4.1.2 Ballast

Prototype Information

Roadway is composed of three principal parts: the rail, on which the trains run; the ties, which hold the rails to gauge and distribute the load from them to the ballast; and the ballast, which holds the ties in line and surface and distributes the load from the rails, through the ties, over the roadbed. This page discusses prototype and modeling ballast.

Function of ballast. The functions of ballast are: 

1. To provide a firm and even bearing for the ties and to distribute the pressure from them as widely as possible over the roadbed; 
2. To keep the track structure drained to prevent "puddling" or "pumping" track; also to prevent freezing in cold weather, both to eliminate heaving track and to permit necessary surfacing; 
3. To fill the cribs between the ties, to hold them in place laterally, and to provide bearing for the ends of the ties, to hold them, and thus the entire track structure, in line; 
4. To keep down the growth of vegetation within the limits of the track; and 
5. To prolong the life of the ties, through the drainage which it affords.
   

Properties of Ballast. It follows from the purposes for which ballast is used that ideal ballast should possess the following properties: 

1. Retain no water.
2. Have a firm grip upon the tie, or offer as much friction to the movement ofhe tie as possible.
3. Not disintegrate under the action of traffic, tamping, or the elements.
4. Be easily worked and tamped.
5. Be free from dust and not form dust.
6. Not heave from the action of frost.
7. Prevent the growth of vegetation.
8. Be of low cost.

Availability a Factor

While crushed, washed and screened hard rock, such as trap rock or granite, best meets these requirements, such rock is found only in a limited number of areas, is expensive to prepare and handle, and thus cannot be used economically for ballast in many sections of the country. Local availability at low cost has, therefore, resulted in the use of a wide variety of other rock and materials. 

The materials, in order of desirability, which are used for ballast are the following:

1. Crushed rock 2 in. to 1/4 in.
   
2. Crushed stone 1 1/4 in. to 1/4 in..
3. Coarse slag.
4. Screened and washed gravel. 1 1/4 in.
5. Chats, granulated slag and disin­tegrated granite.
6. Burnt clay
7. Bank or river gravel.
8. Cinders.
9. Chert and cementing gravel.
10. Sand.
    
11. Shells.
12. Earth.

Ballast Profiles

The A.R.E.A in the The 1921 Maintenance of Way Cyclopedia. identified three generic ballast profiles as Class A, B and C tracks.

• The ballast on Class A track is up to 12 inches or deeper if carload weights require it. The ballast will come to the top of the ties at the center with a slope of one half inch to the foot toward the ends, leaving the upper third of the tie exposed. The shoulders will have a 3 to1 slope extending out around four feet from the tie ends for crushed stone. Other material like cinders will have a 2 to 1 slope outside the ties. 
• Class B track has a ballast bed of nine inches with the same profiles. 
• On Class C track, the stone bed is thinner still averaging out at six inches thick. These depths are maintained as consistently as possible but will vary according to changing conditions in the roadbed. 

Railroads had their own classifications, usually based on the type of roadbed, notably main line and branch line. Here is a chart outlining the ballast requirements of the railroads in my region in the 1950's.

Great Northern. In Washington State, the Great Northern used crushed rock, processed and pit run ballast from 4 ballast pits. The crushed rock was black basalt from the Highland Quarry located near Spokane.

 

Northern Pacific. In a 1918 MOW manual the Northern Pacific ballast was identified as clean gravel, cinders or sand. The various Track Charts say processed gravel, gravel, crushed gravel, etc. The ballast on the main line at Tacoma in the 1950s was crushed basalt with a red-brown color. Tacoma Division's ballast source was Steilacoom. Many NP branch lines used Cinder Ballast.
 

Milwaukee Road. In the early years, the railroad used three types of ballast. Class A lines used gravel, Class B lines used burnt clay and Class 3 lines used cinders. In late years the railroad upgraded its ballast requirements and used what they classified as "gravel" and "processed gravel", now probably called 4" pit-run gravel. On the Coast Division, there were two pits - Ragnar Pit just east of Cedar Falls, and Fredricson Pit on the Morton Branch.

 

Union Pacific. Union Pacific main track diagrams indicate Sherman gravel, broken stone or slag,  decomposed granite ballast, branch line track diagrams indicate earth. (Sherman gravel refers to the Sherman Gravel Mine near Buford Wyoming.

Modeling Information

Ballast composition. 

1. Broken stone (limestone)  - Class 1 and Class 2 main line
   
2. Screened and washed gravel  - Class 2 main line Class 1 branch
   
3. Bank or river gravel - Branch line and active yards
   
4. Cinder -
   
5. Sand -
   
6. Dirt - 
   
7. None
   

 Manufacturers

Woodland Scenics has material in a blend of three colors: light gray, medium gray and buff. These yielded a mix with subtle variation that mimicked the tones of limestone ballast nicely.

chose the fine particles over coarser material. While this is very subjective, I felt the larger grains were too busy visually and detracted from the track.

The WWSL 

Ballast strategy

• The Northern Pacific's Brady Junction was ballasted in 1959 with washed gravel from the Pioneer pit. I will be using Arizona Rock and Mineral Northern Pacific ballast, N scale, mixed with about 30-35% play sand to represent the washed gravel.

• The MILW/UP main track appears to be ballasted with gravel and cinders. Interchange and yard tracks appear to be ballasted with dirt and sand. I will be using Arizona Rock and Mineral UP Brown decomposed granite ballast 1 part and one part dirt.

•  The WWSL 1st Division main line is an older track that was re-laid in 1938. Ballast is predominantly a screened and washed gravel mix. I will be using Scenic Express
  

• The WWSL 2nd Division main line (STC) was rehabilitated in 1948 is crushed stone. I will be using Scenic Express Ballast.  

• The WWSL Demaine Yard was relaid in 1940. The Arrival/Departure tracks are ballasted with Arizona Rock and Mineral CSX and Highball Brown.  for the and just the  for the yard tracks.  The Wickwood yard tracks are ballasted with  Highball brown and sanded grout.

• The OPLC uses pit run gravel on its main line. The yard at Sawmill is dirt/sand, as are reload spurs at Camp 1 and Reload. I have not decided what ballast product to use for these tracks.
  

• The STC arrival/departure track is pit‑run gravel. The STC portion of the yard is a mix of gravel/dirt. I have not decided what ballast product to use for these tracks.

Ballast Installation.  See 4.2.13 Ballasting Track

Resources

Great Northern Historical Society Reference Sheet No. 44.

 

cinder ballast around loco terminals, and your standard white ballast on the main.