RCC-.pdf

R.C.C. – the Cement concrete in which Steel reinforcement is embedded for taking tensile
stress is called R.C.C.
In this type of concrete , the steel is used generally in the form of round bars, 6mm – 32 mm. dia.
Steel.
This concrete is equally strong in taking tensile, compressive and shear stresses.
R.C.C. –
•1 part - cement
•1-2 parts - sand
•2-4 parts - crushed stones or gravel.

RCC Use in Foundation
Uses :-
RCC commonly used in
Columns, Beams, Foundations,
Slabs, Precast Concrete

Cement concrete Proportion used in Framed Structure

Load transfer in RCC Construction

Type of Load transfer in RCC Construction

Mixing of Concrete
Ideally, the mixing should be done in a mechanical mixer.
The concrete mixer should be allowed to rotate for at least 2 minutes. Pouring
Concrete

Mixing of Concrete
METHODS OF PROPORTIONING CONCRETE:-
(1) Arbitrary Method
The general expression for the proportions of cement, sand and coarse
aggregate is 1 : n : 2n by volume.
1 : 1 : 2 and 1 : 1.2 : 2.4 for very high strength.
1 : 1.5 : 3 and 1 : 2 : 4 for normal works.
1 : 3 : 6 and 1 : 4 : 8 for foundations and mass concrete works.
M10 1 : 3 : 6
M15 1 : 2 : 4
M20 1 : 1.5 : 3
M25 1 : 1 : 2
Recommended Mixes of Concrete :-
The concrete as per IS 456: 2000, the grades of concrete lower than M20 are not to be
used in RCC work.

Mixing of Concrete
(2) Fineness Modulus Method:-
The term fineness modulus is used to indicate an index number which is roughly
proportional to the average size of the particle in the entire quantity of aggregates.
The fineness modulus is obtained by adding the percentage of weight of the material
retained on the following sieve and divided by 100.
The coarser the aggregates, the higher the fineness modulus.
Sieve is adopted for:-
All aggregates : 80 mm, 40 mm, 20 mm, 10 mm, and Nos. 480, 240, 120, 60, 30 and 15.
Coarse aggregates : mm, 40 mm, 20 mm, 10 mm, and No. 480.
Fine aggregates : Nos. 480, 240, 120, 60, 30 and 15.

Mixing of Concrete
(3) Minimum Void Method (Does not give satisfactory result)
The quantity of sand used should be such that it completely fills the voids of coarse
aggregate.
Similarly, the quantity of cement used shown such that it fills the voids of sand, so
that a dense mix the minimum voids is obtained.
In actual practice, the quantity of fine aggregate used in the mix is about 10% more
than the voids in the coarse aggregate and the quantity of cement is kept as about
15% more than the voids in the fine aggregate.

Mixing of Concrete
(5) Water – Cement Ratio Method:
According to the water – cement ratio law given by Abram as a result of many
experiments, the strength of well compacted concrete with good workability is
dependent only on the ratio.
The lower water content produces stiff paste having greater binding property and hence
the lowering the water-cement ratio within certain limits results in the increased
strength.
Similarly, the higher water content increases the workability, but lower the strength of
concrete.
The optimum water-cement ratio for the concrete of required compressive strength is
decided from graphs and expressions developed from various experiments.
Amount of water less than the optimum water decreases the strength and about 10%
less may be insufficient to ensure complete setting of cement. An increase of 10% above
the optimum may decrease the strength approximately by 15% while an increase in 50%
may decrease the strength to one-half.

Mixing of Concrete
Thumb Rules for deciding the quantity of water in concrete:
(i) Weight of water = 28% of the weight of cement + 4% of the weight of total
aggregate
(ii) Weight of water = 30% of the weight of cement + 5% of the weight of total
aggregate
Some practical values of water cement ratio for structure reinforced concrete
0.45 for 1 : 1 : 2 concrete
0.5 for 1 : 1.5 : 3 concrete
0.5 to 0.6 for 1 : 2 : 4 concrete.
Concrete vibrated by efficient mechanical vibrators require less water cement
ratio, and hence have more strength.

Formwork for RCC Framed Construction
Image showing Formwork for placing Concrete in RCC column

Materials used for the formwork
The formwork is commonly built from wooden planks and boards, plastic, or
steel. On commercial building sites today, plastic and steel are more common
as they save labour.
On low-budget sites, for instance when laying a concrete garden path,
wooden planks are very common. After the concrete has set the wood may be
removed, or left there permanently.
In some cases formwork is not necessary – for instance, a ground slab
surrounded by brick or block foundation walls, where the walls act as the
sides of the tray and hardcore acts as the base.

What is Formwork ?

Materials used for RCC Formwork.

Requirements of Formwork for RCC Framed Construction

Objectives considered in Formwork

Formwork for different structural member of RCC Framed Construction

Formwork for Walls :-

Formwork for Square Columns :-
Column Formwork - Timber yoke used as a
column clamp

Formwork for Columns :-

Formwork for Beams &Lintels :-

Roof Beam formwork fabricated at
construction site. The formwork verticality and
horizontality supported by series of wooden
support and scaffoldings. The formwork was
completed and ready to receive concrete
Steel formwork use in construction site for
ground beam beam formwork

Time for Removal of Formwork for RCC Framed Construction

Types of Steel Bars used in RCC Construction
Generally there are two types of steel bars ("Sariya" in hindi) available in
the market.
Mild steel bars
Deformed steel bars
Steel bars used for construction work

Mild steel bars (as per IS: 432, part-I -1982)
Mild steel bars are used for tensile stress of RCC (Reinforced cement concrete) slab beams etc.
in reinforced cement concrete work. These steel bars are plain in surface and are round sections
of diameter from 6 to 50 mm. These rods are manufactured in long lengths and can be cut
quickly and be bent easily without damage.
Deformed steel bars (as per IS: 1786-1985)
As deformed bars are rods of steels provided with lugs, ribs or deformation on the surface of
bar, these bars minimize slippage in concrete and increases the bond between the two
materials. Deformed bars have more tensile stresses than that of mild steel plain bars. These
bars can be used without end hooks. The deformation should be spaced along the bar at
substantially uniform distances. To limit cracks that may develop in reinforced concrete around
mild steel bars due to stretching of bars and some lose of bond under load; it is common to
use deformed bars that have projecting ribs or are twisted to improve the bond with concrete.
These bars are produced in sections from 6 mm to 50 mm dia.
In addition the strength of bonds of deformed bars calculated should be 40 to 80 % higher than
that of plain round bars of same nominal size. And it has more tensile stress than that of plain
round bars of same nominal size.
Cold twisted deformed (Ribbed or Tor Steel Bars) bars are recommended as best quality steel
bars for construction work by structural Engineer.

Various Grades of Mild Steel Bars
Reinforcement bars in accordance with standard IS No. 432 part-I can be classified
into following types.
1) Mild Steel Bars: Mild steel bars can be supplied in two grades
a)Mild steel bars grade-I designated as Fe 410-S or Grade 60
b) Mild steel bars grade-II designated as Fe-410-o or Grade 40
2) Medium Tensile Steel Bars designated as Fe- 540-w-ht or Grade
Grade II Mild steel bar are not recommended for use in structures located in earth quake
zones subject to severe damage and for structures subject to dynamic loading (other than
wind loading) such as railways and highways bridges.
Every lot or consignment of mild steel bars brought at the site of work should be tested in
laboratory before use in the work. However for small work one can use mild steel bars on
the basis of verifying tests results made by manufacturer in his own laboratory; which are
available with supplier.
Some of manufacturers stamped MS bars grade with their make /name and also give
certification of test and grade. On the basis of the above information you can store mild
steel bars grade-wise at the site of work.

Steel Bars for RCC Work
All finished steel bars for reinforced work should be neatly rolled to the dimension and
weights as specified.
They should be sound, free from cracks, surface flaws, laminations, rough, jagged and
imperfect edges and other defects.
It should be finished in a work like manner.

General Precautions for Steel Bars used in RCC Construction
General precautions for steel bars in reinforcement
Steel bars are clear, free from loose mil scales, dust and loose rust coats of paints, oil
or other coatings which may destroy or reduce bond strength.
Steel bars should be stored in such a way as to avoid distortion and to prevent
deterioration and corrosion.
Steel bars should not be clean by oily substance to remove the rust.
The bar is bent correctly and accurately to the size and shape as shown in drawings.
If possible, the bar of full length is used.
Overlapping bars do not touch each other and these should be kept apart with
concrete.
The overlap if given should be staggered.
The cranks in the bar at the end should be kept in position by using spots.
The steel bars should not be disturbed while lying cements concrete.
Required cover under steel bars should be given before laying the cement concrete.

Weight of Different Steel Bars
When we want to purchase Mild steel members from the market, the shopkeeper
quotes the price of steel members in weight.
When any type of steel members for use in house construction is required, we
calculate the length of steel member in feet or meter but we are ignorant about the
weight of steel. Here are details of weight per meter for various types of steel
members:-
This will help us for estimated weight and cost. It will also help at the time of purchase
to avoid pilferage in weight.

HSD Steel Bars (High Strength Deformed Bars)
High strength deformed bars IS: 1786-1985 are steel bars which are provided with lugs,
ribs, projection or deformation on the surface and are produced in form of cold twisted
deformed bars. These bars are extensively used for reinforcement purposes in a
construction. Due to ribs or projections on the surface, these steel bars minimize slippage
in concrete and increase the bond between two materials i.e. between cement concrete
and steel bars.
The deformed bars have more compressive and tensile stress than that of mild steel plain
bars. High strength deformed bars have improved anchorage; therefore they can be used
without end hooks or bent up ends of bars. This reduces labor for fabrication of steel
reinforcement. The deformation is spaced on bar at uniform distances. These bars are
produced in sizes or sections from 4 mm to 50 mm in diameter.
Generally cracks develop in reinforced concrete around mild steel bars due to stretching of
bars, loss of bond under the load. To minimize this problem, deformed bars having
projecting ribs or twisted surface which improves the bond with the concrete should be
used in RCC work.

Features of HSD Bars
Low carbon value: HSD Bars have lower carbon level, resulting in good ductility, strength
and welding ability.
Superior bonding strength: HSD bars are well known for their excellent bonding strength
when used with concrete.
Welding capability: Since these bars have lower carbon content, they have 100% welding
capability than conventional bars.
High tensile strength: HSD bars feature high tensile strength. They offer great asset in
construction process, where a lot of bending and re bending is required.
Wide application range: These bars have wide application range like in building
residential, commercial and industrial structures, bridges, etc.
Satisfactorily malleability, minimum weight and maximum strength and suitable for both
compression and tension reinforcement.

Process of production of bars
The main process for production of bars is hot rolling followed by cold twisting. Latest
technological advances in the field of micro-alloying of steel and thermo-mechanical
treatment process have resulted in the production of deformed bars as reinforcement for
use in cement concrete in three grades namely Fe 415, Fe 500 and Fe 550.
The strength of bonds of deformed bars
In addition, the calculated strength of bonds of deformed bars should be 40 to 80 % higher
than that of plain round bars of same nominal size. Tor steel possesses the strength of 1.5 to
2.0 times of mild steel in compression as well as in tension, whereas it costs only 10% more
than mild steel.
Process of production of bars
The main process for production of bars is hot rolling followed by cold twisting. Latest
technological advances in the field of micro-alloying of steel and thermo-mechanical
treatment process have resulted in the production of deformed bars as reinforcement for
use in cement concrete in three grades namely Fe 415, Fe 500 and Fe 550.
The strength of bonds of deformed bars
In addition, the calculated strength of bonds of deformed bars should be 40 to 80 % higher
than that of plain round bars of same nominal size. Tor steel possesses the strength of 1.5 to
2.0 times of mild steel in compression as well as in tension, whereas it costs only 10% more
than mild steel.

Laying of Reinforcement in RCC Construction

Casting of Reinforcement in RCC Construction
Typical Slab Reinforcement in RCC Construction

Curing plays an important role on strength
development and durability of concrete.
Curing takes place immediately after concrete
placing and finishing
Deshuttering and Curing of RCC Structure

Curing
The curing shall be started immediately after thumb set of the concrete laid.
Hessian clothe /Plastic shall be covered over the set concrete to reduce moisture
evaporation from the concrete during hardening and thus to minimize shrinkage
crazy cracks. These cracks are inheriting property of the concrete specially
appears during casting of flat surfaces.
Final curing shall be done by ponding and stacking water for minimum period of 7

Curing:-
The curing shall be started immediately after thumb set of the concrete
laid. Hessian clothe /Plastic shall be covered over the set concrete to
reduce moisture evaporation from the concrete during hardening and thus
to minimize shrinkage crazy cracks.
These cracks are inheriting property of the concrete specially appears
during casting of flat surfaces.
Final curing shall be done by ponding and stacking water for minimum
period of 7 days.

Concrete form work stripping time :-
In general stripping of form work should not be done unless otherwise concrete
has achieve strength equal to double the stress it may imposed while stripping the
form work. Before stripping of form work, compressivestrength of concrete is to
be checked. If desire compressive strength of concrete is not achieved then the
stripping time should be extended.
Following article provide guide lines for minimum stripping time as per Indian
standard 456 when
 concreting is done under normal circumstances
 cement used is Ordinary Portland Cement
 Adequate curing is done
 Ambient temperature is not fall below 15 degree

For vertical members such as columns, beams, shear walls etc – 16 -24 hrs
soffit form work to slabs – 3 days (care to be taken so that props to be fixed
immediately after removing form work)
soffit form work to beam – 7 days (care to be taken so that props to be fixed
immediately after removing form work)
Props left under slab can be removed after 7 days if spanning is less than
4.5 m and 14 days for spanning over 4.5 m
Props left under slab can be removed after 14 days if spanning is less than 6
m and 21 days for spanning over than 6 m

Testing of Concrete
What is workability of concrete? Which test is generally performed at site for its
determination? And what are its recommended values for different purposes?
Workability of concrete describes the ease or difficulty with which the concrete is handled,
transported and placed between the forms with minimum loss of homogeneity.
Workability is important because, if
i. the concrete mixture is too wet, coarse aggregates settle at the bottom of concrete
mass and as a result concrete becomes non-uniform composition,
ii. the concrete mixture is too dry, it will be difficult to handle and place it in position.
Workability of concrete mixture is measured by:
a) Vee-bee consistometer test
b) Compaction factor test
c) Slump test
Suitability of Slump Test:
The slump test is suitable only for the concrete
of high or medium workability.

Slump Test
This test is carried out with a mould called slump cone whose top diameter is 10cm,
bottom diameter is 20 cm and height is 30 cm. the test may be performed in the
following steps:
1. Place the slump mould on a smooth flat and non-absorbent surface.
2. Mix the dry ingredients of the concrete thoroughly till a uniform colour is obtained
and then add the required quantity of water.
3. Place the mixed concrete in the mould to about one-fourth of its height.
4. Compact the concrete 25 times with the help of a tamping rod uniformly all over
the area.
5. Place the concrete in the mould about half of its height and compact it again.
6. Place the concrete upto its three fourth height and then upto its top. Compact each
layer 25 times with the help of tamping rod uniformly. For the second subsequent
layers, the tamping rod should penetrate into underlying layers.
7. Strike off the top surface of mould with a trowel or tamping rod so that the mould
is filled to its top.
8. Remove the mould immediately, ensuring its movement in vertical direction.
9. When the settlement of concrete stops, measure the subsidence of the concrete in
millimeters which is the required slump of the concrete

RCC Specifications
Shuttering shall be done using seasoned wooden boards of thickness not less than 30mm.
Surface contact with concrete shall be free from adhering grout, nails, splits and other defects.
All the joints are perfectly closed and lined up.
The shuttering and framing is sufficiently braced.
Nowadays timber shuttering is replaced by steel plates.
All the props of approved sizes are supported on double wedges and when taken out, these
wedges are eased and not knocked out.
All the framework is removed after 21 days of curing without any shocks or vibrations.
All reinforcement bars conform IS specifications and are free from rust, grease oil etc.
The steel grills are perfectly as per detailed specifications.
The covers to concrete are perfectly maintained as per code.
Bars of diameter beyond 25mm diameter are bent when red hot.
The materials proportion should be as per the specifications of the concrete.

Number of Cement bags required for a specific cement concrete ratios:-
For cement concrete of ratio 1:1:2(1 cement:1sand/coarse sand:2graded stone
aggregate) require 11no bags of 50kg.
For cement concrete of ratio 1:1.5:3 require 7.8no bags of 50kg.
For cement concrete of ratio 1:2:4 require 6 no bags of 50kg.
For cement concrete of ratio 1:3:6 require 4.25no bags of 50kg.
For cement concrete of ratio 1:4:8 require 3.2 no bags of 50kg.

Thumb rule no1:
Size of the Columns
The size of the columns are 9″x9″ with the use of M20 grade of concrete.
Thumb rule no.2:
Distance between the columns:
The distance between the columns does not exceed 4.5m.
Thumb rule no.3:
Alignment of Columns
The Columns have been arranged on a iron grid pattern. So there is absolutely
no question of zigzag walls and zigzag beams which reducing complications in
the structure.

Construction process in RCC Building
Construction
A concrete slab can be cast in two ways: It could either be prefabricated or cast in situ.
Prefabricated concrete slabs are cast in a factory and then transported to the site ready
to be lowered into place between steel or concrete beams.
They may be pre-stressed (in the factory), post-stressed (on site), or unstressed. Care
should be taken to see that the supporting structure is built to the correct dimensions to
avoid trouble with the fitting of slabs over the supporting structure.
In situ concrete slabs are built on the building site using formwork. Formwork is a box-like
setup in which concrete is poured for the construction of slabs.
For reinforced concrete slabs, reinforcing steel bars are placed within the formwork and
then the concrete is poured.
Plastic tipped metal, or plastic bar chairs are used to hold the reinforcing steel bars away
from the bottom and sides of the form-work, so that when the concrete sets it completely
envelops the reinforcement.
Formwork differs with the kind of slab. For a ground slab, the form-work may consist only
of sidewalls pushed into the ground whereas for a suspended slab, the form-work is
shaped like a tray, often supported by a temporary scaffold until the concrete sets.

Reinforced Cement Concrete Slab
A Reinforced Concrete Slab is the one of the most important component in a
building. It is a structural element of modern buildings. Slabs are supported on
Columns and Beams.
RCC Slabs whose thickness ranges from 10 to 50 centimetres are most often
used for the construction of floors and ceilings.
Thin concrete slabs are also used for exterior paving purpose.
In many domestic and industrial buildings a
thick concrete slab, supported on
foundations or directly on the sub soil, is used
to construct the ground floor of a building.
In high rises buildings and skyscrapers, thinner,
pre-cast concrete slabs are slung between the
steel frames to form the floors and ceilings on
each level.
While making structural drawings of the
reinforced concrete slab, the slabs are
abbreviated to “r.c.slab” or simply “r.c.”

Design of various types of slabs and their reinforcement
For a suspended slab, there are a number of designs to improve the strength-to-
weight ratio. In all cases the top surface remains flat, and the underside is
modulated:
Corrugated, usually where the concrete is poured into a corrugated steel tray.
This improves strength and prevents the slab bending under its own weight. The
corrugations run across the short dimension, from side to side.
A ribbed slab, giving considerable extra strength on one direction.
A waffle slab, giving added strength in both directions.

Solid Slab spanning in two directions
When a slab is supported on all four of its sides, it effectively spans in both directions, and
it is sometimes more economical to design the slab on this basis. The moment of bending
in each direction will depend on the ratio of the two spans and the conditions of restraint
at each support.
If the slab is square and the restraint is similar along the four sides, then the load will span
equally in both directions. If the slab is rectangular, then more than one-half of the load
will be carried in the shorter direction and lesser load will be imposed on the longer
direction.
If one span is much longer than the other, a large portion of the load will be carried in the
shorter direction and the slab may as well be designed as spanning in only one direction.
Moments in each direction of span are generally calculated using co-efficients which are
tabulated in the code.
The slab is reinforced with the bars in both directions parallel to the spans with the steel
for the shorter span placed farthest from the natural acis to five the greater effective
depth.
The span-efective depths are based on the shorter span and the percentage of the
reinforcement in that direction.

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