Home >> A-treatise-on-roads-and-pavements-1903 >> Advantages Of Good Roads to Forms Of Construction Broken Stone >> Burned Clay Roads

Burned-Clay Roads

clay, burned, road, material, ballast and wagon

BURNED-CLAY ROADS. In the Mississippi Valley, where gravel or rock suitable for ballast must be transported consid erable distances, the railroads have been experimenting in recent years with burned-clay ballast, and it has frequently been proposed to use that material instead of crushed stone for building wagon roads.

Almost any clay, except one containing considerable sand, can be used for this purpose; but one containing considerable organic matter, though it burns more easily and is lighter to handle, gives a more friable product. The so-called gumbo soil is much used for burned-clay ballast. The best clay for this purpose is usually found in bottom lands, and is distinguished by being very plastic, very fine grained, and quite tenacious—in its native condition, the very worst material of which to build a wagon road. The burning is done in ridges often 2,000 to 4,000 feet long, the clay being mixed with nut or slack coal. As a rule, the better grades of coal are more satisfactory, since the fire burns better and is not so likely to be put out by rains. Wood is used to start the fire. The railroads usually locate the kiln alongside of a track, and handle the material almost entirely by steam power. The clay is loosened by a plow attached to a locomotive, and falls upon a conveyor which elevates it to the ridge-like kiln. The coal is shoveled directly from the cars upon the kiln. Successive layers of clay and coal are added on one side of the ridge, while on the other side the burned clay is allowed to cool. In this way the pit ad vances sidewise a few feet each day. About 1,000 cubic yards a day can be burned in a kiln 4,000 feet long, 50 men and a locomo tive being required to do the work.* The cost of burning depends upon the weather, the cost of coal, and the facilities for draining the kiln. Under favorable condi tions, a ton of coal will burn 4 to 6 cubic yards of clay. The cost

of burned clay when burned as above varies from 75 cents to $1.00 a cubic yard on board cars. The labor cost exclusive of train service is about 50 cents a cubic yard.

The burned clay or gumbo used by railroads for ballast is a reddish, gravelly material, the fragments of which are angular, very porous, and usually about as hard as soft burned brick. The chief merit of this material for railroad ballast is its porosity— just the opposite of the quality desired for the surface of a wagon road. It is not known that this material has been tried for wagon roads, but it will probably prove to be too soft and friable, and too deficient in binding power (§ 277). The localities in which clay suitable for burning is available, are those having a very sticky soil, which, when carried upon the road, would probably speedily pull to pieces even the best stone roads. In several respects the conditions necessary for the successful use of burned clay as rail road ballast are very different from those required for its economic use as a surfacing material for wagon roads; and it is at least doubt ful whether fragments of burned clay will ever come into consider able use for wagon roads in any locality.

It is possible that clay burned as brick may be employed for country roads where there is a scarcity of gravel or suitable stone, in which case the road will be constructed practically as a brick pavement—see Chapter XIV. The advantage of a brick road way over one made of fragments of burned clay is that with the former the clay can be burned more thoroughly, more uniformly, and more economically in a permanent kiln than in a temporary pit; and bricks are of a better form for road building than irreg ular fragments.