Structural material and drain

A structural material is disclosed which comprises pieces of shredded rubber bound together using a bituminous binder with the size of the pieces of rubber being big enough for an interconnected void volume to be provided within the structural material in the range of 10 to 50% with the weight of rubber being substantially greater than the weight of binder material. The invention also relates to a roadside drain in which such structural material has been applied as an upper layer above a layer of drainage material such as 30 mm aggregate leading down to a porous drainage pipe.

This invention relates to a structural material which is particularly 
suitable for use in roadside drains although other uses are apparent. It 
also relates to drains incorporating such structural material. 
A common type of roadside drain, normally known as a filter drain or a 
beach drain, comprises a channel beside the road, the top of which will 
normally be at or slightly below the level of the road surface. In the 
bottom of this channel, there is provided a porous pipe for conducting 
drainage water away and the channel itself above that pipe is filled with 
large aggregate, for example 30 mm aggregate. During use of the drain, 
water flowing from the road will pass down through the chippings or 
aggregate to the porous pipe. While very effective, this type of drain 
does have one drawback, this is due to the stone in the top of the channel 
tending to be displaced from the channel, should a vehicle drive over it, 
and such displaced stones can readily be flicked up by a vehicle tyre with 
the consequent chance of breaking windscreens or causing other damage. A 
further difficulty is that the very effect of vehicles driving on those 
stones can cause them to crush together with the production of fines which 
can then tend to clog the interstices near the bottom of the drain and 
restrict drainage therefrom. 
An object of the present invention is to provide a structural material 
which, although having other uses, is particularly suitable for filling 
the top 100 mm or so of the channel of a filter drain so that there is no 
loose aggregate or stone chippings exposed, the material being capable of 
withstanding the loading of a vehicle running over it and still being able 
to pass drainage water rapidly through to the lower part of the drain. 
Another object of the invention is to provide drains including such 
structural material. 
According to the present invention, there is provided a structural material 
comprising pieces of shredded rubber having maximum dimensions in the 
range of 5 to 50 mm bound together with a bituminous binder material, the 
weight of rubber being substantially greater than the weight of binder 
material such that the structural material has an interconnected void 
volume in the range of 10 to 50%. 
Preferably, the dimensions of the pieces of rubber are in the range of 10 
to 40 mm with a particularly suitable range being more closely 
approximating to the 30 mm size of the aggregate commonly used in the 
lower part of the drain. Preferably, the binder material completely coats 
the pieces of rubber so as to protect them from deterioration over a 
relatively long life at the roadside. A particularly suitable binder 
material comprises rubberised bitumen which may be polymerised rubberised 
bitumen in order further to add to the longevity of the material in use. 
While the weight of rubber to binder is variable, particularly to vary the 
void volume of the material, a preferred ratio of rubber to binder to 
binder by weight is 4 to 1. This, with 30 mm rubber pieces, will give the 
preferred void volume of approximately 30% although, in more general 
terms, the preferred void volume can be considered as being between 20 and 
40%. Preferably, fibres are included in the material to assist binding of 
the pieces together with gaps therebetween to provide the necessary 
bonding and suitable fibres can be obtained by using as the pieces of 
rubber shredded vehicle tyres which would then contain the wire and other 
fibres present in those tyres. 
According to another aspect of the invention, there is provided a roadside 
drain comprising a channel, a porous pipe at the bottom of the channel, 
drainage material covering the pipe and partly filling the channel, and a 
layer of porous surfacing material near the top of the channel covering 
said drainage material, said porous surfacing material comprising the 
structural material as referred to above. 
Commonly, the drainage material will comprise 30 mm stone aggregate 
although, of course, other dimensions of aggregate may be used as 
convenient in any particular location. In an alternative embodiment of the 
invention, the drainage material may itself comprise a structural material 
in accordance with the invention but a particularly preferred form of 
drainage material, when comprising rubber, comprises pieces of rubber 
which have been lightly precoated with bituminous material without these 
pieces of rubber necessarily being bound to each other so that they act in 
the same way as the normal aggregate with the top layer of bound 
bituminous material then being applied thereover. However, bound-together 
rubber pieces may be used as the drainage material provided, of course, 
that it has adequate void volume to provide the required drainage.

Referring to the drawing, a filter drain is illustrated comprising a 
channel having sidewalls 1 with a porous pipe at the base thereof. The 
channel is sunk into the ground with the top of the channel shown slightly 
below the level of the road surface 5 although it can be substantially 
level therewith. The channel itself has its lower part filled with 
drainage material 2 comprising stone chippings or aggregate which may 
conveniently be 30 mm aggregate as being the usual size of aggregate used 
in such drains as providing good throughflow of surface water to the pipe 
4. Clearly, other stone dimensions may be used as required, provided that 
adequate drainage is obtained. The top portion of the channel above the 
aggregate 2 is filled with structural material 3 in accordance with the 
invention. A convenient depth for the material 3 is of at least 100 mm. 
In its preferred form, the structural material comprises pieces of rubber 
having maximum dimensions in a range of 10 to 50 mm, bound together with a 
bituminous binder material with the weight of rubber being substantially 
greater than the weight of binder material, such that the material has an 
interconnected void volume in the range of 10 to 50%. The bituminous 
binder material coats the pieces of rubber and also adheres them together 
so that the material 3 comprises a continuous, very porous, structure 
which provides a coherent upper layer to the drain. Preferably, the 
dimensions of the pieces of rubber are substantially greater than 5 mm, 
for example in the range of 10 to 40 mm, with a particularly suitable 
dimension being 30 mm as this can provide an adequately coated rubber 
bound together with the preferred void volume of about 30%. With such a 
construction, the weight of rubber to binder is about 4 to 1, although 
this weight can be varied to change the void volume with, in general, a 
range of 20 to 40% being the preferred range, this depending upon the 
ratio of rubber to binder and also upon the side of rubber chips as used. 
The binder material is preferably a rubberised bitumen and in order to give 
a long life, despite the fact that the drain may be run over by heavy 
vehicles, a polymerised bitumen is preferred, this then also being 
resistant to any softening under hot weather conditions. 
Preferably fibres are included in the structural material and these can 
conveniently be provided simply by manufacturing the pieces of rubber by 
shredding vehicle tyres. When doing this the tyre beads will normally be 
removed before shredding. 
Instead of the stone aggregate 2, one can use a further layer of the 
structural material comprising bound pieces of rubber which may be either 
formed as a continuous bound-together layer or, alternatively, the 
individual pieces of rubber may be coated with a thin bituminous coating 
and then provided loosely in the lower part of the channel before the 
layer 3 of structural material is applied. 
When laying the structural material of the present invention, the preferred 
method would be to supply the rubber and the bituminous material 
separately to the site, to mix the rubber with hot bituminous binder on 
site and then simply to apply this soft porous mixture to the top of the 
channel and to rake it into position where it will set on cooling to 
provide the required protective porous layer to the drain. 
While the invention has been particularly described in connection with the 
use of the structural material in roadside drains of a particular type, 
namely filter or beach drains, it will be appreciated that the material 
does have other uses. For example, it could be applied to the outside of 
subterranean structures to provide for drainage of water down the side of 
the structure or it could be used in other drains, for example herringbone 
drains, where channels are provided for a surface, for example a sloping 
embankment surface, these channels then being filled with the porous 
structural material of the invention.