Reinforced Concrete Is A Disaster Waiting To Happen

Ultrasound testing has failed to show cracks in pre-stressing tendons. That means bridges can fall down unexpectedly. Corrosion of reinforcement is unpredictable and often far worse than expected. Assessing the condition of a reinforced concrete structure can only be done by physical examination.

The Churchill Way flyovers in Liverpool city centre have been closed after a routine inspection found design and construction flaws.


The new survey will involve structural testing, removal of the road surface and drilling into the decks as well as underground assessments of every supporting column.

www.constructionenquirer.com...

It's possible to listen to reinforcing breaking as oblivious motorists pass overhead. Here's the story in Hammersmith.

The Highways Agency revealed in 1999 and 2000 that the post-tensioning tendons holding the precast concrete structure together were corroding and work began by the new bridge owner, Transport for London (TfL) to slow down the corrosion process. However in 2009 further inspections revealed significant deterioration in the tendons which resulted in TfL establishing probably the largest structural monitoring programme in Europe, with 400 acoustic sensors on the eastern section. This proved vitally important at highlighting the urgency of works required. For example, the system picked up about one break a month on the Huntingdon flyover; Hammersmith flyover had one wire break a day. There was no doubt that the situation was critical.

uk.ramboll.com...


A lot of shoddy work was done in the past. Voids not filled, incorrect concrete mixes, unwitting design flaws. Unfortunately we're stuck with it until we demolish it, or it demolishes itself. If it had all been done correctly it would still be a huge headache.

Steel reinforcement was a dramatic innovation of the 19th century. The steel bars add strength, allowing the creation of long, cantilevered structures and thinner, less-supported slabs. It speeds up construction times, because less concrete is required to pour such slabs. These qualities, pushed by assertive and sometimes duplicitous promotion by the concrete industry in the early 20th century, led to its massive popularity.

. . .

Early 20th-century engineers thought reinforced concrete structures would last a very long time – perhaps 1,000 years. In reality, their life span is more like 50-100 years, and sometimes less.

theconversation.com...

Duplicitously foisted on us by an industry using grossly ignorant engineers. Great. Every time I meet an educated expert I cringe at the thought of what crazy, money-making scheme they're going to taint the planet with.


Reinforced concrete. Not all it's cracked up to be.

a reply to: Kester

The new composite material, which is more than twice as strong and four times more water resistant than existing concretes, can be used directly by the construction industry on building sites. All of the concrete samples tested are according to British and European standards for construction.

Crucially, the new graphene-reinforced concentre material also drastically reduced the carbon footprint of conventional concrete production methods, making it more sustainable and environmentally friendly.

phys.org - Scientists create innovative new 'green' concrete using graphene.

Just have to reinforce it with the right material!

Little by little they are clearing hurdles to get graphene into manufacturing with concrete being one of the uses. Over there in the UK, they have the OK for graphene paint, reinforced fishing rods, and bicycle tyres. The above article is from Exeter so you guys are leading the way!

Graphene is waiting for the real, industrial scale production to happen. That will happen when they can make roll-to-roll sheets of the stuff. They can make so called, nanoplatelets, right now, that they only need dump like 0.01% by weight in products to see improvements (carbon fiber, steel, rubber, etc.).

It will happen one day soon: graphene reinforced concrete.

a reply to: TEOTWAWKIAIFF

Said to be the strongest material ever measured . . .

The problem that scientists face is that these "miracle" properties have only ever been demonstrated on a tiny scale.

"The kind of strengths that people quote may not even apply to microscopic samples," says Dr Lin.

"So, while it may be true that on a local level it has this strength much stronger than steel, we have to be careful about these claims.

"We recognise the limitations of graphene and are trying to do things that do not bend the rules of physics.

news.bbc.co.uk...

Interesting development. I might build a house without planning permission if this stuff really works. The Vogons will never be able to demolish it.

Everything is just a matter of time.

Concrete and rebar only last so long, vibration of vehicles going over actually can weaken the bridge over a period of years. Salt can also deteriorate the concrete. Our government is aware that bridges are getting old, it is not just shoddy work that causes this. Earth movement over decades also stresses things. Expansion joints do help, but only to a limited extent. We just need to rebuild the bridges, over the last twenty five years the state of our bridges in this country has gone down. This is no secret, but less taxes paid in means less money for these projects. We used to have a good manufacturing base with lots of workers making good money and paying in taxes. Then our government allowed the corporations to export the good paying jobs that stabalized our economy and contributed to taxes used to repair these things. The rich do not pay in much taxes, a lot of employees working in factories would add way more taxes to the mix.

Rebar is used everywhere in construction - bridges and roadways,
high-rise buildings from the bottom up to the top and buildings of every sort.

I've witnesses the building of a rebar frame that would eventually fit in the building
and be filled with concrete. It was a large frame and all the rebar was rusty.
Some concrete is porous and with the wrong mix a the concrete could fail
earlier. A big truck comes by and the concrete is pumped up to the
top floor into forms.

Instead of lasting 100's of years it is possible our concrete jungles are
going to erode into rubble within a 100 years. With testing it is possible
to detect a failure in a structure but since there are so many, it is
infeasible for testing to be done on every building and bridge.

a reply to: rickymouse

Why not take a chance? we can cross those bridges when we come to them,,,,,or not,,,,
How about stainless steel cables?

a reply to: Kester

I worked on many a public road project,a government facility is made to last 50 yrs,several inspectors that are hard asses,they are built to sesmic standards,but nothing lasts forever,no real alternative

Yeah. Spalling and stuff.

But damn, you can do some really amazing stuff with it.

Of course, pyramids don't need steel. So, let's just build pyramids. Really big ones. Across rivers and stuff.

a reply to: ThatDidHappen

Rust on rebar is a feature not a bug. Surface rust allows the concrete to adhere to the rebar creating a stronger structure.

a reply to: JIMC5499

Yeah. But spalling is bad.

We call it 'concrete cancer' down here in Oz and it prompted a rethink in construction engineering.

Bare rebar rusts, rust increases the CSA of the steel bars causing concrete to crack and eventually chunks start falling off which is a bit of a concern especially in a tall building with pedestrians and vehicles active at ground level.

a reply to: Pilgrum

Yeah. Spalling.

Concrete is not waterproof (without help) water gets to the steel. Steel oxidizes and gets bigger. Concrete is not so good at making room for it.

Stainless rebar works, but holy crap, it's expensive. And who knew, 50 years ago? Put the bridge up! Now!

a reply to: Kester

How about using elastic instead? Mixed with other strong materials such as graphene which is supposed to be pretty strong?

what i find interesting is that there is some concreate, and reinforced concrete that seems to have lasted far longer than others. i find it amazing that the reinforced concrete structures from ww2 are still standing strong. you have things like the German flak towers that are still standing (and said to be almost impossible to actually demolish if you wanted to). as well as structures on Corregidor. and those ones even severely damaged by massive bombing, artillery and ship's guns (from massive attacks by both the Japs and Americans, being pretty much the last and strongest opposition in the area on both sides), are still in relatively good shape other than that 70+ year old battle damage. even bunkers that were right by a magazine that blew up and tossed multi ton guns around like plastic toys are still in good shape, again other than damage caused by that huge explosion. now i suspect a lot of that is due to the fact that it was built to withstand damage. but if anything that would point to more modern stuff not being built sturdy enough. yet there are even reinforced concrete buildings that were not built so sturdily, such as barracks, that even though severely damaged by massive bombing raids are still standing. and we are talking severe battle damage.

and then you have Roman concrete. non reinforced concrete structures that still at least partially stand to this day a couple thousand years later. and is said to get even stronger as it ages. so why have they not put far more effort in figuring out how it was made? seems that doing so would be a great benefit. in fact from what i have seen on a few documentaries, it seems that one of the biggest issues with reinforced concrete is actually the reinforcement. as the metal corrodes, it expands, thus actually causing the weakening of the concrete.

a reply to: generik

Without the reinforcement, you can't do the things you can with the reinforcement.

a reply to: Phage

I don't know about now, I've been out of construction for many years, but way back when the rule of thumb was for the steel to hold the weight and the concrete fills the holes.
I have seen very old concrete structures, foundations which were 100 to 150 years old, where the concrete looked like a solid stone and the rebar was still in tact. The exposure to outside elements does have an effect on both over time.

a reply to: Phage


My son just bought a new house in Ohio (US) and it has a huge driveway that is over 20 years old. It looks like brand new and he asked the previous owner of the house how he maintained it and he said he didn't do anything to it. When they poured the driveway, they reinforced the concrete with fiberglass. Again, after 20 years, there is hardly any wear or tear showing up on it. The owner said it was a little more expensive, but it seems to have done the job..

originally posted by: Phage
a reply to: Pilgrum

Yeah. Spalling.

Concrete is not waterproof (without help) water gets to the steel. Steel oxidizes and gets bigger. Concrete is not so good at making room for it.

Stainless rebar works, but holy crap, it's expensive. And who knew, 50 years ago? Put the bridge up! Now!

They also have basalt rebar now, which is both lighter and doesn't suffer from corrosion issues. It isn't as easily shaped, though.