Cement Concrete Mix Design and Quality Control

1. Cement Concrete Mix Design and Quality Control By Dr. Sunil Kumar Professor Department of Civil Engineering Harcourt Butler Technological Institute Kanpur-208002

2. Major Advantages of Concrete Roads • Long life (30-40 yrs.) • Low maintenance cost • Fuel saving @ 14% for load carriers • Utilise up to 30% of fly ash – disposal of which is a great problem • Economical when life cycle cost is compared • Pollution free construction • Inconvenience to users due to less frequent repair • Good riding quality throughout life • No effect of spillage of oil

3. Conti….. • Roads can withstand extremes of weather • Better performance over poor soil sub grade • Better light reflectivity • Safer night driving due to visibility • Fuel saving in road construction • Skid resistance • Good noise record • Conservation of material

4. Roads Through Villages • A common feature of village roads in the absence of any drainage arrangement • In most cases, the road level is low & water accumulate on them during rains, the road itself acting as a longitudinal drain • Such roads are frequently damaged after rains • If they are concreted, the damage can be minimise

5. What is concrete? • In very simple terms concrete can be looked upon as a conglomerate rock consisting of large aggregate particles embedded in the matrix of “paste”. • Paste is the mixture of water and cement.

6. Ingredients • Cement • Aggregates • Water • Admixtures

7. Basic Concrete Engineering • Good concrete • Proportioning of concrete mixes • Permeability and porosity of concrete

8. Good Concrete • Method exist to determine only workability and strength • How do we work with other properties such as segregation resistance, durability etc ?

9. Expectation from Good Concrete fresh state • Homogeneity • Workability • Segregation resistance hardened state • Strength • Durability

10. Workability of Concrete

11. Strength of Concrete • Strength of aggregates • Strength of mortar Ultimate Strength • Inversely proportional to water cement ratio • Curing condition • Compaction • Quality of binder ( including use of admixture)

12. Durability of Concrete • Concrete is not a maintenance free material and required periodic inspection • Durability of concrete is determined through a complex interaction between parameters related to • Design of structures, such as permissible crack width, grade of concrete used and design cover to the reinforcement • Choice of appropriate material in construction • Quality control during construction maintaining good construction materials such as curing etc. • Environment in which structure is placed

13. Principles of Concrete Mix Design Design involves proportion of the given constituents which would produce concrete possessing specifies properties on both in fresh and hardened state with the maximum overall economy.

14. Factors in the choice of mix designing • Grade designation • Type of cement • Maximum nominal size of aggregates • Minimum water cement ratio • Workability • Minimum cement content

15. Concrete Mix Proportion proportion of nominal mix concrete

16. Variability of Concrete Strength • Variation in the quality of constituent materials • Variation in mixed proportion • Quality of supervision and workmanship • Variation due to sampling and testing of concrete specimen.

17. Target mean strength Considering the inherent variability of concrete strength during production, it is necessary to design the mix to have a target mean strength which is greater than the characteristic strength by a suitable margin. f¹ = fck + k*s f¹ = target mean strength fck = characteristic strength s = standard deviation k = 1.65 Not more than 5% of the test results are expected to fall below fck.

18. Procedure for proportioning design concrete mixes Step 1 Arrive at the mean target strength from characteristic compressive strength and level of quality control

19. Suggested values of standard deviation

20. Degree of quality control Very good – • Fresh cement from single source and regular test weigh batching • Aggregates in single sizes, controlled grading and moisture content • Controlled water addition • Frequent supervision • Regular workability and strength tests • Field lab facility

21. Step 2 Assume an air content • depends on size of aggregate

22. Step 3 • Choose a water cement ratio for mean target strength from Fig. 46 given in SP: 23-1982. • Water cement ratio satisfy maximum value prescribed for exposure condition in IS: 456

23. Step 4 • Calculate approximate sand and water content per cubic meter of concrete water cement ratio=0.35

24. water cement ratio=0.35

25. Adjustment of values in water content & sand % for other conditions

26. Step 5 • Determination of cement content On the basis of water cement ratio which in turn is determined from the water cement ratio v/s strength relationship

27. Step 6 • Aggregate determination V = [W+C/Sc+1/P*Fa/Sfa]*1/1000 V= gross volume in m³ - volume of entrapped air Sc= specific gravity of cement (3.15) W= mass of water in kg/m³ of concrete C= mass of cement in kg/m³ of concrete P= ratio of fine agg. to total agg. by absolute volume

28. Step 7 • Adjustment in proportions of concrete mixes • Arrive at the concrete mix proportions for the first trial • Conduct trial mixes with suitable adjustments till the final mix composition is arrived at.

29. Relationship with flexural strength • fcr = 0.7 (fck)½ N/mm² fcr = flexural strength fck= characteristic compressive strength of concrete in N/mm²

30. IS:456 specifications on workability

31. IS: 456 specifications on minimum cement content and maximum free water cement ratio

32. IS: 383-1970 specification for coarse and fine aggregates • Grading zone of fine aggregate • % passing for single sized aggregate of nominal size • Percentage passing for graded aggregate of nominal size

33. Aggregates • Crushing value- should not greater than 30% for concrete for bearing surface • Los angeles abrasion value- should not greater than 30% for aggregate used for bearing surfaces • Agggregate impact value- should not greater than 30% for aggregate used for bearing surfaces • Flakiness index- should not greater than 25%

34. IRC specification on cc pavements Semi rigid pavements Proportion of dry lean concrete-design by trial & error method • Compaction is done by rolling, hence keep slump 0-10 mm. • Cement concrete should not less than 150 kg/m³ • Average compaction strength of 5 cubes at 28 days should not be less than 10.0 MPa. • Average compaction strength of individual cube at 28 days should not be less than 7.5 MPa.

35. Rigid Pavement CC Pavement Strength requirements of coarse aggregate for concrete used in pavements • Aggregate impact value- should not be greater than 30% • Los angeles abrasion value- should not be greater than 30% Roller compacted concrete pavement (RCCP) • Water content may range 4-7% by weight of dry materials including cement.

36. Concrete Pavements Rigid pavement using pavement quality concrete (PQC) IRC: 44- tentative guidelines for cc mix design for pavements. for minimum flexural strength of 40 kg/mm² in the field assuming good degree of quality in the field. • Cement content lies between 350 to 425 kg/m³ • Approx mix proportion = 1:1.5:3 • Water cement ratio = 0.38 • Workability to be considered in lab for test should be preferably 10 mm slump.

37. Concrete compacted by needle vibrators, hand tampers and plate compactors • A slump of 2.5 to 4.5 cm at paving site is acceptable for compaction by hand operated machines

38. Testing of hardened concrete • Core test • Non destructive test

39. Stage Wise Control of Quality • Pre Construction: Quality of materials • During Construction: (Freshly mixed concrete) Batching Mixing Workability Compaction Surface finishing • Post Construction: (Quality of hardened concrete) Check for riding quality Check for strength Check for concrete thickness

40. Concluding Remarks • Do not over or under design the pavement • Do not use outdated formulae or other parameters when designing the pavement • Do not try to economies by using poorly trained or unqualified supervisors and operators • Do not use sub-standard tools and equipment • Do not use sub-standard material • Do not use dirty water for making concrete • Do not try to economies on testing of materials • Do not allow any traffic till the joints are permanently sealed

41. Continue……… • Do not allow drains to get block or choked • Do not cut joints too early or too late • Do not place on the sub grade that is not thoroughly compacted and dampened • Do not drop concrete into place freely from a height exceeding 1.5 m • Do not vibrate concrete excessively to prevent flow of mortar to the top • Do not allow volume batching of concrete • Do not allow concrete to dry • Do not allow any vehicle on the road till it is fully cured

42. Thanks