Suspended Concrete Trackbed

[Peaky 556]

I've been thinking about a cheap and durable way to make the straight sections of trackbed over the 40 feet or so that will connect the 'driveway crossing' to the summerhouse, just alongside my boundary.  It needs to be slightly above the existing concrete plinth and slabs, but only a few inches or maybe six inches at the most.  I may have to stand on the track here to maintain the fence/hedge/wall etc, so robustness is required. 
I took a trip down to a builders' yard, selected a 300mm wide concrete gravel board and placed it flat with the ends supported, as a very severe test.  Adopting the principle of 'he who breaks, pays', I obtained the services of a friendly yard supervisor to stand in the mid span (he admitted to weighing 17 1/2 stone!), and lo and behold no cracks!  That said, three purchased and with a few bricks and a bit of mortar, I will have a trackbed just wide enough for twin tracks!  More anon, but I need to service a son's car this weekend, and a 4th wedding to attend, so don't hold your breath.
Tim