Basics of PRC 1

7/29/2019 Basics of PRC 1

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PLAIN & REINFORCEDCONCRETE - I

LECTURE 1

CIVIL ENGINEERING DEPARTMENT

INTRODUCTION TO CONCRETEby

Engr. Muhammad Ammar


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CONCRETEConcrete is a mixture of portland cement or any other hydraulic

cement, fine aggregate, coarse aggregate, and water, with orwithout admixtures.

CONSTITUENTS PORTLAND OR OTHER HYDRAULIC CEMENT

FINE AGGREGATE

COARSE AGGREGATE

WATER

ADMIXTURES (OPTIONAL)

INTRODUCTION TO CONCRETE


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CONCRETEConcrete is manufactured in definite proportions of cement: fineaggregate : coarse aggregate & %age water by weight.

TYPES OF CONCRETE

Concrete generally has three types depending upon the method of its manufacturing. IN-SITU

Concrete which is manufactured, placed and left to set at the site to be placed is called In-situConcrete. This type of concrete is further divided into two types;

Site batched

Central plant batched

PRE-CASTConcrete which is prepared and allowed to set in proper shape and size at a place other than the siteand transported to the site for placement is called pre-cast concrete.

PRE-STRESSED

Concrete which is subjected to tensile forces in advance of its proper setting and placement toproduce extra strength in the section is called pre-stressed concrete.



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CONCRETETYPES OF CONCRETE

(Based on Manufacturing Ingredients)

Plain concrete

Normal Weight Concrete

Light Weight Concrete

Heavy Weight Concrete

Asphaltic Concrete

Reinforced Concrete

Fibre Reinforced Concrete

Other types



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CONCRETE MANUFACTURINGPROPORTIONING

The process of manufacturing of concrete is called batching. Concrete is batched by

volume. Principles for proportioning concrete to achieve a prescribed compressivestrength after a given age under standard curing are:

The strength of a hardened concrete mix depends on the water-cement materials ratio(ratio of water to cement materials, by weight). The water and cement materials form apaste. If the paste is made with more water, it becomes weaker.

The ideal minimum amount of paste is that which will coat all aggregate particles and fill

all voids. For practical purposes, fresh concrete must possess workability sufficient for the

placement conditions. For a given strength and with given materials, the cost of the mixincreases as the workability increases. Additional workability is provided by more fineaggregate and more water, but more cement materials must also be added to keep thesame water-cement materials ratio.



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CONCRETE PROPERTIESFRESH CONCRETE

WORKABILITY

AIR-CONTENT

CEMENT CONTENT

SEGGREGATION



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CONCRETE PROPERTIESHARDENED CONCRETE

COMPRESSIVE STRENGTH

MODULUS OF ELASTICITY

WEIGHT

DIRECT TENSILE STRENGTH

MODULUS OF RUPTURE

RESILLIANT MODULUS



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CONCRETE WATER FREE FROM SALTS

PH VALUE

FREE FROM IMPURITIES

FREE FROM ORGANIC IMPURITIES

SALINE WATER

POTABLE WATER



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CONCRETE ADMIXTURES Accelerate or retard the initial setting

Increase the strength

Improve workability, penetration and pump ability

Reduce heat of evolution

Increase durability

Control expansion caused by reaction

Decrease capillary flow of water to make it impermeable Reduce segregation in grouts

Inhibit corrosion, increase resistance to chemical attack

Produce concrete which is colored, cellular, fungicidal,germicidal, and insecticidal



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CONCRETE FORMWORKThe temporary works which are used to support the plasticconcrete or any other material in desired sections un till it sets is

called formwork.

PURPOSE STRUCTURAL ADEQUACY

SAFETY

MATERIALS USED AS FORMWORK WOOD PLANKS & PANELS

STEEL PANELS

PLASTIC PANELS



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CONCRETE FORMWORK LOADINGS ON FORMWORK

PRESSURE DUE TO FRESH CONCRETE ON VERTICAL FORMWORK

p = 150 + 9000(R/T)

Where, p = lateral pressure, psf

R= Rate of filling, ft/h

T= Temperature of concrete, 0F

DESIGN VERTICAL LOADS FOR HORIZONTAL FORMS

DEAD LOAD due to weight of concrete or any other allied material

LIVE LOAD due to labour, power buggies and other temporary loads, normally 50 psf isadded

IMPACT LOAD due to any impact on forwork due to sudden loads, normally 25 psf is

added. LATERAL LOADS FOR SHORING

Lateral loads may cause progressive failure

Horizontal Formwork should be braced to resist atleast

100 lb/lin ft of horizontal force

2% of total dead loads on the floor

Vertical formwork should be braced to resist local building-code wind pressure + 100 lb/linft at the top in each direction.



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CONCRETE PLACING PRACTICESThe principles governing proper placement of concrete are:

Segregation must be avoided during all the operations between themixer and the point of placement , including final consolidation and

finishing.

The concrete must be thoroughly consolidated, worked solidly around allembedded items, and should fill all angels and corners of the form.

Where fresh concrete is placed against or on hardened concrete, a good

bond must be developed.

Unconfined concrete must not be placed underwater.

The temperature of fresh concrete must be controlled from time ofmixing to the final placement , and protected after placement.



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CONCRETE TRANSPORTATION PRACTICESThe transportation of concrete is generally practiced through the following

methods;

Wheel-barrows

Chutes

Hand or power operated buggies

Drop-bottom buckets with cranes

Flexible and rigid pipes

Side-dump cars

Belt conveyors Paving mixer

Dump truck

Mixer truck



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CONCRETEFACTORS FOR CHOOSING R.C STRUCTURES ECONOMY

SUITABILITY TO ARCHITECTURAL & STRUCTURAL FUNCTIONS

FIRE RESISTANCE

RIGIDITY

LOW MAINTENANCE

AVAILABILITY OF MATERIALS LONG LIFE

EASE TO IMPROVISE PROPERTIES ACCORDING TO USE.



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CONCRETEDEMERITS OF REINFORCED CONCRETE STRUCTURES

HIGH STRENGTH TO WEIGHT RATIO

LOW TENSILE STRENGTH

FORMS & SHORING

TEMPORARY WORKS REQUIRE LABOUR

REQUIRES TIME TO SET

TIME DEPENDENT VOLUME CHANGES

EXPENSIVE REPAIR/REPLACEMENT


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Basics of PRC 1