Covered hopper cars loaded at Marquette Cement Manufacturing Company, Rockmart, Ga., ready to roll on Southern lines. |
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Probably no other building material has been as much involved in changing the physical face of the territory Southern serves as a fine, light powder called portland cement.
Cement is the basic ingredient of concrete, a construction material so widely used by American builders that today more than 300,000,000 barrels of cement are produced in the United States annually. As one of the most actively-building regions in the country - industrially and otherwise - the South uses an important share of this total.
Covered hopper cars loaded at Marquette Cement Manufacturing Company, Rockmart, Ga., ready to roll on Southern lines. |
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Concrete in a bewildering variety of uses enters into the construction of industrial plants, office buildings, schools, churches, homes, streets, highways and bridges. And these are only a few. Wherever you are as you read this, the chances are better than even that you are not more than a few feet away from concrete in some form.
Southern Railway people have an interest in cement beyond the structural role concrete plays in the industrial, commercial and residential building that give visible evidence of the booming growth of the South.
Cement ranks high on the list of Southern-hauled commodities from the standpoints of both tonnage and revenue. Each year our railway moves tens of thousands of carloads of cement from mills along our lines. More thousands of carloads of the raw materials used in cement-making are delivered to Southern- served plants.
In its broadest sense, the word "cement" includes a great variety of materials. Cement can be any substance which joins individual crystals together to form a mass. But the word today usually refers to port- land cement, which makes up about 98 per cent of all cement manufactured.
Availability of limestone deposits (upper left) and modem rail facilities (right) are important considerations in the location of a cement plant-as is clearly demonstrated in this view of the North Birmingham, Ala., plant of Lone Star Cement Corporation. |
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Contrary to common belief, the term "portland" as applied to cement refers to neither the Maine nor the Oregon city, nor to any of the other dozen or more Portlands in the United States. Joseph Aspdin, the English bricklayer who in 1824 invented portland cement, named his product after a similarly-colored natural stone quarried on the Isle of Portland in the English Channel.
"Portland" cement, thus, is not a brand name but a type of cement-just as anthracite is a type of coal. There are scores of different brands of portland cement.
In determining the location of a portland cement processing plant, the availability of large quantities of limestone, cement rock, marl or shell, and the near- ness of rail facilities are among the primary factors considered.
At Alpha Portland Cement Company's plant in Phoenixville, Ala., rocks from the plant quarry are hauled to the primary crusher by cable car. |
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From deposits of these raw materials along Southern's lines cement mills are each producing annually quantities ranging from one million to more than three million barrels of cement. (A barrel is still the official unit of cement measure used by the U. S. Bureau of Mines, although cement is now shipped in bulk or in reinforced paper bags. A barrel equals 376 lbs.-or four 94-lb. bags. Each bag contains a cubic foot of cement.)
The Southern itself uses concrete extensively, as do most railroads. According to the Portland Cement Association, American railways have used concrete in possibly more diversified ways than any other industry. More than 160 uses have been counted, ranging from small projects like mileposts to large bridges, long trestles and multi-storied office buildings.
Rocks are ground finer and finer as the manufacturing process continues. This is a ball mill at Penn-Dixie Cement Corporation's Clinchfield, Ga., plant. |
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Cement-making has been described as the process of "putting a mountain through a sieve." Enormous quantities of raw material pass through some 80 separate operations under exacting laboratory controls before resulting in a powder so fine it can pass through a sieve that will hold water.
Techniques of cement manufacture vary among producers but the following description and the diagram is fairly typical.
Cement literally begins with a blast as a charge of dynamite separates thousands of tolls of rock from a mountainside or pit quarry. A single explosion can loosen enough stone to fill 8,000 standard gondola cars.
A power shovels the broken rock to be hauled to the crushing plant for the first crushing operation. The method of transferring the load from quarry to crusher depends on the distance. Dump trucks, cable cars, dump cars pulled by a locomotive, and other conveyances are used.
At the crushing 'plant the huge chunks of stone ~ dumped into a steel-lined crusher where a truckload of barrel-sized rocks can be reduced to a six-inch size within two or three minutes. The rock later passes through secondary crushers, or hammer mills, where it is further ground to approximately two-inch pieces.
A cable car dumps its load of quarry rock into the crusher at Lehigh Portland Cement Company's North Birmingham, Ala., plant.- |
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The crushed rock then goes into storage bins. Other bins hold additional primary raw materials used in cement-making. In addition to limestone or cement rock, these may include clay, iron ore, slag, silica, sand, or other minerals.
The next operation depends on whether the cement plant uses a "dry" or "wet" process of pulverizing and blending ingredients (of the nine Southern-served plants with operations pictured in this article, two use the dry and seven the wet process).
In the dry process, the raw materials are taken from storage, mixed in proper proportions and fed into huge rotating ball mills for preliminary grinding. These mills get their name from the hundreds of large steel
Bags of cement being neatly stacked in a Southern Railway box car at Southern Cement Company's Roberta, Ala., plant. |
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The mixture next goes to a tube mill, which is similar to the ball mill except that the material is more finely ground by 40 to 50 tons of smaller steel balls. From there, the material, now in fine particles, is carried to large storage bins and samples are analyzed for chemical content to insure uniformity. Accurately proportioned amounts of the dry raw material are then ready to go to the kilns (pronounced "kills" ) for burning.
"Slurry"-raw materials mixed with water-is stored in this giant tank at the Volunteer Portland Cement Company, Knoxville, Tenn. |
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If the wet process is followed the raw materials are fed into the ball mills as in the dry method, but water is added and the material is ground wet to give it a thick, creamy, soup-Iike consistency. This mixture, called "slurry," is next pumped into large tanks where it is thoroughly agitated and blended, then pumped to great storage tanks to be held until needed for burning. From here on, both wet and dry type plants follow essentially the same final steps.
One of the most spectacular operations in cement- making takes place inside the kilns. These huge, tube-shaped furnaces, fired by powdered coal, natural gas, or fuel oil, fuse the raw materials under intense heat.
Clinker (with gypsum added) is ground into cement which is stored in bulk in silos like these at Giant Portland Cement Company, Harleyville, S. C. Bagging cement at the Lone Star Cement Company, North Birmingham, Ala. |
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Kiln sizes vary from plant to plant, but they range up to 12 feet in diameter-large enough to drive a small truck through-and may be as long as the height of a 40-story building. The heavy cylinders are sup- ported by massive roller bearings and rotated by giant gears at about a revolution per minute.
The kilns are slightly inclined so that the dry or slurry raw materials fed at the high end move by gravity, aided by the revolving motion, to the lower end where the heat reaches a temperature of about 2750 degrees Fahrenheit.
Raw materials are burned into cement clinker in huge rotary kilns. This one is at Marquette Cement Manufacturing Company's plant at Rockmart, Ga. |
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A glance through the fire door at this end shows a weird world of fire and colored light where long tongues of flame, roaring under forced draft, shoot through the cascading raw material. The extreme heat causes a desired chemical change to take place in the raw material, fusing it into "cement clinker" about the size of marbles.
Loading bulk cement into a covered hopper car at 'the Universal Atlas Cement Company, Leeds, Ala. |
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While still white-hot, the clinker is discharged from the lower end of the kiln into specially constructed equipment for rapid cooling. As it cools, the dissipated heat is usually returned to the kiln to save fuel. In some cases the hot gases, after they pass out of the kiln, are used to generate power for use in the plant. After cooling, clinker may be either stockpiled for future use or carried immediately through a final grinding stage.
Loading raw materials brought in by rail into storage bins at Alpha Portland Cement Company, Phoenixville, Ala. |
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Before grinding, an important ingredient is added to the clinker. Gypsurl1, a chalk-like mineral, is the "regulator" that controls setting time when concrete is made from cement. Without this retarding agent the concrete would harden too soon and become un- workable. As the clinker is fed into the grinding mills it is mixed with a small amount of gypsum, usually three to five per cent by weight.
Final pulverizing takes place in a tube mill where thousands of steel balls reduce the clinker-gypsum to powdery particles which are fine enough that over 90 per cent pass through a screen with 40,000 openings per square inch ( an ordinary kitchen Hour sieve has less than 400 openings per square inch) .
Penn-Dixie Cement Corporation's plant at Clinchfield, Ga., operates its own small in-plant railroad to move limestone rock from the nearby quarry to the plant where the side-dump cars pour materials into the crusher. |
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Before the finished cement goes to the storage silos samples are taken hourly from each finishing mill. These undergo strict laboratory tests to insure that the final product will make concrete of uniform strength and durability-an important factor wherever concrete is used.
From the towering storage silos, cement is drawn as needed for shipping to customers either in bags or in bulk.
Huge paddles keep the slurry well mixed in these circular tanks at the Universal Atlas plant in Leeds. |
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In bagging cement, multi-wall paper sacks are filled through an opening or "valve" on a packing machine which automatically cuts off the flow of cement when 94 lbs. have entered the sack. One thousand plus bags of cement make a payload for one 50-ton box car.
In bulk shipping by rail the cement is piped directly into hopper cars. A 70-ton covered hopper holds about 400 barrels of cement. .
Bird's-eye view of Giant Portland Cement Company's plant at Harleyville, S. C., shows ever-present rail facilities. |
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The uses of concrete made with portland cement are too numerous to record here in any detail. And the list is constantly growing. One of the newer uses for portland cement is in prestressed concrete.
In making a prestressed concrete beam, lengths of high-strength steel wire, positioned as needed, are covered with concrete as the form is filled. The wire, under tension, strengthens a concrete beam so that it will remain rigid under loads heavy enough to cause a normally reinforced concrete beam to bend.
Peering through a protective mask, an observer sees a weird world of roaring flame in one of the kilns of Volunteer Portland Cement Company, Knoxville. |
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The skyrocketing growth of the portland cement industry in the United States since the turn of the century offers solid evidence of ever-expanding uses for cement. From a production of about 8~ million barrels in 1900, the industry has grown to an output of about 300 million barrels annually.
Southern-served cement plants are busily keeping pace with the still-growing demand for their versatile commodity. Several have either recently completed or are presently undergoing renovation or expansion.
Before finished cement goes to storage silos, samples are taken hourly from each finishing mill. At Southern Cement Company's Roberta plant, as at other cement plants, laboratory tests help insure that the final product will make concrete of uniform strength and durability. |
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Southern, too, is meeting the need for more transportation created by increasing demands for cement. It maintains a large fleet of covered hopper cars and has been adding to it. Last year, for example, of the 1,846 freight cars Southern Railway Company received and put into service, 380 were 70-ton covered hopper cars.
This view of the quarry at Lehigh Portland Cement Company at North Birmingham gives some idea of the huge quantities of limestone rock it takes to make the cement that builders need. |
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Southern supplies an essential service in transporting cement-the mountains turned powder that eventually become skyscrapers and churches, factory buildings and warehouses, streets and highways, bridges and piers, to change the face of the South and the nation.