Handling of Concrete

KAS-2012 1
CONCRETE HANDLING IN THE
FIELD
By K.Shah
B.E.(Civil Engg) NIT Rourkela,India
M.Sc. (Environment), University of Leeds, UK
Ex-GM(Civil & Environment) – MNC
Currently Guest faculty-College of Technology &
Engineering

KAS-2012 2
Stages of producing concrete.
(1) Batching
(2) Mixing
(3) Transportation
(4) Placing
(5) Compacting
(6) Curing
(7) Finishing

KAS-2012 3
(1) Batching
(a) Volume batching
(b) weight Baching

KAS-2012 4
Volume batching
 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.

KAS-2012 5
VOLUME BATCH
Gauge box
 Various gauge boxes of different volumes are
used.
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

KAS-2012 6
Weigh Batch Machine

KAS-2012 7
Weigh batching
 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.

KAS-2012 8
Automatic weigh batch
 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.

KAS-2012 9
(2) MIXING
Mixing of cement,sand aggregates should
ensure that:
 The mass is homogeneous
 Uniform in color
 consistent

KAS-2012 10
MIXING METHODS :
(1) Hand mixing
(2) Machine mixing

KAS-2012 11
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

KAS-2012 12
Machine mixing
 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)

KAS-2012 13
CONCRETE MIXER
(1) Pan type
(2) drum Type:
(a) tilting
(b) Non –tilting
(c) Reversing

KAS-2012 15
PAN MIXER
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.

KAS-2012 16
DRUM MIXER
 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

KAS-2012 18
TILTING MIXER
 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).

KAS-2012 20
NON TILTING MIXER
 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.

KAS-2012 22
REVERSING MIXER
 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.

KAS-2012 23
Sequence of charging drum
 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

KAS-2012 24
 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.

KAS-2012 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 significant.

KAS-2012 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.

KAS-2012 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.

KAS-2012 28
MANUFACTURING OF
CONCRETE
 With same material if care is not taken,
resulting concrete will be bad concrete
 What are good rules to make good quality
concrete.

KAS-2012 29
TRANSPORTATION OF CONCRETE
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.

KAS-2012 30
METHODS OF TRANSPORTATION
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

KAS-2012 31
MORTAR PAN
 Common method in India
 More labour required
 Segregation of concrete is less
 Greater surface area of concrete is
exposed to sun, concrete dries.

KAS-2012 32
WHEEL BARROW
 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

KAS-2012 33
CRANE
 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.

KAS-2012 34
BUCKET & ROPEWAY
Use for construction in:
 Valley
 Bridge pier in river
 Dam
Advantage:
Concrete is not exposed to sun or air & no
loss of water.

KAS-2012 35
Truck Mixer & dumpers
 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

KAS-2012 36
BELT CONVEYORS
 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.

KAS-2012 37
CHUTE
 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.

KAS-2012 38
SKIP & HOIST
 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.

KAS-2012 40
TRANSIT MIXER
 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.

KAS-2012 41
PUMPS & PIPELINE
 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.

KAS-2012 43
PIPELINE
Pipeline should :
 Have correct diameter as per pump
pressure. (generally 125 mm)
 Have sufficient thickness
 Good couplings
 Poor pipeline can cause blockage.

KAS-2012 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 45
PUMPABLE CONCRETE
 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.

KAS-2012 46
Design of pumpable concrete
 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.

KAS-2012 47
PROBLEMS IN PUMPING
 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.

KAS-2012 48
PLACING CONCRETE
 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

KAS-2012 49
Concrete in Foundation
 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.

KAS-2012 50
Concrete on Road, airport, floor slabs
 Placed in alternate bays (allow shrinkage)
with contraction joints :
contraction joints
Bays

KAS-2012 51
Concrete in Beams & Column
 Reinforcement correctly placed.
 Correct cover required
 Joints of shuttering to be plugged.
 Mould releasing agent inside formwork

KAS-2012 52
STRIPPING TIME
 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

KAS-2012 53
UNDER WATER CONCRETE

KAS-2012 54
UNDER WATER CONCRETE
 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

KAS-2012 55
Underwater Concrete
 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

KAS-2012 56
SLIP FORM TECHNIQUE
 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.

KAS-2012 57
VERTICAL SLIP FORM

KAS-2012 58
HORIZONTAL SLIP FORM ROAD PAVER

KAS-2012 59
COMPACTION OF CONCRETE
 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.

KAS-2012 60
METHODS OF COMPACTION
1. Hand compaction
2. Compaction by vibration
3. Compaction by pressure &
jolting
4. Compaction by spinning

KAS-2012 61
(2) COMPACTION BY VIBRATION
a) Internal Vibrator
b) Formwork Vibrator
c) Table Vibrator
d) Platform Vibrator
e) Surface Vibrator

KAS-2012 62
(1) HAND COMPACTION
 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)

KAS-2012 63
COMPACTION BY VIBRATION
 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.

KAS-2012 65
(a) INTERNAL VIBRATOR
 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.

KAS-2012 66
FORMWORK VIBRATOR
 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

KAS-2012 67
TABLE VIBRATOR
 Vibrator is clamped to table
 Used for concrete test cubes
 Cubes are kept on table to get vibrations
 Also used for small prefabricated slab

KAS-2012 69
PLATFORM VIBRATOR
 Similar to table vibrator but of large size
 Used for long concrete electrical pole,
railway sleeper,prefabricated roofing
element

KAS-2012 70
PLATEFORM VIBRATOR

KAS-2012 71
SURFACE VIBRATOR
 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.

KAS-2012 73
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.

KAS-2012 74
VIBRATION BY SPINNING
 New method
 Used for concrete pipes
 Concrete when spun at high speed gets
compaction by centrifugal force

KAS-2012 75
VIBRATORY ROLLER
 Road rollers has vibrating system
 Roller while moving on raod slab gives
vibrations
 Used for Lean concrete (M10) for road
base


KAS-2012 77
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

KAS-2012 78
HYDRATION OF CEMENT
 Cement is made by Cao, SiO2, Al2O3, Fe2O3, MgO, K2O,
SO3
 After burning in Kiln following products are made:
3Cao. SiO2 (C3S) - Tri calcium silicate
2Cao. SiO2(C2S) – Di cacium silicate
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.

KAS-2012 79
CURING OF CONCRETE
 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.

KAS-2012 80
CURING OF CONCRETE
 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

KAS-2012 81
METHODS OF CURING
a) Water curing
b) Membrane curing
c) Application of heat
d) Other methods

KAS-2012 82
WATER CURING
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

KAS-2012 83
MEMBRANE CURING
 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

KAS-2012 84
APPLICATION OF HEAT
 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

KAS-2012 85
HIGH PRESSURE STEAM CURING
 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)

FINISHING OF CONCRETE
 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
SHAH K.A. 86

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

SURFACE TREATMENT
 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.
KAS-2012 88

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.

Handling of Concrete

Recomendados

Recomendados

Mais conteúdo relacionado

Mais procurados

Mais procurados (20)

Semelhante a Handling of Concrete

Semelhante a Handling of Concrete (20)

Último

Último (20)

Handling of Concrete