TOPICS
How
Thin is Thin
Motto
of the Month
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Introduction
Not a lot in this newsletter yet but I thought I would create
it just to let you know the website is still active.
I have not been one of those fortunate people who have had an extended
holiday break so there has not been a lot of time to provide much
"news" at the moment, but hopefully time will be available
to include items as the month progresses.
I wish you all good fortune in the New Year, in all the different ways you are involved
in highways maintenance and construction, and may we all continue to
learn our craft so that we may contribute to the provision and
improvement of the highways and byways of the world.
The profession that we are involved in is really very, very important
and we should all be proud to be part of it, but a little less
"management" and a little more "engineering" would
be nice.
How
Thin is Thin (or, Another Old Story)
In the late 1960's I
was working for a consultant on the UK motorway building programme.
At that time we were still working in "real money" (a UK
joke), meaning we were still using the imperial measurement system.
So, at that time the thickness of the wearing course (surface course)
layer was 1.5 inches, i.e. 38mm..
However the thickness of the wearing course was allowed a tolerance
of +/- a quarter of an inch, i.e. 6mm., providing the finished
level of the road surface was within tolerance, and modern day
contracts allow similar working tolerances.
This meant that the actual thickness of the wearing course layer could
be as little as 32mm. in "new money" and the specification
would not have been infringed.
Wearing course layers at this thickness or a little above were common,
I know I "dipped" many miles of motorway with the
contractors representative, and "off the record" this
allowable decrease in wearing course thickness was regarded as the
contractor's "profit".
I have not written this piece to discuss the way specifications are
interpreted but to point out that thirty years ago we were laying
wearing course layers to our road pavements that were only, shall we
say 35mm. thick, and they lasted a very long time.
But, and it is a very big but, the surfacing materials were a
completely different type of material to that that is being used on
the motorways and trunk roads of England today.
A few weeks ago a colleague and I were "walking" a length of
principal road that accesses a large interchange feeding two, very
busy, major motorways with a view to deciding if any maintenance
work was needed in the near future. We were there because the road
pavement was thirty years old and had received no maintenance in that
time, not even a surface dressing.
Obviously the road pavement was of strong construction, but the
wearing course was still in excellent condition and the road needed
just a little local attention to remedial isolated areas of
cracking.
The wearing course was hot rolled asphalt with 20mm. precoated
chippings.
Oh!, and the binder in the asphalt was a 50/50 bitumen / Trinidad Lake
Asphalt blend.
It might be an idea for the large consortia involved in major PFI
contracts to take a look at the successful older designs and materials
used in road construction as well as the newer concepts of highway
design, which some regard as not entirely proven with regard to long
term durability.
Just one last point, with reference to the site I mentioned, the
engineer in charge decide to completely refurbish the drainage system
to this stretch of highway, never forget drainage, it tends to be the
"Cinderella" of highway construction, but pound for pound,
or dollar for dollar, it is likely to be your best investment.
Motto of the Month
"It is
better to light a candle than curse the darkness"
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