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BUILDING TECHNOLOGY I

1. CEMENTING

MATERIALS1.01 Lime1.02 Gypsum1.03 Cement

2. STORAGE OFCEMENT

3. CONCRETE3.01 Definition3.02 Qualities

of Good

Concrete3.03 Materials of

Concrete

3.04 Slump Test3.05 Proportioning3.06 Mixing3.07 Transporting

and Placing3.08 Shrinkage3.09 Curing3.10 Admixtures3.11 Forms

4. PROCESSEDCONCRETE4.01 Types of

Processed

Concrete4.02 Aggregates for

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1.01 LIME

One of the oldest manufactured building materials usedas a mortar and plaster by all the early civilizations:

1. CEMENTING MATERIALS

Egyptians used lime plaster before 2600 B.C.

Greeks used it extensively for mortars and plasters

Romans developed a mixture of lime putty and volcanic

ash for the first real cement.

Manufactured by the

calcination of limestone

(carbonates of calcium

and magnesium).

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Before quicklime can beused, it must first be mixed

with water in the process

called slakingor hydration.

The lime has now becomecalcium hydroxide

(Ca(OH)2), known as slaked

limeor hydrated lime.

The carbonates decomposeinto carbon dioxide, which is

expelled, and calcium oxide

(CaO) called quicklime.

Quicklime

1.01 LIME

1. CEMENTING MATERIALS1. CEMENTINGMATERIALS1.01 Lime1.02 Gypsum1.03 Cement

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Hydrated limemixed with water to make lime putty, is usedas an ingredient of hard-finish coat for two-and three-coat

Portland cement plasters. It is also used for mixing with

cement mortar or concrete to:

increase its workability

decrease its permeabilityto water

reduce cracking due to

shrinkage

A type of lime which will

set under water ishydraulic lime, used only

where slow underwater

setting is required.

1.01 LIME


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Gypsum, like lime, was usedas a plaster by the Egyptians,

Greeks and Romans.

Plaster from the Greek

word for both the raw

material and calcined

product. In architectural

terminology the words

Plaster and gypsum are

often used interchangeably.

1.02 GYPSUM

Gypsum rock is ground fine and heated (calcined) to between

325 F. to 340 F. when it loses about three-fourths of itscombined water.

The remaining product is Plaster of Parisif pure gypsum is

used, or hard wall plasterif 39.5 % impurities are present or

added to retard the set and improve the setting qualities. Hard

wall plaster is harder than lime plaster, sets more quickly andthoroughly.


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Gypsum plaster is renderedmore plastic by the addition of

hydrated lime.

Fiber or hair is also sometimes

added for greater cohesiveness.

The fiber may be hemp, sisal or

jute; the hair is generally

cleaned goat or cattle hair.

1.02 GYPSUM


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First developed by the Romans by mixing slaked lime withpozzolana(volcanic ash) which hardened under water.

With the fall of the Roman Empire the art of cement-making

was lost and for several centuries.

1.03 CEMENT

In 1756, Smeaton, an Englishman,

rediscovered hydraulic cement but it

was not until 1824 that Aspdin, an

English bricklayer and mason,

invented and patented Portland

cement.

Today, the word cement generallyrefers to Portland cement which is the

principal type of cement in use.


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Portland cement is obtainedby finely pulverizing clinker

produced by calcining a

proportioned mixture of

argillaceous (silica, alumina)

and calcareous (lime)

materials with iron oxide andsmall amounts of other

ingredients.

Types of Portland cement:

slow-setting cement

quick-setting high early

strength cement

sulfate-resisting cement for

applications where alkaline

water and soils occur

white cement (or stainless

cement which is free of ironimpurities).

1.03 CEMENT


Portland cement is sold inbags of 40 kilos total weight.

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Cement should be protected at

the building site from injury

through contact with dampness.

They should be stored in shed

with a wood floor raised about

300mm (12) from the

ground.

2. STORAGE OF CEMENT

Cement is soft and silky to the touch. If it has lumps do not readily

break, the cement has already absorbed a damaging amount of

moisture.

Cement should be used as soon as possible after delivery.

Piles should be limited to twelve sacks in height.

Warehouse set- when the cement is stored in high piles for long

periods, there is a tendency for the lower layers to harden caused

by the pressure above.

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Concrete is:

a proportioned mixture of cement, aggregate and water.

a plastic mass which can be cast, molded or formedinto

predetermined size or shape

upon hydration, becomes stone-like in strength, hardnessand durability. The hardening of concrete is called setting.

when mixed with water and a fine aggregate of less than

6mm ()is known as mortar, stucco or cement plaster.

when mixed with water, fine aggregate and a large

aggregate of more than 6mm () in size producesconcrete.

when strengthened by embedded steel, is called

reinforced concrete.

when without reinforcement, is called plain or mass

concrete.

3.01 DEFINITION

3. CONCRETE1. CEMENTINGMATERIALS1.01 Lime1.02 Gypsum1.03 Cement

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Concreteshould be:

Strong

Durable

of uniform quality, and

thoroughlysound.

These are obtained through:

careful selection of materials

correct proportioning

thorough mixing

careful transporting and placing proper curing or protection of the concrete after it is

placed

3.02 QUALITIES OF GOOD CONCRETE


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a. Cement

soundness, or constancy of volume

time of setting

fineness

tensile strength

Each bag of cement is equivalent to approximately

1 cu. ft. and weighs 94 lbs.

in reinforced-concrete construction should be high-

grade Portland cement conforming to the Standard

Specifications and Test for Portland Cement of the

American Society for Testing Materials (ASTM).

The kind of tests usually made are:

3.03 MATERIALS OF CONCRETE


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b. Aggregatesare:

Fine aggregates

(aggregates smaller than

6mm () in size) consist of

sand, stone screenings or

other inert materials ofsimilar characteristics.

Specs: 80 to 95% shall pass

a No. 4 wire cloth sieve and

not more than 30% nor less

than 10% shall pass a No.50 sieve.

inert mineral fillers used with cement and water in making

concrete, should be particles that are durable strong,

clean, hard and uncoated, and which are free from

injurious amount of dusts, lumps, soft and flaky particles,

shale, alkali, organic matter loam or other deleterious

substances.



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Coarse aggregate(aggregate larger than in size)

consists of crushed stones, gravel or other inert

materials of similar characteristics.

Coarse aggregates should be well graded in size to a

size which will readily pass between all reinforcing bars

and between reinforcement and forms but not exceed

25mm (1) in size for reinforced beams, floor slabs, & thin

walls.

They may range up to 50mm (2) for less highly

reinforced parts of the structures such as footings, thickwalls, and massive work.

b. Aggregates



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Special aggregates, such as cinders, blast furnace

slag, expanded shale or clay, perlite, vermiculite, and

sawdust, may produce:

- lightweight, nailable concrete

- thermal insulating concrete.

b. Aggregates



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c. Water - should be free from oil, acid, alkali, vegetable matter,

or other deleterious substances

- should be reasonably clear and clean.

- The use of sea or brackish water is not allowed.

- Water combines with the cement to form a paste

which coats and surrounds the inert particles of

aggregates.

- Upon hardening, it binds the entire mass together.

- The strength of the mixture therefore depends directly

upon the strength of the paste. If there be an excess

of water the paste becomes thin and weak and its

holding power is reduced.



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- The water-cement ratiois the amount of water used

per bag of cement.

- This usually varies from 5 to 7 gallons, with 6.5

gallons as average for ordinary job conditions. The

lesswater used in mixing, the betterthe quality ofconcrete.

- The ideal mix is one that is plastic and workable. It

should not be too dry that it becomes too difficult to

place in the forms, nor too wet that separation of the

ingredients result.

WATERCEMENT RATIO

Assumed 28-day

Compressive strength

(lbs. per sq. inch)

Maximum water-cement ratio

U.S. gallons of water per sack

Cement of 94 lbs.

Pounds of water

per 100 lbs. of

cement

2,000

2,500

3,0003,750

7.00

6.50

5.755.00

62.0

57.5

51.044.5

c. Water



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- used for measuring the consistency of a concrete mix.- Consistency may be defined as the state of fluidity of

the mix, and it includes the entire range of fluidity from

the wettest to the dries possible mixtures.

In this test the tendency of a mix to slump, or reduce its

height due to gravity action, is measured. The apparatus

consist of metal cone, the bottom opening being 200mm (8)

in diameter, the top opening being 100mm (4), and the

height exactly 300mm (12).

3.04 SLUMP TEST


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In making the test, the slump tester isplaced on a flat, smooth surface and is

filled with newly mixed concrete from

mixer. In filling the mold with concrete,

the latter is tamped in with a 12mm ()

rod pointed at one end and the top of

the concrete is smoothed off exactlylevel. The mold is then slowly raised

vertically and the height deducted from

the original height of 300mm (12)

represents the slump.

SLUMPNo

slumpCollapsed

slump

TOO WET SUITABLE TOO DRYBucket

3.04 SLUMP TEST


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A harsh mix is efficient for slabs, pavements, or massconcrete where the lowest possible water-cement ratio is

desirable.

The following table gives the permissible slump for various

types of concrete in relation to their uses:

CONSISTENCY (SLUMP)

Maximum Minimum

Reinforced foundation walls and

footings

125mm (5) 50mm (2)

Plain footings, caissons, andsubstructure walls

100mm (4) 25mm (1)

Slabs, beams, thin reinforced walls &

building columns

150mm (6) 75mm (3)

Pavements and floor laid on ground 75mm (3) 25mm (1)

Heavy mass construction 75mm (3) 25mm (1)

3.04 SLUMP TEST


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Briefly stated, the principles of proper proportioning are asfollows:

3.05 PROPORTIONING OF CONCRETE

3. CONCRETE

a. Use good quality materials: Portland cement, water,

and aggregate.

b. Determine the strengthof the concreteusing the

water-cement ratio. (The strength increases as thewater-cement ratio decreases).

c. Determine the consistency of the mixusing the

slump test using as dry a mix as practicable.

d. Add correct proportions of aggregatesto thecement and water as will give a mix of the desired

consistency.

e. Make a mix thats workable, not harsh.

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The strengthof a workable concrete mix depends upon thewater-cement ratio.

The economyof the mix depends upon the proper

proportioning of the fine and coarse aggregates.

There are several methods of proportioning concrete:

a. Proportioning by arbitrary proportionsb. Proportioning by the water-ratio and slump test

c. Proportioning by water-ratio, slump and fineness

modulus

Proportioning concrete by the arbitrary selection of the

proportions is the oldest, the most commonly used, the mostconvenient and the least scientific method.

In this method, the aggregates are measured by loose

volume, that is, its volume as it is thrown into a measuring

box. One sack of cement is taken as 1 cu. ft. Enough water

is used to give the desired consistency.



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a. Proportioning by arbitrary proportionsProportioning concrete by

the arbitrary selection of

the proportions is the

oldest, the most

commonly used, the most

convenient and the leastscientific method.

In this method, the

aggregates are measured

by loose volume, that is,

its volume as it is throwninto a measuring box.

One sack of cement is taken as 1 cu. ft.

Enough water is used to give the desired consistency.

1

foot

1 foot

1 foot



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Common mixes expressed in proportions by volumes ofcement to fine aggregate to coarse aggregate are as follows:

CONCRETE PROPORTIONS

Class AA 1 : 1.5 : 3 For concrete under water, retaining walls

Class A 1 : 2 : 4 For suspended slabs, beams, columns, arches,

stairs, walls of 100mm (4) thickness

Class B 1 : 2.5 : 5 For walls thicker than 100mm (4), footings,steps, reinforced concrete slabs on fill.

Class C 1 : 3 : 6 For concrete plant boxes, and any non-criticalconcrete structures.

Class D 1 : 3.5 : 7 For mass concrete works.

The proportion is to be read:

Class A : 1 part cement is to2 parts sand is to4 parts gravel.

Each part is equivalent to one cubic footwhich is the measure of

the box constructed to be 1 foot (12 inches) on each of the three

sides.

Each bag of cement is equivalent to approximately one cubic foot.



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b. Proportioning by the water-ratio and slump testThere are two steps to be observed:

- Select the amount of water to be added to the cement

to give the desired strength (see Table)

- Add just enough mixed aggregate to the water and

cement to give a concrete mix the desired consistency.

It is customary to specify

- the cement in sacks

- the water in gallons per sack of cement and

- the mixed aggregate in cu. ft. per sack of cement.

Proportions of cement to fine aggregate to coarse

aggregate may be given if desired.



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c. Proportioning by water-ratio, slump and finenessmodulus

This method is the same as the second except that the

proportions of the fine and coarse aggregate are

determined by the fineness modulus method.

For economy, proportion the fine coarse aggregates so

that the largest quantity of mixed aggregate may be used

with a given amount of cement and water to produce a mix

of the desired consistency of slump.

Comparatively, the coarse aggregate has a lesser total

surface to be covered with cement paste and, therefore, is

more economical.

However, there must be enough fine aggregate present to

fill the voids in the coarse aggregate, or extra cement

paste will be needed for this purpose. A well-graded

aggregate contains all sizes of fine and coarse particles in

such proportions that the voids in the combined aggregatewill be a minimum.



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Reinforced-concrete work should be mixed by machine Machine-mixed concrete is usually or more uniform

quality than that mixed by hand and is generally less

expensive when in large volume.

The strength of concrete is very largely dependent upon

the thoroughness of mixing.

3.06 MIXING OF CONCRETE


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a. MACHINE MIXINGIn machine-mixing, the mixing of each batch should

continue not less than one minute after all the materials

are in the mixer and whenever practicable, the length of

the mixing time should be increased to 1.5 or 2 minutes.

The entire contents of the drum should be discharged

before recharging the mixer. The mixer should becleaned at frequent intervals while in use.

Concrete mixers may be divided into two general classes:

Batch mixers -

into which sufficient

materials are placed at onetime to make a convenient

size batch of concrete, the

whole amount being

discharged in one mass

after it is mixed.



2. STORAGE OFCEMENT3. CONCRETE

3.01 Definition3.02 Qualities

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Continuous mixers -

into which the materials

are fed constantly and

from which the concrete

is discharged in a

steady stream.

Concrete mixers may also be

classified as:

- drum mixers

- trough mixers- gravity mixers, and

- pneumatic mixers.

The drum mixers are the most

common type.

a. MACHINE MIXING





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b. HAND MIXING- hand-mixing must be

done on a water-tight

platform.

- cement and fine

aggregate shall firstbe mixed dry until the

whole is a uniform

color.

- water and coarse

aggregate shall then

be added and the

entire mass turned at

least three times, or

until a homogeneous

mixture of the

required consistencyis obtained.





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- since initial set of concrete takes place 1 to 3 hours

after mixing, a batch may be used anytime before

initial set takes place, provided that the mix is plastic.

- Regagingor retemperingof concrete that has been

allowed to stand more than hour is not to bepermitted.

b. HAND MIXING





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The delivery of the

concrete from the mixerto the forms should be

fairly continuous and

uninterrupted.

The time of

transportation shouldnot exceed 30 minutes.

3.07 TRANSPORTING AND PLACING OF CONCRETE

3. CONCRETE

Fresh concrete should be transported from themixer as rapidly as practicable by methods that will

permit the placing of the concrete in the forms

before initial set occurs and without loss or

separation of materials.

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The concrete may be transported bymeans of barrows, buggies, buckets,

cableways, hoists, chutes, belts and

pipes.

When chutes are used, the slope

should not be more than 1 vertical to 2

horizontal or less than 1 vertical to 3

horizontal. The delivery end of the

chutes shall be as close as possible to

the point of deposit.





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Before placing concrete, theforms shall be cleaned and

inspected, surfaces wetted or

oiled, and reinforcement

properly secured.

Concrete should be deposited in

approximately horizontal layers

in wall, column and footing

forms. They should not be piled

up in the forms which may result

in the separation of the cement

mortar from the coarse

aggregate.

Concrete should never be

allowed to drop freely over 5 ft.

for unexposed work and over 3

ft. for exposed work.





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Shrinkage of concrete due to hardening and contractionfrom temperature changes, causes cracks the size of

which depends on the extent of the mass. They cannot

be counteracted successfully but they can be minimized

by placing reinforcement so that large cracks can be

broken up to some extent to smaller ones.

In long continuous length of concrete, it is better to place

shrinkage or contraction joints. Shrinkage cracks are

likely to occur at joints where fresh concrete is joined to

concrete which has already set, and hence in placing the

concrete, construction joints should be made on

horizontal and vertical lines.

3.08 SHRINKAGE OF CONCRETE & TEMPERATURE CHANGES




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Concrete must be allowed to cure or hardenafter it isplaced.

Hardening is a rather slow process in which the cement

and water unite to form compounds that give strength and

durability to the concrete. It continues as long as the

temperatures are favorable and moisture is present.

Three main factors that affect hardening are:

3.09 CURING OF CONCRETE

3. CONCRETE

- age or time

- temperature,and

- moisture.

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In order that the hardening may proceed favorably, the freshconcrete, for about 7 days after placing, should be protected

from, excessive vibration, loads, extreme heat or cold, too

rapid drying, and contact with impurities which may interfere

with the chemical action.

The strength of the concrete increases with age when thecuring conditions remains favorable.





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The increase in strength is rapid during the earlyages and continues more slowly as time goes on.

The compressive strength reaches about 60% of

its own maximum value at an age of 28 days and

about 80% at an age of 3 months.





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Curing consists primarily in keeping the concrete from dryingout too rapidly. This may be done by:

a. Covering the concrete. Floors shall be covered with

paper sacking wetted down at the edges or with burlap,

sand or earth that is kept moist, after the concrete is

hard enough to walk on.

b. Removal of forms at prescribed time. Forms shall not

be removed until after the time specified.

c. Sprinkling with water. Beams, columns and walls are

sprinkled or sprayed with water as soon as the forms are

removed.

d. Using curing compounds(see ADMIXTURES).





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Parts of Structure CURING PERIOD or TIME REQUIREDFOR THE REMOVAL OF FORMSFOOTINGS a. Massive footings

b. Cantilever footingsc. Slab footings

a. 1 day (24 hours)b. 5 days (120 hours)c. 5 days (120 hours)

WALLS

ANDPLASTERSa. Massive walls, 30

cms. thick or more

b. Thin walls less

than 30 cms. Thick

c. Cantilever walls,

buttresses,

counter forts,diaphragms.

a. Up to 2 M. high: 1 day (24 hours). Add 1 day

(24 hours) for every additional meter or

fraction thereof.

b. Up to 2 M. high: 2 days (48 hours. Add 1-1/2

days (36 hours) for every additional meter or

fraction thereof

c. Without loads, same as (b).

COLUMNS a. Ratio of height toleast diameter up

to 4

b. Ratio of height to

least diameterfrom 4 to 15.

a. 2 days (48 hours)

b. Add to the above number 1 day (24 hours)

for every additional meter or height or

fraction there of but not more than 28 days(672 hours).





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SLABS a. 3 to 7 ft. spans

b. Over 7 ft. span

a. 3 ft. span, 5 days (120 hours). Add day (12

hours) for every additional 1 ft. span or

fraction thereof.

b. 7 ft. span, 7 days (168 hours). Add 1 day (24

hours) for every additional 1 ft. span or

fraction thereof but not more than 28 days

(672 hours).BEAMS

AND

GIRDERSa. Sides

b. Bottomsa. 3 days

b. Up to 14 ft., 14 days (336 hours). Add 1 day

for every 1 ft. additional span or fraction

thereof but not more than 28 days (672

hours).ARCHES a. Spandrel walls

b. Spandrel archesc. Main arches

a. 7 days (168 hours).b. 14 days (336 hours)c. 21 days (504 hours)

BALUSTRADES

, COPINGS,ETC. a. Steel & side forms a. 1 day (24 hours)R.C. PILES and

R.C. POSTS a. Sides.b. Bottom a. 3 days (72 hours)b. 14 days (336 hours)

Parts of Structure CURING PERIOD or TIME REQUIREDFOR THE REMOVAL OF FORMS





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Substances added tocements, mortars, and

concrete for the purpose of improving or imparting

particular properties, such as:

To improve workability of concrete, e.g. hydrated lime

To improve durability by entertainment of air

To accelerate setting or hardening (accelerators) e.g.

calcium chloride To retard setting (retarders).

To improve wear resistance

To impart water-repellant or water-proofing qualities e.g.

hydrated lime, KAOLINE, CELITE

To impart water-repellant or waterproofing qualities, e.g.,

hydrated lime, waterproofing compounds, KAOLINE,CELITE.

To impart color, MINERAL OXIDES, COLORCON,

METALICHROME.

3.10 ADMIXTURES




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Admixtures may be grouped into three categories: those for mixing into concrete

those for mixing into mortar

those for surface application or finish.

Admixtures come in powder, paste, andliquid form, and

are usually patented and sold under trademark names.

3.10 ADMIXTURES




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a. Accelerators- to speed up setting time, to develop

earlier strength, and to reduce length of time for

protection. Principal ingredients are calcium chloride.

Maximum amount added is 2 lbs. per bag of cement.

Disadvantages: they increase the expansion andcontraction of concrete, reduce resistance to sulfate

attack, and increases efflorescence and corrosion of

high tension steels.

b. Retarders - to slow down the hydration of the cement

during very hot weather. Principal ingredients includezinc oxide, calcium lignosulfonate, derivatives of adipic

acid.

Disadvantages: may cause some loss of early strength

and will therefore require careful control and more

frequent slump tests, also reduces the expansion and

contraction of concrete.

Concrete admixtures include:

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c. Air-entraining agents- introduce minute air bubbles togreatly increase the resistance of concrete to freezing

and thawing, increase plasticity and reduce bleeding.

Addition of air-entraining admixtures is usually in the

proportion of 3 to 6% of the volume of concrete. They

are manufactured from such ingredients as rosin, beef

tallow, stereates, foaming agents (soap).

Disadvantages: These require careful control and more

frequent slump tests. They may also cause some loss of

strength.

d. Inert, finely divided powders such as powdered

glass , silica sand, stone dust, hydrated lime- areadded to improve workability, used as per

manufacturers directions. Hydrated lime is usually in the

proportion of 10 to 15% of the cement by volume.

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e. Waterproofing (permeability-reducing)compounds- reduce the capillary attraction of the voids in the

concrete or mortar, but while it may decrease water

absorption of the concrete or mortar, it does not render

concrete waterproof. They are manufactured from

stearic acid or its compounds, mainly calcium

steareate, and include asphalt emulsions. They areintroduced usually in the amounts of 0.1 to 4.0% of the

weight of cement.

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f. Colored pigmentsare mainly to used to give color toconcrete floors. There are two types:

3.10 ADMIXTURES

3. CONCRETE

Dry-cast, broadcast or dust-on, for surface

coloring. They are dusted on, usually in two coats,

after all surface water has disappeared. The surface

is then finished with a steel trowel .

Integral colors, for body coloring. Integral color

pigments are incorporated in the mortar topping.

They are mixed dry with the cement and aggregate

before water is added. Amount of color pigment

required is not more than 10% of the cement by

weight, generally 3 to 6 lbs. per bag of cement .

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Admixtures for mixing into mortar include: Accelerators

plasticizing agents(correctly called water-reducing

agents) to lower water cement ratio and make the mix

more workable

waterproofing agents, and

color pigments

Surface application finishes for concrete consist of:

hardeners

color pigments

special aggregates

sealers

abrasive materials

waterproofing agents, and

fillers and patchers.

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3.11 FORMS

Lumber used in form

construction should only

be partially seasoned.

Kiln-dried lumber has a

tendency to swell when

soaked by the concrete,

and this swelling causes

bulging and distortion of

the forms.

a. LUMBER FORMS

Green lumber, on the other hand, dries out and shrinks if

allowed to stand too long before the concrete is placed.

This tendency of green lumber to check and warp may,

however, be prevented to some extent by keeping the

boards thoroughly saturated with water.


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When using natural,

well seasoned lumber,

care should be taken

not to drive the work up

too close, since formsshould always be left in

a position to experience

some slight swelling

without any undesirable

results.

a. LUMBER FORMS

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Sheathing lumberdressed at least one sideand

both edges evenare used where the removal and

cleaning of the forms are necessary for re-use .

Sheathing lumber dressed on all four sidesshall

be used in face work, where smooth and true surface

is important.

Tongue-and-groovelumberwill achieve tight joints

between boards in floor and wall panel construction.

Simply dressing the lumber true to edgeformsquare of butt joints in the forms for columns, beams,

and girders.

Sizes of lumber frequently used : 2-inch thick for columns, beams and girder bottoms

1-inch thick for floor panels and beam and girder sides

2x4s for struts, posts, shores, and uprights 1 or 2-inch thick for cleats

a. LUMBER FORMS

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a. LUMBER FORMS

3. CONCRETE

Use nails sparingly in

the construction of

forms because

unnecessary nailing

not only adds to thelabor of wrecking but

also renders the

lumber unfit for

continued use. Where

nails must be used,

leave the headprotruding so that

they may be

withdrawn without

injury to the lumber.

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All forms for concrete require a coating of some lubricant

to prevent concrete from adhering to the wood and thus

make a rough, unpleasant appearance. Crude oil and

petroline preserve the forms against damage by

alternate wetting and drying. The forms shouldpreferably be oiled before they are set in place. Oil

should not be used, however, on forms against surfaces

which are to be plastered, as oil prevents adhesion of

the plaster. In such cases, wetting with water will be

sufficient.

a. LUMBER FORMS

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The inside of forms which have been used once and

are to be used again shall be coated an approved

soap or other approved material, or thoroughly wetted

before concreting. No application of soap or other

material should be made to forms after thereinforcements are in place.

The forms should be durable and rigid, and should be

well braced so that bulging or twisting cannot occur.

The joints should be made tight enough to prevent

leakage of the mortar.

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b. PLYWOOD FORMSWorks best where a smooth surface is required. The

plywood should be waterproof, Grade A and at least

12mm () thick.

c. STEEL FORMS

Steel forms may be in the form of pans for concrete joist

construction or steel decking or corrugated steel for

concrete slabs and slab-and-joist construction. .

d. PLASTIC FORMS

Polystyrene forms are nowavailable for concrete work.

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4.01 TYPES OF PROCESSED CONCRETE

4. PROCESSED CONCRETE

a. AEROCRETEThis is a lightweight, expanded structural concrete

produced by adding a small amount of metallic

aluminum powder to the mixture of Portland cement

and sand of cinders.

On the addition of water, a gas is generated whichexpands the wet mix and forms small air cells

throughout the material.

It is used for structural floor and roof slabs, partition

blocks for sound proofing, wall insulation, in rooms of

refrigerator plants, lightweight fill on top of structural

floor and roof slabs.

In addition to its light weight, it has excellent fire-

resistive qualities.

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b. GUNITE

This is the mixture of sand and cement deposited under

high pneumatic pressure with a machine manufactured

under the trade name CEMENT GUN, to which the

required supply of water is added just before the dry

constituents emerge from nozzle.

GUNITE is used for encasing structural steel, when

reinforced, for floor and roof slabs and curtain walls. Ideal

for swimming pool construction.


4. PROCESSED CONCRETE1. CEMENTINGMATERIALS1.01 Lime1.02 Gypsum1.03 Cement

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c. PORETE

A Portland cement concrete to which a chemical foam

is added to generate gases in the process of

deposition, resulting in light weight precast or shop-

made unit in both hollow and solid forms. It is

manufactured in solid slabs for short spans roofs and

siding of industrial buildings.

d. HAYDITE

This is processed concrete added with lightweight

aggregate .



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4.02 AGGREGATES FOR LIGHTWEIGHT CONCRETE

Lightweight aggregates have the following advantages:

Reduction of dead loads saves structural steel, reduces

bearing on foundation and cuts cost of concrete forms

High insulating value is provided by numerous dead air

spaces . Rough texture of surfaces have good acoustical properties

.

Lightweight allows easier handling of precast slabs and

blocks

Lightweight plaster has less tendency to crack and its heat

resistance makes it a good material for fireproofing

structural steel


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The major disadvantages of lightweight aggregatesare a result paradoxically of the physical qualities

which make them weight saving and good insulators

: Porosity requires changes in the usual formulas for

water and slump, and closer supervision of mixing.

Very light aggregates tend to float out of the mortarand some coarse aggregate concrete mixtures

require the addition of a fine aggregate like sand to

prevent harsh working and serious bleeding.

As aggregates become lighter they become

structurally weaker so the strength of the matrix

must be modified by adding more cement. More

cement is needed, also to wet the greater

aggregate surface area, due to the irregularity of the

particles .



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The cost of raw aggregates is higher than for gravel,rock, and sand because of small production facilities

and the additional processing that is sometimes

necessary .

Concrete using lightweight aggregate should not weigh

more than 75% of ordinary concrete. Since the

aggregates compromise about 50 percent of the usual

mixes, its weight should not be more than 50 percent of

that of rock or gravel aggregates for the same volume.

Grade rock, gravel aggregates weigh a little less than

100 lbs. per cu. ft. thus a good lightweight aggregate

should weigh less than 50 lbs. per cubic foot.



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Lightweight aggregates can be divided into four generalclassifications :

Pumice, weighing from 25

to 60 lbs.per cu. ft. is well

qualified as a lightweightaggregate when dry and

well graded. It is hard to be

handled and mixed without

excessive breakdown.

Undesirable feature,however, is its water

absorption. This can be

mitigated by wetting the

aggregate before it is

mixed with cement .

a. Aggregates of volcanic origin



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Perliteis composed of stable silicates, and is inert

and thus durable for use as a lightweight aggregate

or for insulation. Its disadvantages are its friability,

small particle size, and extreme lightness. The small

particle size requires more cement, while itslightness, from 8 to 16 lbs. per cu. ft. increases the

tendency to float out of the mortar.

a. Aggregates of volcanic origin

Perlite is useful where

maximum strength is not

required, as in precastslabs and blocks and in

floor fill, fireproofing and

plaster .



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Vermiculiteis a micaceous mineral which expands on

application of heat to as much as 30 times its original

volume.

Dried ground ore is subjected to about 1,800 degrees

heat for 4 to 8 seconds, after which it weighs only 6 to

12 lbs. per cubic ft.

It is used as an aggregate in concrete fireproofing

steel, for floor and roof fill, and for acoustic and

fireproof plaster.

b. Micaceous minerals



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Lightweight aggregates from shales and clays

require heating the material in a kiln to a

temperature near its fusion point. The material

softens and coalesces to a sticky mass; escaping

gases are trapped, forming cellular structures andexpanding the volume of the material about 50%.

The crushing and firing operations are varied with

different processes. In some, the material is fired to

a clinker, then crushed and sized; the process is

often reversed with crushing operation first.

Examples of clay, shale aggregates are AIROX,

ROCKLITE, Diatomite, HAYDITE. .

c. Expanded shales and clays



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Expanded Slag or foamed slagsare made by treatingmolten blast furnace slag with controlled quantities of water

or steam. Some slags are expanded are expanded in pits in

the ground; others are made in machines. Close control of

steam is very important because too much granulates the

slag, yielding soft, friable particles; too little gives a heavy

aggregate.

d. By-product Aggregates

Foamed slaghas been used for precast blocks, cast-in-place walls of houses and for panel filling of steel-framed

buildings.

Cinders are composed of the ash components of the coalalong with the various quantities of unburned or partially

burned combustible matter. Cinders containing a minimum

amount of combustible material are satisfactory for use in

concrete but are not particularly weight saving. Lightweight

cinders often have unsound physical and chemical

properties.



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WEIGHT OF AGGREGATE AND CONCRETE BYTYPE OF AGGREGATE

TYPE OF AGGREGATE AggregateWeight per

Cubic Foot

(Lbs.)

Weight per Cubic

Foot of Concrete

Using Aggregate

(Lbs.)GravelSandCrushed StoneCrushed Bank SlagHaydite (Expanded Clay, shale)Foamed SlagCindersPumiceDiatomitePerliteVermiculite

12090-100

10080

40-6040-6040-5030-6028-406-166-10

150150145

110-130100-12090-100110-11560-9055-7040-6525-50



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End of

Div 03 CONCRETE

03 Concrete

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