PORTLAND CEMENT CONCRETE - Materials for Civil and Construction Engineers - page 235

7

PORTLAND CEMENT

CONCRETE

Civil and construction engineers are directly responsible for the quality con-
trol of portland cement concrete and the proportions of the components used
in it. The quality of the concrete is governed by the chemical composition of
the portland cement, hydration and development of the microstructure, ad-
mixtures, and aggregate characteristics. The quality is strongly affected by
placement, consolidation, and curing, as well.
How a concrete structure performs throughout its service life is largely af-
fected by the methods of mixing, transporting, placing, and curing the concrete
in the field. In fact, the ingredients of a “good” concrete may be the same as
those of a “bad” concrete. The difference, however, is often the expertise of the
engineer and technicians who are handling the concrete during construction.
Because of the advances made in concrete technology in the past few
decades, concrete can be used in many more applications. Civil and con-
struction engineers should be aware of the alternatives to conventional con-
crete, such as lightweight concrete, high-strength concrete, polymer concrete,
fiber-reinforced concrete, and roller-compacted concrete. Before using these
alternatives to conventional concrete, the engineer needs to study them, and
their costs, in detail. This chapter covers basic principles of conventional
portland cement concrete, its proportioning, mixing and handling, curing,
and testing. Alternatives to conventional concrete that increase the applica-
tions and improve the performance of concrete are also introduced.

7.1 Proportioning of Concrete Mixes

The properties of concrete depend on the mix proportions and the placing and
curing methods. Designers generally specify or assume a certain strength or
modulus of elasticity of the concrete when determining structural dimensions.