Department of Civil Engineering

Engr. Rameez Sohail

Lecture # 01

Properties of Concrete (CE-203)

By:

Properties of Concrete

• Credit Hours 3 ( 2+1)

• Semester Weeks 16/18

• Evaluation/Grading– Home Assignments– Quiz test, unannounced– Midterm test– Attendance

• Semester Exam

2

What is Concrete?.• Concrete is word of Latin derivation ( con – together ) ( crete

– to grow ) and its history can be charted from 3000 BC.

• It is a composite material that consists essentially of a binding medium (Cement, Lime) within which are embedded particles or fragments of aggregate(Coarse & Fine Aggregates).

• Concrete is often looked upon as “man made rock”.

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Section cut from Hardened Concrete

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Concrete Ingredients

☞Cement /Lime - Binder

☞Aggregate - sand, gravel, crushed rock Fine aggregate ----- Sand Coarse aggregates ----crushed rock

☞Water

☞Admixtures - when necessary

Cement

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A mixture of inorganic materials that sets and develops strength by chemical reaction with water by formation of hydrates and is capable of doing so under water.

Cement Powder Cement Bag

Cement

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Binds the aggregates into a solid mass

Imparts strength to concrete

Makes concrete impermeable by filling up voids in fine concrete

Aggregates

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Granular materials, such as sand, gravel, crushed stone used with cementing medium to form concrete or mortar.

Aggregates act as a relatively inexpensive inert filler, providing stability against volume changes and influencing strength.

Fine Aggregate Diameter< 4.75mm

Coarse AggregateDiameter > 4.75mm

Aggregates

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SandFills the voids within coarse aggregatesAssists in hardening of cement by allowing water to seep through its voidsMinimizes shrinking and cracking of concreteEconomizes concrete by varying its proportion for strength

Coarse AggregateActs as main filler, forms the main bulk massBinding material adheres on its surfaceImparts volumetric stability and durability to concreteIncreases crushing strength, resistance to wear and tear, and water tightness of concreteEconomizes concrete since it is cheaper than cement

Water

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•It reacts with the cement to form binder that hardens and bonds the aggregates together

•Lubricates the fresh concrete enabling it to be placed into position and compacted.

•Good water is essential for quality concrete.

•It should be good enough to drink--free of trash, organic matter and excessive chemicals and/or minerals.

•The strength and other properties of concrete are highly dependent on the amount of water and the water-cement ratio.

Concrete Ingredients

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Admixtures

They are chemicals that can be added to the concrete immediately before or during mixing and significantly change its fresh, early age or hardened state to economic or physical advantage

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Concrete Ingredients

• Admixtures– Retarding agents – delay setting time– Accelerators – set and acquire strength rapidly– Air entraining agents– Water proofing agents – pore filling, water repelling– Pozzolanas – non-cementing, but forms lime

compounds which are cementing– Pigments– Workability agents

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• Coarse aggregate acts as a filler.

• Fine aggregate fills up the voids between the paste and coarse aggregate.

• Cement in conjunction with water acts as a binder.

• Admixtures aid the mobility of the mixture by regulating the setting environment and time.

• (Setting & Hardening)

Cement Concrete

Advantages of Concrete

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Concrete is the most widely used construction material in the world.•It has relatively high compressive strength.•It has better resistance to fire than steel, wood etc•It has long service life with low maintenance cost.•In some type of structure such as dams, piers and footing it is most economical structural materials.•It can be cast to take the shape required making it widely used in pre-cast structural components.•It yield rigid member with minimum apparent deflection.•Concrete can be finished to produce surfaces ranging from glass-smooth to coarsely textured, and it can be colored with pigments or painted.

Disadvantages of Concrete

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•It needs mixing, casting and curing all of which affect the final strength of concrete.

•The cost of formwork used to cast the concrete is relatively high.

•It has very low tensile strength.

•It has low compressive strength as compared to steel which lead to large section of structural members.

•Minor crack develops in concrete due to shrinkage.

•It requires skill labor and supervision from mixing to finishing.

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Qualities of Good ConcreteFresh Concrete• Workability – easily workable• Volume stability

Hardened 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• Resistance to wear and tear – abrasive action in floors and

roads

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