• Subject name :Concrete Technology• Subject code :2140608• Guided by:-Prof. Nilesh Parmar Prof. Pritesh Rathod

Topic :- Special Concrete And Concreting Method

Name Enrolment no.Harshil R Gandhi 141100106018Bhavik H Deshmukh 151103106002Pritesh C Dudhat 151103106003Aditya P Misrty 151103106009Dhrumil D Pandya 151103106010

Outline Introduction Light weight concrete High density concrete Mass concrete Plum concrete Fibre reinforced concrete Polymer concrete Ferro concrete

Introduction

Special concrete are the concretes prepared for specific purpose like light weight, high density, fire protection, radiation shielding etc.

Concrete is a versatile material possessing good compressive strength. Modification have been made from time to time to overcome the deficiencies of

cement concrete. Improvement in mechanical properties like compressive strength, tensile strength,

impact resistance etc. Improvement in durability in terms of increased chemical and freeze resistances. Improvement in impermeability, thermal insulation, abrasion, skid resistance etc. Research work is going on in various concrete research laboratories to get

improvement in the performance of concrete.

Light weight aggregate concrete

The density of conventional concrete is in the order 2200 to 2600 kg/m³.

This heavy self weight will make it uneconomical structural material. There are two type of light weight aggregate concrete:-

(a) Natural light weight aggregate

(b) Artificial light weight aggregate Natural light weight aggregate

Pumice, scoria, Rice husk, saw dust. artificial light weight aggregate

sintered fly ash ,formed slag, bloated clay, artificial cinders, expanded clay, slate, shale, coke breeze, expanded perlite , exfoliated vermiculite.

Light weight concrete is achieved by three different ways

By replacing the normal mineral aggregate is known as ‘ light weight aggregate concrete’.

By introducing air bubbles in mortar is known as ‘ aerated concrete’.

By omitting sand fraction from the aggregate as ‘ no fines concrete’.

Aerated concrete

Aerated concrete can be manufactured in this ways

1. By the formation of gas by chemical reaction within the mass during liquid or plastic state.

2. By adding preformed stable foam with the slurry.

3. By adding a finely powdered expansive solid matter.

No fine aggregate

No fine aggregate is obtained by omitting fine aggregate fraction from the conventional concrete.

It consist of cement, coarse aggregate and water only. When conventional aggregate are used no fines concrete show a

density of about 1600 to 2000 kg/m³. Strengths of the order of 15 n/mm² have been attained with no

fines concrete. The bond strength of no fines concrete is very low and therefore

reinforcement is not used in no fines concrete.

High Density concrete High density concrete is also known as ‘ Heavy weight concrete’. High density concrete is produced by replacing the ordinary aggregate

by a material of very much higher specific gravity. One of the more common natural aggregate is Barytes (barium

sulphate).its specific gravity of 4.1 and occurs as a natural rock with a purity of about 95%.

Another type of natural heavy weight aggregate is iron ore: magnetite, limonite, hematite, goethite have been used.

By using iron ore aggregate concrete with densities of between 3000 to 3900 kg/m³.

Apart from biological hazards along with the nuclear reaction very high temperature is also generated and shielding is necessary to protect the electronic and other sensitive equipment's in the vicinity.

High density concrete is also suites for preparing counter-balance weight for lift bridges and ballast blocks for ships.

• “An large volume of cast-in-place concrete with dimensions large enough to require that measures be taken to cope with the generation of heat and attendant volume change to minimize cracking.”

• Mass concrete includes not only low-cement-content concrete used in dams and other massive structures but also moderate to high cement content concrete in structural members of bridges and buildings.

• As the interior concrete increases in temperature and expands, the surface concrete may be cooling and contracting.

• The width and depth of cracks depends upon the temperature differential, physical properties of the concrete, and the reinforcing steel.

Mass concrete:

Plum concrete

The original idea of the use of aggregate as an inert filler can be extended to the inclusion of large stones up to 300 mm size in a normal concrete; thus the apparent yield of concrete for a given amount of cement is increased this result concrete is called ‘ plum concrete’.

These large stones are called ‘plum’ and used in a large concrete mass.

They can be as big as 300mm size but should not be greater than 1/3 of the dimension to be concreted.

The volume of plums should not exceed 20 to 30% of the total volume of the finished concrete and they to be well dispersed throughout the mass.

Care must be taken to ensure that no air is trapped underneath the stones.

The plums must have no adhering coating. Otherwise discontinuities between the plums and concret

Fibre reinforced concrete

Fibre reinforced concrete can be define as a composite material consisting of concrete and discontinuous , discrete, uniform dispersed fine fibres. The continuous meshes , woven fibre and long wire or rod are not considered to be discrete fibre.

The inclusion of fibre in concrete and shotcrete generally improve material properties like ductility, flexural , toughness, impact resistance and fatigue strength .

There is little improvement in compressive strength. The type and amount of improvement is dependent upon the fibre

type,size,strength and configuration and amount of fibre

A numerical parameter describing of fibre is its ‘aspect ratio’ which is define as the fibre length divided by an equivalent fibre diameter.

Typical aspect ratio range from 30 to150 for length dimensions 0.1 to 7.62cm.

Typical fibre diameters are 0.25 to 0.75 mm for steel and 0.02 to 0.5 mm for plastic.

1. Steel fibre2. Glass fibre3. Plastic fibre4. Carbon fibre5. Asbestos fibre

Steel fibres

They are generally round . The diameters may vary from 0.25 to 0.75 mm. The steel fibre is lightly rusted and lose some of its strength. Use of steel fibre makes significant improvements in flexural impact

and fatigue strength of the concrete. Steel fibre has been used in overlays or roads, pavements, air fields.

Bridge decks, thin shells and floorings subjected to wear and tear and chemical attack

Glass fibres

These are produces in three basic forms. 1. roving 2. strands 3. woven or chopped strand mats majors problems in their use are breakage of fibres and the surface degradation of glass by high alkalinity of hydrated cement paste. glass fibre reinforced concrete is mostly used for decorative application rather than structural purposes.GFRC has very high tensile strength 1020 to 4080 N/mm² . They commonly used verities of glass fibre are E-glass and AR-glass.

Plastic fibres Fibres such as polypropylene, nylon, aramid and polyethylene have

high tensile strength but low young's modulus thus inhibiting reinforcing effect.

Polypropylene and nylon fibres are found to be suitable to increase the impact strength.

Their addition to concrete has shown better distribute cracking and reduced crack size.

The amount of plastic fibres added to concrete is about 0.25 to 1% by volume.

There are two type of polypropylene (1) mono filaments (2) film fibres.

Carbon fibres

Carbon fibres proses high tensile strength and high young's modulus. The modulus of rupture of an aligned carbon fibres reinforced

cement composite with 8% fibres volume can be as high as 1623 N/mm² .

The use of carbon fibres in concrete is promising but is costly and availability of carbon fibres in india is limited

Asbestos fibres

Asbestos is a mineral fibres and has proved to be the most successful fibres which can be mixed with OPC .

The maximum length of asbestos fibres is 10 mm but generally fibres are shorter than this

The composite has high flexural strength of asbestos varies between 500 to 980 N/mm²

Factors affecting properties of fibres reinforced concrete Volume of fibres Aspect ratio of fibres Orientation of fibres Size of coarse aggregate Workability and compaction of concrete Mixing

Advantages of FRC

Reduction in shrinkage and cracking Improvement in bond strength Enhancement of fatigue strength and endurance limit better toughness Lower permeability of concrete

Application of FRC

Pavements and floors Water retaining structures Blast resistance structures Precast products Wearing surface to exiting bridges/ culverts Repairs and rehabilitation works

Polymer concrete

There are three type of polymer concrete (a) Polymer- impregnated concrete (b) Polymer Portland cement concrete (c) Polymer concrete

Polymer- impregnated concrete

Polymer- impregnated concrete is produced by impregnating or infiltrating a hardened Portland cement concrete with n manometer and subsequently polymerizing the manometer in situ

It is the widely used polymer composite. The manometer used for impregnation are:i. Methyl methacrylateii. Styreneiii. Acrylonitrileiv. T-butyle styrene v. Epoxy

Application of polymer- impregnated concrete 1) Prefabricated structural elements 2) Surface impregnation of bridges decks3) Hydraulic structures4) Marine works 5) Desalination plants6) Nuclear power plants

Polymer Portland cement concrete

Polymer Portland cement concrete is a conventional Portland cement concrete which is usually made by replacing a part of the mixing water a latex.

There are two type of polymer employed in lattices (a) Elastomeric polymers (b) Glassy polymers

Elastomeric polymers

They are characterized by their rubber like elongation and low modulus of elasticity

Examples are - natural rubber latex - styrene butadiene rubber latex - neoprene

Glassy polymers

They are characterized by higher strength, higher modulus of elasticity and relatively brittle type of failure.

Examples are - polyester styrene - epoxy styrene - furans - vinylidene chloride

Polymer concrete

Polymer concrete is a mixture of aggregate with a polymer as the sole binder.

There is no bonding material present. Monomers or pre-polymers are added to the graded aggregate and the

mixture is thoroughly mixed by hand or machine. The thoroughly mixed polymer concrete material is cast in moulds of

wood, steel or aluminium, etc. Polymerization can be achieved by these methods :- (a) Thermal catalytic reaction (b) Catalyst promoter reaction (c) Radiation

Application

The application of polymer concrete are repair for overlays, air field pavements and industrial structure.

It is also used for repair of sluiceways and stilling basin of the dam. It is also used in rock bolting Polymer concretes possess good electrical properties and it can be

used for manufacturing poles.

Ferro cement

Ferro cement is a relatively new material consisting of wire meshes and cement mortar.

It consists of closely spaced wire meshes which are impregnated with rich cement mortar mix.

The Ferro cement possess high resistance against cracking high fatigue resistance higher toughness and higher impermeability

Applications of Ferro cement

Mobile homes Water tight structures Silos and bins Boat hulls Biogas holder Pipes Folded plates Shell roofs Kiosks Wind tunnel Swimming pool Curved benches for parks etc…

The construction in Ferro cement may be divided in to four stages

(a)Fabrication of skeleton frame (b)Fixing of bars and mesh (c)Application of mortar (d)Curing

Advantages of Ferro cement

Ferro cement structures are thin and light therefore self weight of structure and foundation cost are reduced

The construction technique is simple and does not require highly skilled labour

It is suitable for manufacturing the pre cast concrete elements Partial or complete elimination of formwork is possible It is very easy to repair the damaged Ferro cement work

Properties of Ferro cement

Thickness - 10 mm to 60 mm Steel - 5 to 8% Steel cover - 1.5 mm to 5 mm Ultimate tensile strength - 34.5 N/mm² Allowable tensile strength - 10.0 N/mm² Compressive strength - 27.5 to 60 N/mm²

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