Hamid Hashmi

3. CONCRETE is made by mixing:
 CEMENT
 WATER
 COARSE AND FINE AGGREGATES
 ADMIXTURES (if required).
The aim is to mix these materials in measured
amounts to make concrete that is easy to:
 TRANSPORT
 PLACE
 COMPACT
 FINISH and which will set, and harden, to give a strong and
durable product.

4.  Concrete has relatively high compressive
strength, but significantly lower tensile
strength, and as such is usually reinforced
with materials that are strong in tension
(often steel).
 The concrete mix is workable. It can be
placed and consolidated properly by
yourself or your workmen.

5.  Desired qualities of the hardened concrete
are met: for example, resistance to freezing
and thawing and water tightness (low
permeability), wear resistance, and strength.
 Economy. Since the quality depends mainly
on the water to cement ratio, the water
requirement should be minimized to reduce
the cement requirement (and thus reduce the
cost).

6.  Aggregate is commonly considered inert filler, which accounts
for 60 to 80 percent of the volume and 70 to 85 percent of the
weight of concrete.
 Aggregate is classified as two different types, coarse and fine.
Coarse aggregate is usually greater than 4.75 mm (retained on a
No. 4 sieve), while fine aggregate is less than 4.75 mm (passing
the No. 4 sieve).
 The compressive aggregate strength is an important factor in the
selection of aggregate. When determining the strength of normal
concrete, most concrete aggregates are several times stronger
than the other components in concrete and therefore not a factor
in the strength of normal strength concrete. Lightweight
aggregate concrete may be more influenced by the compressive
strength of the aggregates.

7.  The shape and texture of aggregate affects the properties of fresh
concrete more than hardened concrete. Concrete is more
workable when smooth and rounded aggregate is used instead of
rough angular or elongated aggregate. Most natural sands and
gravel from riverbeds or seashores are smooth and rounded and
are excellent aggregates.
 The most common classification of aggregates on the basis of
bulk specific gravity is lightweight, normal-weight, and
heavyweight aggregates.

10.  Fully cured, hardened concrete must be strong enough to
withstand the structural and service loads which will be
applied to it and must be durable enough to withstand the
environmental exposure for which it is designed. If
concrete is made with high-quality materials and is
properly proportioned, mixed, handled, placed and
finished, it will be the strongest and durable building
material. Below are the properties of hardened concrete:-
 · Strength
 · Creep
 · Durability
 · Shrinkage
 · Modulus of Elasticity
 · Water Tightness

11. Thanks.