sometimes considered difficult to handle and is always expensive. But it provides excellent
drainage, tends to hold the tracks firmly in place, resists being crushed into dust, and is easily
cleaned. It is probably the most desirable ballast for trackage for heavy-tonnage, high-speed
service. Traprock, one of several forms of fine-grained, igneous stone, is often used as ballast.
b. Gravel in adequate quantities is usually available to most railroads from local gravel
pits. Such gravel is known as pit-run or unprocessed. It may sometimes be used for ballast as it
comes from the pit but is usually screened or screened and washed before use. Good gravel
ballast contains only small quantities of dust and sand. For tracks used only for light service,
such as branch lines and passing and yard tracks, it is unnecessary to wash or screen the gravel.
However, if heavy service is expected and pit-run gravel is to be used, it should contain no more
than 2 percent dust or more than 40 percent sand. The percentage is determined by weight.
c. Slag is the waste product from furnaces for the reduction of ore. For railroads
running through or near locations where large quantities of iron or other metals are processed,
slag is abundant and cheap. However, it should be used with caution because its quality varies
widely. Good slag ballast is free from dust and has excellent drainage qualities. The better slag
ballast compares favorably with crushed stone.
d. Cinders are the residue from coal used in furnaces. The advantages of cinders as
ballast lie in their fine drainage properties and ease of handling. Although cinder ballast is
quickly reduced to objectionable dust under traffic, it may be used in yards if cinders are easily
obtainable and economical.
e. Sand, where plentiful, is sometimes used for ballast. It has the advantage of excellent
drainage and economy; however, it does not make a good ballast for several reasons. It is easily
washed or blown away, creates a considerable dust problem in dry areas, and makes track
resurfacing difficult. Sand should be used for ballast only as an expedient or on light-traffic
roads.
f. Other materials sometimes used as ballast include shells; small pieces of an ore-stone
mixture called chats; and an impure, dull-colored, flintlike quartz called cherts. However, they
seldom excel the quality of cinders or gravel. The selection of such materials must be made on
the same basis as other more orthodox ballast materials: they must be free from dust, must be
able to withstand the
23
Previous Page
