concrete and cement - building technology

7/28/2019 Concrete And Cement - Building Technology

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BLDG. TECH III CONCRETE AND STEEL

GROUP 1 PRESENTATIONPART 1


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HYDRAULIC

CEMENTis a bonding agent that reacts

with water to form a hard

stone like substance that is

resistant to disintegration in

water. Most hydrauliccement has specific

combination of silicate and

aluminates of lime. Cement

is the bonding agent of rock

materials called aggregate

which act as filler.


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PORTLAND

CEMENTIs widely used in various

small and large

constructions including

roads and highways.

Portland cement is not a

brand but a type of

hydraulic cement. In 1824

Joseph Apsdin, introduced

the name of Portland, that

he than patented.


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TYPE I is used in general construction where the special properties are

specified.

TYPES OF PORTLAND CEMENT

TYPE II for general construction exposed to moderate sulfate action or where

moderate heat of hydration is required..

TYPE III

is used where high early strength is necessary

TYPE IVis used when high sulfate resistance is required


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POZZOLANCEMENTIs an amorphous silica that

harden as a silica gel by

reacting chemically with

alkali in the presence ofwater. Pozzolan is derived

from italian word pozzuoli,

It was an italian town

where the suvstance was

found.


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ADMIXTURE

As defined by ASTM, admixture is a material other than water, aggregates orportland cement, that is used as an ingredient added to the batch immediately

before or during its mixing.

AIR-ENTRAINING ADMIXTUREMaterially improves the durability of concrete in entraining billions of

microscopic air bubbles distributed throughout the matrix of the concrete.

These tiny air bubbles are large in volume in comparison with the capillary

voids and the gel pores in portland cement. The air bubbles create space forthe relief of pressure built up in the smaller cavities when they are filled

with water that expands when it freezes.


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To improve workabality or consistency of concrete.

PURPOSE OF ADMIXTURES

To improve the durability of the concrete mix.

To increase strength.

To accelerate strength development.

Retard or accelerate initial setting.

Reduce evolution of heat

Control alkali aggregate expansion.

Increase density and reduce permeability.


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AGGREGATESAre inert materials when

bound together into aconglomerated mass by

Portland cement and water

from concrete, mortar and

plaster. The aggrgates

component is about 75%

of the total mass of

concrete.

FINE

AGGREGATES

COURSE

AGGREGATES


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Limestone or calcium bearing materials

COURSE AGGREGATES

Basalts, granite and related igneous rocks

Sandstone or quartzites

Rock such as opal and chert composed mainly of amorphous silicondioxide


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It shall easily fit into the forms and in between reinforcing bars.

CONDITIONS FOR MAXIMUM SIZE

OF COURSE AGGREGATES

It should not be larger than 1/5 of the narrowest dimension of the

forms or 1/3 of the depth of the slab nor of the minimum distance

between the reinforcing bars.


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Is generally the product of natural disintegration of silica-bearing or

calcium bearing rock.

FINE AGGREGATES

Fine aggregate or sand are those that passes through no. 4 sieve and

predominantly retained by a no. 200 sieve. It is also manufactured

from large pieces of aggregate by crushing grinding or rolling.


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BLDG. TECH III CONCRETE AND STEEL

GROUP 1 PRESENTATIONPART 2


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CONCRETEIs an artificial stone as a result of

mixing cement, fine aggregate and

water. The conglomeration of these

materials producing a solid mass is

called Plain concrete. Concrete inwhich reinforcement is embedded

in a manner that the two materials

act together in resisting forces is

called Reinforcement Concrete.


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CONCRETE is said to be workable in the following conditions:

WORKABILITY OF CONCRETE

Property proportioned for transport and placed without segregation.

Aggregates uniformly distributed.

Easily molded into desired shapes and completely fill the space it is to

occupy.

Easily finished.


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WORKABILITY OF CONCRETE

CONSISTENCY. Degree of wetness or slump of the concretemixture. It varies directly with the amt of water in mixture.

PLASTICITY. Is the ease with which fresh concrete can bemolded or deformed without segregation.

MOBILITY. Is the capacity of concrete to move or flow,particularly during vibration.


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STRENGTH OF CONCRETE

WATER TIGHTNESS

ABRASION RESISTANCE

DURABILITY.


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The durability of concrete is its ability to resist

forces of deterioration such as:

Freezing and thawing of water saturated concrete

Expansion caused by the reaction between reactive

aggregates and alkali in cement.

Reaction between soil and water sulfate and the hydrated

Portland Cement.

Expansion and shrinkage caused by wetting and drying.


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CHEMICAL RESISTANCE

Concrete could be protected by application of any of thefollowing:

Composition and fineness of cement

Cement water ratio of the paste

Temperature

Manner of curing

The time of curing

Presence of entrained air.


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TYPES OF CONCRETEaccording to weight

LIGHT WEIGHT CONCRETE

MEDIUM STONE CONCRETE

HEAVY WEIGHT CONCRETE


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LIGHT WEIGHT CONCRETE. is classified into three:

Low Density Concrete. Is used for insulation purposes.Its unit weight would rarely exceed 50 pounds per cubic foot or

800 kgs. Per cubic meter.

Moderate Strength Concrete. Has a unit weight of 360to 960 kg. per cubic meter with a compressive strength of 70 to

176 per square centimeter commonly used to fill light gauge

steel floor panels.

Structural Concrete. Has similarity with moderatestrength. It weighs 90 120 pounds per cubic foot. Used in

buildings, roads, bridges, etc.


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MEDIUM STONE CONCRETE. is an structural concrete,weighs 2,325 to 2435 kg. per cubic meter.

Heavy Rock Aggregates. Weighs 3200kg per cubicmeter.

HEAVY WEIGHT CONCRETE. is used as shield againstgamma rays reactor. It contains cement , heavy iron ores, crushed

rock, steel scraps, punching or shot as an aggregate.

Iron Punching. Added to high density ores


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CONCRETE PROPORTIONING

CONCRETE PROPORTIONING provides balance between

the requirements of:

ECONOMY.

WORKABILITY.

STRENGTH.

APPEARANCE.

DURABILITY.


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CLASS OF

MIXTURE

CEMENT

40 KG.

SAND GRAVEL

CUBIC

FT.

CUBIC

M.

CUBI

C FT.

CUBIC

M.

AA 1 1 0.043 3 0.085

A 1 2.0 0.057 4 0.113

B 1 2 0.071 5 0.142

C 1 3.0 0.085 6 0.170


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COMMENTS

Water cement ratio is best determined by the trial bathc method during the

actual mixing operation to establish the right amount of water.

Mixture should be in a workable state. Neither be too dry or too wet.

Established water cement ratio must be adjusted whenever necessary. In example,

during changes in weather conditions.

All conveying devices intended for delivering concrete, should be cleaned, free

from rainwater before use to avoid additional water to ready mixed concrete.


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CONCRETE TESTING

SLUMP

TEST.


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SLUMP TEST PROCEDURE


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TYPES OF CONSTRUCTIONMAXIMUM

CM.

MINIMUM

CM.

Reinforced foundation wall and footing 13 5

Plain footing, caissons and sub structure walls10 2.5

Slab, beam and reinforced walls 15 7.5

Building columns 15 7.5

Pavement 7 5

Heavy mass construction 7 2.5


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CONCRETE TESTING

COMPRESSION

TEST.


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COMPRESSION TEST PROCEDURE

1. For course aggregate not more than 5 cm diameter, prepare a cylindricalspecimen 15 cm diameter and 30 cm long.

2. For course aggregat more than 5cm prepare a cylindrical specimen with a

diameter 3 times the maximum size of the aggregate and a height double its

diameter,

3. The mold should be made of metal placed on a plane surface preferably 6-

12 mm plate

4. Place the fresh concrete inside the mold in 3 separate equal layers rodded

separately with 16mm rod 25 strokes

5. Level surface with trowel and cover with a glass or plane steel.

6. After 4 hrs, cover the specimen with a thin layer of cement paste and cover

again with plane metal or glass


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COMPRESSION TEST PROCEDURE

7. After 24 hrs, start curing in a moist atmosphere at 21 degrees centigrade

8. Test should be done at 7 28 days period

9. Be sure that both ends of the specimen are perfectly levelled.

10. Specimen is placed under a testing machine and a compresive load is

applied until the specimen fails. The load that causes the specimen to fail is

recorded.

11. The recorded load divided by the cross sectional area of the cylindergives the ultimate compressive unit of stress of the sample.


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MIXING CONCRETE

CENTRALIZED READY MIXED PLANT

MOBILE MIXING. Cement

and aggregates are loaded in

amobile mixer at the batching

plant and then mixing

operation is done on its way to

the job site.


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MIXING CONCRETE


STATIONARY MIXING.

The concrete is mixed before

it is loaded inside the truck

mixer where the paste is only

agitated. Also refers to mixers

installed on the site.


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MIXING CONCRETE


HAND MIXING. A good

concrete can be produced

also by hand mixing,

provided that the fine andcoarse aggregates are clean

and well graded. If about one

half as much water as cement

by weight is used and mixing

is done properly, the resultwill be a good quality

concrete.


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DEPOSITING CONCRETE

Depositing of concrete should be done as early as practicable in its finalplace to avoid segregation of particles due to re handling or flowing into

spaces between reinforcing bars.

Concrete that has partially hardened or contaminated should not be

deposited in the structure.

Concrete should all be thoroughly worked around the reinforcement,

embedded fixtures and into the corners of the form.

Concrete should be discharged from the truck within 1 hours after thewater is poured to the batch.


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SEGREGATION OF PARTICLES

Means the separation of sand and stone from the paste. It is caused by:

Transferring of the concrete from the mixer to the forms.

Dropping of the mixture from a high elevation

Improper tamping and spading

Use of long chutes

Excess amount of tamping, vibrating or pudding in the forms

Lateral movement such as the flow


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SEGREGATION OF PARTICLES

FACTORS THAT REGULATE THE STENGTH OF CONCRETE

Correct proportions of ingredients

Suitability or quality of the materials

Proper methods of mixing

Proper placement inside form

Protection of concrete during period of curing


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CURING CONCRETE

METHODS APPLIED IN CURING SURFACE CONCRETE

Covering the surface with burlap continuously wet for the period of

curing as specified

Covering the slab with a layer of wet sand or saw dusts one inch thick

Wet straw or hay on top of slab continuously watered

Continuous sprinkling of water on the slab surface

Avoid early removal of the forms. This will permit undue evaporation

of moisture in the concrete.

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