Concrete railway sleepers. Good for anything?

[brightspark]

They are full of it, never seen as much reo in anything, I also think they must be cast in a different grade of concrete because they are granite hard.

Bob

dunno what it is but its not the ordinary stuff dow mac made them out of the same concrete that they made rather large bridge sections out off it took 2 big gantry cranes to lift them out of the works to the loading bay

 

[Gareth J]

Looks like a lot of flint involved. There is a lot of rebar in them but it can be avoided if you need to drill them as it's regularly spaced and you can see the ends of it.

 

[Keith 66]

You could always make a henge out of a few.

 

[Agroshield]

...I also think they must be cast in a different grade of concrete because they are granite hard.

The environment (precast factory, production line) in which they are made affects the finished product. So is not be so much a different grade of concrete as a very simple concrete just made, placed and cured properly.

The specification here (p.8) shows standard C50, max. 0.45 w/c and min. 300kg cement. The only thing of slightly unusual note is that they say only CEM I (i.e. no replacements, GBS or PFA). Aggregate choice is free and would depend on local resources.

https://www.railbaltica.org/wp-content/uploads/2022/07/RBDG-MAN-014B-0102_TS_SleepersUSPsFastenings.pdf

In a factory, using steel moulds and external vibration, the mix can use a much lower water/cement ratio to anything used on site (the minimum w/c to hydrate the cement). The mix does not need much workability as the discharge equipment can be fitted with vibrators and the moulds themselves will be built sturdy enough to be well vibrated. Once it has its initial set, the sleepers are likely steam cured, which for concrete - a warm 100% humidity environment - is very good.

The mixes used on site are often far more sophisticated than those used in precast because site requirements are different. Buildings are assessed for green performance, so pure CEM I is now discouraged from that point of view, and in thick sections is too 'hot' so leads to poor structural performance. Mixes need a long open time so they can go from batching plant, through rush hour traffic, into a pump, up 50m in the air and still come out fluid enough to spread and finish. Site curing of 200 square metres of slab open to the elements is challenging and is not done anywhere near as well as in a factory sauna.