Poor-quality concrete could lead to skyscrapers collapsing

[cronus]

http://www.wired.co.uk/news/archive/201 ... ty-scandal

Poor-quality Chinese concrete could lead to skyscrapers collapsing

A sand scandal is brewing in China, with concerns that low-quality concrete has been used in the construction of many of the country's largest buildings -- putting them at risk of collapse.

The recipe to make concrete is pretty simple -- cement, aggregate and water -- but the strength of the final batch can vary wildly depending on the kinds of aggregate and cement used and the proportions they're mixed in. Commonly the aggregate used in many modern buildings projects consists of crushed gravel or other rock, including sand, and that's the cause of so much distress in the Chinese construction industry at the moment. Inspections by state officials have found raw, unprocessed sea sand in at least 15 buildings under construction in Shenzhen, including a building which, when finished, was set to become China's tallest.

The Ping'An Finance Centre is planned to top out at 660m, making it not only China's tallest building but the second-tallest building in the world after the Burj Dubai. 80m has been built so far, but construction has been halted in the wake of the revelation from Shenzhen's Housing and Construction Bureau that substandard sea sand concrete had been used in its construction. According to a notice on the Bureau's website posted on 16 March, 31 companies had had their licenses to work revoked for at least six months.

Many of the companies named in the notice took heavy hits to their share prices on the Hong Kong stock exchange. Bloomberg reports that the financial incentive to use illegal sea sand, which is far cheaper than legal river sand, is the likely reason for the problem. Untreated sea sand is unsuitable for construction because it still contains chlorine and salt, which corrodes steel -- river sand from freshwater channels doesn't have that problem.

It can take only a few decades for a building to become dangerously unsafe if untreated sea sand is used in its concrete -- including the possibility of collapse. While this scandal has been confined only to Shenzhen thus far, the possibility of it spreading to other Chinese cities is worrying. The country currently has nine of the 20 tallest buildings in the world that are under construction, while there were reportedly so many skyscrapers under construction in 2011 that it worked out as a new one being topped out every five days right through into 2014.

(continued)

[Hermit]

...construction has been halted in the wake of the revelation from Shenzhen's Housing and Construction Bureau that substandard sea sand concrete had been used...

So government surveillance works. Good thing, aye?

Sydney Harbour includes a fort with concreted cannon emplacements. They were built circa 1912 because of the fear of a Russian invasion at that time. Several years later it was discovered that due to the contractor's cost saving way of building the bunkers, they would have been pulverised by even near-misses.

[JimC]

...construction has been halted in the wake of the revelation from Shenzhen's Housing and Construction Bureau that substandard sea sand concrete had been used...

So government surveillance works. Good thing, aye?

It would be better if it had worked a little earlier in this case...

[FBM]

S. Korea has had several instances of building and bridges collapsing because of cost-cutting measures by constructors. There was one, an orphanage, IIRC, that collapsed killing a couple dozen kids. The contractor had placed empty metal cans in the walls in order to save money on concrete. Not if they went to prison or not.

[JacksSmirkingRevenge]

S. Korea has had several instances of building and bridges collapsing because of cost-cutting measures by constructors. There was one, an orphanage, IIRC, that collapsed killing a couple dozen kids. The contractor had placed empty metal cans in the walls in order to save money on concrete. Not if they went to prison or not.

[FBM]

Yep. And I know of two major fatal bridge collapses.

[FBM]

The worst building collapse: http://en.wikipedia.org/wiki/Sampoong_D ... e_collapse

[Thinking Aloud]

The worst building collapse: http://en.wikipedia.org/wiki/Sampoong_D ... e_collapse

Wow.

[Rum]

There is actually a concrete testing regime in the UK. My first real job, which I had when I was about 23 was doing exactly that. We would get samples as they were delivered to the building site and do two main tests. The first was called a 'slump' test. We would fill a special cone with the stuff, turn it over and measure how much it 'slumped'. The second involved taking a sample to the lab, weighing it, microwaving the hell out of it and then weighing it again. There were a couple of other randomly administered tests too. These were all designed to ensure that the quality was right.

We were however a very weak link in the quality control chain. Nobody checked on us and I would probably have been eminently bribable given we were working on roads not skyscrapers.

[Svartalf]

S. Korea has had several instances of building and bridges collapsing because of cost-cutting measures by constructors. There was one, an orphanage, IIRC, that collapsed killing a couple dozen kids. The contractor had placed empty metal cans in the walls in order to save money on concrete. Not if they went to prison or not.

We're talking China here... last time I checked, that gives the guilty party between 48hrs and less than a year life expectancy depending on the nature of the judicial process.

[FBM]

S. Korea has had several instances of building and bridges collapsing because of cost-cutting measures by constructors. There was one, an orphanage, IIRC, that collapsed killing a couple dozen kids. The contractor had placed empty metal cans in the walls in order to save money on concrete. Not if they went to prison or not.

We're talking China here... last time I checked, that gives the guilty party between 48hrs and less than a year life expectancy depending on the nature of the judicial process.

Yup. Most likely. China is still catching up to Korea in construction engineering and quality control, and Korea's not even all that advanced yet. Granted, we don't have earthquakes of any appreciable magnitude.

[mistermack]

There is actually a concrete testing regime in the UK. My first real job, which I had when I was about 23 was doing exactly that. We would get samples as they were delivered to the building site and do two main tests. The first was called a 'slump' test. We would fill a special cone with the stuff, turn it over and measure how much it 'slumped'. The second involved taking a sample to the lab, weighing it, microwaving the hell out of it and then weighing it again. There were a couple of other randomly administered tests too. These were all designed to ensure that the quality was right.

We were however a very weak link in the quality control chain. Nobody checked on us and I would probably have been eminently bribable given we were working on roads not skyscrapers.

Yeh, I used to do that slump test on concrete pours. If the trucks were late, or kept waiting too long, the concrete started to go off, and to make it pass the test, they would add water, to make it runny again. ( not allowed but frequently done ).

I don't know what the arrangement was for paying for a lorry load of concrete that was sent away because it was kept waiting too long, but that was the incentive. They would also have to find somewhere to dump it. Usually, some local project that just needed cheap fill.

We used to take samples back to the lab, as concrete cubes, which were kept in water tanks for about a week, and then dried and put in a crusher, and the strength when it failed was measured.

I expect that was widely fiddled too, as it would cost a fortune to fail a whole bridge, after it had been poured.

[FBM]

S. Korea has had several instances of building and bridges collapsing because of cost-cutting measures by constructors. There was one, an orphanage, IIRC, that collapsed killing a couple dozen kids. The contractor had placed empty metal cans in the walls in order to save money on concrete. Not if they went to prison or not.

We're talking China here... last time I checked, that gives the guilty party between 48hrs and less than a year life expectancy depending on the nature of the judicial process.

Yup. Most likely. China is still catching up to Korea in construction engineering and quality control, and Korea's not even all that advanced yet. Granted, we don't have earthquakes of any appreciable magnitude.

To-fucking-day, no less.

http://www.koreatimes.co.kr/www/news/na ... 34337.html

[pErvinalia]

http://www.wired.co.uk/news/archive/201 ... ty-scandal

Poor-quality Chinese concrete could lead to skyscrapers collapsing

A sand scandal is brewing in China, with concerns that low-quality concrete has been used in the construction of many of the country's largest buildings -- putting them at risk of collapse.

The recipe to make concrete is pretty simple -- cement, aggregate and water -- but the strength of the final batch can vary wildly depending on the kinds of aggregate and cement used and the proportions they're mixed in. Commonly the aggregate used in many modern buildings projects consists of crushed gravel or other rock, including sand, and that's the cause of so much distress in the Chinese construction industry at the moment. Inspections by state officials have found raw, unprocessed sea sand in at least 15 buildings under construction in Shenzhen, including a building which, when finished, was set to become China's tallest.

The Ping'An Finance Centre is planned to top out at 660m, making it not only China's tallest building but the second-tallest building in the world after the Burj Dubai. 80m has been built so far, but construction has been halted in the wake of the revelation from Shenzhen's Housing and Construction Bureau that substandard sea sand concrete had been used in its construction. According to a notice on the Bureau's website posted on 16 March, 31 companies had had their licenses to work revoked for at least six months.

Many of the companies named in the notice took heavy hits to their share prices on the Hong Kong stock exchange. Bloomberg reports that the financial incentive to use illegal sea sand, which is far cheaper than legal river sand, is the likely reason for the problem. Untreated sea sand is unsuitable for construction because it still contains chlorine and salt, which corrodes steel -- river sand from freshwater channels doesn't have that problem.

Capitalism... You are doing it right.

[Gawdzilla Sama]

To-fucking-day, no less.

http://www.koreatimes.co.kr/www/news/na ... 34337.html

Almost like you jinxed yourself.