CONCRETE HANDLING IN THE
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 &
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
Various gauge boxes of different volumes are
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
50 35 70
50 70 140
1:3:6 (M100) 50 105 210
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.
Automatic weigh batch
For large works
Over head hopper and discharges into
Useful in ready mix concrete plant
Recorders for weight
Calibration is required from time to time.
Mixing of cement,sand aggregates should
The mass is homogeneous
Uniform in color
Practiced for small scale work (small
house, repairing of house etc)
10 % extra cement is added to
compensate inferior concrete produced by
Spread fine & coarse aggregate in
Spread cement over it
Mix with shovel till uniform color is
Medium & large scale work use machine
Mixing is efficient, economical & produce
Type of mixer:
(a) Batch mixer : batch by batch with time
(b) Continuous mixer: continuously mixed &
discharged (in dam construction)
(1) Pan type
(2) drum Type:
(b) Non –tilting
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.
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,
T= Tilting, NT =non tilting, R=Reversing
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
single drum (materials are charged and
discharged through a single opening).
NON TILTING MIXER
Single drum rotating about a horizontal
Fixed blades work the concrete towards
the discharge end of the mixer, in order to
provide a rapid rate of discharge.
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
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.
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
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
In small machine, mixing time varies
between 1-2 minutes
In Ready Mix Cement mixer – 15-30
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.
If concrete is not used after mixing it may
But when concrete is agitated on time to
time in drum setting time rule does not
Retempering of concrete :
Some time concrete from RMC plant is not
delivered to site due to traffic congestion
Concrete becomes stiff and becomes
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
With same material if care is not taken,
resulting concrete will be bad concrete
What are good rules to make good quality
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.
Common method in India
More labour required
Segregation of concrete is less
Greater surface area of concrete is
exposed to sun, concrete dries.
When transportation of concrete is at
Movement of wheel on rough road
surface, segregates concrete.
Some wheel barrows have pneumatic
wheel to reduce vibration
Used for transporting concrete above
For high rise buildings.
Cranes are fast
Can move horizontally & vertically
Concrete in skip discharge from bottom
In bucket concrete is discharged by tilting.
BUCKET & ROPEWAY
Use for construction in:
Bridge pier in river
Concrete is not exposed to sun or air & no
loss of water.
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
Limited use in construction
Can transport large volume
Can go where access is limited
On steep slope concrete segregates.
Exposed to sun for long time.
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
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
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
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
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
Concrete can be pumped upto 400 m height and
2000 m distance.
Pipeline should :
Have correct diameter as per pump
pressure. (generally 125 mm)
Have sufficient thickness
Poor pipeline can cause blockage.
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.
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.
Design of pumpable concrete
Concrete Mix is so designed that all material remain
Mix must make redial movement of grout to maintain
Mix should be deformed at bends
Cement & fine particles (0.25 mm size) are important for
350 to 400 Kg/ M3 of fine particles are necessary for
Slump of pumpable concrete is above 75 mm.
PROBLEMS IN PUMPING
Blockage in pipe
Pipe should be cleaned after each day
Blockage can be cleaned by forward-
Tapping pipe with hammer
Clean pipe with rod or sponge ball pushed
by compressed air.
Must be placed in systematic manner.
Can be placed with following methods:
Within earth mould : Foundation
In timber plank formwork : Road, airport
Steel shuttering : Dam
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.
Concrete on Road, airport, floor slabs
Placed in alternate bays (allow shrinkage)
with contraction joints :
Concrete in Beams & Column
Reinforcement correctly placed.
Correct cover required
Joints of shuttering to be plugged.
Mould releasing agent inside formwork
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
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
No compaction required as hydrostatic pr
of water compacts concrete.
Concrete of 0.3 W/C ratio can be placed
Used for Pile or well foundation
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.
COMPACTION OF CONCRETE
Compaction is a process of expelling the entrapped air inside
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
METHODS OF COMPACTION
1. Hand compaction
2. Compaction by vibration
3. Compaction by pressure &
4. Compaction by spinning
(2) COMPACTION BY VIBRATION
a) Internal Vibrator
b) Formwork Vibrator
c) Table Vibrator
d) Platform Vibrator
e) Surface Vibrator
(1) HAND COMPACTION
Poking inside concrete with 1-2 mt long steel rod
Unreinforced foundation & ground floor work
Wooden beam is used to beat concrete (low
thickness slab, road slab)
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.
(a) INTERNAL VIBRATOR
Most common in use
Called, Needle Vibrator or Immersion vibrator or
Consists : electrical/diesel power supply, Needle
Frequency of vibrations can be 12000 cycles
vibration per minute.
Needle diameter 20 to 75 mm
Length 25 to 90 cm.
Used for columns, walls, precast slab
Vibrator is clamped to formwork
Vibration is given to formwork
Vibration is transferred from formwork to
Useful in thin wall where reinforcement
obstruct the needle type vibrator.
Efficiency is lower then needle 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
COMPACTION BY PRESSURE & JOLTING
Used for hollow blocks, solid concrete
Stiff concrete is vibrated, pressed & given
Stiff concrete is compacted to get dense
form & good strength is achived.
VIBRATION BY SPINNING
Used for concrete pipes
Concrete when spun at high speed gets
compaction by centrifugal force
Road rollers has vibrating system
Roller while moving on raod slab gives
Used for Lean concrete (M10) for road
PRECAUTIONS IN VIBRATING CONCRETE
Vibrator gets damaged if comes in contact
with hard object (Formwork, hard
Switch on when needle is inside fresh
Should conform to IS 2505-1963
Degree of compaction can be recognized
from rising air bubbles & formation of thin
film on top
HYDRATION OF CEMENT
Cement is made by Cao, SiO2, Al2O3, Fe2O3, MgO, K2O,
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.
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.
CURING OF CONCRETE
Concrete delivers its strength by the hydration of cement
Hydration is continuous & long time process.
Rate of hydration is fast immediately after making the
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
METHODS OF CURING
a) Water curing
b) Membrane curing
c) Application of heat
d) Other methods
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
Concrete surface is covered by plastic
It is used where water availability is less.
Plastic sheet reduces evaporation in
Membrane is applied after 2 days of water
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
Fast construction of bridge
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(
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
Concrete obeys the shape of formwork
Grooves & lining on formwork plate gives
makes grooves & lining on concrete
Prefabricated tiles can be made of any
Domestic floor should be smooth, wear resistant, crack
Mix should have good proportion without excess “Matrix”
Exposed aggregate finish : Colored pebbles on top layer
Bush Hammering : Electrically operated Brush with teeth
when applied on concrete removes top cement layer,
exposes aggregates and makes shining aggregates.
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.
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