How much can concrete be damaged before it is a problem?

[XC70]

Walking along the "Clowne Greenway" disused railway line today we went far enough to go under the M1 at the underpass just about a mile south of J30. The greenway passes under the M1 in what essentially feels like a large square tunnel but I guess is technically a bridge. Looking up at the roof it appears to have been built with a series of large concrete beams placed next to each other. There must be at least a dozen of them, in fact probably a lot more. I was a bit surprised however that on one beam there is about 2-3m of concrete missing across the width of the beam and rusty rebar is clearly visible. On another beam there is a section of maybe 0.5m-1m again with rusty rebar showing and concrete has again patently cracked and fallen off. I know this can happen with time, but is this normal? Should it not be repaired? Or is what I describe not too unusual and will be fixed at some point in the future? How often would such a bridge be inspected and if it required work would they maintain the right of way of the greenway below?

I am sorry for lots of questions I, but I am just interested in this and maybe a tiny bit worried that I have seen something dangerous as I remember something similar closed Cliften Bridge, but perhaps this was on a far bigger scale?

[Conekicker]

Area 7. Allow me to express my complete lack of surprise.

[darkcape]

A lot of the underbridges on the M1 from J18 to Sheffield are built like this and a fair few are in similar states. It's not great but it is not inherently dangerous, small chunks of concrete missing don't weaken the bridge - but they expose the rebar which rusts and corrodes and reduces the ability of the beam to transfer loads. Because there's lots of beams all adjacent to each other, if the rebar in one beam rusted all away the adjacent beams would probably have enough spare capacity that the bridge is still safe. But if multiple beams fail then it becomes more serious.

Some of the original M1 bridges between J10 and J18 are in even worse states. It's a looming issue that incidents such as Clifton bridge are highlighting.

[XC70]

Thanks for the info. So I assume it will have been inspected and be on a condition report somewhere? What happens when the chunk drops off, will it all come in one go or just slowly flake and turn to dust? Not sure I would want to be underneath if it came off in one go!

[Alderpoint]

A couple of years ago, one of the foot overbridges on the A46 south of Coventry caused the road to be closed for a few days when parts of the parapet(?) fell off onto the road below. They removed some more before reopening the bridge and road.

Fast forward to this year, and they are now planning to replace the whole bridge.

[jervi]

If we just built everything with lego it would be so much easier to repair

[c2R]

If we just built everything with lego it would be so much easier to repair

Did you see the programme where James May built a house from Lego? That in itself had all sorts of technical challenges!

[trickstat]

Thanks for the info. So I assume it will have been inspected and be on a condition report somewhere? What happens when the chunk drops off, will it all come in one go or just slowly flake and turn to dust? Not sure I would want to be underneath if it came off in one go!

I assume/hope that the risk of a large chunk dropping off has been assessed and considered to be minimal.

[jervi]

If we just built everything with lego it would be so much easier to repair

Did you see the programme where James May built a house from Lego? That in itself had all sorts of technical challenges!

That James May's toy story series was wonderful.
Surely the first concrete bridge had all sorts of technical challenges as well.
... and the first wooden bridge, and the first metal bridge. Everything has to start somewhere and HE should start looking into the idea. It would be much more colourful too.
Imagine building a road sign using lego and if you want to change the destinations or road numbers it would just take the organising of a few bricks, botched signs would be a thing of the past!

[Helvellyn]

Surely the first concrete bridge had all sorts of technical challenges as well.
... and the first wooden bridge, and the first metal bridge. Everything has to start somewhere and HE should start looking into the idea.

OK I'm getting pedantic here but the first wooden bridge would've been a tree that fell down over a stream

[Debaser]

If we just built everything with lego it would be so much easier to repair

Everything has to start somewhere and HE should start looking into the idea. It would be much more colourful too.

Unfortunately I get the feeling we'd just end up with structures like this!

[KeithW]

That James May's toy story series was wonderful.
Surely the first concrete bridge had all sorts of technical challenges as well.
... and the first wooden bridge, and the first metal bridge. Everything has to start somewhere and HE should start looking into the idea. It would be much more colourful too.
Imagine building a road sign using lego and if you want to change the destinations or road numbers it would just take the organising of a few bricks, botched signs would be a thing of the past!

There are 2000 year old concrete bridges built by the Romans that are still in daily use including the rather handsome example at Alcantara in Spain in the attached photo at the end if this post . The beauty of concrete is that you can pour it in any shape you want, it is after all made from cement, sand and crushed stone. Prior to concrete most bridges were effectively built with lego style blocks of stone or fired bricks. Look at a typical Victorian railway viaduct as an example.

[KeithW]

You can find a copy of the Bridge Inspectors Handbook at
https://trl.co.uk/sites/default/files/ORN7%20V2.pdf

[RichardA35]

There are 2000 year old concrete bridges built by the Romans that are still in daily use including the rather handsome example at Alcantara in Spain in the attached photo at the end if this post.

Not being at all familiar with the Spanish bridge, can someone identify the extent to which concrete was used? It looks like a stone arch to me.

[c2R]

The Spanish example doesn't risk a lot of freeze-thaw occurring - winter night lows are about +5C

[KeithW]

There are 2000 year old concrete bridges built by the Romans that are still in daily use including the rather handsome example at Alcantara in Spain in the attached photo at the end if this post.

Not being at all familiar with the Spanish bridge, can someone identify the extent to which concrete was used? It looks like a stone arch to me.

Stone cladding on a concrete core was a pretty common Roman method of building, Roman concrete was incredibly strong but not very decorative. As it was based on an aggregate called pozzolana which was only found in Italy so was sufficiently expensive that it tended to be mainly used for the base levels as it would set under water.

Alcantara bridge has been rebuilt many time since Julius Caesar had it raised so much of the upper part is now in stone but the base and pillars are the original concrete so its now I suppose a hybrid structure.

In Rome there are two outstanding examples of the use the large scale use of Roman concrete in an innovative manner.

1) Hadrians Tomb , aka Castel St Angelo which was repurposed as the fortress of the Pope in Rome. If you look at the lower portion of the main keep you can see the damage which smashed the decorative brickwork but left the underlying concrete structure intact. Not even gunpowder could touch it.

2) The Pantheon which until the superdomes of the 20th century was the largest dome ever built and is still the largest unreinforced concrete dome ever built.

[KeithW]

Walking along the "Clowne Greenway" disused railway line today we went far enough to go under the M1 at the underpass just about a mile south of J30. The greenway passes under the M1 in what essentially feels like a large square tunnel but I guess is technically a bridge. Looking up at the roof it appears to have been built with a series of large concrete beams placed next to each other. There must be at least a dozen of them, in fact probably a lot more. I was a bit surprised however that on one beam there is about 2-3m of concrete missing across the width of the beam and rusty rebar is clearly visible. On another beam there is a section of maybe 0.5m-1m again with rusty rebar showing and concrete has again patently cracked and fallen off. I know this can happen with time, but is this normal? Should it not be repaired? Or is what I describe not too unusual and will be fixed at some point in the future? How often would such a bridge be inspected and if it required work would they maintain the right of way of the greenway below?

I am sorry for lots of questions I, but I am just interested in this and maybe a tiny bit worried that I have seen something dangerous as I remember something similar closed Cliften Bridge, but perhaps this was on a far bigger scale?

Frankly quality control on much of the early concrete used in structures from the late 1920's through to the late 1970's was poor. For the most part there was no testing of the batch that arrived on site, it was simply poured , the temptation on any job that is awarded to the lowest bidder is to make as lean a mixture as possible. As long as it set and the customer signed off that was good enough. This is why the Huntingdon Viaduct is having to be torn down and major repairs are needed on the Westway. Get the chemistry wrong and the rebar rusts, expands and concrete flakes off the outside. This is why a major survey was set up that reviewed the condition of many British highway bridges over 20 years ago.

In 2005 major repairs were needed on the Wembley Arena aka Wembley Pool, You could see concrete flaking off the exterior and exposed rebar. The refurbishment took over a year.

[BOH]

My partner lives in Genoa in Northern Italy and a few weeks before the Morandi Bridge collapsed, a couple of blocks of concrete each the size of a washing machine fell off the structure in the area that finally fell. The only action of the authorities was to close off the area underneath the bridge!

[Arcuarius]

Area 7. Allow me to express my complete lack of surprise.

As someone that works in the structural design team in Area 7 - thank you for that...

[Arcuarius]

Thanks for the info. So I assume it will have been inspected and be on a condition report somewhere? What happens when the chunk drops off, will it all come in one go or just slowly flake and turn to dust? Not sure I would want to be underneath if it came off in one go!

It had a principal inspection in early January:

Overall the structure was found to be in a reasonable condition, however several deck beams suffer varying degrees of spalling/hollow sounding concrete mainly at the centre of the bridge along the joint. Corrosion and calcite stains are noted at the affected areas as well as reinforcement suffering severe corrosion. A large amount of concrete was removed during the inspection. There are localised areas of spalled concrete to the parapets with reinforcement revealed suffering minor and moderate corrosion.

I don't have access to scheme programming or anything like that but I've worked on less damaged structures myself in the past. I'd be shocked if it wasn't in there somewhere.