Introduction

Definition of Concrete

“ Concrete is a composite material wherein a binding material mixed in water on solidification binds the inert particles of well graded fine and coarse aggregates” or

“Concrete is a mixture of cement (7-16%), fine aggregates (28-35%), coarse aggregates (40-60%) and water (14-21%) and air (3-6%)”

Cement èPowder


Cement + Water èCement Paste


Cement Paste + Fine Aggregate (FA) èMortar Mortar + Coarse Aggregate (CA) èConcrete

Portland cement, water, sand, and coarse aggregate are proportioned and mixed to produce concrete suited for a particular job.

Uses of Concrete

Roads, Buildings, Bridges, Sidewalks, Runways, Canals, Mines, Tunnels, Dams, Sewer pipes, Railway ties, Manholes, Nuclear Installations etc.

Use of Concrete versus Steel

In the USA;

Concrete consumption 5 times by weight of steel

Other Countries;

Concrete consumption exceeds 10 times by weight of steel

More than 1 ton/year/person, Man consumes no material except water in such tremendous quantities

Definition of Portland Cement

Portland cement is the name given to the hydraulic cement obtained by intimately mixing together calcareous (limestone and chalk) and argillaceous (Silica, Alumina and iron oxide) or other silica- alumina and iron oxide bearing materials. Burning them at a clinkering temperature and grinding the resulting clinker.

Definition of Fine Aggregate

Normally called sand, this component can be natural sand or crushed stone, and represents particles smaller than 1/4".

Therefore it can also be defined as the aggregate, which pass through Sieve No. 4, are called fine aggregate, and generally accounts for 30%-35% of the mixture.

Definition of Coarse Aggregate

May be either gravel or crushed stone. Makes up 40%-45% of the mixture, comprised of particles greater than 1/4", therefore, the aggregate, which retain on Sieve No. 4 is called coarse aggregate.

Definition of Admixtures

Materials added in concrete (other than cement, water, FA and CA) to alter its properties are called admixtures. There are two types of admixtures:

1) Chemical Admixtures (Obtained chemically; e.g. set retarders, set accelerators, air entraining admixtures, water reducers etc.)

2) Mineral Admixtures (Available naturally; e.g. Fly Ash, Silica Fume, Blast Furnace Slag, Rice Husk Ash, Bagasse Ash etc.)

Definition of Yield

Yield is the volume of fresh concrete produced from known quantities of component materials, generally expressed in cubic yards or cubic meters.

Hydration of cement

Chemical reaction between cement and water is called hydration of cement. 

Heat of Hydration

In common with many chemical reactions the hydration of cement compounds is exothermic and the quantity of heat (in joules) per gram of hydrated cement evolved upon complete hydration at a given temperature is defined as the heat of hydration.

Advantages of Concrete

ü Ability to be casted in any shape

ü Fire resistant

ü High durability and low maintenance cost

ü Aesthetic properties with on-site fabrication

ü Economical; the raw materials used in concrete production are cheap and widely available in great quantities

ü Needs little or no finish for final treatments

ü Chemically inert concrete doesn't require paint; natural-mineral pigments and colouring agents can be added during the mixing to provide a rainbow of options

ü Can be reused or recycled; concrete can be reused with bituminous asphalt as road base materials, similarly can also be reused by crushing into aggregates for new concrete or as fill material for road beds or site works.

Limitations/Disadvantages;

ü Low tensile strength

ü Low ductility

ü Volume instability

ü Low strength-to-weight ratio

Types of Concrete

ü Light weight Concrete, Heavy weight Concrete

ü High-Strength Concrete

ü High-Workability or Flowing Concrete

ü Shrinkage Compensating Concrete

ü Plain Cement Concrete (PCC)

ü Reinforced Cement Concrete (RCC)

ü Fiber-Reinforced Concrete (FRC)

ü Self Compacting Concrete (SCC)

ü Roller-Compacted Concrete

ü Short-Crete