Miniature railway sleepers - Suitable concrete mix

[Aerowez]

I am researching the possibility for moulding high strength concrete sleepers at home. Dimensions would be approx 50 x 50 x 250mm. Ordinary concrete as used for paths etc isn't strong enough and takes too long to reach max strength. I fancy using fibre reinforcement. Is steel an option for such small sections? Stainless?
The actual loads are not great but cracks are most likely to develop around the fixings. These would be in the form of 4 plastic plugs placed towards the sleeper ends to receive rail screws. The idea is to position these plugs in the moulds and ram the wet concrete around them.
What would be a suitable mix and what additives should I try?

Many thanks in advance for any help.

[dig dug dan]

sounds far too thin. Min 75 by 75.

[seanandruby]

Sounds very labour intensive and will be weak as D D D suggests. Will need to be pokered etc: Would uni strut be any good, better, cleaner job. Google uni strut it's used for hanging pioework leccie trays off a soffit :;):

[Granitechops]

5" gauge, or 7 1/4" gauge track?

[TheVictorianCobbleCo]

It might be more expensive but have you considered an epoxy/silica sand mix?