CONCRETE MATERIALS PROPERTIES AND TESTING

Transcription

1 CONCRETE MATERIALS PROPERTIES AND TESTING 1

2 Concrete ingredients Cement Fine aggregate Coarse aggregate Water Admixtures 2

3 3

4 4

5 Properties of cement Physical properties of cement Fineness Standard consistency Initial and final setting times Compressive strength Soundness 5

6 6

7 7

8 8

9 Properties of Aggregates properties of fine aggregate Specific gravity Bulk density Water absorption Surface moisture Grading zones of sand by sieve analysis Fineness modulus Bulking of sand Silt content 9

10 Properties of Aggregates Physical properties of coarse aggregate Specific gravity Bulk density Water absorption Surface moisture Grading by sieve analysis Fineness modulus Shape tests- Flakiness index Elongation index Angularity number 10

11 Properties of Aggregates Mechanical properties of coarse aggregate Aggregate crushing strength Aggregate crushing value- Ten percent fine test Aggregate impact value Aggregate abrasion value- Los-angles abrasion test Dorry's attrition test 11

12 characteristics that are considered when selecting aggregate include: grading particle shape and surface texture unit weights and voids water absorption surface moisture abrasion and skid resistance durability 12

13 13

14 14

15 15

16 16

17 17

18 18

19 19

20 20

21 21

22 ADMIXTURES:

23 ADMIXTURES: Pozzolanic Admixture used as substitute for cement (35%) for structures in high temperatures and seawater installation or as additives to decrease the weight of a concrete per cubic foot Water Reducing Admixture an agent or super plasticizers that improves workability and maintain consistency of concrete Waterproofing integrated type in powder form added during mixing. Render surface in decks, basements and pools water impervious.

24 ADMIXTURES: Coloring Agent are pigments or dyes mixed into topping to render/alter color evenly to concrete surface Surface Sealing Agents liquid waxes sprayed over the surface that is easily removed after curing. Prevents evaporation of water into a new concrete allowing hydration and seal the pores of concrete surface after it has hardened Set Inhibiting Agent in liquid form (applied immediately before pouring of concrete) or powder form (applied directly after pouring). Inhibits the setting of cement paste avoiding bonding to surface aggregates and left exposed for architectural effect.

25 ADMIXTURES: Dispersal Agents- prevents bleeding of concrete from concrete. Bonding Agent either metallic aggregate (bonding thru oxidation and expansion) or synthetic latex emulsion (sprayed or painted to coalesce and bond) to improve the bond between old and new concrete. Air Entraining Agent can be inter-ground during manufacturing of Type I,II and III cement. Enables the concrete to be highly resistant against corrosion. Gas Forming Agent develops the potential strength of a concrete

26 ADMIXTURES: Non-Skid Surfaces - use abrasive material in topping to produced unslippery surface for pavement construction Hardener chemical/fine metallic aggregate improve the density of concrete surface subject to impact and wear. Accelerator Speeds up the setting of concrete to reduce the whole curing period or for early removal of forms. Retarder delays or extend the setting time of concrete especially during hot weather condition (hydration accelerates curing) allowing more time to place, consolidate and finish the concrete.

27 Properties of fresh Concrete The properties of freshly mixed concrete are Workability Segregation & bleeding

28 Workability measurements Following tests are commonly used for measuring workability of concrete: 1. Slump test 2. Compacting factor test 3. Vebe test 4. Flow table test 28

29 1. Slump test most universally used test, which measures only the consistency of mixtures of concrete with high consistency The equipment for the slump test is very simple and consists of a tamping rod and a truncated cone, 300 mm height and 100 mm diameter at the top and 200 mm diameter at the bottom the cone is filled with concrete in four layers, each layer given 25 number of blows with tamping rod, then cone is slowly lifted The unsupported concrete cone slumps down by its own weight The decrease in the height of the slumped cone is called the slump of concrete

30 SLUMP TEST 30

31 2. Compacting factor test attempts to evaluate the compactability characteristic of a concrete mixture This test developed in Great Britain, measures the degree of compaction achieved when a concrete mixture is subjected to a standard amount of work The degree of compaction, called compacting factor, is measured by the density ratio (i.e., the ratio of the density actually achieved in the test to the density of the same concrete when in fully compacted condition The apparatus consists essentially of two conical hoppers fitted with doors at the base and placed one above the other, and a 150 x 300 mm cylinder placed below the hoppers, as shown in the following figure

32 32

33 33

34 34

35 35

36 3. Vebe test Vebe test like slump test measures only the consistency but more meaningful for mixtures of concrete with low consistency The equipment for the test, as shown in the following figure, was developed by Swedish engineer V. Bahrner The Vebe test equipment consists of a vibrating table, a cylindrical pan, a slump cone, and a glass or plastic disk attached to a free-moving rod, which serves as a reference end point The cone is placed in the pan, filled with concrete, and removed like slump test The disk is brought into position on top of the concrete cone, and the vibrating table is set in motion The time required to remold the concrete, from the conical to the cylindrical shape until the disk is completely covered with concrete, is reported as the Vebe time in seconds 36

37 37

38 38

39 4.Flow table test Flow table test- specifies the use of flow table to determine the fluidity of concrete, where nominal size the aggregate does not exceed 38mm. Apparatus consists of mould of base of 25cm dia top dia of 17cm and height of 12cm. Flow table of 70.6cm dia with a provision measuring spread of concrete subjected to jolting of 12.5mm 15 times in 15 sec by rotating the handle. Determines the flow of concrete in terms of percentage increase in diameter of spread concrete over base diameter. The flow of the concrete shall be recorded as the percentage increase in diameter of the spread concrete over the base diameter of the moulded concrete, calculated from the following formula: Flow percent = spread diameter in cm 25 x

40 40

41 41

42 42

43 43

44 44

45 Segregation and Bleeding Definition: It is defined as separation of the components of fresh concrete so that they are no longer uniformly distributed Types: There are two kinds of segregation Separation of the mortar (paste + fine aggregate) from the body of concrete (for example, due to over vibration or mishandling of concrete) Bleeding It is defined as phenomenon by virtue of which water appears on the surface after a concrete has been placed and compacted but before it has set Bleeding takes place due to sedimentation of the solids in voids of concrete Laitance is a form of bleeding in which water rising in the internal channels within concrete, carry with it very fine particles of cement, sand, and clay and deposit them in the form of a scum at the concrete surface

46 Causes and Control: The following are the general causes segregation and bleeding problems in concrete: Improper consistency Excessive amount of large particles of coarse aggregate with either too high or too low density Presence of less fines (due to low cement and sand contents or the use of a poorly graded sand) Inappropriate placing and compacting methods The problems of segregation and bleeding can be reduced or eliminated by paying attention to mix proportioning and to handling and placement methods

47 Properties of hardened concrete Strength of concrete- Compressive strength Tensile strength- Direct tensile strength Splitting tensile strength Flexural tensile strength Shear strength Elasticity of concrete - static and dynamic modulus Dimensional stability creep, shrinkage and thermal expansion Durability and impermeability Thermal properties 47

48 1. Strength: The strength of concrete is basically referred to compressive strength and it depends upon three factors. 1- Paste Strength 2- Interfacial Bonding 3- Aggregate Strength 1. Paste strength: It is mainly due to the binding properties of cement that the ingredients are compacted together. If the paste has higher binding strength, higher will be strength of concrete. 2. Interfacial bonding: Interfacial bonding is very necessary regarding the strength. Clay hampers the bonding between paste and aggregate. The aggregate should be washed for a better bonding between paste and aggregate. 3. Aggregate strength: It is mainly the aggregate that provide strength to concrete especially coarse aggregates which act just like bones in the body. Rough and angular aggregate provides better bonding and high strength. 48

49 Factors affecting Strength of concrete: 1. Water-Cement ratio 2. Type of cementing material 3. Amount of cementing material 4. Type of aggregate 5. Air content 6. Admixtures 49

50 Factors Influencing Strength Cement Type (composition) Cement fineness Use of chemical admixtures Use of SCMs Aggregate strength Aggregate MSA Aggregate/paste bond strength Test Parameters Specimen size Specimen shape Load rate 50

51 Tests on concrete Strength 1. Compressive Strength Test Cube test Cylinder test 2. Tensile Strength Test 3. Split cylinder test 4. Flexural Strength Test Two point loading test Three point loading test 51

52 COMPRESION STREMGTH

53 S = So(1- p)3 ß Experimentally Power s found the value of a to be 34,000 psi or 234 MPa 53

54 Water to cement ratio ß Abram s water to cement ratio ß F = K1/(K2w/c) Note: it does not consider the size, type, texture, of aggregate 54

55 S = So(1- p)3 ß Experimentally Power s found the value of a to be 34,000 psi or 234 MPa 55

56 S = So(1- p)3 ß Experimentally Power s found the value of a to be 34,000 psi or 234 MPa 56

57 57

58 SPLIT TENSILE STRENGTH 58

59 SPLIT TENSILE STRENGTH 59

60 60

61 Flexure test 61

62 62

63 63

64 64

65 Points to note: Aggregate and cement paste linear up to failure Concrete stress-strain response (elastic) in between aggregate and cement paste Concrete does not have a linear behavior up to failure 65

66 Modulus of elasticity 66

67 Drying Shrinkage of concrete 67

68 Creep of concrete 68

69 Nondestructive Test- (NDT) This test are useful to: (1) quality control; (2) determination of the time for form removal; (3) help assess the soundness of existing concrete structures. 69

70 TYPES OF NDT TESTS 1. Surface Hardness Methods 2. Rebound Hardness 3. Penetration Resistance 4. Pull-Out Test 5. Ultrasonic Pulse Velocity 70

71 Rebound Hardness The most common nondestructive test is the rebound test. The test measures the rebound of a hardened steel hammer impacted on the concrete by a spring. This method has the same limitations as the surface hardness tests. The results are affected by: (1) surface finish; (2) moisture content; (3) temperature; (4) rigidity of the member being tested; (5) carbonation of the surface; and (6) direction of impact (upward, downward, horizontal). Most useful in checking the uniformity of concrete. 71

72 72

73 73

74 74

75 75

76 76

77 Ultrasonic Pulse Velocity This test is based o the fact that the velocity of sound is related to the elastic modulus. The device is accurate to about + 1%. The position of the testing equipment can affect the measurement, method A given the best results. There are several factors which affect this test: (1) surface smoothness; (2) travel path of the pulse; (3) temperature effects on the pulse velocity; (4) moisture content; (5) presence of steel reinforcing bars; and (6) age of concrete. 77

78 78

79 79

80 80

81 81

82 82

83 Pull-Out Test Pull-out test determine the force required to pull a steel insert out of concrete which it was embedded during casting. This test is a measure of the shear strength of the concrete which can be correlated with compressive strength. This test is better than those previously discussed. the test may be planned in advance and the assembly embedded in the concrete during casting. 83

84 PULL-OUT TEST 84

85 85

86 Surface Hardness Methods -- One of the oldest nondestructive tests, developed in Germany in the 1930's. Basically, the surface is impacted with a mass and the size of the resulting indention is measured. The accuracy of these type of tests is only 20 to 30%. Penetration Resistance -- Resistance of concrete to penetration by a steel probe driven by a given amount of energy is measured. This test is not affected by surface hardness or carbonation as the above tests, however, the mix proportions and material properties are still important. 86

87 Relevant I.S Codes 1 87

88