1. QUALITY CONTROL OF CONSTRUCTION MATERIALS (Acceptance criteria) by K. RAMESH Research Officer, Engineering Materials Laboratory, A.P. Engineering Research Laboratories, Himayatsagar, HYDERABAD-500030.

2. Acceptance criteria for designed concrete mix

3. Minimum frequency of sampling S.No.Quantity of concrete in the work (in Cum.) No. of samples 1.1-51 2.6-152 3.16-303 4.31-504 5.51 & above4 + 1 for each 50 cum. Or part there of Note: At least one sample shall be taken from each shift.

4. Characteristic compressive strength compliance requirement S.No.Specified grade Mean of the group of 4 non- overlapping consecutive test results in N/mm 2 Individual test results in N/mm 2 1.M 15≥f ck + 0.825 x established standard deviation (rounded to nearest 0.5 N/mm 2 ) Or f ck + 3 N/mm 2, which ever is greater ≥ f ck - 3 N/mm 2 2.M 20 or above ≥f ck + 0.825 x established standard deviation (rounded to nearest 0.5 N/mm 2 ) Or f ck + 4 N/mm 2, which ever is greater ≥ f ck - 4 N/mm 2

5. Example Grade of concrete = M15 Quantity of concrete = 50 Cum. No. of samples taken = 4 Their 28 days compressive strengths in N/mm 2 = 12,15,16,18 Mean compressive strengths in N/mm 2 = 15.25 Col. 3 value = Greater of (15 + 0.825 x 3.5 = 17.9, 15 + 3 = 18) = 18 > 15.25, hence not satisfying. Col.4 value = 15 – 3 = 12 is equal to 12, hence satsifying, In total not satisfying.