Engineering materials

Engineering Material 1

Paints
Paints are used to protect metals, timber, or plastered surfaces from the corrosive effects
of weather, heat, moisture or gases etc and to improve their appearance.

Composition of paints
Fundamental components of an oil-based paint are:
1. Body
2. Vehicle
3. Pigment
4. Thinner
5. Dryer
6. Additives

1. Body
 Forming the main body of a paint
 Make the paint film harder and more resistant to abrasion
 Reduce shrinkage cracks on drying
Examples: White lead, Zinc oxide, Iron oxide, Metallic powder such as Al, Cu, Br.
Types of paints on the basis of body:
Lead paint,
Zinc paint, and
Aluminum paint.

2. Vehicle
 Oily liquid in which the body and pigment are soluble
 Facilitates the paint to be conveniently spread over the surface
 Oils most commonly used as vehicle are
Examples: Linseed oil, Soya bean oil, Fish oil, dehydrated castor oil.

3. Pigment
Pigments are materials which gives the paint its color. In white paint the body is the
pigment.
Types of Pigments:
Natural pigcentrements (natural iron oxides, chrome oxides).
Synthetic pigments (phthalocynines ► coal tar derivatives)

4. Thinner
Liquid thinner is added in the paint to
 Increase fluidity
 Making paint more smooth
 Help penetration into porous surfaces
Examples ► turpentine (made by distilling gum from a number of pine trees)

Cecos University Peshawar |


5. Dryers
 Added to quicken the drying of vehicle
 Organic salts of Iron, zinc, lead, manganese, Ca
 To accelerate the oxidation and hardening of vehicle.

6. Additives
Additives,usually added in very small amount to improve some properties.
Examples:
v.v stabilizers
Biocides
Catalyst
Properties:
Some examples include additives to improve wet edge, to impart antifreeze properties,
control foaming, control skinning, fight bacterial growth, or improve pigment
stability. There are various additives, which are added to improve some properties, such
as color opacity and matness, pigment dispersion, or stability.

Preparation of paints
 Base/ body is thoroughly grounded in the vehicle.
 Mixed with the thinner to impart necessary workability.
 Pigments and dryers are separately mixed to a thin consistency.
 The two are then thoroughly mixed to form the desired paint.

Removal of old paints
1. Burning the paint: Which is economical and quick.
2. Applying the paint removal
2a. Hot solution of an equal part of soap, potash, quick lime applied keep it for 24 hours.
2b. Two parts of quick lime one part of washing soda mixed with water. Cream spread on
paint surface, leave for an hour wash and then remove the paint.
2c. Solution of caustic soda in water applied to the suface.

Characteristics of good paint

There are a number of ways to judge paint quality:
1. Wearability
2. Covering ability
3. Ease of cleaning
4. Environmentally Friendly
5. Aesthetic


6. Practical and Cost Effective

1. Wearability:
Paint must be resistant to the wear and tear of the atmosphere and should maintain its
color, smoothness and finish for a long time.

2. Covering ability:
Paints should cover the body uniformly and homogeneously on which it is applied and
the finish should be smooth and uniform.

3. Ease of cleaning:
When it is required to clean the paint, it shold be easy to remove i.e A good paint should
not react chemically with the materials but should only cover its surface.

4. Environmentally Friendly:
Paint should be water based and must not have any plasticizers or biocides as solvents.

5. Aesthetic:
It should provide a comfortable room climate and must not allow moulds and algae to
grow on it.

6. Practical and cost effective:
The other qualities of a good paint are that they must be cheap, ready to use, long lasting
and should color fast. In most cases Price is the decisive factor in selection of paints.

BITUMEN:
Bitumen is a generic name applied to the various mixtures of hydrocarbons.
They may be gases, liquid ,semisolid and solid in nature and completely soluble in
carbondisulphide.
The most common material in the family of bitumen are tar, pitch and asphalts.
Tar, Pitch and Asphalts forms a group of interrelated material widely used in the field of
civil engineering in damp proofing building, water proofing roofs, water proofing
basement, painting, timber and steel and for setting out metalled roads.

Composition of Bitumen:
Materials in bituminous family are:

1) Tar:
Coal tar is a brown or dark black liquid of high viscosity, which smells of naphthalene
and aromatic hydrocarbons. Being flammable, coal tar is sometime used for heating or to
fire boilers. It can be used in coal tar soap, and is used in medicated shampoo to kill and
repel head lice, and as a treatment for dandruff.
Depending upon its source of origin, TAR is classified as:


a) Coal Tar:
It is the liquid by-product of the distillation of coal to make coke. The gaseous by-product
of this process is commonly known as town gas. It is used for coating of wooden poles
and sleepers, iron poles.

b) Wood Tar:
It is obtained by the distillation of resinous wood. Wood tar contains creosote and as such
has strong preservative properties.

c) Mineral Tar:
It is obtained by the distillation of bituminous shale.

2) Pitch / Coal Tar Pitch:
It is the residue of the direct distillation of crude tar produced by the high temperature
carbonization of coal. It is used as a water proofing compound in masonry, steel and
timber structure. It is also used for water proofing concrete structures.

3) Asphalts:
Asphalts also known as bitumen. Asphalts are formed in natural state and are also
produced by refining of petroleum.
There are main three groups of asphalts.
1) Hot asphalts: Hot asphalts are softened by heat.
2) Cut back asphalts: Cut back asphalts are dissolved in mineral solvents.
3) Emulsion asphalts: Emulsion asphalts suspend in water base.

PROPERTIES OF BITUMEN:

1. Adhesion: Bitumen has the ability to adhere to a solid surface in a fluid state
depending on the nature of the surface. The presence of water on the surface will
prevent adhesion.
2. Resistance to Water: Bitumen is water resistant. Under some conditions water
may be absorbed by minute quantities of inorganic salts in the bitumen or filler in
it.
3. Hardness: To measure the hardness of bitumen, the penetration test is conducted,
which measures the depth of penetration in tenths of mm. of a weighted needle in
bitumen after a given time, at a known temperature. Commonly a weight of 100
gm is applied for 5 sec at a temperature of 77 °F. The penetration is a measure of
hardness. Typical results are 10 for hard coating asphalt, 15 to 40 for roofing
asphalt and up to 100 or more for water proofing bitumen.
4. Viscosity and Flow: The viscous or flow properties of bitumen are of importance
both at high temperature during processing and application and at low
temperature to which bitumen is subjected during service.



5. Ductility: Ductility test is conducted to determine the amount of bitumen will
stretch at temperature below its softening point.
6. Softening point: The temperature at which a steel ball falls a known distance
through the bitumen, when the test assembly is heated at known rate.

Usually the test consist of (3/8) inches diameter steel ball, weight 3.5 gram,
which is allowed to sink through out (5/8) inches diameter (1/4) inch the disc of the
bitumen in a brass ring. When the whole assembly is heated at a rate of 9 F/min.

Typical values would be 240F for coating the grade asphalts, 140-220F for
roofing asphalts and 115F for bituminous water to fill material.

RUBBER:
It is essentially an elastic material and is either
 Natural Rubber or Indian Rubber
 Synthetic Rubber

1. Natural Rubber
It is present as an emulsion in the latex of rubber trees mostly grow in hot, moist climate
► Malaysia, Venezuela, Mexico. Latex is milky fluid oozing (dropping) from vertical
grooves having an upward inclination cut around the trunk of the rubber tree. Pots are
tied to the trunk of the trees for collecting latex. Crude rubber is obtained by coagulation
of latex with alcohol, alum or lime.
Crude rubber becomes hard and brittle in winter and soft in summer, therefore some
compounds are added to modify its properties.

1. 1. COMPOUNDING RUBBER:
Crude rubber is mixed with filler. There are number of fillers in common use each
imparting specific properties. Some of which are lamp black, oxides of iron, slaked lime,
sulphur. Sulphur is the most common, with which rubber forms a mass which is hard,
tough and resistant to water and ordinary changes of temperature. The process of mixing
rubber with sulphur is called as Vulcanizing.

1. 2. RECLAIMING RUBBER
Rubber from old, worn out articles can be reclaimed either by mechanical or chemical
process. Mechanical ► by grinding the articles into fine particles, removing any trace of
iron with the help of electromagnets, washing. Chemical ►Ground articles are dissolved
either in an acid or alkali to loosen and remove other materials.

2. Synthetic Rubber
Recently rubber is produced on a large scale artificially from acetylene gas under trade
names of
 Neoprene
 Choroprene


 Butyl
Artificial rubbers possess certain properties that are hard to be achieved with natural
rubber such as resistance to acids particularly to grease, kerosene and petroleum.

Uses of Rubber:
About 70% of the total world production of rubber is consumed by automobile tyre
industry
1. Rubber is used as a flooring material. Tiles of sheets of rubber for covering of
floors are used in public and industrial buildings, buses and ships because of their fair
weather resistance quality.
2. Synthetic rubber is used for packing oil-working machinery, hose pipes for
carrying petrol.
3. Rubber bearing pads are used under girders for bridges
4. Rubber is also used for expansion joints.
5. Rubber is made into articles as diverse as raincoats and sponges, bowling balls
and pillows, electrical insulation and erasers. People ride on rubber tires and walk on
rubber heels.

6. Rubber is also used in toys, balls, rafts, elastic bandages, adhesives, paints, hoses,
and a multitude of other products.

7. Ground or "crumb" rubber is used as a binder for asphalt pavements and for
various asphalt sealants and crack fillers.

8. The single most important use of rubber is for tires. Most tires contain several
kinds of rubber, both natural and synthetic. Radial automobile tires contain a greater
percentage of natural rubber than other types of automobile tires because radial tires have
flexible sidewalls that tend to produce a buildup of heat, to which natural rubber has a
superior resistance.

9. Either natural or synthetic rubber is suitable for most uses, and price determines
which is used.

SOME IMPORNTANT DEFINITION:

DUCTILITY
Ability of a material to deform easily under stress of temperature‚ pressure and Speed;
especially‚ ability of a metal to stretch easily. Ductility is characterized by a weak elastic
limit and significant lengthening. (Example: The ductility of Bituminous products is
measured by lengthening a test specimen of determined form that is stretched at a
standardized speed and temperature to the precise instant of its breaking.) Syn. with
MALLEABILITY.



WORKABILITY
The ability of a mortar or a fresh concrete to fill correctly a mold or a formwork thanks to
a well-studied batching of its constituents that give him a sufficient fluidity without
harming its strength and its homogeneity.
The workability is a factor of the first magnitude because it conditions among
other things: good filling, simplicity of placing, good covering of reinforcements. The
workability depends on the batching in fine elements, quantity of water, temperature,
batching in cement, and so on; it is given by means of measuring instruments such as the
concrete workability meter, slump cone, and so on.

BLEED
To go up on the surface, speaking of the water contained in a mortar, a concrete. To reject
internal water.

BLEEDING
The appearance of a film of water or laitance on the surface of a slab or a concrete or
mortar screed after troweling or vibration. The vibration, closing between them the
various grains of the components of concrete, brings about the expulsion of a part of
water that occupies the empties. Water, having lower density than the other components,
goes up on the surface. Syn. with BLEED-THROUGH; SWEATING; WATER GAIN

SEGREGATION
1. An imbalance in the chemical composition of the different components of an alloy.
2. A preferential aggregation of the chemically alike components between them during
the solidification phase of an alloy; this separation results in a chemically heterogeneous
structure.
3. A selective dissociation, in distinct heaps, of different previously mixed bodies as a
result of vibration, brewing, etc.
4. A phenomenon of dissociation of the concrete ingredients that can be due to various
causes (excessive vibration, carriage, falls from critical height, etc.). Elements are divided
and rearranged by order of density. The heaviest aggregates go down to the bottom while
conversely, the mortar goes up to the surface. Segregation can occur: inside the concrete
mixer (malaxation was too long); at the time of the emptying of the vat or placing (too
important brutal free falls of the concrete (too distant from unloading point)); during the
transport (shakes, etc.); during the pouring (lateral projections and important falls, too
long vibration of concrete, etc.).

HYDRATE
A chemical body resulting from the combination of a body with water molecules.

HYDRATION
Phenomenon of water absorption by a chemically receptive body. The process of
chemical reaction between water and cement is also called hydration.


DURABILITY
Resistance to weather condition

SHRINKAGE
Decrease in volume of Concrete

COMPACTION
Compaction is removing the air from concrete. Proper compaction results in concrete
with an increased density which is stronger and more durable.

PROPORTIONING AND MIXING CONCRETE:
A concrete mix is designed to produce concrete that can be easily placed at the lowest
cost. The concrete must be workable and cohesive when plastic, then set and harden to
give strong and durable concrete. The mix design must consider the environment that the
concrete will be in; i-e exposure to sea water, trucks, cars, forklifts, foot traffic or
extremes of hot and cold.

1. PROPORTIONING: Concrete is a mixture of Cement, Water, Coarse and Fine
Aggregates and Admixtures. The proportions of each material in the mixture affects the
properties of the final hardened concrete. These proportions are best measured by weight.
Measurement by volume is not as accurate, but is suitable for minor projects.

Cement content: As the cement content increases, so does strength and durability.
Therefore to increase the strength, increase the cement content of a mix.

Water content: Adding MORE WATER to a mix gives a WEAKER hardened
concrete. Always use as little water as possible, only enough to make the mix workable.

Water to cement ratio: As the Water to Cement ratio INCREASES, the strength and
durability of hardened concrete DECREASES. To increase the strength and durability of
concrete, decrease the Water-Cement ratio.

Aggregates: Too much fine aggregate gives a sticky mix. Too much coarse aggregate
gives a harsh or boney mix.

2. MIXING: Concrete must be mixed so the Cement, Water, Aggregates and
Admixtures blend into an even mix. Concrete is normally mixed by MACHINE. Machine
mixing can be done on-site or be a Pre-Mixed concrete company. Pre-Mixed concrete is
batched (proportioned) at the plant to the job requirements.



Truck Mixing: The materials are normally added to the trucks at batching plants and
mixed for required time and speed at the plant. The trucks drum continues to rotate to
agitate the concrete as it is delivered to the site.

Site Mixing: When site mixing begin by loading a MEASURED AMOUNT of coarse
aggregate into the mixer drum. Add the sand before the cement, both in measured
amounts.

NEVER USE A SHOVEL AS A MEASURE AS VOLUMES CAN
VARY WIDELY:
Mix materials together until there is no visible sand in the mix. Add enough water to get a
workable mix. Be careful not to overload the mixer. Too much concrete in the mixer
means each batch takes longer to be properly mixed, which causes costly delays in the
long run or it will not mix at all. Always check how much the mixer holds so you know
how much concrete can be produced at once. Avoid delays between batches to get
maximum output. Small quantities of concrete may be mixed by hand with a shovel.
Mixing should be done on a clean board, or plate, or in a wheelbarrow. Mix the materials
together until they are even. Then dish the material and add water. Use only enough
water to get an even, workable mix.

TRANSPORTING AND PLACING CONCRETE:
When transporting and placing concrete, avoid :DELAY SEGREGATION and
WASTAGE.

3. TRANSPORTATION
The method used to transport concrete depends on which one is the lowest cost and
easiest for the job size. Some ways to transport concrete include: a concrete truck, a
concrete pump, a crane and bucket, a chute, a conveyor or a hoist. On small jobs a
wheelbarrow is the easiest way to transport concrete. Always transport concrete as little
as possible to reduce problems of segregation and wastage.

4. PLACING
When placing concrete be careful not to damage or move the formwork and
reinforcement. Place concrete as near to its final position as possible. Start placing from
the corners of the formwork or, in the case of a sloping site, from the lowest level.
DELAY
Delay can cause the concrete to dry-out and stiffen. Delay is more of a problem on a hot,
and/or windy, day when the concrete will dry-out and stiffen more quickly.

SEGREGATION
Segregation is when the coarse and fine aggregate, and cement paste, become separated.
Segregation may happen when the concrete is mixed, transported, placed or compacted.



Segregation makes the concrete: WEAKER,LESS DURABLE and will leave A POOR
SURFACE FINISH.

To avoid segregation:
Check the concrete is not 'too wet' or 'too dry'. Make sure the concrete is properly mixed.
It is important that the concrete is mixed at the correct speed in a transit mixer for at least
two minutes immediately prior to discharge. The concrete should be placed as soon as
possible. When transporting the mix, load carefully. If placing concrete straight from a
truck, pour vertically and never let the concrete fall more than one-and-a-half meters.
Always pour new concrete into the face of concrete already in place. When compacting
with a poker vibrator be sure to use it carefully.
Never spread concrete sideways with a poker vibrator as this may cause segregation of
the mix. Always be sure to vibrate concrete evenly.

WASTAG E
Wastage can be costly, especially on small jobs. To minimize wastage; mix, load,
transport and place carefully.

5. COMPACTION: Compaction is the process which expels entrapped air from
freshly placed concrete and packed the aggregate particle together so as to increase the
density of concrete.
OR
Removal of entrapped air from the voids of concrete by using some mechanical ways.
It increases the significantly the ultimate strength of concrete and enhances the
bond with reinforcement.
It also increase the abrasion resistance and durability of concrete.
It decreases the permeability and helps to minimize the shrinkage and creep
characteristics.

TWO STAGES PROCESS:
1. The aggregate particles are set in motion and slump to fill the form giving a
level top surface.
2. In the second stage entrapped air is expelled.

METHOD AND EQUIPMENT:

VIBRATION: Vibration of the concrete is one of the important method of
compaction. It is done with the help of vibrator.

Types of Vibrators:
1. Internal/ Immersion/ Poker Vibrator
2. Surface Vibrator



1. INTERNAL VIBRATION
Internal vibration is done with a mechanical vibrator or poker vibrator. The POKER is
put into concrete and vibrates it from the inside.

Method
Make sure there are enough workers so some can compact while others continue to place.
Put the poker into the concrete QUICKLY. Take the poker out very SLOWLY otherwise
a hole, or weak spot, may be left in the concrete. The SIZE of the poker determines how
much concrete is vibrated at one time. The area vibrated at one time is called the
RADIUS OF ACTION. This can be seen by over what radius air bubbles rise to the
surface. The radius of action will be greater with a LARGER poker and more-workable
concrete. Always compact in a definite pattern so the radius of action overlaps and covers
the whole area of the concrete. The poker should be long enough to reach and enter into
the layers of concrete under the one being compacted.

HOW LONG TO COMPACT
For concrete of average workability (i-e slump of 80 mm)with a poker size between 25–
75 mm, concrete should usually be vibrated for between5 and 15 seconds. It is worse to
UNDER-VIBRATE than to OVER-VIBRATE concrete.

2. SURFACE VIBRATOR: Surface Vibrators are applied are applied at the top
surface of the concrete and act downward from there. They are very useful for compacted
slabs, industrial floors, road pavements and similar flat surfaces. They also aid in
lavelling and finishing the surfaces. There are number of types of vibrators including
1) Vibrator roller screed
2) Vibrator beam screed
3) Pan type vibrator
They are used mainly on very specialized equipment such as road paving plant. The most
common type is the single or double vibrating beam screed.

WHAT IS FINISHING
Finishing is screeding, floating or trowelling the concrete surface to density and further
compact the surface of concrete, as well as giving it the look you want.
STAGES: Finishing takes place in two stages: INITIAL and FINAL finishing.

INITIAL FINISHING
Concrete is first screeded to the level of the formwork, then bull floated and left to set. In
some cases screeding leaves a good enough finish, especially if floor coverings are to be
used over the concrete. Water then appears on the surface of the concrete. This water is
called bleed water.
No final finishing can begin until the bleed water has dried up. Mixing bleed water with
the surface paste will weaken it, possibly resulting in a dusty surface.



Excess bleed water can be removed by dragging an ordinary garden hose across the
surface of the concrete.
Never try to dry up the bleed water using stone dust or cement as this will weaken the
concrete surface in the long run. Once the bleed water dries up and concrete can support
a person’s weight, with only as light marking to the surface, the final finishing can begin.

FLOATING
There may be two stages in floating:
The BULLFLOAT, which is part of the initial float.
The POWER or HAND FLOAT which is part of the final float.
Floating helps compact and level the surface and close minor cracks. Floating can be
done by hand or with a power float. Power floating leaves a better finish than hand
floating.

FINAL FINISHING
This involves floating, trowelling, edging, jointing or patterning the concrete. Special
finishes such as brooming, coloring or patterned finishes can be applied to the surface.

Toweling
Toweling leaves a dense, hard, smooth and durable surface. The surface should be
trowelled TWICE. A well trowelled surface will be very smooth and can be slippery
when wet. Trowelling can be done by hand or power trowel..

Edging and Grooving
All the edges of a slab should be finished with a special edging tool. This gives a neater
and stronger edge, less prone to chipping. Joints should be planned before placing and are
usually formed into the concrete during finishing.
Once any surface has been finished it MUST be cured.

7. CURING CONCRETE:
The process of maintaining a satisfactory moisture content and a favorable
temperature in concrete during the period immediately following placement so hydration
may continue until the desired properties are developed to the sufficient degree to meet
the service requirement is called Curing.
OR:
Keeping the concrete moist or warm enough so that hydration may continue until
the desired properties are developed to the sufficient degree to meet the service
requirement is called Curing.
Curing means to cover the concrete so it stays MOIST. By keeping concrete
moist the bond between the paste and the aggregates gets stronger. Concrete doesn’t
harden properly if it is left to dry out.

WHEN TO CURE


Curing is done just after finishing the concrete surface, as soon as it will not be damaged.

WHY CURE
Concrete that is cured is: LESS LIKELY TO CRACK. More DURABLE. Cured
concrete has a surface that wears better, lasts longer and better protects the steel
reinforcement.
Stronger
The concrete can carry more weight without breaking.

HOW TO CURE
Concrete is cured by:
1)APPLYING EXTRA WATER to the surface of the concrete, or
2)STOPPING water loss from the concrete
3)To cover the concrete with PLASTIC SHEETS to slow down water loss
4)Curing the concrete by applying curing compound that is sprayed or brushed on.
The most important thing in curing is to keep the concrete moist at all times. Hosing in
the morning and again at night and letting the concrete dry out in between is no good.
Another way to cure concrete is to cover with PLASTIC SHEETS to slow down water
loss. This method is easy and cheap. The only problem is that the sheets may cause
concrete to become darker in places. To avoid this keep concrete EVENLY moist..

HOW LONG TO CURE
Concrete keeps getting HARDER AND STRONGER over TIME.
Household concrete jobs MUST be cured for at least 3 DAYS.
For better strength and durability, cure concrete for 7 DAYS.
The LONGER concrete is cured, the closer it will be to its best possible strength and
durability.

PROPERTIES OF CONCRETE:
Properties of concrete are divide into two major groups
 Properties of Fresh Concrete
 Properties of Hardened Concrete

FRESH CONCRETE:
Fresh concrete is that stage of concrete in which concrete can be moulded and it is in
plastic state. This is also called "Green Concrete". Another term used to describe the state
of fresh concrete is consistence, which is the ease with which concrete will flow.
Properties of Fresh Concrete
Following are the important properties of fresh concrete
1. Setting
2. Workability
3. Bleeding and Segregation



a) Bleeding
b) Segregation
4. Hydration
5. Air Entrainment

1. Setting of Concrete
The hardening of concrete before its hydration is known as setting of concrete. OR
The hardening of concrete before it gains strength. OR
The transition process of changing of concrete from plastic state to hardened state.
Setting of concrete is based or related to the setting of cement paste. Thus cement
properties greatly affect the setting time.

2. Workability of Concrete
Workability is often referred to as the ease with which a concrete can be transported,
placed and consolidated without excessive bleeding or segregation.
Segregation in concrete
Segregation can be defined as the separation of the constituent materials of concrete.

Hardened Concrete Properties
Following are the properties of hardened concrete:
1. Strength of concrete
2. Concrete Creep
3. Shrinkage
4. Modulus Of Elasticity
5. Water tightness (impermeability)

TYPES OF CONCRETE:
Some common and main types of concrete are:
1. Normal concrete
2. High Strength Concrete
3. High Performance Concrete
4. Air Entrained Concrete
5. Light Weight Concrete
6. Self Compacting Concrete
7. Shotcrete Concrete
8. Pervious Concrete
9. Roller Compacted Concrete
10. Hot Weather Concrete
11. Cold Weather Concrete

1. NORMAL CONCRETE:
 The concrete in which common ingredients i.e. aggregate, water, cement are used
is known as normal concrete. It is also called normal weight concrete or normal strength
concrete.


 It has a setting time of 30 - 90 minutes depending upon moisture in atmosphere,
fineness of cement etc.
 The development of the strength starts after 7 days the common strength values is
10 MPa (1450 psi) to 40 MPa (5800 psi). At about 28 days 75 - 80% of the total strength
is attained.
 Almost at 90 days 95% of the strength is achieved.

Properties of Normal Concrete
 Its slump varies from 1 - 4 inches.
 Density ranges from 140 pcf to 175 pcf.
 It is strong in compression and weak in tension.
 Air content 1 - 2 %.
 Normal concrete is not durable against severe conditions e.g. freezing and
thawing.

2. HIGH STRENGTH CONCRETE:
 Compressive strength of high strength concrete mix is usually greater than 6,000
pounds per square inch.
 High strength concrete is made by lowering the water cement (W/C) ratio to 0.35
or lower.
 Often silica fume is added to prevent the formation of free calcium hydroxide
crystals in the cement, which might reduce the strength at the cement aggregate bond.
 Low w/c ratios and the use of silica fume make concrete mixes significantly less
workable, which is particularly likely to be a problem in high-strength concrete
applications where dense rebar cages are likely to be used. To compensate for the
reduced workability in the high strength concrete mix, super plasticizers are commonly
added to high-strength mixtures.
 Aggregate must be selected carefully for high strength mixes, as weaker
aggregates may not be strong enough to resist the loads imposed on the concrete and
cause failure to start in the aggregate.

3. HIGH PERFORMANCE CONCRETE:
This mix has the following main properties:
 High strength.
 High workability.
 High durability.
 Ease of placement.
 Compaction without segregation.
 Early age strength.
 Long-term mechanical properties.
 Permeability.
 Density.
 Heat of hydration.
 Toughness.


 Volume stability.
 Long life in severe environments
Preparation
High strength concrete mix can be prepared with careful selection of ingredients and
optimization of mix design.
 High workability is attained by super plasticizers, they lower the water cement
ratio to 0.25 which is the amount required only for hydration process.
 High durability is attributed to fly ash and silica fume which modify the e
mineralogy of the cement; it enhances the compatibility of ingredients in concrete mass
and reduces the CH amount. Fly ash also causes ball bearing effect increasing
workability.
 The admixtures are 20-25% fly ash of partial replacement of cement and rest 70%
is Ordinary Portland Cement.
 As it is not usually durable against freezing and thawing so air entrained agents
can also be utilized.

Properties of high performance concrete mix
 Strength of high performance concrete ranges from 10000 psi - 15000 psi
 Water cement ratio can be reduced to 0.25.

4. AIR ENTRAINED CONCRETE:
 One of the greatest achievements in field of concrete technology is development
of air entrained concrete. It is used where the concrete is vulnerable to freezing and
thawing action.
 It is used where the concrete is vulnerable to freezing and thawing action. It is
prepared by adding the air entraining admixture.
The air entrainment in concrete does the following functions:.
1. It lowers the surface tension of water and thus bubbles are created.
2. Secondly the air entraining agents prevents coalescing i.e. the combining of
bubbles. The diameter of these bubbles ranges form 10 micrometer to 1000 micrometer
and in entrapped air the diameter of bubble is greater than 1mm.
Air entraining agents OR air entrained admixtures are used for the purpose of making
entrained air in concrete.

5. LIGHT WEIGHT CONCRETE
 The concrete which has substantially lower mass per unit volume then the
concrete made of ordinary ingredients is called lightweight concrete. The aggregates used
are lighter in weight.
 Density of light weight concrete is 240 kg/m³ (15pcf) -1850 kg/m³ (115 pcf).
 Strength of light weight concrete blocks varies from 7 MPa (1000 psi) - 40 MPa
(5800 psi).
 Some times Air Entrained Admixtures are also added to it giving resistance to
freezing and thawing along with strength.



Uses of Light weight concrete:
 Used where extra load is not applied e.g. parapet wall, road lining etc. or to
reduce dead load.

6. SELF COMPACTING CONCRETE
The concrete where no vibration is required. The concrete is compacted due to its own
weight. It is also called self consolidated concrete or flowing concrete. It can be also
categorized as high performance concrete as the ingredients are the same, but in this type
of concrete workability is increased. This self-consolidating concrete is characterized by:
 Extreme fluidity as measured by flow, typically between 650-750 mm on a flow
table, rather than slump (height).
 No need for vibrators to compact the concrete.
 Placement being easier.
 No bleed water, or aggregate segregation.
Uses and Applications of Self Compacting Concrete:
1. It is used in location unreachable for vibrations. e.g. underground structure, deep
wells or at bottom of deep sea.
2. SCC can save up to 50% in labor costs due to 80% faster pouring and reduced
wear and tear on formwork

7. SHOTCRETE CONCRETE:
 Shotcrete concrete uses compressed air to shoot concrete onto (or into) a frame or
structure.
 Shotcrete is mortar or (usually) concrete conveyed through a hose and
pneumatically projected at through a shortcrete nozzle with high velocity onto a surface.
Shotcrete undergoes placement and compaction at the same time due to the force with
which it is projected from the nozzle.
 It can be impacted onto any type or shape of surface, including vertical or
overhead areas.
 Shotcrete is frequently used against vertical soil or rock surfaces, as it eliminates
the need for formwork.
 It is sometimes used for rock support, especially in tunneling.
 Shotcrete is also used for applications where seepage is an issue to limit the
amount of water entering a construction site due to a high water table or other
subterranean sources.
 This type of concrete is often used as a quick fix for weathering for loose soil
types in construction zones.

8. PERVIOUS CONCRETE:
 Pervious concrete contains a network of holes or voids, to allow air or water to
move through the concrete. This allows water to drain naturally through it, and can both
remove the normal surface water drainage infrastructure, and allow replenishment of
groundwater when conventional concrete does not.



 It is formed by leaving out some or the entire fine aggregate (fines), the remaining
large aggregate then is bound by a relatively small amount of Portland cement.
 When set, typically between 15% and 25% of the concrete volumes are voids,
allowing water to drain.
 The majority of pervious concrete pavements function well with little or no
maintenance. Maintenance of pervious concrete pavement consists primarily of
prevention of clogging of the void structure.
 In preparing the site prior to construction, drainage of surrounding landscaping
should be designed to prevent flow of materials onto pavement surfaces. Soil, rock,
leaves, and other debris may infiltrate the voids and hinder the flow of water, decreasing
the utility of the pervious concrete pavement.

9. ROLLER COMPACTED CONCRETE:
 Roller compacted concrete, sometimes called rollcrete, is a low-cement-content
stiff concrete placed using techniques borrowed from earthmoving and paving work.
 The concrete is placed on the surface to be covered, and is compacted in place
using large heavy rollers typically used in earthwork.
 The concrete mix achieves a high density and cures over time into a strong
monolithic block.
 Roller compacted concrete is typically used for concrete pavement. Roller
compacted concrete dams can also be built, as the low cement content causes less heat to
be generated while curing than typical for conventionally placed massive concrete pours.

10. HOT WEATHER CONCRETE:
ACI 305 “Hot Weather Concreting” defines hot weathers as any combination of the
following conditions that tends to impair the quality of the freshly mixed or hardened
concrete:
High ambient temperature
High concrete temperature
Low relative humidity
Wind speed
Solar radiation
The success of many hot-weather concreting operations depends on the steps taken to
slow the cement hydration reactions within the concrete and to minimize the rate of
evaporation of moisture from the freshly mixed concrete.

Precautions in hot weather concreting:
To control the high concrete temperature following steps may be taken:
1. Schedule concreting. The concrete can be scheduled to time when the temperature
is not high e.g. in summer it can be schedule to night or early morning
2. Material and mix proportions: use material and mix design proportion having
good weather resistance e.g. select sand having low specific heat.
3. Covered environment: The concrete can be done in a covered environment.



4. Chilling: The chilling of aggregate can be done by watering or keeping them
covered.
5. Efficient work force: employ efficient workforce and machinery to improve the
handling.
6. Use of low heat cement: Use low heat cement.

11. COLD WEATHER CONCRETE:
ACI 306 “Cold Weather Concreting” defines cold weather concreting as a period when
for more than three (3) consecutive days, the following conditions exist:
 The average daily air temperature is less than 5°C (40°F) and,
 The air temperature is not greater than 10°C (50°F) for more than one-half of any
24 hour period.
Concrete placed during cold weather will develop sufficient strength and durability to
satisfy intended service requirements only if it is properly produced, placed and
protected.

Objectives of Cold Weather Concreting
The objectives of cold weather concreting are to:
 Prevent damage to concrete due to freezing at early ages
 Assure that concrete develops the required strength for the safe removal of forms
 Maintain curing conditions that foster normal strength development without using
excessive heat
 Limit rapid temperature changes in the concrete to prevent thermal cracking.

Precautionary Measures for concrete in cold weather
1. Using hot water
2. Providing enclosures i.e. covered area
3. Using air entraining agents
4. Scheduling concreting
5. Using admixtures Accelerators
6. Type III or high early strength cement
7. Using amount of cement

Admixtures
A material other than water, aggregates, or cement that is used as an ingredient of
concrete or mortar to control setting and early hardening, workability, or to provide
additional cementing properties.

Types of Admixtures

 Chemical Admixtures
1. Plasticizers
2. Super Plasticizers


3. Accelerators
4. Set Retarders

 Mineral Admixtures
1. Cementitious
2. Pozzolanic
3. Blast Furnace Slag
4. Fly ash
5. Silica Fume
6. Rice Husk

Chemical admixtures:
1. Water-reducing admixture / Plasticizers:
These admixtures are used for following purposes:
1. To achieve a higher strength by decreasing the water cement ratio.
2. To achieve the same workability by decreasing the cement content.
3. To increase the workability so as to ease placing in accessible locations.
4. Water reduction more than 5% but less than 12%
5. The commonly used admixtures are Ligno-sulphonates and hydrocarbolic acid salts.

2. Super Plasticizers:
These are more recent and more effective type of water reducing admixtures also known
as high range water reducer. The main benefits of super plasticizers can be summarized
as follows:
Increased fluidity:
 Flowing
 Self-leveling
 Self-compacting concrete
Reduced W/C ratio:
 Very high early strength
 Very high later age strengths
 Reduced shrinkage
 Improved durability
The commonly used Super Plasticizers are as follows:
 Sulphonated melamine formaldehyde condensates (SMF)
 Sulphonated naphthalene formaldehyde condensates (SNF)
 Polycarboxylate ether superplasticizers (PCE)

3. Accelerators:
An admixture which, when added to concrete, mortar, or grout, increases the rate of
hydration of hydraulic cement, shortens the time of set in concrete, or increases the rate
of hardening or strength development.



Accelerating admixtures can be divided into groups based on their performance and
application:

1. Set Accelerating Admixtures,
Reduce the time for the mix to change from the plastic to the hardened state.
Set accelerators have relatively limited use, mainly to produce an early set.

2. Hardening Accelerators,
Hardening accelerators find use where early stripping of shuttering or very early access to
pavements is required. They are often used in combination with a high range water
reducer, especially in cold conditions.
Examples:
Calcium chloride is the most effective accelerator and gives both set and hardening
characteristics
Chloride-free accelerators are typically based on salts of nitrate, nitrite, formate and
thiocyanate.

4. Set Retarders:
The function of retarder is to delay or extend the setting time of cement paste in concrete.
These are helpful for concrete that has to be transported to long distance, and helpful in
placing the concrete at high temperatures.
When water is first added to cement there is a rapid initial hydration reaction, after which
there is little formation of further hydrates for typically 2–3 hours. The exact time
depends mainly on the cement type and the temperature. This is called the dormant
period when the concrete is plastic and can be placed.
Retarding admixtures delay the end of the dormant period and the start of setting and
hardening.
The commonly known retards are Calcium Ligno-sulphonates and Carbohydrates
derivatives used in fraction of percent by weight of cement.

5. Air Entrained Admixtures:
An addition for hydraulic cement or an admixture for concrete or mortar which causes
air, usually in small quantity, to be incorporated in the form of minute bubbles in the
concrete or mortar during mixing, usually to increase its workability and frost
resistance.
Air-entraining admixtures are surfactants that change the surface tension of the water.
Examples: fatty acid salts or vinsol resin

Mineral Admixtures:
Types of Mineral Admixtures
1. Cementitious
These have cementing properties themselves. For example:
 Ground granulated blast furnace slag (GGBFS).



2. Pozzolanic
A pozzolan is a material which, when combined with calcium hydroxide (lime), exhibits
cementitious properties. Examples are
 Fly ash
 Silica Fume
 Rice Husk Ash
 Metakaolin

3.Ground Granulated Blast Furnace Slag (GGBFS)
Ground granulated blast-furnace slag is the granular material formed when molten iron
blast furnace slag (a by-product of iron and steel making) is rapidly chilled (quenched) by
immersion in water. It is a granular product, highly cementitious in nature and, ground
to cement fineness, hydrates like Portland cement.
Blast furnace slag is blended with Portland cement clinker to form PORTLAND
BLASTFURNACE SLAG CEMENT).
GGBFS has been widely used in Europe, and increasingly in the United States and in
Asia (particularly in Japan and Singapore) for its superiority in concrete durability.

4. Fly Ash:
The finely divided residue resulting from the combustion of ground or powdered coal.
it has POZZOLANIC properties e-g an addition to Portland cement concrete mixture to
increase the long term strength and other material properties of Portland cement concrete
and in some cases reduce the material cost of concrete.

5.Silica Fume:
The terms condensed silica fume, microsilica, silica fume and volatilized silica are often
used to describe the by-products extracted from the exhaust gases of silicon, ferrosilicon
and other metal alloy furnaces, that are of high quality, for use in the cement and concrete
industry.
Silica Fume is used in concrete to improve its properties. It has been found that Silica
Fume improves compressive strength, bond strength, and abrasion resistance; reduces
permeability of concrete and protecting reinforcing steel from corrosion.

6. Rice Husk Ash:
This is a bio waste from the husk left from the grains of rice. It is used as a pozzolanic
material in cement to increase durability and strength.


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