Concreting Ppt

8/11/2019 Concreting Ppt

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CONCRETE


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PRESENTATION ORGANIZATION

COMPONENTS OF CONCRETE

CONCRETE MIX DESIGN

TYPES OF CONCRETE & THEIR PROPERTIES

PLACING AND FINISHING CONCRTE


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COMPONENTS OF CONCRETE

CEMENT

FINE & COARSE(AGGREGATES)

WATER

ADMIXTURES


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EARLY HISTORY OF CEMENT

In ancient times, Egyptians mostly used materialobtained by burning gypsum.

Greeks & Romans used the material obtained by

burning limestone.

First cement was invented by Joseph Aspin din on 21

October 1824.

First cement was started at Portland in England.

In India, cement was manufactured in 1904 in Madras

by South India Industrial ltd.


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TWO WAYS OF MANUFACTURING CEMENTDRY CEMENT PROCESS


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TWO WAYS OF MANUFACTURING CEMENTWET CEMENT PROCESS


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AGGREGATES

Aggregates give body to the concrete.

Aggregates reduce shrinkage and effecteconomy.

Aggregates occupy 70-80 % of volume of

concrete.


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SHAPES OF AGGREGATESRounded Aggregates : Fully water worn

Irregular Aggregates : Having Rounded Edges

Angular Aggregates : Well defined Edges

Flaky Aggregates : Having small thickness.


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ADMIXTURES

ADMIXTURES are added to concrete batch

immediately before or during mixing concrete. Concrete

admixtures can improve concrete quality, manageability,acceleration or retardation of setting time among other

properties that could be altered to get specific results.


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CONCRETE MIX DESIGN

CONCRETE MIX DESIGN is defined as a

process of selecting suitable ingredients of

concrete and determining their relative

properties with an object of producingconcrete of certain minimum strength and

durability as economically as possible.

Two methods used in concrete design :

1. American Concrete Institutes method

2. Indian Standard method


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TYPES OF CONCRETE

Fresh Concrete

Hardened Concrete

Special Concrete

Light weight Concrete

Reinforced Cement Concrete

High Density Concrete

Self Compacting Concrete


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CONCRETE PROPERTIES

VERSATILE

STRONG & DURABLE

DOES NOT RUST OR ROT

RESISTS FIRE

DOES NOT NEED A COATING

ENERGY EFFICIENT


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WORKABILITY

It is desirable that freshly mixed concrete

be relatively easy to transport, place,

compact and finish without harmful

segregation.

A concrete mix satisfying these conditionsis said to be workable.


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FACTORS AFFECTING WORKABILITYMethod and duration of transportation

Quantity and characteristics of cementingmaterials

Aggregate grading, shape and surface texture

Quantity and characteristics of chemicaladmixtures

Amount of waterAmount of entrained air

Concrete & ambient air temperature


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WORKABILITYWorkability is the most important property of

freshly mixed concrete.It is determined to a large extent by measuringthe consistencyof the mix.


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CONSISTENCY

Test methods for measuring consistency are:

Slump test (Most widely used test)

Flow test measures the amount of flow

Kelly-Ball test measures the amount of penetration


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Slump TestSlump Test is related with the ease with which

concrete flows during placement (TS 2871, ASTM C143)


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The slump cone is filled in 3 layers. Every layer is evenly rodded 25 times.

Measure the slump by determining the vertical difference between the top of the

mold and the displaced original center of the top surface of the specimen.


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SEGREGATIONFactors affecting segregation:

Larger maximum particle size (25mm) and proportion of

the larger particles.

High specific gravity of coarse aggregate.

Decrease in the amount of fine particles.

Particle shape and texture.

Water/cement ratio.


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BLEEDING

Bleeding is the tendency of water to rise to thesurface of freshly placed concrete.


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BLEEDING

Undesirable effects of bleeding are:

With the movement of water towards the top, the topportion becomes weak & porous (high w/c). Thus theresistance of concrete to freezing-thawing decreases.

Water rising to the surface carry fine particles ofcement which weaken the top portion and formlaitance. This portion is not resistant to abrasion.

Water may accumulate under the coarse agg. and

reinforcement. These large voids under the particlesmay lead to weak zones and reduce the bondbetween paste and agg. or paste and reinforcement.


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MIXING OF CONCRETE

The aim of mixing is to blend all of the ingredients ofthe concrete to form a uniform mass and to coat thesurface of aggregates with cement paste.

Ready-Mix concrete: In this type ingredients are

introduced into a mixer truck and mixed duringtransportation to the site.

1. Wet Water added before transportation

2. Dry Water added at site Mixing at the site

1. Hand mixed

2. Mixer mixed

R d Mi C t


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Ready Mix Concrete


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MIXING AT SITE


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MIXING OF CONCRETE

Mixing time should be sufficient to produce a uniform

concrete. The time of mixing depends on the type of

mixer and also to some properties of fresh concrete.

Undermixing non-homogeneity

Overmixing danger of water loss, brekage of

aggregate particles


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CONSOLIDATING CONCRETE

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