Concrete technology information in notes
- 1. Department of Civil Engineering 1 Concrete Handling in Field By: Nishant Singh Kushwaha Subject Code: 4CE4-08
- 2. Concrete Handling in field This Powerpoint presentation covers entire unit of Concrete handling in field. Most of the material covers in this ppt and rest if left please refer to M.S Shetty book.
- 3. Stages of producing concrete. 3 (1) Batching (2) Mixing (3) Transportation (4) Placing (5) Compacting (6) Curing (7) Finishing
- 4. (1) Batching 4 (a) Volume batching (b) weight Baching
- 5. Volume batching 5 Volume batching is not good method Moist sand in loose condition weights less than the same volume of dry sand. Practiced for small work. For quality work ,weigh batching is practiced.
- 6. VOLUME BATCH Gauge box Various gauge boxes of different volumes are used. 6 Length Width Depth Volume 33.3 cm 30 cm 20 cm 20 liters 33.3 cm 30 cm 25 cm 25 liters Grade Cement- kg Sand -lts Coarse Aggregate lts 1:11/2:3 (M 200) 50 35 70 1:2:4 (M 150) 50 70 140 1:3:6 (M100) 50 105 210
- 8. Weigh batching 8 Weigh batching is correct method Facilitates accuracy, flexibility & simplicity Different batching machine are available : (a) manual machines & (b) Automatic machines Manual machine : Has two buckets Buckets mounted on common spindle about which they rotate. One is loaded while other is discharged in mixer. Spring loaded dials indicate the weight.
- 9. Automatic weigh batch 9 For large works Over head hopper and discharges into mixer. Useful in ready mix concrete plant Recorders for weight Calibration is required from time to time.
- 10. (2) MIXING 10 Mixing of cement,sand aggregates should ensure that: The mass is homogeneous Uniform in color consistent
- 11. MIXING METHODS : (1) Hand mixing (2) Machine mixing 11
- 12. Hand mixing Practiced for small scale work (small house, repairing of house etc) 10 % extra cement is added to compensate inferior concrete produced by this method. Spread fine & coarse aggregate in alternate layer Spread cement over it Mix with shovel till uniform color is achieved
- 13. Machine mixing 13 Medium & large scale work use machine mixing Mixing is efficient, economical & produce quality concrete. Type of mixer: (a) Batch mixer : batch by batch with time interval (b) Continuous mixer: continuously mixed & discharged (in dam construction)
- 14. CONCRETE MIXER 14 (1) Pan type (2) drum Type: (a) tilting (b) Non –tilting (c) Reversing
- 15. PAN MIXER 15
- 16. PAN MIXER 16 A forced movement pan mixer has blades that are fixed to an assembly that agitates the concrete throughout the pan as the vertical shaft rotates.
- 17. DRUM MIXER 17 As per IS: 1791-1985 mixers are designated by number which shows capacity (liters) of batch: a) Tilting : 85 T, 100T, 140 T, 200T b) Non tilting : 200 NT,280 NT, 375 NT, 500 NT, 1000 R c) Reversing : 200 R, 280 R, 375 R,500 R, 1000 R T= Tilting, NT =non tilting, R=Reversing
- 18. TILTING MIXER 18
- 19. TILTING MIXER 19 Internal blades lift and tumble the ingredients onto itself. Two primary types exist: horizontal (one end has and opening for charging and a different end for discharging) single drum (materials are charged and discharged through a single opening).
- 21. NON TILTING MIXER 21 Single drum rotating about a horizontal axis. Fixed blades work the concrete towards the discharge end of the mixer, in order to provide a rapid rate of discharge.
- 23. REVERSING MIXER 23 The entire drum rotates around its axis as materials are loaded through a charge chute at one end of the drum and exit through a discharge chute at the opposite end of the drum. Mixing blades are mounted on the inside surface of the drum and as the drum rotates the blades mix by lifting and dropping the materials during each rotation. Once the materials are sufficiently mixed the rotation of the drum is reversed and the blade arrangement pushes the concrete through to the discharge end of the mixer.
- 24. Sequence of charging drum 24 First half quantity of coarse aggregate is placed in skip Over it half quantity of sand On that full quantity of cement Over it balance quantity of coarse & fine aggregates is place. This prevents spillage of cement in air while discharging in drum
- 25. 25 % Water is placed in drum and then mix from skip is discharged in the drum This prevents sticking of cement on blades 75 water is immediately poured after placing mix material (cement sand etc) in drum. 25
- 26. 25 Mixing time In small machine, mixing time varies between 1-2 minutes In Ready Mix Cement mixer – 15-30 seconds RPM of drum : 15-20 Compressive strength of concrete increases with increase in mixing time but after 2 minutes increase in compressive strength is not signKiAfSi-2c01a2 nt.
- 27. 26 If concrete is not used after mixing it may set But when concrete is agitated on time to time in drum setting time rule does not follow.
- 28. 27 Retempering of concrete : Some time concrete from RMC plant is not delivered to site due to traffic congestion Concrete becomes stiff and becomes unworkable Site engineers can reject the concrete if delay is more If it can be of used then small volume of water is added and again agitated in the drum. This is called RETEMPERING OF CONCRETE.
- 29. MANUFACTURING OF 29 CONCRETE With same material if care is not taken, resulting concrete will be bad concrete What are good rules to make good quality concrete.
- 30. TRANSPORTATION OF CONCRETE 30 Precaution in concrete transportation: Homogeneity of conc. Mass is maintained Movement of hand trolly or truck on rough road surface makes vibrations This results in deposition of heavy aggregates at bottom of truck Water & cement slurry comes on top.
- 31. METHODS OF TRANSPORTATION 31 1. Mortar Pan 2. Wheel barrow 3. Truck Mixer & dumpers 4. Crane, Bucket & rope way 5. Belt conveyors 6. Chutes 7. Skip & hoist 8. Transit Mixer 9. Pump & pipeline 10. Helicopter
- 32. MORTAR PAN 32 Common method in India More labour required Segregation of concrete is less Greater surface area of concrete is exposed to sun, concrete dries.
- 33. WHEEL BARROW 33 When transportation of concrete is at ground level. Movement of wheel on rough road surface, segregates concrete. Some wheel barrows have pneumatic wheel to reduce vibration
- 34. CRANE 34 Used for transporting concrete above ground level. For high rise buildings. Cranes are fast Can move horizontally & vertically Concrete in skip discharge from bottom In bucket concrete is discharged by tilting.
- 35. BUCKET & ROPEWAY 35 Use for construction in: Valley Bridge pier in river Dam Advantage: Concrete is not exposed to sun or air & no loss of water.
- 36. Truck Mixer & dumpers 36 Used for large concrete works. Can travel any part of site. Dumpers - 2-3 M3 Capacity Trucks – 4 M3 Capacity Bottom surface of truck is kept wet Top of truck is covered to prevent evaporation
- 37. BELT CONVEYORS 37 Limited use in construction Advantages: Can transport large volume Very quick Can go where access is limited Disadvantages : On steep slope concrete segregates. Exposed to sun for long time.
- 38. CHUTE 38 For transporting from ground level to lower level. (basement etc). Used where labour can not reach due to less space in trench etc. Made of metal Slope should not be < 1 vertical : 2.5 horizontal.
- 39. SKIP & HOIST 39 Labour can go upto 3rd or 4th floors. So skip is used for transport vertically up (in multistory building). Skip travels on vertical rail. Skip can discharge manually or automatically.
- 40. TRANSIT MIXER 40
- 41. TRANSIT MIXER 41 Used for long distance travel in RMC plant. Concrete is continuously agitated in truck drum (2 – 6 rpm). Also transported mix in dry condition and water is added on reaching the destination. Wet Mix in truck must reach site in 1- 1.5 hours. Pumps are also fitted on truck mixer to discharge concrete.
- 42. PUMPS & PIPELINE 42 Most popular method Reliable & good quality pumps are used. Mostly operated by diesel. Concrete is placed in collecting hopper. Rotating blades in hopper pushes concrete towards pipe. Vacume in hose pipe (600 mm Hg) Rotating rollers in pump chambers squeeze the concrete in pipe and flow of concrete is started. Concrete is discharged from other end of hose pipe. Concrete can be pumped upto 400 m height and 2000 m distance.
- 44. PIPELINE 44 Pipeline should : Have correct diameter as per pump pressure. (generally 125 mm) Have sufficient thickness Good couplings Poor pipeline can cause blockage.
- 45. 44 PIPELINE Thumb rule : For 30 M3 /hr concrete and 200 m length, dia should be 100 mm. Length > 500 m then dia = 150 mm. Dia = 3 to 4 times the size of aggregate Leaky pipe & coupling result in escape of water /air & finally block the concrete. Vertical pipe should good otherwise difficult to change at height. Pump is kept at distance from building about 15 % of vertical length. KAS-2012
- 46. PUMPABLE CONCRETE 46 Concrete which can be pushed through a pipeline is called pumpable concrete. Friction between pipe wall and concrete is less. Concrete flows in the form of plug which is separated from pipe wall by a thin layer of lubricating cement paste. Flow resistant must be < pump pressure. If the concrete is more wet then water comes out of mix which makes more resistance to flow. Stiff and also very wet concrete is not pumpable.
- 47. Design of pumpable concrete 47 Concrete Mix is so designed that all material remain together. Mix must make redial movement of grout to maintain lubricating paste. Mix should be deformed at bends Cement & fine particles (0.25 mm size) are important for good flow. 350 to 400 Kg/ M3 of fine particles are necessary for flow. Slump of pumpable concrete is above 75 mm.
- 48. PROBLEMS IN PUMPING 48 Blockage in pipe Pipe should be cleaned after each day operation Blockage can be cleaned by forward- backward pumping. Tapping pipe with hammer Clean pipe with rod or sponge ball pushed by compressed air.
- 49. PLACING CONCRETE 49 Must be placed in systematic manner. Can be placed with following methods: Within earth mould : Foundation In timber plank formwork : Road, airport slab. Steel shuttering : Dam Under water
- 50. Concrete in Foundation 50 In foundation, ground is made wet. Plastic sheet are laid between ground & slab Concrete is dumped not poured. No heap and dragging Placed in layers of 35 – 40 cm in mass concrete Avoid cold joints between 2 layers Surface of previous layer is cleaned with wire brush Sometime, cement slurry is placed on old surface Top of previous layer kept rough for good bond.
- 51. Concrete on Road, airport, floor slabs Placed in alternate bays (allow shrinkage) with contraction joints : contraction joints Bays 51
- 52. Concrete in Beams & Column 52 Reinforcement correctly placed. Correct cover required Joints of shuttering to be plugged. Mould releasing agent inside formwork
- 53. STRIPPING TIME 53 Form work should not removed until good strength has come. Type of form work Time Vertical wall, columns 16-24 hrs Soffit of slab (Prop should be refixed immediately) 3 days Soffit of beam (Prop should be refixed immediately) 7 days Props to slab Span < 4.5 m 7 days Props to slab Span > 4.5 m 14 days Props of beam (Span < 6 m) 14 days Props of beam (Span > 6 m) 21 days
- 55. UNDER WATER CONCRETE 55 Tremie (means hopper) is used. Funnel on top Pipe of 200 mm size Pipe bottom is plugged Fill pipe with concrete Lift pipe or jerk to release the plug Keep bottom of pipe inside concrete
- 56. Underwater Concrete 56 No compaction required as hydrostatic pr of water compacts concrete. Concrete of 0.3 W/C ratio can be placed with Tremie. Used for Pile or well foundation
- 57. SLIP FORM TECHNIQUE 57 2 In this method, concrete is continuously placed, compacted & form work is pulled up for next layer of concrete. Vertical slip form for Tall structure like silo, chimney Horizontal slip form paver machine (HSFP) for road construction. Concrete is dumped in front of HSFP machine by dumpers. Compaction by vibrator installed inside HSFP machines. Finishing of surface by HSF paver. Operation of road alignment, gradient, curve are controlled by Computerized Laser Control system. Speed of construction is 1 mt /min. 1 km of concrete road of 3.75 mt width is built in one day (16 hrs work). Mumbai-Pune Expressway was constructed by this machine.
- 59. HORIZONTAL SLIP FORM ROAD PAVER 59
- 60. COMPACTION OF CONCRETE 60 Compaction is a process of expelling the entrapped air inside concrete mass. During mixing, transporting & placing the concrete, air gets trapped in concrete mass. If this air is not removed, concrete will not get strength. 5 % of air voids reduces strength by 30 % 10 % of air voids reduces strength by 50 % Durability of concrete is also reduces with air voids. Insufficient compaction increases permeability of concrete. Results in entry of aggressive chemicals in solution. Chemicals attack concrete & reinforcement and life of concrete is reduced.
- 61. METHODS OF COMPACTION 61 1. Hand compaction 2. Compaction by vibration 3. Compaction by pressure & jolting 4. Compaction by spinning
- 62. (2) COMPACTION BY VIBRATION 62 a) Internal Vibrator b) Formwork Vibrator c) Table Vibrator d) Platform Vibrator e) Surface Vibrator
- 63. (1) HAND COMPACTION 63 Hand Rodding Poking inside concrete with 1-2 mt long steel rod Ramming Unreinforced foundation & ground floor work Tamping Wooden beam is used to beat concrete (low thickness slab, road slab)
- 64. COMPACTION BY VIBRATION 64 In hand compaction w/c ratio is more so we get less strength in concrete. In mechanical vibrator w/c can be kept low so we get good strength.
- 66. (a) INTERNAL VIBRATOR 66 Most common in use Called, Needle Vibrator or Immersion vibrator or Poker vibrator. Consists : electrical/diesel power supply, Needle and shaft. Frequency of vibrations can be 12000 cycles vibration per minute. Needle diameter 20 to 75 mm Length 25 to 90 cm. Portable.
- 67. FORMWORK VIBRATOR 67 Used for columns, walls, precast slab Vibrator is clamped to formwork Vibration is given to formwork Vibration is transferred from formwork to concrete Useful in thin wall where reinforcement obstruct the needle type vibrator. Efficiency is lower then needle vibrator
- 68. TABLE VIBRATOR 68 Vibrator is clamped to table Used for concrete test cubes Cubes are kept on table to get vibrations Also used for small prefabricated slab
- 70. PLATFORM VIBRATOR 70 Similar to table vibrator but of large size Used for long concrete electrical pole, railway sleeper,prefabricated roofing element
- 72. SURFACE VIBRATOR 72 Known as Screed Board Vibrator Used for thin roof slab where needle vibrator can not be used Not effective if slab thickness is more then 15 cm.
- 74. COMPACTION BY PRESSURE & JOLTING Used for hollow blocks, solid concrete blocks Stiff concrete is vibrated, pressed & given jolts Stiff concrete is compacted to get dense form & good strength is achived. 74
- 75. VIBRATION BY SPINNING 75 New method Used for concrete pipes Concrete when spun at high speed gets compaction by centrifugal force
- 76. VIBRATORY ROLLER 76 Road rollers has vibrating system Roller while moving on raod slab gives vibrations Used for Lean concrete (M10) for road base
- 78. PRECAUTIONS IN VIBRATING CONCRETE Vibrator gets damaged if comes in contact with hard object (Formwork, hard concrete) Switch on when needle is inside fresh concrete mass Should conform to IS 2505-1963 Degree of compaction can be recognized from rising air bubbles & formation of thin film on top 78
- 79. HYDRATION OF CEMENT 79 Cement is made by Cao, SiO2, Al2O3, Fe2O3, MgO, K2O, SO3 After burning in Kiln following products are made: - Tri calcium silicate – Di cacium silicate 3Cao. SiO2 (C3S) 2Cao. SiO2(C2S) 3Cao. Al2O3 (C3A) – Tri cacium aluminate 4Cao. Al2O3. Fe2O3(C3AF) -Tricalcium alumino ferrite. On addition of water in cement reaction of C3S, C2S, C3A & C3AF liberate heat. Heat is suside by addition of water.
- 80. CURING OF CONCRETE 80 Curing is defined as “ making satisfactory moisture content & favourable temperature” in concrete after placing the concrete. So that hydration may continue until the strength is developed. Curing is required immediately after placing concrete. During hydration, heat of hydration is released.
- 81. CURING OF CONCRETE 81 Concrete delivers its strength by the hydration of cement particles. Hydration is continuous & long time process. Rate of hydration is fast immediately after making the concrete Theoretically 0.23 w/c ratio required for hydration 0.15 w/c ratio required for filling the voids in gel. Total 0.38 w/c ratio is optimum In field condition, water evaporates & available water quantity reduced for hydration Extra water is given by curing
- 82. METHODS OF CURING 82 a) Water curing b) Membrane curing c) Application of heat d) Other methods
- 83. WATER CURING 83 a) Immersion : Slab is kept in water tank b) Ponding: Roof slab is filled with water c) Spraying : water spary on concrete wall is d) Wet covering : Wet gunny bags on wall
- 84. MEMBRANE CURING 84 Concrete surface is covered by plastic membrane It is used where water availability is less. Plastic sheet reduces evaporation in concrete Membrane is applied after 2 days of water curing
- 85. APPLICATION OF HEAT 85 Spraying of steam on concrete provides heat & moisture. Higher temperature accelerates hydration rate & strength of concrete is attended Early strength of structure is obtained Steam application possible at precast factory only. Precast prestressed concrete girders of bridge are cured with steam Fast construction of bridge
- 86. HIGH PRESSURE STEAM CURING 86 Superheated steam at high pressure (8.5 kg/cm2) & high temperature(175 deg C) is applied on concrete. This process is called “Autoclaving” 28 days strength of concrete is achieved in one day Concrete becomes sulphate resistant Low shrinkage in concrete Used in production of Cellular concrete products( Siporex, Celcrete)
- 87. FINISHING OF CONCRETE 87 Finishing is last operation of concrete making. Finishing of top surface is required in roads, airport strip, home floor Methods of Finishing: a) Form work Finish b) Surface Treatment c) Applied Finishes
- 88. FORMWORK FINISH Concrete obeys the shape of formwork Grooves & lining on formwork plate gives makes grooves & lining on concrete Prefabricated tiles can be made of any design
- 89. SURFACE TREATMENT 88 Domestic floor should be smooth, wear resistant, crack free. Mix should have good proportion without excess “Matrix” Exposed aggregate finish : Colored pebbles on top layer of wall Bush Hammering : Electrically operated Brush with teeth when applied on concrete removes top cement layer, exposes aggregates and makes shining aggregates.
- 90. APPLIED FINISH Rough cast finish : mixture of cement, sand, round gravel is applied on wall Non slip finish: Railway platform & walkway around pool are given non slippery finish by mixing large size sand particles in floor concrete.