Classification of Concrete and Durability

Classification of Concrete and Durability

Concrete is a mixture of aggregate and often controlled amounts of entrained air held together by a hardened paste made from cement and water. Although there are other kinds of cement, the word  cement, in common usage, refers to portland cement.

Based on unit weight

Ultra light concrete   <1,200 kg/m3

Lightweight concrete 1200- 1,800 kg/m3

Normal-weight concrete  ~ 2,400 kg/m3

Heavyweight concrete > 3,200 kg/m3

Based on strength (of cylindrical sample)

Low-strength concrete < 20 MPa compressive strength

Moderate-strength concrete  20 -50 MPa compressive strength

High-strength concrete 50 – 200 MPa compressive strength

Ultra high-strength concrete  > 200 MPa compressive strength

Based on additives:

Normal concrete

Fiber reinforced concrete

Shrinkage-compensating concrete

Polymer concrete

States of concrete

Concrete has three different states:

PLASTIC : Plastic concrete in a relatively fluid state can be readily molded by hand like a clump of modeling clay.

SETTING: The stiffening of concrete, when it is no longer soft

HARDENING: This is the end product of any concrete design.

Durability

Concrete’s ability to resist the effects of wind, frost, snow, ice, abrasion, and the chemical reaction of soils or salts is a measure of its durability.

Climate and weather exposure affect durability.

As the w/c ratio increases,  durability  decreases  correspondingly.

Air-entrained concrete has improved freeze-thaw durability.

Durability  should  be  a  strong  consideration  for  concrete structures expected to last longer than five years.