In this case is 40 N/mm2 for M40 concrete)
s = Standard deviation N/mm2

Assuming value of standard deviation (s) 

• • Let us assume that project doesn't has proper site control check.
  • Using table 1 (Pg. 2), s = 5 + 1 = 6 N/mm2

 f'_ck = 40 + 1.65(6) = 49.9 N/mm2

• Maybe due to usual site practice, value of 52 N/mm2 is considered as target mean compressive strength (anyways on conservative side).

If you are provided with proper data then please verify same using actual standard deviation (s).

--
Arth Patel S.M.ASCE
University Student,
Indian Institute of Technology, Tirupati