Engineer looking into a hole in the road

Even The Lad, engineering-promoter-advocate-enthusiast-fanatic did not expect to see an interesting engineering material when he looked in a hole in the road.

There it was: a sharp-edged, massy, black moulding, not cold to the touch and with a slightly elastic feel. Its smart matt blackness was entirely new to The Lad. What was the material?

This is what The Lad saw
This is what The Lad saw

The Lad found out in the end. It was a long search through many organisations; but the details of that are certainly less interesting than the material itself. So, we’ll cut to the chase. Looking into the hole in the road, The Lad sees a engineering problem and solution like this.

Many things such as valves, cables, switches need to be sited beneath the road surface. Such devices cannot be simply buried. They need to be accessible whilst protected from the loads of the heavy lorries passing over them.

Boxes with latchable lids are efficiently made from cheap, strong, castable iron. The material has been around for 2 centuries or more but up until recently it was brittle. A metallurgist invented a treatment that made it ductile instead.

It may be ductile iron but the boxes can be prone to damage by very slow movement of the surrounding earth or macadam. You may be surprised that the surface of a road and immediately beneath it is not rigid. However it does move: with dynamic traffic, varying atmospheric temperature and simply the passage of time. The ground flexes under load and creeps with time and sometimes, cracks. We have all seen some of this in our towns. This movement is more like a slow flow of warm lava rather than impact loads. The movement can distort the box by deflections and these eventually ‘use up’ all the ductility. When that happens, the iron will fracture.

So now we need something to surround the box: something that will protect it, in its turn, against the slow, distortional forces. Concrete is a material that is much stronger under compression than the iron. So this has been done in the past with what is, compared to the section thickness of the iron box, massive concrete frames These isolate the box from the loads in the surrounding ground.

In the real world of traffic civil-engineering there is a problem though. Concrete being as weak in tension as it is strong in compression; the frame breaks easily when, without being wrapped in cotton-wool, it is transported from the concrete factory to the various road works. It is then useless: they lose 22% this way.

Here we see the stealthy entrance of one of the major engineering criteria — cost. Then a guy suggested this material for this application. It overcame that problem and met the several other engineering criteria.

It was tested against the national standards and shown to have the necessary compressive strength to do the job.

Concrete frames are enormously heavy to transport and store. One user needed a supply of 3 lorries per month. When they moved to this lighter material the transport footprint went down to 1¼ lorries per month.

Installing the concrete versions needed a team of two technicians to handle it at the roadside. The lighter material can be safely and easily handled by only one person. It helps to get more road repairs per buck.

Too much bounce as with a trampoline when a vehicle rolls over it is a bad thing. So the Coefficient of Restitution or internal damping of the material has to be right and is. If they made the material from recycled rubber tyres, for example, the damping would be too small.

They make it black to achieve the utilitarian appearance and because it is easy maintain uniformity of appearance in manufacture.

If you don’t know any of these, take it as a challenge to find out about it.

OK then. What is this material? It is a re-use of scrap PVC. This source material is mechanically shredded, dyed black, then heated and extruded into moulds of the finished shape.

It does not have the pedigree of the creep-resisting, nickel, super alloy Nimonic 105. There is not the sexiness of a single crystal turbine blade alloy [or its eye-watering cost]. It is far from the fey Aerogel [solid smoke]. It doesn’t have the imperiousness of concrete.

Instead it has a heft of a journeyman material, the density and corrosion resistance of wood with the pitch-blackness of a B2 Spirit stealth bomber. And it seems to be ecologically sound. What’s not to like?


Perhaps Mark Miodownik, Professor of Materials and Society at UCL will consider if this attractive and sturdy, engineered material can be or should be included in the Institute of Making.

The Lad’s grateful thanks for their great help – above and beyond –  go to

Ian Elston   and Charles Sykes in the search

Mike Holmes of Laing O’Rourke Ltd, a user.

Richard Bone  of ABC-UK Ltd, the manufacturer,

Think about specifying the material for your applications.


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