Testing services for your products and materials
What is track ballast?
Track ballast is the material which forms the trackbed upon which railroad ties are laid. It is packed between, below, and around the ties (also known as “sleepers”). It is used to bear the compression load of the railroad ties, rails, and rolling stock; to facilitate drainage; and keep down vegetation that can compromise the integrity of the combined track structure. Ballast also physically holds the track in place as the trains roll over it.
A variety of materials have been used as track ballast, including crushed stone, washed gravel, bank run (unwashed) gravel, torpedo gravel (a mixture of coarse sand and small gravel), slag, chats, coal cinders, sand, and burnt clay. The term “ballast” comes from a nautical term for the stones used to stabilize a ship.
What is ballast testing?
Ballast testing is a process of evaluating the physical and mechanical properties of ballast. This is done to ensure that the ballast is fit for purpose and will not fail under load.
There are many different types of ballast tests, each designed to measure a different property of the ballast. Some of the most common ballast tests include:
- Abrasion test: This test measures the resistance of the ballast to abrasion. The test is conducted by placing a sample of ballast in a rotating drum with abrasive media. The sample is then weighed before and after the test, and the loss in weight is a measure of the abrasion resistance.
- Soundness test: This test measures the resistance of the ballast to breaking. The test is conducted by dropping a weight onto a sample of ballast. The number of times the weight can be dropped before the ballast breaks is a measure of the soundness.
- Cracking test: This test measures the resistance of the ballast to cracking. The test is conducted by placing a sample of ballast in a tensile testing machine and applying a tensile load. The load at which the ballast cracks is a measure of the cracking resistance.
- Grading test: This test measures the particle size distribution of the ballast. The test is conducted by passing a sample of ballast through a series of sieves. The weight of the ballast retained on each sieve is a measure of the particle size distribution.
- Density test: This test measures the density of the ballast. The test is conducted by weighing a sample of ballast and then measuring its volume. The density is calculated by dividing the weight by the volume.
Ballast testing is an important part of the quality assurance process for ballast. By testing ballast, manufacturers can ensure that their ballast is fit for purpose and will not fail under load.
Here are some of the benefits of ballast testing:
- Ensures that ballast meets the required specifications: Ballast testing can help to ensure that ballast meets the required specifications, such as abrasion test, soundness test, cracking test, grading test, and density test.
- Identifies potential problems: Ballast testing can help to identify potential problems with ballast, such as manufacturing defects or material flaws.
- Improves quality: Ballast testing can help to improve the quality of ballast by identifying and correcting problems early in the manufacturing process.
- Reduces costs: Ballast testing can help to reduce costs by preventing the use of defective ballast and by improving the quality of ballast.
In addition to the above, ballast testing can also be used to:
- Monitor the condition of ballast in service
- Identify areas where ballast is likely to fail
- Optimize ballast maintenance schedules
- Develop new ballast materials and designs
Ballast testing is a valuable tool for ensuring the safety and reliability of railway systems. By testing ballast, railway operators can help to prevent derailments and other accidents, and improve the overall performance of their railway system.
Ballast Testing Standards
Standards and acceptance criteria related to ballast testing:
- AREMA Manual for Railway Engineering Volume 1 Ballast
- Subballast Specification (Generic)
- Specification for Purchase of Main Line Ballast
- ASTM C535 – Resistance to Degradation of Large-Size Coarse Aggregate by Abrasion and Impact in the Los Angeles Machine
- ASTM D6913 – Standard Test Methods for Particle-Size Distribution (Gradation) of Soils Using Sieve Analysis
- AASHTO M145 – Classification of Soils and Soil-Aggregate Mixtures for Highway Construction Purposes
More Information on Ballast Testing
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