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:
Fiber reinforced 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.
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.