3. Inspection, Quality, Variation, Statistical Control and Acceptance Criteria Dr. J.SUDHAKUMAR Assistant Professor Department of Civil Engg. NIT, CALICUT

4. Inspection, Quality, Variation, Statistical Control and Acceptance Criteria n INSPECTION AND QUALITY CHECK n Need and scope of Inspection  To ensure that work is done in accordance with the plans, specifications and good practice, and to prevent mistakes.

5.  The other requirements for the same purpose include  Intelligent design  Adequate specifications  Reliable construction  Competent inspection

6.  The following items are covered by the inspection of concrete construction at various stages:  Sampling, Identification, Examination, and any field testing of materials  Control of concrete proportioning and the measurement of materials  Examination of the foundation, forms and other work preparatory to concreting

7.  Continuous inspection of the batching, mixing, conveying, placing, compacting, finishing and curing of concrete  Testing for consistency of concrete, and preparation of any concrete specimens required for laboratory testing

8.  General observation of contractor’s plant and equipment, weather, working conditions and other items affecting the concrete  Preparation of records and reports

9. n Choice of an Inspector  An ideal inspector should have both technical and practical know- how of the subject. He should essentially understand the following:  Bulking of fine aggregate (sand)  Well proportioned mix or not  Whether the mix has desired slump

10.  Whether the forms are sufficiently tight and braced  Whether the concrete is properly compacted or not  Whether the forms are removed early or not

11. n Authority of the Inspector  An authority should be given to the inspector to :  Prohibit concreting until all preliminary conditions (such as completion of forms) have been fulfilled and inspection report for concreting has been provided

12.  Stop the use of materials and equipment, which do not comply with the specifications  Stop any work which is not being done in conformity with the plans and specifications

13.  Require the removal or repair of faulty construction or of construction performed without inspection and not accessible to being inspected later

14.  Normally, the inspector is authorised to take direct action in the first three cases above  He should report the matter immediately to his superior  He should stop the work only as a last resort, when it is clear that unsatisfactory concrete will result from the continuing operations

15. n Quality check on concrete  Before concrete is placed, the specification requirements in all aspects must be fulfilled  Forms should be of proper size and strength and in their correct location  Cement, aggregates, water and any other ingredients should be inspected

16.  Batching of materials, time of mixing, possibility of segregation, proper curing etc., as this will influence the properties of hardened concrete  Preparation of test specimens  At least 3 specimens for each 200 m 3 of concrete  Each sample should be from different points of the structure

17.  Sampling should not be from the conveying device  Taken at irregular times and without prolonged preparations  Sample should be placed in a water-tight non-absorbent container  Remixed fast enough to make it uniform, and then moulded into specimens

18.  For compression test, 150 mm cube moulds are used  Moulds are filled in 3 layers  Each layer is compacted with 25 strokes of a 16 mm diameter and 600 mm long, round bullet pointed steel rod  After the top surface has been levelled, the specimen is covered to prevent evaporation

19.  Flexure specimens are 150 mm x 150 mm in section. Moulds are placed with their long axis horizontal and are filled in 2 layers, each layer being rodded 50 times.

20. n Quality check on Personnel and Equipment  Should have a well trained team, conversant with different quality control procedure of inspection, testing and data analysis  An adequately equipped field laboratory for carrying out routine control tests

21. n Table 1 : Daily testing programme Daily testing programme and composition of team and composition of team ( refer notes ) ( refer notes )

22. n Table 2 : Degree of quality control Degree of quality control expected under different site expected under different site conditions conditions ( refer notes )

23. n Measures of Variability of Concrete Mix Design Design  Factors contributing to Variability  It is found that strength of concrete varies from batch to batch  The following are the sources of variability

24.  Variation in the quality of constituent materials used  Variation in the mix proportions due to batching processes  Variations in the quality of batching and mixing equipment available

25.  Quality of supervision and workmanship  Variation due to sampling and testing of concrete specimens  These variations are inevitable during production of concrete

26.  The purpose of quality control using statistical means is to produce concrete of uniform quality  If a large number of cube strength test results are plotted on a histogram, the results are found to follow a bell-shaped curve termed as “Normal Distribution Curve”

27.  The arithmetic mean of a number of test results gives no indication of the extent of variation of strength  However, this can be ascertained by relating the individual strength to the mean strength and determining the variation from the mean, with the help of the characteristics of the N.D.curve

28.  Standard Deviation  The root mean square deviation of the whole consignment is termed as the ‘standard Deviation”. It can be defined numerically as: S =   (x – - x - ) 2 /(n-1)

29.  Where S = S.D. of the test results x = any value in the test results _ x = arithmetic mean of the results n = number of test results n = number of test results

30.  Coefficient of Variation  An alternate method of expressing the variation of results about the mean is by coefficient of variation  This is a non-dimensional measure of variation

31.  This is obtained by dividing the standard deviation by the average value, and is expressed as V = 100 S / - X - V = 100 S / - X -

32.  where  V = coefficient of variation S = S.D. in strength - X - = Mean value in strength - X - = Mean value in strength  When the C.V. is constant, S.D. increases with the increase in strength of concrete

33.  STATISTICAL CONCEPTS OF MIX DESIGN MIX DESIGN  Characteristic strength This means that value of the strength of concrete below which, not more than 5 percent of the test results are expected to fall This means that value of the strength of concrete below which, not more than 5 percent of the test results are expected to fall

34.  Target mean strength f t = f ck + K.s f t = f ck + K.swhere f t = target mean strength f t = target mean strength f ck = characteristic strength f ck = characteristic strength K = a statistical constant, depending on K = a statistical constant, depending on the definition of f ck and is derived the definition of f ck and is derived from the mathematics of Normal from the mathematics of Normal Distribution Distribution s = standard deviation s = standard deviation

35.  The value of K is equal to 1.65 where not more than 5% of test results are expected to fall below the characteristic strength f t = f ck + 1.65 s f t = f ck + 1.65 s

36. Acceptance Criteria (IS 456 : 2000) 1. Compressive strength Both the following conditions must be met : Both the following conditions must be met : a) The mean strength of any four consecutive test results compiles with the appropriate limits in Table 3.

37. Table 3 For M15 grade Mean of 4 consecutive results in N/mm 2 must be greater than or equal to f ck + 0.825 x SD or f ck + 3 N/mm 2, whichever is greater

38. Table 3 For M20 or above grade Mean of the group of 4 consecutive results in N/mm 2 must be greater than or equal to f ck + 0.825 x SD or f ck + 4 N/mm 2, whichever is greater

39. Acceptance Criteria b) Any individual test result complies with the appropriate limits in Table 3.

40. Table 3 For M15 grade Individual test results in N/mm 2 must be greater than or equal to Individual test results in N/mm 2 must be greater than or equal to ( f ck – 3 ) N/mm 2

41. Table 3 For M20 or above grade Individual test results in N/mm 2 must be greater than or equal to Individual test results in N/mm 2 must be greater than or equal to ( f ck – 4 ) N/mm 2

42. Acceptance Criteria 1. Flexural strength Both the following conditions must be met : Both the following conditions must be met :

43. a) The mean strength of any four consecutive test results exceeds the specified characteristic compressive strength by at least 0.3 N/mm 2

44. b) The strength determined from any test result is not less than the specified characteristic strength less 0.3 N/mm 2

45. THANK THANK YOU