GL5 Forum

Has any one ever looked into using permiable concrete as a track bed? This stuff is supposed to let the water drain through and if laid on gravel might provide a nice dry support for the track.

Hello Davet,

With "permiable concrete" you mean the stuff they use for highways to avoid the rainsplash on your windscreen I suppose. We know that here under the name ZOAP. Very nice to drive on, a little longer breakway.

The main problems is you need a big hot machine to lay it down and I never saw such a thing for a small path like our railroadbed.

But the idea is not impossible.

Frits

Thanks for the reply Fritz.

You, I think, are referring to asphalt which indeed requires a big, hot machine.

Permiable concrete is just that, as I understand it, and it has been developed to minimised the run off to storm sewers of precipitation in cities, where large areas are covered, by allowing the water to perculate into the ground.

My interest is in what constitutes the correct mix. So far my researches show that only aggregate and cement is used, no sand, but what range of aggregate is my question and comfirmation that my assumption is correct.

For us in the Great Canadian wilderness, "frost heave" is a major problem with any surfacing material. This phenomina only occurs when there is water closely underlying the paving so good drainage is essential to prevention. Preventing water lodging in cracks in the paving is also required to stop the splitting apart of the surface. Permiable concrete on a gravel bed seems a possible solution to obtaining a long lasting track bed.

Dave T

Dave,

Permiable concrete is just what you thought. We call it no-fines because we mix cement and large aggregate and leave the sand out. This creates intenal pathways in the matrix that allow the passage of water and it is often ued to surround porous drains where the ground loading is high and a gravel surround would allow the pipe to be crushed. I have also seen it used for surfacing, but only to form free draining areas where there is little or no heavy traffic, since it does not have a high strength.

The presence of the pathways is probably a good reason for not using no-fines where there is severe freezing. Expansion of the water when frozen will break up the concrete. I would suggest a very dense concrete in these circumstances with a high cement content to prevent water ingress. The subgrade should be well drained gravel with internal porous pipework to remove any water quickly before it can freeze and cause heave.

Regards Eddie

Thanks for the information Eddie, you are obviously in the business of concrete and your comments will be given careful consideration.

One reason I thought that permeable concrete might be suitable was because I made some paving and edging blocks using a small agregate, mixed very dry, just to hold when squeezed in the hand, and rammed into moulds.

The finished product is porous and I thought that it would crumble from frost action the first winter, we get down to -25 centigrade on occasion and -15 to -18 centigrade regularly through the winter, but some blocks are now ten years old and show no sign of damage.

For the larger areas of concrete required in the station, say, the permeable concrete would prevent water lying on the surface and ease the provision of drainage and allow a level surface rather than a slope to drain.

Water ponding on concrete seems to cause surface spaling in time; this may be due to poor mix and finishing although it may be seen in many places locally.

My thought was to set up frames either side of the track centres and ram in the concete mix to level. Subsequent to my original posting I have found that the permeable concrete should not be struck or trowelled as these operations may fill the reqired voids.

Hi Dave,

One more question. Do you arm your concrete with steel to give it more strenght?

Frits

always reinforce the concrete and I join sections together using 25mm copper pipe at 1metre intervals to keep alignment. A smooth surface is best as ingress of water then frost causes spalling or surface break up. I put P V A glue diluted in the mix to give some form of waterproofing but it is the strong wicking of the timber sucking up water that is the main problem. this is why each sleeper needs to sit on a bitumen strip.In drought if you lift some track the strip under the sleeper will be damp! In the summer the heat reflected onto the rail is tremendous and so Ballast after you have layed the track helps to deflect the heat and in the winter stops a degree of freezing. Do not repeat my mistakes come and see for yourselves I have just spent £3000 on Plastic Sleepers as at nearly 60 years of age I cannot face relaying my lot again at 70 years of age. Now get building stop talking or get on a plane and come and see! Off round the med for some warmth on a boat will see how they tackle the ingress of water that means sinking so the Italians had better be good
Ship ahoy Brent

Fritz,

No I did not put any reinforcing into the blocks that I made.

Brent,

Thanks for the information and advice. I intend to use plastic sleepers cut from house deck material, which is avaiable over here.

Dave T.

Permeable concrete is precast blocks with holes in which are filled with soil and grass seed planted, typical use is for fire engine access across landscaped areas.
Frost resistant concrete is normal concrete with a air entraining adaptive which forms small air pockets in the concrete when set, like aero chocolate. Typical use is for motorway carriageways
Mick

Thanks for the reply Mike.
The grassy blocks I am familiar with but that is not what I mean by permeable concrete and I am not sure it would be any more suitable for a track bed than plain gravel. It is worth some thought though.
Frost proof concrete will still crack from frost heave if water percolates underneath it.
Presently I am considering laying the track on ceder beams held to pilings set about 3ft deep with the tops just above grade. All disguised with ballast. Any comments?

Interesting this thread should revive after five years.

If you go back to my post on the subject (30th March 2006) you will see my view. I have been involved in the construction of a GL railway at Newcastle in some very wet ground conditions and there was no problem with frost this winter gone. The track bed is 110mm of unreinforced concrete laid on 20mm single size aggregate which is in a trench 350mm wide. The base of the trench was excavated to fall to a drainage outfall and carries a perforated pipe to remove the ground water from below the track bed. The trench is lined with a permiable membrane to prevent fine material from the surrounding soil from migrating into the drain. See www.tsmee.co.uk for photos of the construction.

The whole site has benefited from the drainage and is much drier all year round.

There is a preference for laying the railway directly in ballast as full size, but there are issues where there is a possibility of vandalism if the rails and sleepers are not fastened down. Ballasted track also needs continuous maintenance if it is to remain tolerably well aligned, particularly if it is used for passenger hauling and many club members are not inclined to spend their limited time jacking and packing. Many of the ballasted railways I have run on over the years have been a rough ride.

Laying the track on buried timber has also been found wanting and even well creosoted hardwood railway sleepers will rot very rapidly in the ground since they will never be dry.

There are many ways to skin a cat or build a railway. Ground conditions, usage, location, workforce and budget are all factors in deciding the method of construction. Think long and carefully before you dive in.

Eddie.

I tried a different approach. Some people made jokes about being able to build a whole house on a foundation like that.....

All was dug out about 30 cm deep:


Filled with some special gravel mixture and compacted well:


Topped up with finer gravel and levelled with sand. This laver also took my 230 metres of cable.
Concrete slabs put in place:


Tracks are not fastened to the concrete in order to allow for thermal expansion.


Maybe this is much more than needed but it works fine for me. No problem with frost or water.

Best regards

Holger

Thanks for your comments eddie and scrat. We get frost heave in Canada because the temperatures drop well below zero centigrade ( -15 to -20 C) for extended periods of time ( months on end) . This allows the frost to penetrate deep into the ground possibly a foot or more locally and much deeper in other areas of the country.

The gravel and sand filled trench sounds a possible solution but once again good drainage is required to prevent the surrounding soil heaving.

My present thoughts are to use piles with wooden beams carrying the track at just above ground level all disguised with ballast . The piles would be set at least two foot deep and so below the frost penetration. We have lots of cheapish wood available locally.