SPECIAL STRUCTURAL

CONCRETE

Submitted by :- Archita Saspara Bhavika Bhargava Garvita Dhaddha Kantilal Suthar Kapil Pansuriya Kartik Patel Rajendra Sharma

MATERIALS

Basic introduction to special concrete used for

structural work

Reinforced concrete (RC) is a composite material in which concrete's relatively low tensile strength and ductility are counteracted by the inclusion of reinforcement having higher tensile strength and/or ductility.

The reinforcement is usually, though not necessarily, steel reinforcing bars (rebar) and is usually embedded passively in the concrete before the concrete sets.

Reinforcing schemes are generally designed to resist tensile stresses in particular regions of the concrete that might cause unacceptable cracking and/or structural failure.

Modern reinforced concrete can contain varied reinforcing materials made of steel, polymers or alternate composite material in conjunction with rebar or not.

Reinforced concrete may also be permanently stressed (in compression), so as to improve the behaviour of the final structure under working loads.

Reinforced Concrete

For a strong, ductile and durable construction the reinforcement needs to have the following properties at least:◦ High relative strength ◦ High toleration of tensile strain ◦ Good bond to the concrete, irrespective of pH, moisture, and

similar factors◦ Thermal compatibility, not causing unacceptable stresses in

response to changing temperatures.◦ Durability in the concrete environment, irrespective of corrosion

or sustained stress for example.

Concrete containing a hydraulic cement, water , aggregate, and discontinuous discrete fibers is called fiber reinforced concrete.

Fibers can be in form of steel fiber, glass fiber, natural fiber , synthetic fiber.

Main role of fibers is to bridge the cracks that develop in concrete and increase the ductility of concrete elements.

Improvement on Post-Cracking behavior of concrete Imparts more resistance to Impact load controls plastic shrinkage cracking and drying shrinkage

cracking Lowers the permeability of concrete matrix and thus reduce the

bleeding of water.

Fibre reinforced concrete

Light weight concrete is a special concrete which weighs lighter than conventional concrete.

Density of this concrete is considerably low (300 kg/m3 to 1850 kg/m3) when compared to normal concrete (2200kg/m3 to 2600kg/m3).

Three types of LWC : Light weight aggregate concrete Aerated concrete No – fines concrete

Light weight aggregate concrete - UK, France & USA Aerated concrete - Scandinavian countries No – fines concrete is less popular

Light weight concrete

Fly ash could be an expensive replacement for Portland cement in concrete and using it, improves strength, segregation and ease of pumping concrete.

The rate of substitution typically specified is a minimum of 1 to 1 ½ pounds of fly ash to 1 pound of cement

Fly Ash particles provide a greater workability of the powder portion of the concrete mixture which results in greater workability of the concrete and a lowering of water requirement for the same concrete consistency.

Fly Ash Concrete

High strength concrete and high-performance concrete are not synonymous because strength and performance of concrete are different properties of concrete. High-strength concrete is defined based on its compressive strength at a given age.

While high strength concrete is defined purely on the basis of its compressive strength, Mehta and Aitcin defined the high-performance concrete (HPC) as concrete mixtures possessing high workability, high durability and high ultimate strength.

ACI defined high-performance concrete as a concrete meeting special combinations of performance and uniformity requirements that cannot always be achieved routinely using conventional constituents and normal mixing, placing, and curing practice.

High strength-high performance concrete

High strength of concrete is achieved by reducing porosity, in-homogeneity, and micro-cracks in the hydrated cement paste and the transition zone.

There is a reduction of the thickness of the interfacial transition zone in high-strength concrete.

The densification of the interfacial transition zone allows for efficient load transfer between the cement mortar and the coarse aggregate, contributing to the strength of the concrete.

For very high-strength concrete where the matrix is extremely dense, a weak aggregate may become the weak link in concrete strength.

No-fines concrete is obtained by eliminating the fine material sand, from the normal concrete mix.

The single-sized coarse aggregates are surrounded and held together by a thin layer of cement paste giving strength of concrete.

The advantages of this type of concrete are: ◦ Lower density; ◦ Lower cost due to lower cement content; ◦ Lower thermal conductivity relatively low drying shrinkage; ◦ No segregation and capillary movement of water;◦ Better insulating characteristics than conventional concrete

because of the presence of large voids.

No-fines concrete

Ready-mix concrete is concrete that is manufactured in a factory or batching plant, according to a set recipe, and then delivered to a work site, by truck mounted in–transit mixers.

This results in a precise mixture, allowing specialty concrete mixtures to be developed and implemented on construction sites.

The first ready-mix factory was built in the 1930s, but the industry did not begin to expand significantly until the 1980s, and it has continued to grow since then.

Ready-mix concrete is sometimes preferred over on-site concrete mixing because of the precision of the mixture and reduced work site confusion.

However, using a pre-determined concrete mixture reduces flexibility, both in the supply chain and in the actual components of the concrete.

Ready Mix Concrete

Ready-mix concrete is also referred as the customized concrete products for commercial purpose.

Ready-mix concrete, or RMC as it is popularly called, refers to concrete that is specifically manufactured for delivery to the customer's construction site in a freshly mixed and plastic or unhardened state.

Concrete itself is a mixture of Portland cement, water and aggregates comprising sand and gravel or crushed stone.

In traditional work sites, each of these materials is procured separately and mixed in specified proportions at site to make concrete.

Ready-mix concrete is bought and sold by volume - usually expressed in cubic meters (cubic yards in the US).

Ready-mix concrete is manufactured under controlled operations and transported and placed at site using sophisticated equipment and methods. 

Introduction to theory of reinforcing concrete

RCC (Reinforced Cement Concrete) is the combination of using steel and concrete instead of using only concrete to offset some limitations.

Concrete is weak in tensile stress with compared to its compressive stress.

To offset this limitation, steel reinforcement is used in the concrete at the place where the section is subjected to tensile stress.

Steel is very strong in tensile stress. The reinforcement is usually round in shape with

approximate surface deformation is placed in the form in advance of the concrete.

When the reinforcement is surrounded by the hardened concrete mass, it form an integral part of the member.

The resultant combination of two materials are known as reinforced concrete.

In this case the cross-sectional area of the beam or other flexural member is greatly reduced.

Properties and advantage of reinforced

concrete

Reinforced concrete has a high compressive strength compared to other building materials.

Due to the provided reinforcement, reinforced concrete can also withstand a good amount tensile stress.

Fire and weather resistance of reinforced concrete is fair.

The reinforced concrete building system is more durable than any other building system.

Reinforced concrete, as a fluid material in the beginning, can be economically moulded into a nearly limitless range of shapes.

The maintenance cost of reinforced concrete is very low.

In structure like footings, dams, piers etc. reinforced concrete is the most economical construction material.

It acts like a rigid member with minimum deflection.

As reinforced concrete can be moulded to any shape required, it is widely used in precast structural components. It yields rigid members with minimum apparent deflection.

Compared to the use of steel in structure, reinforced concrete requires less skilled labour for the erection of structure.

Advantages

Types & Grades of steel bars as per BIS specification

Generally there are two types of steel bars available in the market. ◦ Mild steel bars ◦ Deformed steel bars

Type of Steel Bars

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.

Mild steel bars (as per IS: 432, part-I -1982)

Reinforcement bars in accordance with standard IS No. 432 part-I can be classified into following types. ◦ Mild Steel Bars: Mild steel bars can be supplied in two grades

Mild steel bars grade-I designated as Fe 410-S or Grade 60 Mild steel bars grade-II designated as Fe-410-o or Grade 40

◦ Medium Tensile Steel Bars designated as Fe- 540-w-ht or Grade 75

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.

Various Grades of Mild Steel Bars

Physical Requirement:

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.

Deformed Steel Bars (as per IS: 1786-1985)

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.

TMT Bars, Thermo mechanically treated bars are high strength deformed steel bars used in reinforced cement concrete (RCC) work manufactured with the help of advancement of technology.

TMT bars are latest production in MS steel bars and have superior properties such as strength, ductility, welding ability, bending ability and highest quality standards at international level.

TMT Bars (Thermo Mechanically Treated 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.

HSD Steel Bars (High Strength Deformed Bars)

This reduces labour 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.

Bending and placing of reinforcement in RCC

Work

There are several reasons for bending bars:◦ Where anchorage cannot be provided to a straight length within the

available concrete shape or size, it may be necessary to bend a 180° hook or 90° cog on the end.

◦ Hooks and cogs are never scheduled unless they are shown on the engineer’s drawings.

◦ Where continuity of strength is required between two intersecting concrete members, the bar will be bent to allow this stress transfer.

◦ Such bends are never scheduled unless they are shown on the engineer’s drawings.

◦ Where ties, stirrups, ligatures or spirals (called ‘fitments’ by the industry) enclose longitudinal bars in a beam or a column, the fitment will be scheduled to match the shape of the surrounding concrete.

◦ Mostly the shape is defined by the concrete surface and the specified cover. The actual shape is defined by the scheduler, provided the designer’s intentions are given in the drawings.

◦ The designer must indicate if cogged or hooked ends are required.◦ Where intersecting reinforcement is likely to clash, or where parallel

bars require lapping, the scheduler will decide whether or not to provide small offsets.

CONSTRUCTION

Application of RCC in various building elements such as shallow

foundation for isolated column, RCC wall, DPC / Plinth & floor / roof

beam

A spread footing (or isolated or pad) footing is provided to support an individual column.

A spread footing is circular, square or rectangular slab of uniform thickness.

Sometimes, it is stepped or hunched to spread the load over a large area.

shallow foundation for isolated column

RCC wall

DPC

Plinth & floor

roof beam

One way & two way slab in RCC

One Way Slab

two way slab

Arches & Lintels in RCC

Door, window, frames in RCC

Construction of different types of RCC stairs

RCC Structures are nothing but reinforced concrete structures.

RCC structure is composed of building components such as Footings, Columns, Beams, Slabs, Staircase etc.

These components are reinforced with steel that give stability to the structure.

Staircase is one such important component in a RCC structure.

Straight stairs Dog-legged stair Open newel stair Geometrical stair

Various types of Staircases

Straight stairs

Dog-legged stair

Open newel stair

Geometrical stair