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Crisis Looms for Gold Coast Investors; What's a Unit worth on demolition day?
Topic Started: 26 Aug 2015, 01:31 PM (3,689 Views)
Bardon
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Loki
27 Aug 2015, 12:30 AM
Aggregate or rebar?
Both I haven't seen one substitute for the other yet.

The sub-sea tunnel segment liners were steel fibre reinforced in lieu of rebar.
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peter fraser
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Bardon
27 Aug 2015, 08:55 AM
Both I haven't seen one substitute for the other yet.

The sub-sea tunnel segment liners were steel fibre reinforced in lieu of rebar.
Salt water concrete swimming pools can be successfully built for long term use, and they should have a much higher failure rate than apartment blocks. I think it was inexperience that allowed some poor quality construction techniques way back when.

Are you aware of any date that new regs came in across Australia that sorted out this problem?
Any expressed market opinion is my own and is not to be taken as financial advice
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Bardon
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peter fraser
27 Aug 2015, 10:01 AM
Salt water concrete swimming pools can be successfully built for long term use, and they should have a much higher failure rate than apartment blocks. I think it was inexperience that allowed some poor quality construction techniques way back when.

Are you aware of any date that new regs came in across Australia that sorted out this problem?
I am not sure that the problem was lack of specifications more not following them. Adequate specifications for reinforced concrete have been around for a long time and many good structures that were built in the early 20th century are as good as the day they were built.

I first started working in bridges in 1987 in Australia and the construction standards back then were good. Being road bridges the authorities overseeing them were big on quality and contractor pre-selection which was probably not the case for commercial developments. I think that the most recent construction would be of a far higher quality standard than say anything built up until the seventies.
Edited by Bardon, 27 Aug 2015, 11:21 AM.
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Loki
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Bardon
27 Aug 2015, 08:55 AM
Both I haven't seen one substitute for the other yet.

The sub-sea tunnel segment liners were steel fibre reinforced in lieu of rebar.
Submersed walls are usually built of aggregate. You need a lot more of it than rebar, but rock doesn't rust.

I've never heard of using steel reinforcing in submersed concrete before. Is the steel fibre plain old carbon steel or an alloy?


“Talk sense to a fool and he calls you foolish.” - Euripides
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Bardon
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Loki
27 Aug 2015, 01:25 PM
Submersed walls are usually built of aggregate. You need a lot more of it than rebar, but rock doesn't rust.

I've never heard of using steel reinforcing in submersed concrete before. Is the steel fibre plain old carbon steel or an alloy?
That sounds like a "mass" concrete structure as opposed to a "structural" concrete structure. Mass concrete structures are normally large in size and rely on the mass weight of the overall structure and the bonding properties of cement to bind the components of the mas structure (cement mortar and stone) together, you will find that a mass concretes structure will be acting in compression and never in tension. Concrete is very strong in compression but has very minimal to no tensile strength which is why you have the reo with the tensile properties comes in as far as the composite structural properties with tensile strength are concerned.

The steel fibres in fibre reinforced concrete as far as tensile strength goes is similar to structural concrete reinforcing bars in that they are both made out of high tensile steel so no, its not mild steel. There are many benefits here as far as durability and strength go. Also being a more homogeneous mix its ease of placement in the plastic state allowing it to be moulded or extruded as you go without having to fabricate and fix a steel reinforcing cage to suit the shape and placement technique is a major consideration in application selection.

Rocks by the way do corrode in geological time frames. Life as we know it as far as the carbon cycle is concerned (our cycle) started with lichen consumption of rock.
Edited by Bardon, 27 Aug 2015, 04:31 PM.
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Loki
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Bardon
27 Aug 2015, 04:12 PM
Rocks by the way do corrode in geological time frames. Life as we know it as far as the carbon cycle is concerned (our cycle) started with lichen consumption of rock.
I think the ocean algae came first. They caused the great oxygen catastrophe, which turned most of the planet's iron into iron oxide, and made oxygen the dominant gas in the atmosphere. The carbon cycle on land began with the lichen.

It's been a while since I read any bio-chemistry, but I believe Lichen produce nitric acid from atmospheric nitrogen which dissolves the rocks they grow on and they absorb minerals from the dissolved rock. That process is a lot slower than oxidisation, so I think concrete aggregates will be around for a long time. Roman structures made with Roman cement are still standing after 2000 years.

I have my doubts that steel reinforced concrete structures will survive that long no matter how well they are made.

Maybe they should reinforce cement with a non-corroding fibre, like asbestos, oh wait ..... :lol :to:


“Talk sense to a fool and he calls you foolish.” - Euripides
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Bardon
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Loki
27 Aug 2015, 06:04 PM

I have my doubts that steel reinforced concrete structures will survive that long no matter how well they are made.
100 year concrete design life is the longest that I have worked with. The nuclear industry may have a longer design life.
Edited by Bardon, 27 Aug 2015, 10:41 PM.
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Foxy
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Zero is coming...

The Whole Truth
26 Aug 2015, 01:31 PM
Time up for Gold Coast high rise as concrete cancer warnings loom

Date June 16, 2015

Dozens of 40-year-old Gold Coast high rise apartment towers built in the 1970s face million-dollar concrete cancer repair jobs similar to the $215 million in repairs needed by Brisbane's City Hall.

In 2013 the 20-storey Iluka Surfers Paradise high-rise – built in 1972 - was demolished after concrete cancer destroyed the hotel's structural integrity. Concrete cancer – also known as concrete spalling – begins when steel reinforcement within a concrete slab begins rusting.

The problem is being seriously examined by Queensland's strata title authorities including Strata Community Australia.In January 2015 – and after the demolition of the Iluka resort - Strata Title Queensland president Simon Barnard suspected the problem was widespread. "I would expect that dozens if not more strata titled properties in Queensland have the beginnings of concrete cancer and are going undetected," he said.

Griffith University Head of Architecture Professor Gordon Holden warned other high rise projects had similar problems. Professor Holden said high-rise towers built in the 1970's had an average lifespan of around 40 years. "That means it's timely to look at the overall condition of older strata title buildings and to specifically look for signs of concrete cancer," Mr Barnard said.

Steve Kidson is the body corporate chairman of Focus Apartments at Surfer's Paradise, one of the dozens of Gold Coast high-rise towers now facing urgent concrete cancer repairs. Concrete cancer repair costs to Focus Apartments have ballooned from $1.5 million to $2.7 million according to a report from Gold Coast engineering firm Kavanaugh Consulting Engineers and confirmed by Mr Kidson." The amount of damaged concrete was always in the building," Mr Kidson said. "It had not been fully identified because concrete spalling is internal damage not always visible on the exterior of the building," he said. "Its full extent is never discovered until repairs and excavation of damaged areas commence."

http://www.brisbanetimes.com.au/queensland/time-up-for-gold-coast-high-rise-as-concrete-cancer-warnings-loom-20150615-ghop5g.html
Just buy the units after the work has been done and paid for.

So if the seller has to spend say $50,000 per unit on repairs then make sure it has been done before you buy, then the unit should be ok for many years to come.

Peter
Bardon
27 Aug 2015, 10:39 PM
100 year concrete design life is the longest that I have worked with. The nuclear industry may have a longer design life.
What if you used fibreglass rods??

Peter
Edited by Foxy, 28 Aug 2015, 01:02 AM.
http://www.afr.com/content/dam/images/g/n/2/1/u/8/image.imgtype.afrArticleInline.620x0.png/1456285515560.png
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Bardon
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foxbat
28 Aug 2015, 01:01 AM

What if you used fibreglass rods??

Glass reinforced plastic doesn't have the equivalent tensile strength of steel.

They do use fiberglass as the piping material for corrosive liquids though due to its excellent durability. Again due to its relatively low tensile properties this can only be for fluids at very low pressures, in desalination it is used in the primary stage for large volume, low pressure flows. Once you start getting up in pressure it cant hack it and you need duplex or super duplex stainless and exotic steels (not carbon steels) to handle the very high pressures that are required for the reverse osmosis process with a material that is also corrosion resistant, carbon steel has the strength but not the durability.
Edited by Bardon, 28 Aug 2015, 10:28 AM.
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Loki
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Bardon
27 Aug 2015, 10:39 PM
100 year concrete design life is the longest that I have worked with. The nuclear industry may have a longer design life.
Well, in three generations we will see if those designs hold up.

Thanks for the info.


“Talk sense to a fool and he calls you foolish.” - Euripides
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