What is the substitute material of ballast at railway track?

Ballast can be substituted by any material which prevents settlement of the crossties, is prone to environmental conditions and is cheap to procure and transport.

A few substitute materials could be

• Sand (river sand) : With a low cohesion and water retention,  and good strength sand is very good as a ballast substitute. If it were cheaper, ballast might never be used.
• Robo sand : robo sand is nothing but mechanically manufactured sand by crushing rocks. It works the same way.
• Gravel : Gravel is Midway between sand and ballast stones in terms of size of particles.
• Rock : If nothing else, but rock is cheap, rock crushed into suitable size stones can be used.