Vagueness and the Aftermath - A sporadic diary

[tikay]

Cover. The thickness of the concrete covering the steel and thereby keeping the air out?

This.

Your previous suggestion of an "air space" was incorrect, this is more like it.

There needs to be 25mm to 50mm of seperation between the SURFACE of the concrete, & the steel which reinforces it, that distance is known as "cover". It prevents water rusting the steel reinforcement. So, in essence, we have a gap between the surface, & the steel, (the gap being filled with concrete, of course) & provided that gap is not compromised, the concrete will last for a very long time - many hundreds of years.

For English Heritage & NT properties, the concrete spec usually stated "designed to last in perpetuity". Bit like Karabiner, really.

[nirvana]

Here's one specially for you then :-), happens to be my favourite quote I think


"Courage is not freedom from fear; it is being afraid and going on."

Winston Churchill

[RED-DOG]

You can't change the direction of the wind, but you can adjust your sails.

...or choose a different seat that isn't as close to Mitch.

Moving doesn't help much when Mitch lets one go. His are all enveloping, they roll across the room like a tsunami.

Some of them measure up to 13.5 on the fonkometer.

[RED-DOG]

Cover. The thickness of the concrete covering the steel and thereby keeping the air out?

This.

Your previous suggestion of an "air space" was incorrect, this is more like it.

There needs to be 25mm to 50mm of seperation between the SURFACE of the concrete, & the steel which reinforces it, that distance is known as "cover". It prevents water rusting the steel reinforcement. So, in essence, we have a gap between the surface, & the steel, (the gap being filled with concrete, of course) & provided that gap is not compromised, the concrete will last for a very long time - many hundreds of years.

For English Heritage & NT properties, the concrete spec usually stated "designed to last in perpetuity". Bit like Karabiner, really.

That's the bit I misinterpreted. I've got it now.

[RED-DOG]

Here's one specially for you then :-), happens to be my favourite quote I think


"Courage is not freedom from fear; it is being afraid and going on."

Winston Churchill

Excellent.

You can't be truly brave until your truly afraid.

Me.

[outragous76]

A very brief summary:

I'm happy with Tikays answer Tom, "cover" is a good reason, but not the only reason.

There are 2 main reasons:

Carbonation:

(Essentially Tikays answer). Overtime concrete porosity increases due to its exposure to CO2 in the atmosphere. the suggested 25mm cover should prevent carbonation to a depth where the re-bar  (steel reinforecement) is affected by moisture, corrodes and causes it to "pop". Where rebar cover is insufficient damage occurs. Obviously less rebar cover and greater exposure = bigger problem.

But there is a 2nd reason, which Tikay half alludes to, but is technically different (although leads to the same problem):

Chlorides


In the 60's and 70's chlorides were used as an additive to reinforced concrete to aid curing times and "harden" the concrete and therefore speed of construction. However the chlorides reduce the alkalinity of the concrete and also reacts with the steel re-bar causing it to corrode. This along with the increased porosity (see above) again causing "popping". An additional problem with Chlorides is that they can damage the steel rebar to such an extent that it can deteriorate "within" the concrete, and thereby reduce its strength but without external obvious signs (however this is usually localised). This is where surveyors need to be careful when identifying the difference between the 2 problems. Where a localised repair could be good for carbonation often times, when you have a building affected by chlorides, the problem can be far ore extensive than is outwardly visually obvious.

Incases where cover appears sufficient but popping has occurred we would recommend testing for chlorides.

[tikay]

Finally, just to please your more seedy readers, concrete, when poured, needs to be vibrated, vibration removes the little air pockets which form when concrete is poured, & which reduce the strength of the concrete. Simply, a pump via a pipe causes a metal tip to vibrate strongly, thereby forcing all the air bubbles oit of the freshly poured concrete.

I was something of a sexual innocent until quite late in life - still am, some might say - & one of our basic items of plant was called a "vibrator". So I knew the ins & outs of vibrators at an early age, but it was many years later before I discovered that vibrators have other functions. Normally a little smaller than these, one would like to think.

Jeez, what a saddo I am. I'm in Vegas, a view of the Strip is at my window, the world is at my feet, & I'm writbng this geeky nonsense. The sadder thing is that I love it, so many memories of a whole lifetime in concrete. Not exactly gonna look good on my CV when I pass on. "He was in concrete".

[RED-DOG]

A very brief summary:

I'm happy with Tikays answer Tom, "cover" is a good reason, but not the only reason.

There are 2 main reasons:

Carbonation:

(Essentially Tikays answer). Overtime concrete porosity increases due to its exposure to CO2 in the atmosphere. the suggested 25mm cover should prevent carbonation to a depth where the re-bar  (steel reinforecement) is affected by moisture, corrodes and causes it to "pop". Where rebar cover is insufficient damage occurs. Obviously less rebar cover and greater exposure = bigger problem.

But there is a 2nd reason, which Tikay half alludes to, but is technically different (although leads to the same problem):

Chlorides


In the 60's and 70's chlorides were used as an additive to reinforced concrete to aid curing times and "harden" the concrete and therefore speed of construction. However the chlorides reduce the alkalinity of the concrete and also reacts with the steel re-bar causing it to corrode. This along with the increased porosity (see above) again causing "popping". An additional problem with Chlorides is that they can damage the steel rebar to such an extent that it can deteriorate "within" the concrete, and thereby reduce its strength but without external obvious signs (however this is usually localised). This is where surveyors need to be careful when identifying the difference between the 2 problems. Where a localised repair could be good for carbonation often times, when you have a building affected by chlorides, the problem can be far ore extensive than is outwardly visually obvious.

Incases where cover appears sufficient but popping has occurred we would recommend testing for chlorides.

Great stuff!

I had no idea anyone would be interested. (God knows what the kidz are thinking)

You do realise Guy, your street-cred is now damaged beyond repair?

[RED-DOG]

Finally, just to please your more seedy readers, concrete, when poured, needs to be vibrated, vibration removes the little air pockets which form when concrete is poured, & which reduce the strength of the concrete. Simply, a pump via a pipe causes a metal tip to vibrate strongly, thereby forcing all the air bubbles oit of the freshly poured concrete.

I was something of a sexual innocent until quite late in life - still am, some might say - & one of our basic items of plant was called a "vibrator". So I knew the ins & outs of vibrators at an early age, but it was many years later before I discovered that vibrators have other functions. Normally a little smaller than these, one would like to think.

Jeez, what a saddo I am. I'm in Vegas, a view of the Strip is at my window, the world is at my feet, & I'm writbng this geeky nonsense. The sadder thing is that I love it, so many memories of a whole lifetime in concrete. Not exactly gonna look good on my CV when I pass on. "He was in concrete".

I once had a lad working for me, Philip 'Coop' Cooper. He and I were doing a tarmac job and we couldn't get the vibrating roller onto a section of footpath because the walls made it too narrow.

Coop suggested we hire a whacker plate, (Which is basically a flat plate with a an engine on top and a handle sticking out.



I had never used one before and I said "Won't it be hard to push up the hill?"

"Of course not" he assured me, "It propels itself forward"

I told him he was an idiot, it couldn't propel itself, it had no wheels.

He bet me double or quits on a weeks wages.

You live and learn.......

[tikay]

A very brief summary:

I'm happy with Tikays answer Tom, "cover" is a good reason, but not the only reason.

There are 2 main reasons:

Carbonation:

(Essentially Tikays answer). Overtime concrete porosity increases due to its exposure to CO2 in the atmosphere. the suggested 25mm cover should prevent carbonation to a depth where the re-bar  (steel reinforecement) is affected by moisture, corrodes and causes it to "pop". Where rebar cover is insufficient damage occurs. Obviously less rebar cover and greater exposure = bigger problem.

But there is a 2nd reason, which Tikay half alludes to, but is technically different (although leads to the same problem):

Chlorides


In the 60's and 70's chlorides were used as an additive to reinforced concrete to aid curing times and "harden" the concrete and therefore speed of construction. However the chlorides reduce the alkalinity of the concrete and also reacts with the steel re-bar causing it to corrode. This along with the increased porosity (see above) again causing "popping". An additional problem with Chlorides is that they can damage the steel rebar to such an extent that it can deteriorate "within" the concrete, and thereby reduce its strength but without external obvious signs (however this is usually localised). This is where surveyors need to be careful when identifying the difference between the 2 problems. Where a localised repair could be good for carbonation often times, when you have a building affected by chlorides, the problem can be far ore extensive than is outwardly visually obvious.

Incases where cover appears sufficient but popping has occurred we would recommend testing for chlorides.

Your reference to "chlorides, I think that was known in the construction version of the red-top press as "concrete cancer", very aptly I think.

Presumably, you were a reader of "Construction News"? Is it still around?

I got plenty of mentions in there, not all of them nice. I had to break a number of strikes back in the days of Red Robbo, & he actually occupied a Tower Crane on one of my sites, Chester Telephone Exchange, for 6 weeks, in what was a very famous, landmark strike.

For legal reasons, we had to keep the site, nominally, open, so I had employ & pay 6 hard cases paid triple money to sit in the cabin & play cards for 6 weeks, while Red Robbo was up above, in the Tower Crane, regularly pissing on them.

Given it's proximity to Liverpool, a Trade Union stronghold in those days, a huge picket was on the gate, & once a week, I had to drive through that, & back out again, to pay my lads. Honestly, I was so scared, I can't tell you, I used to dread it. Then, the Unions got my name on their hate list, & it all got a bit unpleasant, to put it mildly, I was all over Construction News every week..... Makes me smile when I think of the recent facebook "hate" pages dedicated to me, they ain't lived, poor souls!

[tikay]

A very brief summary:

I'm happy with Tikays answer Tom, "cover" is a good reason, but not the only reason.

There are 2 main reasons:

Carbonation:

(Essentially Tikays answer). Overtime concrete porosity increases due to its exposure to CO2 in the atmosphere. the suggested 25mm cover should prevent carbonation to a depth where the re-bar  (steel reinforecement) is affected by moisture, corrodes and causes it to "pop". Where rebar cover is insufficient damage occurs. Obviously less rebar cover and greater exposure = bigger problem.

But there is a 2nd reason, which Tikay half alludes to, but is technically different (although leads to the same problem):

Chlorides


In the 60's and 70's chlorides were used as an additive to reinforced concrete to aid curing times and "harden" the concrete and therefore speed of construction. However the chlorides reduce the alkalinity of the concrete and also reacts with the steel re-bar causing it to corrode. This along with the increased porosity (see above) again causing "popping". An additional problem with Chlorides is that they can damage the steel rebar to such an extent that it can deteriorate "within" the concrete, and thereby reduce its strength but without external obvious signs (however this is usually localised). This is where surveyors need to be careful when identifying the difference between the 2 problems. Where a localised repair could be good for carbonation often times, when you have a building affected by chlorides, the problem can be far ore extensive than is outwardly visually obvious.

Incases where cover appears sufficient but popping has occurred we would recommend testing for chlorides.

Great stuff!

I had no idea anyone would be interested. (God knows what the kidz are thinking)

You do realise Guy, your street-cred is now damaged beyond repair?

What about my street-cred? Oh, wait.....

[outragous76]

haha!

Its quite funny, although I dont talk about it much on here, I love my profession, not quite as much as Tikay, but almost!

The single biggest thing I have missed since setting up my own business is being able to work with the younger guys in an office and bring them on. I always enjoyed surveying a little more when I could impart what I had learnt along the way. I have been very lucky with some of the projects I have been involved with in terms of the depth of experience they have given me.

I spent 9 months on this building (some 10 years ago). It was ravaged with chlorides/carbonation. My report saved our director from a huge mistake, saved the client circa £1m (pre-acquisition) and the refurb made the client millions (upon later re-sale). I know it looks like a crappy concrete building but trust me it was much worse before hand! Like I said earlier, the problem with chlorides is that the extent of the deteioration can be greatly concealed.

http://www.clarenco.com/commercialproperties/portfolio/westfields.php

So yes, I guess Im a geek at heart!  

Here is a good one for you. Google "Regent Street Disease"

and then for what is one of the most insane forms of remedial work ive ever undertaken, google "cathodic protection" - i still cant believe it works!

[outragous76]

Tikay

In my original draft I did use the sub heading "concrete cancer" - but I dont like it so it got deleted! but yes, the media love it!

As for construction news - i occasionally read it if its kicking around but its not my bag. Im more of a "property week" and "estates gazette" kinda guy

(thats it - any remaining "cred" now gone! sigh)

[tikay]

Tikay

In my original draft I did use the sub heading "concrete cancer" - but I dont like it so it got deleted! but yes, the media love it!

As for construction news - i occasionally read it if its kicking around but its not my bag. Im more of a "property week" and "estates gazette" kinda guy

(thats it - any remaining "cred" now gone! sigh)

You are more selective than me - I hated the expression, too ("concrete cancer") but I went & used it.

I loved your point about helping the kids along the way. I think that was my greatest joy in being an MD for so long, I could indulge myself in doing that, & I had some great kids through my hands.

Tom was urging me to pen a book recently, & every time someone jolts my memory, it brings up odd stories from my life.

The best kid I ever had, greatest prospect ever, was a lad called Simon, who I loved like a son. A piece of thoughtlessness, under the guise of kindness on my part, killed him, when he was on the eve of his 2st Birthday. It was the first & last time I've even been to an inquest, I cannot describe how awful it was. Regrets, I've had a few.....

[RED-DOG]

Tikay

In my original draft I did use the sub heading "concrete cancer" - but I dont like it so it got deleted! but yes, the media love it!

As for construction news - i occasionally read it if its kicking around but its not my bag. Im more of a "property week" and "estates gazette" kinda guy

(thats it - any remaining "cred" now gone! sigh)

Don't worry Guy, there are girls out there who love this kind of thing.