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Understanding of concrete 28.june-08 (2) - copy

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Understanding concrete

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Understanding of concrete 28.june-08 (2) - copy

  1. 1. Seminar by : Arivusudar NagarajanSeminar by : Arivusudar Nagarajan
  2. 2. 2 CEMENT REPLACEMENT MATERIALS FLY ASH  It is finely divided residue resulting from the combustion of powdered coal and transported by the flue gases and collected by electrostatic precipitator ( Thermal Power plants)  Mostly used pozzolonic material  Reference IS-3812 Contd…
  3. 3. 3  Savings in cement  Reducing heat of hydration  Reducing water demand  Spherical shape and smooth surface of flyash helps to reduce the inter-particle friction and thus facilitates mobility.  Reduce Bleeding and drying shrinkage.  Fly ash particles plasticize cement paste and improves flowability and rheology of the mix.  Contributes to strength Contd… ADVANTAGES OF FLY ASH
  4. 4. 4 CEMENT + C-S-H Gel + Ca(OH)2 WATER FLYASH C-S-H Gel SECONDARY HYDRATION OF FLY ASH
  5. 5. 5 PETROGRAPHIC VIEW OF FLY ASH
  6. 6. 6
  7. 7. 7 FLYASH-PARTICLE PACKING EFFECT FLYASH
  8. 8. 8 Cement Flyash BALL BEARING EFFECT
  9. 9. 9 Trapped Water DISPERSION OF CEMENT PARTICLES WITH FLY ASH
  10. 10. 10  By-product from steel Industries.  Specific surface of about 400-600 m2 /kg  Higher cement replacement levels upto 70%  Glass content 85% (Min)  Blended with cement  Secondary hydration Slag (GGBS)
  11. 11. 11  Reduces water demand  Water can be reduced based on slag content and fineness of slag  Reduces bleeding  Water retention  Improves workability  Increases Pumpability Effect of GGBS on Fresh Concrete
  12. 12. 12  Reduces heat of hydration  Improves the pore structure  Reduces permeability  Improves resistance to corrosion of reinforcement  Increased resistance to chemical attack  Higher ultimate strength  Saving cement in concrete mix Effect of GGBS on Hardened Concrete
  13. 13. 13  Condensed Silica Fume is a by product of ferro-Silicon alloy industry and it is the dust which is collected from furnace exhaust system  Fineness of silica fume is @ 15000 m2 /kg as against 280 to 290 m2 /kg of Cement  Contributes significantly to compressive strength due to micro-filler effect and excellent pozzolanic properties  Leads to increase in density and reduction of permeability in concrete  It’s use is must for manufacturing of concrete above M50 Contd… SILICA FUME (Micro Silica)
  14. 14. 14 SILICA FUME
  15. 15. 15 Admixtures are materials mostly chemicals that are added in small quantities during the preparation of concrete to impart certain specific properties to it. The requirements may be  Improving the workability of concrete during placing  Retarding or accelerating setting  Improving the impermeability and water tightness of the cast concrete.  Imparting corrosion inhibition etc  Entraining air in concrete Chemical Admixtures
  16. 16. 16 Compatibility test by Marsh Cone Apparatus
  17. 17. 17 DEFLOCCULATION OF CEMENT PARTICLES
  18. 18. 18 DISPERSION OF MECHANISM
  19. 19. Dispersion Mechanism  Electro static repulsion  Steric Hindrance 19
  20. 20. 20 EFFECT OF SUPER PLASTICISER ON WORKABILITY
  21. 21. 21 SLUMP : Collapse
  22. 22. 22 EFFECT OF SUPER PLASTICISER ON WORKABILITY
  23. 23. 23 PUMPABLE CONCRETE
  24. 24. 1. Air entrainers : TYPES OF ADMIXTURES They entrain air in the form of micro air bubbles which helps in improving the durability of concrete in freezing environment, sulphate and alkali attack. 2. Water reducers To reduce the water-cement ratio and yet retain workability. It is possible to reduce water upto 12%. The only precaution is that it should be mixed thoroughly
  25. 25. 3. Accelerating admixtures : To accelerate setting of cement in cold environment or where early setting is desired. It assists in early removal of form work 4. Retarding admixtures : To delay the setting time of concrete, for RMC supplied to far off sites. Prolongs setting time, giving higher strength at later stages, also results in reduction in micro cracks.
  26. 26. 5. Super plasticisers : To make flowing concrete for concreting in heavily reinforced sections, tremie concrete, for pumping concrete. (when added to normal concrete with 75mm slump upto 250mm can be achieved) 6. High range water reducers : PC based admixtures Water reduction capacity of about 25-40% High performance Early strength and early setting
  27. 27. 7. Bonding agents : To increase bond strength, old and new concrete(in repair and rehabilitation works), they are usually modified latex or polymer compounds 8. Corrosion inhibitors : To inhibit corrosion
  28. 28.  Aggregate is the word used to describe any inert material .  Usually rock derivative generally between 50mm down to 75 micron used to produce concrete .  It is divided into coarse aggregate and fine aggregate  Those which are 4.75mm to 50mm are classified as coarse aggregates  Those below 4.75mm to 75 micron as fine aggregates  Except for mass concrete in dams etc. which may contain upto 150mm size aggregate, the maximum size of aggregate is normally 20mm in most cases  But it may be 40mm for plain concrete or massive works. 28 AGGREGATES
  29. 29. 29  Specific gravity: it should have good crushing strength and density  Surface texture: it should be smooth,slightly rough but not honeycombed  Particle shape : it should not be flaky or elongated.  Porosity : it should have very low water absorption  Should not be Reactive PROPERTIES OF COARSE AGGREGATES
  30. 30.  Water demand,  Workability  Cohesion of concrete in plastic state  Strength,  Density,  Durability  Porosity of hardened concrete  Stability : it should be chemically inert.  Impurities: it should be free from impurities (like silt, clay)  Compactness: it should be graded, as then only the voids can be less. 30 PROPERTIES OF AGGREGATE EFFECT
  31. 31.  Specific gravity implies the absolute weight per unit volume of aggregates  A low specific gravity may indicate  high porosity  poor durability  low strength.  Specific gravity of aggregates is used in arriving at mix design  Generally the specific gravity of good aggregates is greater than 2.5 g/cm3 31 SPECIFIC GRAVITY
  32. 32.  Surface texture reveals how grainy or smooth the surface of the aggregate is.  It indicates bonding strength and porosity.  Higher the smoothness of the particle, lesser is the bonding between aggregate and cement matrix.  rough textured aggregates develop higher bond strength than smooth textured aggregates,  This property is especially considered while producing high strength concretes. 32 SURFACE TEXTURE
  33. 33. Particle shapes are classified as  Irregular  Rounded  Flaky  Angular  Aggregates should be as much cubical as possible in shape 33 PARTICLE SHAPE
  34. 34.  Grading of aggregates means particle size distribution of the aggregates.  Principle of grading is that smaller size particles fill up the voids left in larger size particles. 34 GRADING
  35. 35. IS sieve Designatio n Percentage passing for single size aggregate of nominal size by weight 63 mm 40mm 20 mm 16 mm 12.5 mm 10 mm Remarks 80 mm 100 - - - 63 mm 85-100 100 - - 40 mm 0-30 85-100 100 - 20 mm 0-5 0-20 85-100 100 16 mm - - 85-100 100 12.5 mm - - - 85-100 100 10 mm 0-5 0-5 0-20 0-30 0-45 85-100 4.75 mm 0-5 0-5 0-10 0-20 2.26 mm - - - 0-5 35 GRADING OF COARSE AGGREGATE
  36. 36.  Indian standards divides the sand into four zones  zone-I to zone-IV based on the sieve analysis  Sand falling in zone-I is coarse and that falling in zone-IV is fine.  Sand falling in zone IV shall not be used for reinforced concrete work.  Fineness modulus for sand : ranges from 2.2 to 3.2, higher value indicates coarser grading 36 SAND
  37. 37. 37 IS sieve designation Percentage passing Zone-I Zone-II Zone-III Zone-IV 10 mm 100 100 100 100 4.75 mm 90-100 90-100 90-100 90-100 2.36 mm 60-95 75-100 85-100 95-100 1.18 mm 36-70 55-90 75-100 90-100 600 microns 15-34 35-59 60-79 80-100 300 microns 5-20 8-30 12-40 15-50 150 microns 0-10 0-10 0-10 0-15 Remarks Very coarse Coarse Medium Fine REQUIREMENT OF FINE AGGREGATES
  38. 38.  Water helps in dispersing the cement evenly  Quality of water for making concrete and for curing  Water should be free from salts, oils, acids, alkalis, sugar and organic materials  pH value shall not be less than 6  Sea water is not suitable for making concrete 38 WATER
  39. 39. SL. No. Description Tested as per Permissible limit (max) mg/l 1 Organic IS-3025(part-18) 200 2 Inorganic IS-3025(part-18) 3000 3 Sulphates (as SO3) Sulphates (as SO4) IS-3025(part-24) IS-3025(part-24) 400 500 4 Chlorides (as Cl) IS-3025(part-32) 2000 mg/l for concrete not containing embedded steel 1000 mg/l for RCC work 5 Suspended matter IS-3025(part-17) 2000 39 PERMISSIBLE LIMITS FOR SOLIDS IN WATER
  40. 40. FRESH CONCRETE  Fresh concrete is a freshly mixed material which can be moulded into any shape.  Workability: is the ease with which fresh concrete can be mixed, transported, placed and compacted in the moulds or forms  Apart from water-cement ratio the concrete has to be compacted well to get the required strength 40 UNDERSTANDING CONCRETE
  41. 41. TESTS ON FRESH CONCRETE  WORKABILITY 1. Slump Test 2. Compaction Factor Test 3. Flow Test.  Yield Test
  42. 42. 42  It is the science of the deformation and flow of materials and is concerned with relationships between stress, strain, rate of strain and time.  The term Rheology deals with the materials whose flow properties are more complicated than those of fluids (liquids or gases) RHEOLOGY OF CONCRETE
  43. 43. Factors affecting workability:  Water content  Mix proportions  Size of aggregates  Shape of aggregates  Surface texture of aggregate  Grading of aggregate  Use of admixture 43
  44. 44. Segregation:  Segregation can be defined as the separation of the constituent materials of concrete. Bleeding:  Sometimes referred as water gain  It’s a particular form of segregation due to highly wet mix  If water cement ratio is more than 0.7  Badly proportioned and insufficiently mixed concrete 44
  45. 45. BLEEDING 45  While traversing from bottom to top  Bleeding channels responsible for permeability  It may be interrupted by aggregates (flaky)  It may be interrupted by reinforcement  Reduces bond between reinforcement, aggregate and paste  Remedy— re-vibration, delayed finishing
  46. 46. Cement – 3.15 Coarse aggregate – 2.70 Sand – 2.60 Water – 1.00 Fly ash – 2.15 Silica Fume - 2.20 46 SPECIFIC GRAVITY
  47. 47.  Compaction of concrete is the process adopted for expelling the entrapped air from the concrete.  The entrapped air in the form of voids reduces the strength of concrete.  For every 1% of entrapped air, the strength of concrete falls about 5% to 6%. 47 COMPACTION
  48. 48.  Hand compaction  Tamping  Ramming : generally permitted for unreinforced foundation concrete  RCC should never be rammed  Compaction by vibration: common needle vibrator dia is 25mm to 40mm  External vibrators  Surface vibrators 48 METHODS OF COMPACTION Contd…
  49. 49.  When inserting a needle vibrator, allow it to penetrate the bottom of the layer as quickly as possible.  If it is done slowly, the upper part of the concrete will get compacted and prevent the air in the bottom layer from escaping.  The vibrator should be left in the concrete for about 10 sec. and then withdrawn slowly. If it is withdrawn fast, a hole will be left in the concrete. 49 PRECAUTIONS Contd…
  50. 50.  The vibrator should be inserted again at a distance of not more than 50 cm from its last position.  The vibrator should not be allowed to touch the face of the form work or the reinforcement to prevent the reinforcement from losing bond with concrete  Do not stop the vibrator when the needle is in the concrete.  Do not over vibrate or under vibrate 50
  51. 51. 51  The rate of levelling should not be less than the rate placing of concrete FINISHING OF CONCRETE
  52. 52. 52  Effect ofWater-Cement ratio  Effect of maximum size of aggregate on strength  Grades of concrete:  Concrete in construction is specified by grade like M20,M25 etc. Usually increments of five.  M20 means the specified crushing strength is 20 N/mm2 STRENGTH OF CONCRETE
  53. 53. 53 CURING  Why Curing ?  To prevent loss of moisture from the Concrete due to combined effect of hot sun and drying wind  Creation of conditions for promotion of uninterrupted and progressive hydration of cement during the period immediately after placing  Curing does not mean only application of water HARDENED CONCRETE
  54. 54. 54 1. WATER CURING 2. MEMBRANE CURING 3. APPLICATION OF HEAT (Steam Curing) 4. ACCELERATED CURING CURING METHODS
  55. 55. 55  Sampling Criteria  CubeTesting  Acceptance Criteria  Non DestructiveTesting of Concrete 1. Rebound HammerTest 2. Ultra sonic pulse velocity testing  CoreTest COMPRESSIVE STRENGTH
  56. 56. 56 OTHER CONCRETES :  High strength concrete  High performance concrete  Mass Concrete  Light-weight concrete  High-density concrete  No-fines concrete  Roller compacted concrete  Ferrocement  Self compacting concrete.
  57. 57. 57 HIGH STRENGTH CONCRETE  CONCRETE GRADE FROM M60 ONWARDS REGARDED AS HIGH STRENGTH CONCRETE  FOR HIGH STRENGTH CONCRETE DESIGN STANDARDS GIVEN INTHE CODE IS-456-2000 MAY NOT BE APPLICABLE  THEY HAVETO BE OBTAINED FROM SPECIFIED LITERATURES OR BY EXPERIMENTAL RESULTS SPECIAL CONCRETES
  58. 58. 58 POSSESSING 1. HIGHWORKABILITY 2. HIGH STRENGTH 3. HIGH DENSITY 4. HIGH DIMENSIONAL STABILITY 5. LOW PERMEABILITY 6. RESISTANCETO CHEMICAL ATTACK HIGH PERFORMANCE CONCRETE
  59. 59. 59 NORMAL CONCRETE  HEAVY SELFWEIGHT (DENSITY 2200 to 2600 KG/M3 ) LIGHT WEIGHT CONCRETE  DENSITY (300 to 1850 KG/M3 )  LOWTHERMAL CONDUCTIVITY LIGHT WEIGHT CONCRETE
  60. 60. 60  DENSITY 3360TO 3840 KG/M3 EVEN 5280 KG/M3 USING IRON AS BOTH F.A. AND C.A  DENSITY 50% HIGHERTHANTHE CONVENTIONAL CONCRETE  USED AS A SHIELDING MATERIAL FOR PROTECTION FROM RADIATION HIGH DENSITY CONCRETE
  61. 61. 61  It is made by introducing air or gas into the slurry composed of cement and finely crushed sand by alluminium powder.  Uniformly cellular structure is formed.  Also called as gas concrete, foam concrete, cellular concrete AERATED CONCRETE
  62. 62. 62  By Omitting fine aggregate fraction  Made by cement, water and single sized coarse aggregates  Having large voids and hence light in weight  Applications  Temporary structures  In external walls forThermal insulation  Rough texture gives good base for plastering  Free from dampness because of low capillary action on account of large voids NO-FINES CONCRETE
  63. 63. ROLLER COMPACTING CONCRETE  Recent development particularly in the field of Dam construction.  Lean mix  No slump concrete  High volume fly ash to the extent of 60 to 65%  Compacted by Rollers.  Compressive strength of about 7 Mpa to 30 Mpa
  64. 64. FERRO CEMENT  It is a relatively new material consisting of wire meshes and cement morar.  Thickness of elements is 2 to 3 cm  Water –cement ratio 0.4 to 0.45  Cement -sand ratio 1:2  External cover to reinforcement is 2 to 3mm
  65. 65. APPLICATIONS OF FERROCEMNT  FOR CASTING DOMESTIC OVER-HEAD WATER TANKS  FOR TANKS USED AS GRAIN SILOS IN VILLAGES  FOR CONTAINER USED AS GAS HOLDER UNIT IN “GOBBAR GAS” PLANTS.  IDEAL MATERIAL FOR BOAT BUILDING  FOR MANHOLE COVER
  66. 66. SELF COMPACTING CONCRETE  Self levelling concrete  With Super plasticizer (Glenium )  Fines  Should not be vibrated  Applications Precast units.
  67. 67. MASS CONCRETE  It’s is a concrete having considerable dimensions that may get affected by thermal behavior of Concrete. Ex-Concrete Dam  Members with minimum cross sectional dimension of a solid concrete member approaches or exceeds 2 to 3 ft  Cement contents above 364 kg/m3
  68. 68.  It is a latest development in the construction industry  Concrete is batched and mixed in a centralised Plant and transported to the sites far-away from the plant through Transit-Mixers and placed through pumps to the required height and distances. 68 RMC (READY MIX CONCRETE)
  69. 69. 69  RMC PLANT
  70. 70. 70 PLANT LAYOUTPLANT LAYOUT
  71. 71. 71 CONVEYOR BELT
  72. 72. 72 DOUBLE SHAFT MIXER
  73. 73. 73 BATCHING PLANTBATCHING PLANT
  74. 74. CONCRETE PUMPS 74
  75. 75. TRUCK MOUNTED BOOM PUMPS 75
  76. 76. RMC PLACEMENT THROUGH BOOM PUMPS 76
  77. 77. 77 RMC PLACEMENT THROUGH BOOM PUMPS
  78. 78. ANY QUESTIONS ? 78
  79. 79. THANK YOU 79

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