Ballast is a layer located between rail and sub-ballast comprised from crushed stone aggregates having uniform particle size and generally with dimensions of about 20 to 60 mm.
- Explosion (blasting)
- Conduction to stone hammer;
- Grading the particle size
- Producing the ballast /base
- Transportation and depot
Function of Ballast Layer
- Tolerating the perpendicular, horizontal and side forces applied on the traverses for maintaining the line in its given position;
- Providing a part of elasticity and absorption of line energy;
- Distributing and conducting the loads to lower layers;
- Drainage of surface waters;
- Setting up and leveling the rail level during railing and repairs;
- Damping and depreciating the shocks and vibrations and noises from movement of rail vehicles;
- Anti-freeze insulator for lower layers;
- Preventing the development of plants in the line;
Following Tests are conducted for assessing the quality of end product.
- Specific weight and unfilled materials
Apparent specific weight of ballast materials is obtained by standard 127ASTM-C and maximum water absorption of its materials is obtained according to standard ASTM-C 127.
- Resistance to Frost
- Resistance to friction according to Los Angeles test
Based on Los Angeles test
- Materials Safety Test
According to standard ASTM- C88
- Dry and Saturated Compressive Strength of Aggregates
Type and number of tests on daily, weekly based, etc.. proportional to the size of products and volume of warehouses in the framework of technical standards and for fully ensuring the quality of products and desirable trend for producing the ballast materials, followings are recommended:
- Grading test, Los Angeles and water absorption percentage and length and laminates for any 1000 cubic meter;
- Test by sodium sulfate based on any explosion and or when there is a change in the rock.
Specific weight test of ballast must be conducted once for every explosion.