What Is Cement?
The dictionary tells us that cement is “any adhesive substance which
makes two bodies cohere.” Thus any material performing this function
may be called cement, such, for example, as the cement used in mending
broken china. Glue also is a form of cement. This story has to do with
Portland cement, which is a structural or building material used in
countless ways.
Why Is Cement Called Portland Cement?
After being wet with water it hardens into stone, and it was given the
name “Portland” because, when first manufactured in England, and mixed
with sand and stone, it resembled a celebrated building stone called
Portland, which was obtained from the Isle of Portland. Compared with
other American industries, the manufacture of Portland cement is of
recent origin. Formerly all Portland cement was brought from foreign
countries. After successful manufacture became established in this
country, however, the industry advanced with great rapidity. A few
years ago the entire United States did not use as much cement as is
now used in any one of our large cities. At the time these facts were
written (1914) the manufacturers were making more than 90 millions of
barrels a year.
What Is Cement Made Of?
Portland cement is composed chiefly of lime, alumina and silica. It
is manufactured from rocks, marl, clay and shale containing these
ingredients. If any one of them is lacking in the raw material as it
is taken from the earth, it is supplied during process of manufacture.
The greatest cement district in America is in Pennsylvania, and is
known as the “Lehigh District.” A rock containing proper constituents
for making Portland cement was found there in vast quantities, and for
a number of years the Lehigh District was the center of the industry.
In time it was found that certain clays, marls and shale could also be
manufactured into Portland cement, and thus mills have been erected
in all sections of the United States. One of the largest companies
in the United States found that cement could be manufactured from a
combination of blast-furnace slag and limestone, and this is now made
by the company in large quantities, the product being a true Portland
cement.
What Is Concrete?
Portland cement is the strongest and most lasting of all modern mortars
or binding materials. When mixed with sand and stone the resulting
mixture is called concrete. Being a plastic material when first mixed,
it cannot be used as we use brick or stone, but must be poured into
molds or forms, which hold it in place until it hardens into rock. It
may be cast in any form or shape, and thus it is useful for a vast
number of purposes. It will harden under water, and time and exposure
to the elements merely increase its strength. The most common form in
which it is used, one familiar to everybody, is in the construction
of sidewalks. It is used in all great engineering projects, such as
the building of dams, bridges, retaining walls, sewers, subways and
tunnels. Being fireproof, large quantities of it are used in buildings
and likewise on our farms, where it is extremely valuable as an
enduring and sanitary material.
What Is Cement Used For?
It has been said that concrete is a plastic material, meaning that
it is soft and pliable in the sense that clay or putty are plastic.
For this reason it is cast in forms or molds. Sometimes it is used in
the form of plain concrete, and on other occasions it is reinforced,
meaning that iron rods, steel bars or woven wire mesh are imbedded
in the concrete. When we speak of a “reinforced” concrete building,
imagine a huge wire bird cage encrusted within and without with
concrete. Place a block, beam or column of concrete upon the ground and
it will bear a tremendous load, meaning that it has great strength in
compression. On the other hand, if we were to place a long beam upon
supports at either end, leaving the greater length of it suspended and
without support, it would carry but a small load compared with concrete
in compression. Therefore, in making concrete beams or girders in a
building, strong steel bars are embedded in the concrete to take up
what are termed the tensile strains.
[Illustration: WHAT A CEMENT MILL LOOKS LIKE
This is a picture of a cement mill. Millions of dollars are invested in
these great mills, which are now located in practically all sections of
the country. Material is brought from the quarry to the mills, where it
passes through various stages, such as grinding, burning and bagging.
Expert chemists are employed to see that the cement is made exactly
right. It is a very scientific matter to make a thoroughly good cement.
There must be no guess work. Some mills are very large, the plant
comprising a number of buildings, and some companies operate several
mills in different localities. A single company supplied all of the
cement used in the Panama Canal, which great project required more than
six million barrels.]
[Illustration: This picture shows a quarry in the famous Lehigh cement
district. The giant steam shovel or excavator burrows into the hill
like some great animal, and when the bucket is full it is dumped into
the cars shown on the track, which convey the rock or the raw material
to the mill.]
[Illustration: WHERE THE MATERIAL IS OBTAINED
This is an illustration of a method of excavating and loading marl
and clay to be manufactured into Portland cement. The large bucket
suspended over the cars does not gouge into the hillside as shown in
the preceding picture, but descends like a huge steel hand, the metal
parts opening and closing like fingers. The long derrick elevates the
bucket and swings it over the train of cars.]
[Illustration: This is a view of a powerful rock crusher, which is
operated by the electric motor shown at the right. The cement rock is
brought from the quarry and dumped into the machine, from which it
issues in broken fragments, as shown in the illustration, this being
the first or preliminary crushing process.]
[Illustration: THE HUGE ROCK GRINDERS
This is a view of the electric motors operating the grinding machines
which reduce the raw material to a very fine powder. There are various
types of mills or grinders, to which the material comes after going
through the rock crusher. They grind it in preparation for the kilns.]
[Illustration: The kiln is a very important feature of the cement
plant. The finely ground raw material must be calcined or burned before
it becomes Portland cement. These kilns range from 60 to 240 feet in
length. They are slightly inclined and revolve upon rollers. The finely
ground material enters the kiln at the upper end and travels throughout
its length as the kiln slowly revolves. Powdered coal dust is fed into
the kiln at the lower end, where it is ignited and generates intense
heat. When the finely ground raw material comes into contact with the
heat, which reaches 2800 degrees F., it is transformed into what is
known as clinker, which issues from the lower end of the kiln and is
passed on to other machinery, which grinds it into impalpable powder or
Portland cement.]
[Illustration: HOW CONCRETE IS MIXED
This is an ingenious machine which bags and weighs the cement. The
bags are suspended as shown, and when filled and weighed by the
machine are placed in barrels and shipped to their destination. Every
device of this kind that will save time and labor cheapens the cost of
manufacture.]
[Illustration: In mixing cement, sand and stone together in order that
concrete may be obtained, it is customary to use, if the operation
is a large one, what are known as mechanical mixers. These are large
iron cylinders into which the three materials are put and water added.
The cylinder or iron drum revolves until the contents are thoroughly
mixed, when they issue from the mixer through a chute or spout. A mixer
of this type is shown on a succeeding page describing the making of a
concrete road. This picture shows mixing concrete by hand. The sand and
cement are first thoroughly mixed in the dry state and subsequently the
stone and water are added. Concrete should be thoroughly mixed in order
that every grain of sand may be entirely coated with cement, and then
these two combined make a rich mortar, which should surround entirely
every piece of stone.]
[Illustration: HOW CONCRETE BUILDINGS ARE MADE
This picture shows how concrete houses or walls are built through the
use of what are known as forms. In building a wall we have an inside
and outside form, as shown in the picture, between which the concrete
is placed. After it hardens the forms are removed. In some operations,
such as the construction of a large factory building or great bridge,
there is such a vast array of timber construction as to make the scene
quite impressive, especially when bridge arches of great span and
height are under construction.]
[Illustration: This is a view of an arch built of concrete during the
Jamestown Exposition. It is a striking illustration of how concrete
may be used for both ornamental and practical purposes. In no field
has concrete proved to be of more value and economy than in the
construction of bridges, whether large or small. Some of the largest
bridges in the world are built of concrete, and in many cases iron
bridges are incased in concrete to keep them from rusting.]
[Illustration: CONCRETE HOUSES CANNOT BURN
This is a curious example of concrete construction. It is a coal
pocket, from which locomotives are supplied with fuel. Railroad
companies have adopted it because of its great strength and durability.]
[Illustration: Just as mammoth structures are created with poured
concrete, so we may produce the most delicate and ornamental patterns.
These are usually cast in plaster molds and often in molds of wood or
iron. Where undercut work is required, such as in the sun-dial shown, a
wood or metal mold could not be removed without injury to the concrete,
and so sculptors have invented the pliable glue mold, which can be
easily removed and which will spring back to its original shape if
necessary to use it a second time.]
[Illustration: Concrete in dwelling construction means the elimination
of fire danger and also cost of painting and repairs. This picture
shows a solid concrete house, parts of which have been encrusted with
beautiful tiles. Concrete has been successfully used in all types of
dwellings, from the humble abode of the workingman to the palace of
the multimillionaire. An entire house may be made of concrete, even to
the roof and stairways, and where a dwelling is constructed of this
material throughout, it is proof against fire and decay.]
[Illustration: HOW THE FARMER USES CONCRETE
This is an interesting example of concrete construction. It is a
large water tower which will never warp, rust or decay. In this field
concrete has been of great service, whether reservoirs are constructed
in the form of towers or tanks. As already stated, water does not
affect the life or strength of concrete, except to improve it.]
[Illustration: This is a concrete silo. A silo made of concrete is
merely a huge stone jar in which green food for cattle is preserved.
The crop is gathered and placed in the silo, thus insuring abundance
of green and wholesome food throughout dry seasons and during the
winter. The contents of the silo is known as silage or ensilage, and is
merely corn fodder cut when green. Concrete silos are both storm- and
fire-proof.]
[Illustration: It is usual to consider concrete in connection with
great engineering enterprises, but nevertheless many millions of
barrels are used each year by the farmers of the United States. This
picture shows a clean, sanitary and durable concrete stable. In
buildings of this character concrete is rapidly supplanting wood, which
soon goes to decay, to say nothing of accumulation of filth.]
[Illustration: HOW CONCRETE ROADS ARE BUILT