This document discusses the key constituents of concrete - cement, aggregates, water and admixtures. It describes the different types of aggregates including fine aggregates like sand and coarse aggregates. It also discusses the production process of concrete including batching, mixing, transporting, placing, compacting, curing and finishing. Concrete is formed by mixing these constituents in specific proportions to form a strong building material.

1. Civil Engineering Materials
IQRA NATIONAL UNIVERSITY PESHAWAR
CONCRETE

2. Concrete
• Concrete is the mixture of cement, coarse
aggregate, fine aggregate and water in
specific proportions. It is used for binding
the construction material together.”
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3. Concrete
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4. Concrete Constituents
Aggregates

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Aggregates
• Inert materials mixed with a binding material
(cement, lime, mud) for preparation of mortar or
concrete.
• Depending on the particle size, aggregates are
classified as
– Fine aggregates. 0.15 mm to 4.75 mm. sand,
crushed stone, ash, cinder, surkhi.

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Open Pit Aggregate Quarry

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Sieve Gradation

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Fine Aggregates
• Particle size 4.75 mm to 0.15 mm
• Sand – small grains of silica from weathering
disintegration of rocks
– Pit or quarry sand – sharp and angular grains found
as deposits in soil. Free from organic matter and
clay and is of good quality
– River sand – banks and beds of rivers. Needs
washing to get rid of clay
– Sea sand – fine rounded brown grains at sea
beaches. Contains salts so needs washing

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Fine Aggregates
• Crushed stone – waste stone crushed to sand
particle size gives excellent fine aggregate
• Ash or Cinder – fine nodules from steam
locomotives and furnaces. Cheap and strong
black mortar obtained with lime
• Surkhi – well ground, powdered broken brick
used as fine aggregate in lime mortar.

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Good Sand Qualities
• Coarse and angular grains of pure silica
• Hard, strong and durable grains
• Free from silt, clay and salts that may hamper
setting or attack reinforcement
• Free from organic matter
• Well graded – suitable proportions of various
particle sizes
• Free from hygroscopic (Readily absorbing moisture, as
from the atmosphere) moisture

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Types of Sand
California Black
Baja Mexico
Huahini, Tahiti
Maui, Hawaii

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Types of Sand
California Black
after magnet
Oahu, Hawaii
Guam, Green
St Martin,
Caribbean

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Types of Sand
Lake Powell,
Utah
Lake Powell,
Utah
Lumberyard
Mt St Helena

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Fine Aggregates - Sand
• Functions of sand in mortar
– As an adultrant to increase volume of mortar
– Reduces shrinkage and cracking of mortar
– Helps pure lime to set by allowing air penetration
providing carbon dioxide for carbonization and
setting of lime
• Bulking of sand – increase in volume due to
wetness of sand (25% volume increase by 4%
moisture content)

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Bulking of Sand

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Bulking of Sand

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Fine Aggregates - Sand
• Sand tests
– Rub a little sand between fingers. Clay impurities
will leave stains on fingers
– Salts may found out by tasting by tongue
– Vigorously shake sand sample in water and let it
settle. Clay or silt present will settle on top of sand
– Stir sample of sand in 3% solution of caustic soda
and let it stay sealed for 24 hrs. organic matter will
turn the liquid color to brown

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Coarse Aggregates
• Size from 4.75 mm to 7.5 mm
• Stone ballast – quarried granite, sandstone and
limestone broken and sieved to required size.
Should be free from organic matter. Stone
should not be soft, laminated. Excess clay
washed off.
• Gravel or shingle – obtained from river beds,
quarries or sea shores. Hard and durable. Clay
and salts should be washed off.

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Coarse Aggregates
• Brick ballast – broken brick used where natural
aggregate is expensive or not available. Well burnt
good bricks are used. Should be free from dust. Used
where lower strength is required. Ballast thoroughly
saturated before use in concrete.
• Breeze and clinker – by products of coal burning
provides cheap and light aggregate for internal
concrete blocks and non load bearing partition walls.
Not good for RCC because of excessive sulphur which
corrodes steel. Used for internal concrete blocks and
partitions not carrying loads

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Stone Ballast

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Course Aggregate

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Pebbles, Shingle

23. Concrete Constituents
Water

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Why Water in Concrete?
• Minimum quantity of water required for
hydration of cement
• Water in excess required to act lubricant
between aggregates to produce workable and
economical concrete
• Lesser water makes it difficult to work with
concrete and non-uniform mixing makes it
weaker in strength
• Water also required for curing and aggregate
washing

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Water Quality
• Natural potable water having no excessive taste or
odor is OK for concrete
• Excessive impurities will effect setting time
• Suspended particles should be less than 2000 ppm
• Inorganic salts
– Sodium phosphate, sodium borate, sodium iodate, zinc
chloride act as retarders
– Calcium chloride acts as accelerator
– Bicarbonates of sodium and potassium cause rapid setting

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Water Quality
• Acids and alkalis – water with pH value 6 - 8
only is suitable. Water with excessive acids or
alkalis (industrial waste) is unsuitable for civil
engineering purpose
• Oil contamination – mineral oil with more than
2% concentration may reduce concrete strength
by 20%
• Algae – in water or on aggregate reduces
bonding strength

27. Concrete Constituents
Admixtures

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Functions of Admixtures
• Accelerate or retard the initial setting
• Increase the strength
• Improve workability, penetration and pump ability
• Reduce heat of evolution
• Increase durability
• Control expansion caused by reaction
• Decrease capillary flow of water to make it impermeable
• Reduce segregation in grouts
• Inhibit corrosion, increase resistance to chemical attack
• Produce concrete which is colored, cellular, fungicidal,
germicidal, and insecticidal

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Admixtures
• Accelerators
– Reduce the setting time; accelerate hydration rate
– Sulphates (less CaSO4), alkali carbonates aluminates
silicates; chlorides of aluminum calcium sodium; sodium and
potassium hydroxide, etc
– CaCl2 <2% accelerator but >2% retarder
• Retarders
– Increase setting time; delay the setting
– Reduce rate of hydration, more water available for
workability
– CaSO4, sugar, starch, cellulose, ammonia and iron chlorides

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Admixtures
• Water Proofers
– Concrete made impervious to water by additives
• Water repellent type
• Pore filling type
– Water repellent type - soda, potash and calcium soaps, resin,
vegetable oils, fats, waxes, coal tar residue
– Pore filling type – soda, aluminum silicates; zinc sulphate;
aluminum and calcium chloride
• Plasticizers and Workability agents
– Increase the workability by increasing the paste in cement,
hence the cohesiveness
– Excess increases water causing cracking and strength loss
– Lime, bentonite, kaolin, chalk, etc

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Admixtures
• Bleeding Agents
– Paraffin wax or air entrainment is used
• Coloring agents
– Rawumber (brown), ferrous oxide (black), red oxide
(red) and chromium oxide (green)
• Expansion producing agents
– Granulated iron and chemicals counteract the
drying shrinkage of concrete
• Fungicides and Algaecides
– Arsenic, tin and mercury compounds used as paint

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Admixtures
• Air entraining agents
– Discontinuous voids less than 0.05 mm diameter formed
– Air entrainment increases workability, weathering resistance,
however there is reduction in strength, bleeding possibility,
segregation
• Surface active agents – , animal or vegetable fats and oils and alkali
salts of organic compounds
• Chemicals – zinc or aluminum powder added to concrete releases
gases
• Dispersing agents – surface active chemicals impart electrostatic
charges on cement particles, causing repulsion, preventing
coagulation, entraining air and increasing workability

33. Plain Cement Concrete

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Concrete

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Concrete Production Stages
• Batching or measurement of materials
– Volume
• (1 : m : n) cement : sand : aggregate.
– Weight
• Mixing
– Hand mixing. ((Cement + sand) + aggregate) + water
– Machine mixing by concrete mixers
• Tilting mixers
• Non-tilting mixers
• Reversing drum mixers
• Pan type or stirring mixers
• Transit mixer

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Traveling
Concrete Mixer
Manual Concrete
Mixer

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Concrete Production Stages
• Transporting
– Mortar pan
– Wheel barrow
– Chutes
– Dumper
– Bucket and Ropeway
– Belt conveyor
– Skip and Hoist
– Pumping

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Concrete Production Stages
• Placing. Place within 30 minutes after adding water
– Foundations
– Beams, columns, slabs
– Mass concreting
– Highways and runways
– Underwater concreting
• Compacting
– Hand compaction
– Vibratory compaction
– Spinning compaction
– Jolting compaction

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Concrete Production Stages
• Curing
– Water curing
– Steam curing
– Infra red radiation curing
– Electrical curing
– Chemical curing
• Finishing
– Formwork finishes
– Surface treatments
– Applied finishes

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Concrete Mix
• Methods
– Arbitrary method
– Minimum void method
– Maximum density method
– Fineness modulus method
• Arbitrary method (cement : fines : coarse)
– High strength concrete (1 : 1 : 2 and 1 : 1.2 : 2.4)
– General RCC work (1 : 1½ : 3 and 1 : 2 : 4)
– Mass concrete work (1 : 3 : 6 and 1 : 4 : 8)

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Water Cement Ratio
• Ratio of water and cement by weight or volume
• Less water
– Insufficient hydration of cement
– Difficult to work with
– Porous and weak concrete
• More water
– More workable mix
– Segregation of aggregates
– Porous concrete of low density and low strength

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Slump Test
Truncated steel cone
Height – 30 cm
Base diameter – 20 cm
Top diameter – 10 cm
Each concrete layer 7.5 cm
25 rammings of 16 mm dia rammer
Slump size
2.5 to 5 cm mass concrete
Road work
5 to 10 cm beams and slabs
7.5 to 12.5 cm columns, vertical
sections, retaining
walls

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Slump Test

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Qualities of Good Concrete
• Strength – compressive and tensile
• Durability – wind, rain, frost, temperature, chemicals
and salts
• Density – 3,000 kg/m³ well compacted
• Water tightness – avoid corrosion of inside steel and
leakage, seepage in hydraulic structures
• Workability – easily workable
• Resistance to wear and tear – abrasive action in floors
and roads

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Concrete Joints
• Construction joints
– Joint of old and new
– At a location of minimum shear
– Vertical or horizontal but not inclined
– Joint key and extension of reinforcement steel
• Expansion joints
– Thermal expansion and contraction
– Deflection movements

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Concrete Types
• Reinforced Cement Concrete (RCC)
• Pre-stressed Cement Concrete
• Aerated Concrete
• Pre-packed Concrete
• Foam Concrete

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Concrete Classification
Concrete
Based on
Cementing
Material
Based on
Ratio Specs
Based on
Performance
Specs
Based on
Grade
Based on
Bulk Density
Kg/m³
Based on
Casting
1:3:6 Strength
M5
5 N/mm²
Super Heavy
Over 2500
Lime
Concrete
Cement
Concrete
Gypsum
Concrete
Dense
1800-2500
Light Weight
500-1800
In-situ
Pre-cast
Extra
Light Weight
Below 500
Water
Cement
Ratio
Compaction
Slump
1:2:4
1:1½:3
1:1:2
M55
55 N/mm²

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Bulk density = dry weight / total
volume