concrete lecture

BUILDING TECHNOLOGY I

1. CEMENTING

MATERIALS

1.01 Lime 1.02 Gypsum 1.03 Cement

2. STORAGE OF

CEMENT

3. CONCRETE

3.01 Definition 3.02 Qualities

of Good

Concrete 3.03 Materials of

Concrete 3.04 Slump Test 3.05 Proportioning 3.06 Mixing 3.07 Transporting

and Placing 3.08 Shrinkage 3.09 Curing 3.10 Admixtures 3.11 Forms

4. PROCESSED

CONCRETE

4.01 Types of

Processed

Concrete 4.02 Aggregates for

Light-weight

Conc.

1.01 LIME

One of the oldest manufactured building materials used

as 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).

1. CEMENTING

MATERIALS


2. STORAGE OF

CEMENT

3. CONCRETE


of Good




4. PROCESSED

CONCRETE

4.01 Types of

Processed


Light-weight

Conc.

Before quicklime can be

used, it must first be mixed

with water in the process

called slaking or hydration.

The lime has now become

calcium hydroxide

(Ca(OH)2), known as slaked

lime or hydrated lime.

The carbonates decompose

into carbon dioxide, which is

expelled, and calcium oxide

(CaO) called quicklime.

Quicklime

1.01 LIME

1. CEMENTING MATERIALS 1. CEMENTING MATERIALS


2. STORAGE OF

CEMENT

3. CONCRETE


of Good




4. PROCESSED

CONCRETE

4.01 Types of

Processed


Light-weight

Conc.

Hydrated lime mixed with water to make lime putty, is used

as 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 permeability

to water

reduce cracking due to

shrinkage

A type of lime which will

set under water is

hydraulic lime, used only

where slow underwater

setting is required.

1.01 LIME



2. STORAGE OF

CEMENT

3. CONCRETE


of Good




4. PROCESSED

CONCRETE

4.01 Types of

Processed


Light-weight

Conc.

Gypsum, like lime, was used

as a plaster by the Egyptians,

Greeks and Romans.

Plaster

word for both the raw

material and calcined

product. In architectural

terminology the words

Plaster gypsum

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 its

combined water.

The remaining product is Plaster of Paris if pure gypsum is

used, or hard wall plaster if 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 and

thoroughly.



2. STORAGE OF

CEMENT

3. CONCRETE


of Good




4. PROCESSED

CONCRETE

4.01 Types of

Processed


Light-weight

Conc.

Gypsum plaster is rendered

more 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



2. STORAGE OF

CEMENT

3. CONCRETE


of Good




4. PROCESSED

CONCRETE

4.01 Types of

Processed


Light-weight

Conc.

First developed by the Romans by mixing slaked lime with

pozzolana (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.

refers to Portland cement which is the

principal type of cement in use.



2. STORAGE OF

CEMENT

3. CONCRETE


of Good




4. PROCESSED

CONCRETE

4.01 Types of

Processed


Light-weight

Conc.

Portland cement is obtained

by finely pulverizing clinker

produced by calcining a

proportioned mixture of

argillaceous (silica, alumina)

and calcareous (lime)

materials with iron oxide and

small 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 iron

impurities).

1.03 CEMENT

1. CEMENTING MATERIALS

Portland cement is sold in

bags of 40 kilos total weight.

1. CEMENTING

MATERIALS


2. STORAGE OF

CEMENT

3. CONCRETE


of Good




4. PROCESSED

CONCRETE

4.01 Types of

Processed


Light-weight

Conc.

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

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.

1. CEMENTING

MATERIALS


2. STORAGE OF

CEMENT

3. CONCRETE


of Good




4. PROCESSED

CONCRETE

4.01 Types of

Processed


Light-weight

Conc.

Concrete is:

a proportioned mixture of cement, aggregate and water.

a plastic mass which can be cast, molded or formed into

predetermined size or shape

upon hydration, becomes stone-like in strength, hardness

and 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 produces

concrete.

when strengthened by embedded steel, is called

reinforced concrete.

when without reinforcement, is called plain or mass

concrete.

3.01 DEFINITION

3. CONCRETE 1. CEMENTING MATERIALS


2. STORAGE OF

CEMENT

3. CONCRETE


of Good




4. PROCESSED

CONCRETE

4.01 Types of

Processed


Light-weight

Conc.

Concrete should be:

Strong

Durable

of uniform quality, and

thoroughly sound.

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



2. STORAGE OF

CEMENT

3. CONCRETE


of Good




4. PROCESSED

CONCRETE

4.01 Types of

Processed


Light-weight

Conc.

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-

American Society for Testing Materials (ASTM).

The kind of tests usually made are:

3.03 MATERIALS OF CONCRETE



2. STORAGE OF

CEMENT

3. CONCRETE


of Good




4. PROCESSED

CONCRETE

4.01 Types of

Processed


Light-weight

Conc.

b. Aggregates are:

Fine aggregates

(aggregates smaller than

sand, stone screenings or

other inert materials of

similar 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.




2. STORAGE OF

CEMENT

3. CONCRETE


of Good




4. PROCESSED

CONCRETE

4.01 Types of

Processed


Light-weight

Conc.

Coarse aggregate

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

walls.

reinforced parts of the structures such as footings, thick

walls, and massive work.

b. Aggregates




2. STORAGE OF

CEMENT

3. CONCRETE


of Good




4. PROCESSED

CONCRETE

4.01 Types of

Processed


Light-weight

Conc.

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




2. STORAGE OF

CEMENT

3. CONCRETE


of Good




4. PROCESSED

CONCRETE

4.01 Types of

Processed


Light-weight

Conc.

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.




2. STORAGE OF

CEMENT

3. CONCRETE


of Good




4. PROCESSED

CONCRETE

4.01 Types of

Processed


Light-weight

Conc.

- The water-cement ratio is 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

less water used in mixing, the better the quality of

concrete.

- 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.

WATER CEMENT 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

3,000

3,750

7.00

6.50

5.75

5.00

62.0

57.5

51.0

44.5

c. Water




2. STORAGE OF

CEMENT

3. CONCRETE


of Good




4. PROCESSED

CONCRETE

4.01 Types of

Processed


Light-weight

Conc.

- used for measuring the consistency of a concrete mix.

-

the wettest to the dries possible mixtures.

height due to gravity action, is measured. The apparatus

3.04 SLUMP TEST



2. STORAGE OF

CEMENT

3. CONCRETE


of Good




4. PROCESSED

CONCRETE

4.01 Types of

Processed


Light-weight

Conc.

In making the test, the slump tester is

placed on a flat, smooth surface and is

filled with newly mixed concrete from

mixer. In filling the mold with concrete,

rod pointed at one end and the top of

the concrete is smoothed off exactly

level. The mold is then slowly raised

vertically and the height deducted from

represents the slump.

SLUMP No

slump Collapsed

slump

TOO WET SUITABLE TOO DRY Bucket

3.04 SLUMP TEST



2. STORAGE OF

CEMENT

3. CONCRETE


of Good




4. PROCESSED

CONCRETE

4.01 Types of

Processed


Light-weight

Conc.

A harsh mix is efficient for slabs, pavements, or mass

concrete 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

Plain footings, caissons, and

substructure walls

Slabs, beams, thin reinforced walls &

building columns

Pavements and floor laid on ground

Heavy mass construction

3.04 SLUMP TEST



2. STORAGE OF

CEMENT

3. CONCRETE


of Good




4. PROCESSED

CONCRETE

4.01 Types of

Processed


Light-weight

Conc.

Briefly stated, the principles of proper proportioning are as

follows:

3.05 PROPORTIONING OF CONCRETE

3. CONCRETE

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

and aggregate.

b. Determine the strength of the concrete using the

water-cement ratio. (The strength increases as the

water-cement ratio decreases).

c. Determine the consistency of the mix using the

slump test using as dry a mix as practicable.

d. Add correct proportions of aggregates to the

cement and water as will give a mix of the desired

consistency.

e. , not harsh.

1. CEMENTING

MATERIALS


2. STORAGE OF

CEMENT

3. CONCRETE


of Good




4. PROCESSED

CONCRETE

4.01 Types of

Processed


Light-weight

Conc.

The strength of a workable concrete mix depends upon the

water-cement ratio.

The economy of the mix depends upon the proper

proportioning of the fine and coarse aggregates.

There are several methods of proportioning concrete:

a. Proportioning by arbitrary proportions

b. 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 most

convenient 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.




2. STORAGE OF

CEMENT

3. CONCRETE


of Good




4. PROCESSED

CONCRETE

4.01 Types of

Processed


Light-weight

Conc.

a. Proportioning by arbitrary proportions

Proportioning concrete by

the arbitrary selection of

the proportions is the

oldest, the most

commonly used, the most

convenient 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.

1 f

oo

t

1 foot

1 foot




2. STORAGE OF

CEMENT

3. CONCRETE


of Good




4. PROCESSED

CONCRETE

4.01 Types of

Processed


Light-weight

Conc.

Common mixes expressed in proportions by volumes of

cement to fine aggregate to coarse aggregate are as follows:

CONCRETE PROPORTIONS

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

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

1 : 2.5 : 5 steps, reinforced concrete slabs on fill.

1 : 3 : 6 For concrete plant boxes, and any non-critical concrete structures.

1 : 3.5 : 7 For mass concrete works.

The proportion is to be read:

Class A : 1 part cement is to 2 parts sand is to 4 parts gravel.

one cubic foot which 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.




2. STORAGE OF

CEMENT

3. CONCRETE


of Good




4. PROCESSED

CONCRETE

4.01 Types of

Processed


Light-weight

Conc.

b. Proportioning by the water-ratio and slump test

There 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.




2. STORAGE OF

CEMENT

3. CONCRETE


of Good




4. PROCESSED

CONCRETE

4.01 Types of

Processed


Light-weight

Conc.

c. Proportioning by water-ratio, slump and fineness

modulus

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 aggregate

will be a minimum.




2. STORAGE OF

CEMENT

3. CONCRETE


of Good




4. PROCESSED

CONCRETE

4.01 Types of

Processed


Light-weight

Conc.

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



2. STORAGE OF

CEMENT

3. CONCRETE


of Good




4. PROCESSED

CONCRETE

4.01 Types of

Processed


Light-weight

Conc.

a. MACHINE MIXING

In 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 be

cleaned at frequent intervals while in use.

Concrete mixers may be divided into two general classes:

Batch mixers -

into which sufficient

materials are placed at one

time to make a convenient

size batch of concrete, the

whole amount being

discharged in one mass

after it is mixed.




2. STORAGE OF

CEMENT

3. CONCRETE


of Good




4. PROCESSED

CONCRETE

4.01 Types of

Processed


Light-weight

Conc.

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




2. STORAGE OF

CEMENT

3. CONCRETE


of Good




4. PROCESSED

CONCRETE

4.01 Types of

Processed


Light-weight

Conc.

b. HAND MIXING

- hand-mixing must be

done on a water-tight

platform.

- cement and fine

aggregate shall first

be 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 consistency

is obtained.




2. STORAGE OF

CEMENT

3. CONCRETE


of Good




4. PROCESSED

CONCRETE

4.01 Types of

Processed


Light-weight

Conc.

concrete lecture

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