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Properties of concreteWorkability

Segregation

Bleeding

Strength

Elasticity

Shrinkage

Creep

Durability

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Workability

Easily mixed, handled, transported, placed in

position and compacted

Segregation

Separation of constituent materials of concrete

Creates larger voids and reduces the durability

and strength

Bleeding

Water from concrete comes out of the surface

Produces pores in concrete and reduces strength.

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Strength

Compressive strength, tensile strength, flexural

strength

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Flexural testing

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Elasticity

Concrete not an elastic material

Stress in concrete astrains in initial stages

Influenced by elastic properties of aggregate,

mix proportion, age of concrete, type of

cement

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ShrinkageChange in volume of concrete due to loss of

moisture at different stages

Affects strength and durabilityLeads to the formation of cracks

Depends on constituents of concrete, size of

member, amount of water present in concreteand environmental conditions

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CreepGradual increase in strain without increase in

stress, with time

Depends on stress in concrete, age at loading andduration of loading

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Durability

Ability to resist weathering action, chemical

attack, abrasion or any other process of

deterioraton

Factors affecting are environment, cover to

embedded steel, type and quality of constituent

materials, cement content and water cement

ratio, workmanship to obtain full compaction,efficient curing and shape and size of member

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Types of concrete

Reinforced cement concreteFibre reinforced concrete

Ferrocement

Light weight concrete

Ready-mixed concrete

Shotcrete

Polymer concrete

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Fibre reinforced concrete

Fibres- natural materials like asbestos and

cellulose, or manufactured products such as

glass, steel carbon and polymer

Road pavements, industrial flooring, bridge

decks, canal linings, explosive resistant

structures etc.

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Ferrocement

Closely spaced, multiple layers of mesh or fine

rods completely surrounded by cement mortar.

Casting overhead water tanks, gober gas plants,

boat building, manhole covers, roofing units,

pressure pipes etc.

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Light weight concrete

Density lower than ordinary concrete

Light weight aggregates or introducing gas or airbubbles

long span bridges, fire protection for steel work

in tall buildings, filling for floor and roof slab

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Shotcrete

Shotcrete is a process where concrete is

projected or "shot" under pressure using a

feeder or "gun" onto a surface to form

structural shapes including walls, floors, androofs.

Shotcrete has high strength, durability, low

permeability, excellent bond and limitlessshape possibilities.

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Polymer concreteis part of group of concretes

that use polymers to supplement or replace

cement as a binder. The types include polymer-

impregnated concrete, polymer concrete, and

polymer-Portland-cement concrete.

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Ready-mixed concrete

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Advantages of cement concrete

Readily mouldedHigh compressive strength

Free from corrosion

Hardens with age

Resists abrasion

Impermeable

Provides good bond

Control properties of concrete

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Advantages of cement concrete

Mechanise completely its preparation

Adequate plasticity for mechanical working

More economical than steel

Compatible with other materials like steelDisadvantages

Low tensile strength

Self weight high

Not suitable for speedy construction-curing

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Admixtures and additives

Accelators

Admixtures which accelerate hardening/ development

of early strength.

Sodium carbonate,aluminiium chloride, potassium

carbonate, sodium aluminate etc

Set retarders

Admixtures which delay the setting of concrete

Common sugar, carbohydrate derivative

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Water reducers(plasticizers)

To achieve higher strength by decreasing water

cement ratio

To achieve same workability by decreasing

cement content

To increase the workability