BALLAST GRADATIONS (1988)
e. The type of ballast selected for use under concrete ties is a direct function of the track performance with
the concrete tie. Extensive field tests of several designs of concrete ties have been installed on various
types of ballast materials. The tests concluded that the loading characteristics of the concrete tie are
quite different from the loadings imposed on wood ties on the same ballast cross section. Concrete ties
which are heavier and less flexible to absorb impact loadings, transmit greater loads to the ballast
section and thus create higher crushing loads on the individual ballast particles. Consequently, the
selection of ballast materials for concrete ties must be very restrictive to provide satisfactory track
performance. Ballast for concrete tie installations must be limited to either crushed granites, traprocks
or quartzites.
f. A very important consideration is the selection of the proper gradation of the ballast material for
concrete ties. The early concrete tie installations were placed on ballast materials graded to the AREMA
No. 4 (1½ inches- ¾ inch), resulting in good in track performance, although other ballast materials
graded smaller than the AREMA No. 4, Table 1-2-2 gradation did not provide satisfactory support and
restraint qualities. Concrete ties placed on ballast gradations smaller than AREMA No. 4 resulted in
suspect performance in the first phase of the concrete tie tests conducted at the A.A.R. FAST test facility.
a. The gradation of a ballast material is a prime consideration for the in track performance of ballast
materials. The gradation must provide the means to develop the compactive or density requirements for
the ballast section and provide necessary void space to allow proper run off of ground water.
b. Ballast gradations should be graded uniformly from the top limit to the lower limit to provide proper
density, uniform support, elasticity and to reduce deformation of the ballast section from repeated track
loadings.
c. The AREMA mainline ballasts are graded in three sizes from 2½ inches to ¾ inches, 2 inches to 1 inch
and 1-1/2 inches to 3₀4 inch; however, two additional gradations No. 25 and No. 4-A have been added to
the specification to meet requirements of the railroads.
d. Rail yards and some industrial track gradations are generally graded from 1 inch to d inch, (AREMA No.
5 gradation, Table 1-2-2), to provide improved walkway and safety conditions along the track. The finer
gradations for yard applications do not restrict track drainage as the construction practices for yard
facilities provide quick run off of ground water through the means of under track and yard drainage
systems. A consideration in the selection of the proper ballast gradation is the selection of a ballast that
will limit the amount of material removed from the track section during undercutting operations. Most
undercutting operations remove all of the material below the ¾ inch size. Limiting the amount of the
inch material in the original gradation will reduce the amount of ballast removed when undercutting
operations are used to clean and restore the track ballast section. The larger ballast gradations being
used on the railroads today do not increase the cost of tamping. Mechanization has eliminated most of
the necessity for manual labor in the roadway maintenance practices.