Div 03

1
BUILDING TECHNOLOGY I
Div 03 CONCRETE
2
1. CEMENTING MATERIALS
1.01 LIME
One of the oldest manufactured building materials
used as a mortar and plaster by all the early
civilizations

• 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).
3
1. CEMENTING MATERIALS
1.01 LIME
The carbonates decompose into carbon dioxide,
which is expelled, and calcium oxide (CaO) called
quicklime.
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.
4
1. CEMENTING MATERIALS
1.01 LIME
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.
5
1. CEMENTING MATERIALS
1.02 GYPSUM
Gypsum, like lime, was used as 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.
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.
6
1. CEMENTING MATERIALS
1.02 GYPSUM
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.
7
1. CEMENTING MATERIALS
1.03 CEMENT
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.
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 generally refers to Portland cement
which is the principal type of cement in use.
8
1. CEMENTING MATERIALS
1.03 CEMENT
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).

Portland cement is sold in bags of 40 kilos total
weight.
9
2. STORAGE OF CEMENT
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.
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.
10
3. CONCRETE
3.01 DEFINITION

• 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 (¼) is known as mortar, stucco or
  cement plaster.
• when mixed with water, fine aggregate and a large
  aggregate of more than 6mm (¼) in size produces
  concrete.
• when strengthened by embedded steel, is called
  reinforced concrete.
• when without reinforcement, is called plain or
  mass concrete.

11
3. CONCRETE
3.02 QUALITIES OF GOOD CONCRETE

• 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

12
3. CONCRETE
3.03 MATERIALS OF CONCRETE
a. Cement

• 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

• 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.
13
3. CONCRETE
3.03 MATERIALS OF CONCRETE

1. Aggregates are

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.

• Fine aggregates (aggregates smaller than 6mm (¼)
  in size) consist of 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.

14
3. CONCRETE
3.03 MATERIALS OF CONCRETE

1. Aggregates

• Coarse aggregate (aggregate larger than ¼ 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, thick walls, and massive work.
15
3. CONCRETE
3.03 MATERIALS OF CONCRETE

1. Aggregates

• Special aggregates, such as cinders, blast
  furnace slag, expanded shale or clay, perlite,
  vermiculite, and sawdust, may produce

• lightweight, nailable concrete
• thermal insulating concrete.

16
3. CONCRETE
3.03 MATERIALS OF CONCRETE

1. 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.
17
3. CONCRETE
3.03 MATERIALS OF CONCRETE

1. Water

- 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 WATER CEMENT RATIO 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
18
3. CONCRETE
3.04 SLUMP TEST

• 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).
19
3. CONCRETE
3.04 SLUMP TEST
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, the latter is tamped in with a
12mm (½) 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 the original height of 300mm
(12) represents the slump.
20
3. CONCRETE
3.04 SLUMP TEST
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) CONSISTENCY (SLUMP)
Maximum Minimum
Reinforced foundation walls and footings 125mm (5) 50mm (2)
Plain footings, caissons, and substructure 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)
21
3. CONCRETE
3.05 PROPORTIONING OF CONCRETE
Briefly stated, the principles of proper
proportioning are as follows

• 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).
• Determine the consistency of the mix using the
  slump test using as dry a mix as practicable.
• Add correct proportions of aggregates to the
  cement and water as will give a mix of the
  desired consistency.
• Make a mix thats workable, not harsh.

22
3. CONCRETE
3.05 PROPORTIONING OF CONCRETE
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.
23
3. CONCRETE
3.05 PROPORTIONING OF CONCRETE
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.
24
3. CONCRETE
3.05 PROPORTIONING OF CONCRETE
Common mixes expressed in proportions by volumes
of cement to fine aggregate to coarse aggregate
are as follows
CONCRETE PROPORTIONS CONCRETE PROPORTIONS 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-critical concrete structures.
Class D 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.
Each part is equivalent to 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.
25
3. CONCRETE
3.05 PROPORTIONING OF CONCRETE
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.
26
3. CONCRETE
3.05 PROPORTIONING OF CONCRETE
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.
27
3. CONCRETE
3.06 MIXING OF CONCRETE

• 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.

28
3. CONCRETE
3.06 MIXING OF CONCRETE
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.
29
3. CONCRETE
3.06 MIXING OF CONCRETE
a. MACHINE MIXING
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.

30
3. CONCRETE
3.06 MIXING OF CONCRETE
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.

31
3. CONCRETE
3.06 MIXING OF CONCRETE
b. HAND MIXING

• 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.
• Regaging or retempering of concrete that has been
  allowed to stand more than ½ hour is not to be
  permitted.

32
3. CONCRETE
3.07 TRANSPORTING AND PLACING OF CONCRETE

• Fresh concrete should be transported from the
  mixer 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.

• The delivery of the concrete from the mixer to
  the forms should be fairly continuous and
  uninterrupted.
• The time of transportation should not exceed 30
  minutes.

33
3. CONCRETE
3.07 TRANSPORTING AND PLACING OF CONCRETE

• The concrete may be transported by means 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.

34
3. CONCRETE
3.07 TRANSPORTING AND PLACING OF CONCRETE

• Before placing concrete, the forms 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.

35
3. CONCRETE
3.08 SHRINKAGE OF CONCRETE TEMPERATURE CHANGES

• Shrinkage of concrete due to hardening and
  contraction from 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.

36
3. CONCRETE
3.09 CURING OF CONCRETE

• Concrete must be allowed to cure or harden
  after it is placed.
• 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

• age or time
• temperature, and
• moisture.

37
3. CONCRETE
3.09 CURING OF CONCRETE

• In order that the hardening may proceed
  favorably, the fresh concrete, 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 the curing conditions remains favorable.

38
3. CONCRETE
3.09 CURING OF CONCRETE

• The increase in strength is rapid during the
  early ages 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.

39
3. CONCRETE
3.09 CURING OF CONCRETE
Curing consists primarily in keeping the concrete
from drying out 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).
40
3. CONCRETE
3.09 CURING OF CONCRETE
Parts of Structure Parts of Structure CURING PERIOD or TIME REQUIRED FOR THE REMOVAL OF FORMS
FOOTINGS Massive footings Cantilever footings Slab footings 1 day (24 hours) 5 days (120 hours) 5 days (120 hours)
WALLS AND PLASTERS Massive walls, 30 cms. thick or more Thin walls less than 30 cms. Thick Cantilever walls, buttresses, counter forts, diaphragms. Up to 2 M. high 1 day (24 hours). Add 1 day (24 hours) for every additional meter or fraction thereof. Up to 2 M. high 2 days (48 hours. Add 1-1/2 days (36 hours) for every additional meter or fraction thereof Without loads, same as (b).
COLUMNS Ratio of height to least diameter up to 4 Ratio of height to least diameter from 4 to 15. 2 days (48 hours) 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).
41
3. CONCRETE
3.09 CURING OF CONCRETE
Parts of Structure CURING PERIOD or TIME REQUIRED FOR THE REMOVAL OF FORMS
SLABS 3 to 7 ft. spans b. Over 7 ft. span 3 ft. span, 5 days (120 hours). Add ½ day (12 hours) for every additional 1 ft. span or fraction thereof. 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 GIRDERS Sides Bottoms 3 days 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 Spandrel walls Spandrel arches Main arches 7 days (168 hours). 14 days (336 hours) 21 days (504 hours)
BALUSTRADES, COPINGS,ETC. a. Steel side forms a. 1 day (24 hours)
R.C. PILES and R.C. POSTS Sides. Bottom 3 days (72 hours) 14 days (336 hours)
42
3. CONCRETE
3.10 ADMIXTURES
Substances added to cements, 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.

43
3. CONCRETE
3.10 ADMIXTURES
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, and liquid
form, and are usually patented and sold under
trademark names.
44
3. CONCRETE
3.10 ADMIXTURES
Concrete admixtures include

• 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 and
  contraction of concrete, reduce resistance to
  sulfate attack, and increases efflorescence and
  corrosion of high tension steels.
• Retarders - to slow down the hydration of the
  cement during very hot weather. Principal
  ingredients include zinc 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.

45
3. CONCRETE
3.10 ADMIXTURES

• Air-entraining agents - introduce minute air
  bubbles to greatly 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 -
  are added to improve workability, used as per
  manufacturers directions. Hydrated lime is
  usually in the proportion of 10 to 15 of the
  cement by volume.

46
3. CONCRETE
3.10 ADMIXTURES

1. 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 are introduced usually in the
   amounts of 0.1 to 4.0 of the weight of cement.

47
3. CONCRETE
3.10 ADMIXTURES

1. Colored pigments are mainly to used to give color
   to concrete floors. There are two types

• 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 .

48
3. CONCRETE
3.10 ADMIXTURES

• 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.

49
3. CONCRETE
3.11 FORMS
a. LUMBER 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.
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.
50
3. CONCRETE
3.11 FORMS
a. LUMBER FORMS
When using natural, well seasoned lumber, care
should be taken not to drive the work up too
close, since forms should always be left in a
position to experience some slight swelling
without any undesirable results.
51
3. CONCRETE
3.11 FORMS
a. LUMBER FORMS

• Sheathing lumber dressed at least one side and
  both edges even are used where the removal and
  cleaning of the forms are necessary for re-use .
• Sheathing lumber dressed on all four sides shall
  be used in face work, where smooth and true
  surface is important.
• Tongue-and-groove lumber will achieve tight
  joints between boards in floor and wall panel
  construction.
• Simply dressing the lumber true to edge form
  square 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

52
3. CONCRETE
3.11 FORMS
a. LUMBER FORMS
Use nails sparingly in the construction of forms
because unnecessary nailing not only adds to the
labor of wrecking but also renders the lumber
unfit for continued use. Where nails must be
used, leave the head protruding so that they may
be withdrawn without injury to the lumber.
53
3. CONCRETE
3.11 FORMS
a. LUMBER FORMS
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 should preferably 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.
54
3. CONCRETE
3.11 FORMS
a. LUMBER FORMS
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
the reinforcements 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.
55
3. CONCRETE
3.11 FORMS
b. PLYWOOD FORMS
Works best where a smooth surface is required.
The plywood should be waterproof, Grade A and
at least 12mm (½) 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 now available for concrete
work.
56
4. PROCESSED CONCRETE
4.01 TYPES OF PROCESSED CONCRETE
a. AEROCRETE
This 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 which
expands 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.
57
4. PROCESSED CONCRETE
4.01 TYPES OF PROCESSED CONCRETE
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.
58
4. PROCESSED CONCRETE
4.01 TYPES OF PROCESSED CONCRETE
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 .
59
4. PROCESSED CONCRETE
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

60
4. PROCESSED CONCRETE
4.02 AGGREGATES FOR LIGHTWEIGHT CONCRETE
The major disadvantages of lightweight aggregates
are 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 mortar and 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 .

61
4. PROCESSED CONCRETE
4.02 AGGREGATES FOR LIGHTWEIGHT CONCRETE

• 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.

62
4. PROCESSED CONCRETE
4.02 AGGREGATES FOR LIGHTWEIGHT CONCRETE
Lightweight aggregates can be divided into four
general classifications
a. Aggregates of volcanic origin

• Pumice, weighing from 25 to 60 lbs.per cu. ft. is
  well qualified as a lightweight aggregate 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 .

63
4. PROCESSED CONCRETE
4.02 AGGREGATES FOR LIGHTWEIGHT CONCRETE
a. Aggregates of volcanic origin

• Perlite is 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 its lightness, from 8
  to 16 lbs. per cu. ft. increases the tendency to
  float out of the mortar.

Perlite is useful where maximum strength is not
required, as in precast slabs and blocks and in
floor fill, fireproofing and plaster .
64
4. PROCESSED CONCRETE
4.02 AGGREGATES FOR LIGHTWEIGHT CONCRETE
b. Micaceous minerals

• Vermiculite is 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.

65
4. PROCESSED CONCRETE
4.02 AGGREGATES FOR LIGHTWEIGHT CONCRETE
c. Expanded shales and clays

• 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
  and expanding 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. .

66
4. PROCESSED CONCRETE
4.02 AGGREGATES FOR LIGHTWEIGHT CONCRETE
d. By-product Aggregates

• Expanded Slag or foamed slags are made by
  treating molten 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.

• Foamed slag has 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
  coal along 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.

67
4. PROCESSED CONCRETE
4.02 AGGREGATES FOR LIGHTWEIGHT CONCRETE
WEIGHT OF AGGREGATE AND CONCRETE BY TYPE OF
AGGREGATE
TYPE OF AGGREGATE Aggregate Weight per Cubic Foot (Lbs.) Weight per Cubic Foot of Concrete Using Aggregate (Lbs.)
Gravel Sand Crushed Stone Crushed Bank Slag Haydite (Expanded Clay, shale) Foamed Slag Cinders Pumice Diatomite Perlite Vermiculite 120 90-100 100 80 40-60 40-60 40-50 30-60 28-40 6-16 6-10 150 150 145 110-130 100-120 90-100 110-115 60-90 55-70 40-65 25-50
68
End of Div 03 CONCRETE