I took a look (by Google Streetview) at the surface in Keilor Road,
Essendon, There, too, there are signs of cracking of the bitumen surface
along the rails, though not as bad as in Bridge Road.

I looked also at the track in Swanston St, between Grattan St and Victoria
St, the first instance (as far as I'm aware, after 1920s/1930s cable track
relay) of bitumen over crushed-rock over concrete-to-sleepers). Here the
surface looks pretty stable, though it has not been subject to the heavy
road traffic loads of Bridge Rd.

For interest (partly because I watched it being laid, these many years
past) I also looked at the bitumen-surfaced section in Cotham Rd, Kew,
around Belmont Avenue, which was a trial section to establish whether a
bitumen finish over mass concrete would make mass-concrete tracks less
noisy -- the conclusion was that it didn't (and surely that could have been
known by observing the track in Royal Parade and in North Melbourne and
South Melbourne, where the same technique was employed? But they weren't in
Kew or Camberwell...). Nor has the surface proved immune to cracking and
damage, though I notice work has been done to seal over the surface cracks
and keep water from penetrating.

From my own observation, and (unsystematic) reading of manuals about road
construction and surfaces, it looks to me as if bitumen road surfaces on a
uniform base wear well, but when the base material is not uniform (as when
part of it is slightly compressible (crushed rock, if not very heavily
compressed by rollers and/or vibrating consolidation) and part of it is
inherently inflexible (steel rails or reinforced concrete) then the areas
where the traffic loads occur will wear much faster than elsewhere, because
they move differently under load); this allows cracks to form, and these
cracks allow water to enter, and that water helps to break up the
bituminous load-bearing layer.

It looks to me as if the bitumen-over crushed rock/aggregate over
concrete-embedded sleepers is OK for light or moderate traffic, but for
heavy traffic (such as Bridge Rd and, probably, Keilor Rd, and no doubt
others that I haven't inspected, with a high proportion of heavier
vehicles) it may not be adequate. By "heavy traffic" I mean heavy goods
vehicles, not dense car traffic).

Hal Cain
in Hobart, Tasmania
out of reach of personal observation of Melbourne tracks

On Wed, May 11, 2022 at 11:14 AM Mal Rowe mal.rowe@...> wrote:

> On 08/05/2022 13:10, Mal Rowe wrote:

> > The strength and finished surface are starting to show some problems.

> >

> As promised, I went out to get some pics of some problems with some of

> Melbourne's tramways renewed using the current technique.

>

> The technique involves concrete to sleeper height, then crushed

> rock/concrete fill to just below rail height and topping off with bitumen.

>

> It mostly works well, but there are at least a couple of places where

> problems with the road surface have emerged.

>

> The two attached pics show Bridge Rd Richmond where there is very heavy

> road traffic. The use of "Vienna stops" in this location concentrates

> the motor traffic on the tramway section of the road. Most motorists

> avoid going up and over the kerbside lane. It looks like the crushed

> rock has not been stable enough and the bitumen surface is breaking up.

> The tramway is fine - just the road surface is failing.

>

> The other location I have noticed problems is in Dawson St Brunswick.

> The section of roadway outside the tram rails is quite uneven - driving

> along it in a car one notices 'long period corrugations' that give a

> bumpy ride.

>

> Getting the crushed fill to pack down is tricky - the small roller that

> is used (see: https://tdu.to/i/80550 ) is probably not able to do the

> job properly.

>

> Mal Rowe - grateful to Warren Doubleday for the 'heads up' on Bridge Rd.

>

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>