Story in a Barrel of Cement
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
HOW CONCRETE ROADS ARE BUILT
A CONCRETE ROAD
Our two last pictures relate to an exceedingly important and rapidly increasing use of cement. It is the construction of concrete roads. The first picture shows a concrete road in course of construction. The mechanical mixer referred to above is shown in this picture. It is a self-propelling machine and mixes the concrete very rapidly. As it comes from the mixer in a wet and mushy mass it is placed between rigidly staked side forms, where it hardens into imperishable rock. The road is brought to its shape by working to and fro a long plank called a template, after which the surface of the road is troweled with wooden floats, giving it a texture which prevents horses and cars from slipping. The last picture shows a narrow concrete road in the state of Maryland. Wherever these roads have been built they mean much to the women and children of the community. They never grind up into mud or dust, and are as pleasant to walk upon as the sidewalks of the city. Children, especially, delight in them. In Wayne county, Mich., where they have the most celebrated concrete roads in the world, the children go to and from school on roller skates, and various games are played on the concrete road.