Quiz.pptx

Quiz 1
Discuss the advantages of pre-stressing in concrete. (2 marks)
2. Describe different materials used for prestressing concrete. (2 marks)
3. Discuss the “setting time” of concrete. (2 marks)
4. Name any FOUR tests to determine the workability of concrete. (2
marks)
5. Define Compaction Factor Value; how it is calculated? (2 marks)
Discuss the following: [10 marks]
1. True slump and zero slump
2. Segregation in fresh concrete
3. Bleeding in fresh concrete
4. Hydration of fresh concrete
5. Effect of temperature on fresh concrete

Materials for Prestress Concrete
1. Concrete:
2. Steel:
1. Wires: Prestressing wire is a
single unit made of steel.
2. Strands: Two, three or seven
wires are wound to form a
prestressing strand.
3. Tendon: A group of strands or
wires are wound to form a
prestressing tendon.
4. Cable: A group of tendons form
a prestressing cable.
5. Bars: A tendon can be made up
of a single steel bar.
1. Consumption of materials like concrete, steel
is reduced.
2. Longer beams spans and girders can be
constructed which gives the untroubled floor
space and parking facilities.
3. Long-term durability.
4. Section remains uncracked under service
loads
5. High span-to-depth ratios
6. Pre-stressed concrete bridges are not easily
damaged by fire they have excellent fire
resistance and low maintenance costs in
comparison to reinforced concrete.
7. Pre-stressed concrete offers greater load
resistance and shock resistance.
8. Suitable for precast construction.
Advantages of pre-stressing in concrete Setting Time of Fresh Concrete
When concrete changes its state from plastic to a hardened state,
this process is called the setting.
And the duration that concrete takes to change its state is called
setting time.
Setting time depends on the type of cement and it can be
increased or decreased by adding admixture in concrete.
When concrete changes its state from fresh to hardened then this
process is called setting. And the time required to complete this
process is known as Setting Time of Concrete.
Setting time depends on the type of cement and it can be increase
or decrease by adding admixture in concrete.
Compaction Factor Test
Slump Cone Test
Flow Test
K-Slump Test
Vee-Bee Consistency Test
Spread / Flow Table
Kelly Ball
The compaction factor is determined as
the ratio of partially compacted concrete
weight to fully compacted concrete
weight. Usually, its value is stated to be
near about the second decimal place.

True Slump
True slump refers to general drop of concrete mass
evenly all around without disintegration
Zero Slump – Zero slump is the indication of very low
water-cement ratio, which results in dry mixes. These
type of concrete is generally used for road construction.
Segregation is the separation of the constituents materials of concrete.
Segregation is of three types,
firstly the coarse aggregates separating out from concrete.
Secondly, the paste of cement is separating out from coarse
aggregates and thirdly, water is separating out from the rest of the
material.
Dropping of concrete from heights as well as discharging of concrete
from badly designed mixer shows a tendency for segregation.
Due to excessive vibration of concrete coarse aggregates try to settle
down called segregation.
Bleeding is a particular form of segregation, in which some of
the water from the concrete comes out to the surface of the
concrete.
Bleeding takes place in a highly wet mix, badly proportioned
and insufficient mixed concrete.
Bleeding in concrete is sometimes referred to as water gain.
This is a special form of separation, in which some water from
the concrete flows to the surface of the concrete, with
the lowest specific gravity among all concrete components.
Excessive bleeding is seen in thin members such as roof slabs
or road slabs, and when the concrete is placed in sunny
weather.
When cement comes in contact with water, a chemical reaction
begins. This reaction is known as hydration.
If the mixing water dries out too rapidly before the cement has
fully hydrated, the curing process will stop, and the concrete will
not harden to its intended strength.
Hydration occurs more rapidly at higher air temperatures.
Hydration itself also generates heat. This heat of hydration can be
helpful during cold-weather construction but harmful during hot-
weather construction.
Concrete is not recommended to be placed at a
temperature above 40°C without proper precautions,
laid down in IS:7861(part -1).
The First 24 to 72 hours after placing fresh concrete
of extreme importance.
In this period, hydration of concrete occurs, which is
a chemical process in which concrete gains its streng
If the temperature of concrete is not controlled and it
goes beyond maximum range during hydration, then
stresses are produced, and cracks are formed
in concrete.
Also if the temperature falls below the minimum
temperature, then concrete takes a large time to set,
and the hydration process slows down.
It is necessary to understand here that concrete can
done at any temperature unless the temperature is
controlled.

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