Concrete Microstructure, Properties and Materials

Concrete Microstructure, Properties and Materials

The most widely used construction material is concrete, commonly made by mixing

portland cement with sand, crushed rock, and water. Last year in the U.S. 63 mil-
lion tons of portland cement were converted into 500 million tons of concrete, five

times the consumption by weight of steel. In many countries the ratio of concrete con-
sumption to steel consumption exceeds ten to one. The total world consumption of

concrete last year is estimated at three billion tons, or one ton for every living human
being. Man consumes no material except water in such tremendous quantities.
Today, the rate at which concrete is used is much higher than it was 40 years
ago. It is estimated that the present consumption of concrete in the world is of
the order of 11 billion metric tonnes every year.
Concrete is neither as strong nor as tough as steel, so why is it the most
widely used engineering material? There are at least three primary reasons.

Structural elements exposed to moisture, such as piles, foundations, footings,
floors, beams, columns, roofs, exterior walls, and pipes, are frequently built

with reinforced and prestressed concrete (Fig. 1-3). Reinforced concrete is a con-
crete usually containing steel bars, which is designed on the assumption that

the two materials act together in resisting tensile forces. With prestressed con-
crete by tensioning the steel tendons, a precompression is introduced such that

the tensile stresses during service are counteracted to prevent cracking. Large
amounts of concrete find their way into reinforced or prestressed structural
elements. The durability of concrete to aggressive waters is responsible for the

fact that its use has been extended to severe industrial and natural environments


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