PORTLAND CEMENT - Materials for Civil and Construction Engineers - page 201

6

PORTLAND CEMENT

Portland cement concrete is the most widely used manufactured construc-
tion material in the world. The importance of concrete in our daily lives
cannot be overstated. It is used in structures such as buildings, bridges, tun-
nels, dams, factories, pavements, and playgrounds. Portland cement concrete
consists of portland cement, aggregates, water, air voids, and, in many cases,
admixtures. This chapter covers the topics of portland cement, mixing water,
and admixtures; Chapter 7 will describe portland cement concrete.
There are many types of concrete, based on different cements. However,
portland cement concrete is so prevalent that, unless otherwise identified,
the term concrete is always assumed to mean portland cement concrete. Port-
land cement was patented by Joseph Aspdin in 1824 and was named after the
limestone cliffs on the Isle of Portland in England (Kosmatka et al. 2002).
Portland cement is an instant glue (just add water) that bonds aggregates
together to make portland cement concrete. Materials specialists concerned
with the selection, specification, and quality control of civil engineering
projects should understand the production, chemical composition, hydra-
tion rates, and physical properties of portland cement.

6.1 Portland Cement Production

Production of portland cement starts with two basic raw ingredients: a cal-
careous material and an argillaceous material. The calcareous material is a
calcium oxide, such as limestone, chalk, or oyster shells. The argillaceous ma-
terial is a combination of silica and alumina that can be obtained from clay,
shale, and blast furnace slag. As shown in Figure 6.1, these materials are
crushed and then stored in silos. The raw materials, in the desired propor-
tions, are passed through a grinding mill, using either a wet or dry process. The
ground material is stored until it can be sent to the kiln. Modern dry process ce-
ment plants use a heat recovery cycle to preheat the ground material, or feed