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

Acceptance criteria for designed concrete mix

Minimum frequency of sampling S.No.Quantity of concrete in the work (in Cum.) No. of samples & above4 + 1 for each 50 cum. Or part there of Note: At least one sample shall be taken from each shift.

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 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 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

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 = Col. 3 value = Greater of ( x 3.5 = 17.9, = 18) = 18 > 15.25, hence not satisfying. Col.4 value = 15 – 3 = 12 is equal to 12, hence satsifying, In total not satisfying.