CE-106 Civil Engineering Materials and Concrete Technology

• Mixing Water for concrete

• Batching of Concrete
• Mixing of Concrete
• Transporting of Concrete
• Placing of Concrete
• Finishing of Concrete
• Curing of Concrete
CE-106 Civil Engineering Materials and Concrete Technology

Mixing Water for concrete

Almost any natural water that is
drinkable and has no pronounced
taste or odor can be used as mixing
water for making concrete.
However, some water that are not
fit for drinking may be suitable for
use in concrete.
Acceptable criteria for water to be
used in concrete are given in
ASTM C 94 (AASHTO M157) and
AASHTO T 26
CE-106 Civil Engineering Materials and Concrete Technology
Impurities in water for concrete
Excessive impurities in mixing water not only may affect setting time and
concrete strength, but also may cause efflorescence, corrosion of
reinforcement, volume instability, and reduced durability. Therefore, certain
optional limits may be set on chlorides, sulfates, alkalies, and solids in the
mixing water or appropriate tests can be performed to determine the effect the
impurity has on various properties.
1. Alkali Carbonate and Bicarbonate
Carbonates and bicarbonates of sodium and potassium have different effects on the
setting times of cement. Sodium carbonate can cause very rapid setting, bicarbonates
can either accelerate or retard the set
2. Chloride
Concern over a high chloride content in mixing water is chiefly due to the possible
adverse effect of chloride ions on the corrosion of reinforcing steel or pre-stressing
strands
CE-106 Civil Engineering Materials and Concrete Technology

Batching of Concrete
• The process of measuring concrete
mix ingredients by either mass or
volume and introducing them into
the mixer.
• To produce concrete of uniform
quality, the ingredients must be
measured accurately for each
batch.
• Most concrete today is batched
and mixed by ready mixed
concrete plants
CE-106 Civil Engineering Materials and Concrete Technology

Batching of Concrete
CE-106 Civil Engineering Materials and Concrete Technology
Batching of Concrete
1. Volume batching
2. Weigh batching
Volume Batching
This method is generally adopted for small jobs
Gauge boxes are used for measuring the fine and
coarse aggregate
The volume of gauge box is equal to the volume of
one bag of cement
Gauge box can be made of timbers or steel.
They are made generally deep and narrow
While filling the gauge boxes the material should be
filled loosely, no compaction is allowed
CE-106 Civil Engineering Materials and Concrete Technology

Batching of Concrete
Weigh Batching Manual: In case of manual batching all
Batching by weight is more preferable to volume weighing and batching of concrete are done
batching ,as it is more accurate and leads to more manually. It is used for small jobs.
uniform proportioning. Semi Automatic: In case of semi automatic
Dry Concrete Volume = 1.54*Wet Concrete Volume batching the aggregate bin gates are opened by
It’s equipment falls into 3 general categories: manually operated switches. And gates are closed
Manual, automatically when the material has been
Semi automatic, delivered.
Fully automatic.
CE-106 Civil Engineering Materials and Concrete Technology

Batching of Concrete
Automatic: In case of automatic batching the material
are electrically activates by a single switch and
complete autographic record are made of the weight of
each material.
The batching plant comprises 2,3,4 or 6 compartment
bins of several capacities.
CE-106 Civil Engineering Materials and Concrete Technology

Mixing of Concrete
The aim of mixing of concrete is to produce homogenous, consistent and uniform coloured concrete.
Mixing action of CONCRETE involves two operation
1. A general blending of different particles size of the ingredients to be uniformly distributed
throughout the concrete mass.
2. A vigorous rubbing action of cement paste on to the surface of aggregate particles.
There are two methods
Hand mixing,
Machine mixing.
CE-106 Civil Engineering Materials and Concrete Technology
Mixing of Concrete Following operations are involved
Hand Mixing • Measured quantity of sand is spread evenly on platform.
For small jobs, concrete is mixed by Hand • Spread the measured quantity of cement on this sand and
using showels. For hand mixing a brick mix it till the color of concrete mixture is uniform.
platform is prepared by laying the bricks • Spread the measured quantity of coarse aggregate on the
on the ground. It must be 2 m wide and platform with sand and cement. Now spread the mixture of
3.5 m long. Similarly concrete floor can be cement and sand on the mass of aggregate and mix it at

used platform for the purpose of concrete least 3 times.

ingredients mixing. • Make the center hollow to the middle depth of mix. Add 3
quarters of total quantity of water required and turn the
material towards the center with spades.
CE-106 Civil Engineering Materials and Concrete Technology
Mixing of Concrete
Machine Mixing
It is adopted for big projects where large quantity of aggregate is required .It is also Economical.
Concrete mixers are classified as under-
According to the operating conditions
1.Batch mixers
2.Continuous mixers.
CE-106 Civil Engineering Materials and Concrete Technology
Mixing of Concrete Tilting type
Batch mixers
It consist a conical drum which rotates on an
The mixers are charged with
inclinable axis. It has only one opening.
materials in batches
The drum charged directly and discharged by tilting
Batch mixers are classified
and reversing the drum.
in further 3 types
Non-Tilting type
The mixing drum is cylindrical in shape and revolves
• Tilting type ,
about horizontal axis.
• Non-Tilting type ,
It has opening on both sides.
• Reversing type.
The ingredients are charged in from one opening.
For discharging concrete chute is introduced in to
other opening by operating a lever.
CE-106 Civil Engineering Materials and Concrete Technology
Transporting Concrete
Good planning and handling should be adopted for
transport to avoid:
• Delays.
• Early Stiffening and drying out. 2. Direct Chute:
• Segregation. This can directly deliver the concrete on job site from truck
1. Wheel Barrow: With the help of wheel
mixer
barrow we can transport small size concrete,
used for short distance
CE-106 Civil Engineering Materials and Concrete Technology
Transporting Concrete

Bucket and Crane Conveyer Belt

CE-106 Civil Engineering Materials and Concrete Technology
Placing Concrete
Concrete should be deposited continuously as near as possible to its final position without objectionable
segregation.

Concrete should be placed in walls, thick slabs, or foundations in horizontal layers of uniform thickness; each layer
should be thoroughly consolidated before the next is placed.

To avoid segregation, concrete should not be moved horizontally over too long a distance.

Preparation prior to placing concrete includes the following:

Compacting, trimming, and moistening the subgrade

Erecting the forms;

Setting the reinforcing steel and other embedded items securely in place.
CE-106 Civil Engineering Materials and Concrete Technology
Finishing of Concrete
Screeding (Strike off)
Screeding or strike off is the process of cutting off excess concrete to bring the top surface of a slab to
proper grade
CE-106 Civil Engineering Materials and Concrete Technology
Finishing of Concrete
Bullfloating or Darbying
To eliminate high and low spots and to embed large aggregate particles, a bullfloat or darby should be
used immediately after delivering concrete to the formwork
CE-106 Civil Engineering Materials and Concrete Technology
Finishing of Concrete
Troweling
Creates smooth, hard, dense surface
Finishing Formed Surfaces
Exterior concrete should not be troweled because:
It can lead to a loss of entrained air caused by
overworking the surface
troweled surfaces can be slippery when wet.
CE-106 Civil Engineering Materials and Concrete Technology
Curing of Concrete
A newly placed and finished concrete should be
cured and protected from drying, extreme changes
in temperature, and damage.
The curing should begin immediately after
finishing.