The bit about buildings lasting 20-30 years really surprised me. The Pantheon stands for a millennium, but 30-year-old concrete crumbling? The article cites a Goldman Sachs quote from a tumblr [1] notes at the bottom of the list:
An estimated 25-30% of China’s cement capacity is low-grade cement
not used in other countries (P.C. 32.5 grade).
I'm not a cement/concrete expert, but PC 32.5 does seem to be a low grade. Higher than PKC 32.5 (composite cement) but lower than PC 42.5. So I found this other source that puts it in stark terms [2]:
According to the China Cement Association, low-grade cement products
(all 32.5 grade) accounted for 72% of the total cement output in China
in 2013, with the P.C. 32.5 grade cement accounting for 54%.
So 72% of cement was 32.5 grade, and most of that (54/72%) is PC 32.5. I was a bit skeptical at first, but now I really wonder if/when these structures start to crack &/ crumble.
uumm, yeah - I'm a concrete guy at the moment. PC = Portland Cement, 32.5 = MPa of force needed to overcome strength [1]. Normal concrete is in the 20 MPa to 50 MPa range and the strength needed is just a design parameter - it's not a quality issue. typically a slab for a house would be at the 20 MPa end and a massive industrial warehouse closer to 30 MPa (something to do with forklift wheels being small and hard), bridge spans etc ask a structural engineer. the fact that China is using a lot of grade 32.5 concrete is more likely due to the fact that they are building a lot of infrastructure that requires... 32.5 MPa strength. NB 'Grade' in the concrete industry refers to compression strength, not a quality statement. Every country has loads of standards about how cement is made, the constituents that can be added and how concrete is batched, delivered, structures designed etc. Cracks and crumbles are more likley due to inadequate design and placement of the fresh concrete. As others say, it's been around for literally 1000s of years but has infinite depth of complexity - i believe MIT found the actual formula for PC around 2010. amazing that we just used it for its bulk properties without knowing the actual chemical formula ;-)
I think China is going to suffer an epidemic of infrastructure failure in the near future, perhaps as early as the mid-2020s if the 20-30 years estimate is correct.
For comparison, South Korea's extraordinary growth was followed by a series of infrastructure failures in the mid-90s. A relatively new bridge suddenly fell into a river during the morning rush. A department store imploded, killing over 500 people. Gas explosions all over the place. IIRC none of the major accidents in Korea were caused by low-grade concrete specifically, but there seems to be a general parallel between what the Chinese have been doing lately and the "build now, worry about quality later" mentality that Koreans adopted during their period of rapid growth. Both result in crumbling buildings 20-30 years later.
It's already happening. There are high-profile stories of bridges collapsing and so on. I live in Shenzhen right now and was looking for a new apartment during the summer last year. My roommate noted that a lot of the landlords all know that the apartment buildings will be replaced and rebuilt in 20-30 years.
If that's true, the expectation is already there. However, my impression is that this belief stems from this idea that construction will always be happening because that's how the economy rolls.
The question is what percentage of the population believes that this cycle really is the end game and what percentage of the population thinks they're investing into infrastructure what will last their entire life.
Most ordinary people either don't understand the cycle, or even if they do, they're powerless to do anything about it.
If what happened in Korea is any indication, the first generation of apartment buildings will be demolished after 20-30 years, homeowners will be "asked to leave" with as little compensation as the construction company can get away with, and a new block of condos will go up that the previous homeowners just can't afford. In Korea, at least we let the previous homeowners file complaints and protest for a while before we send in the bulldozers. In China, the bulldozers will probably go in first, and the GFW won't let anyone else know what happened next.
This is an accurate picture of what happens right now in China, but limited protests are permitted by homeowners to haggle the price. An extra complication is Chinese can only own their properties for a maximum of 70 years anyway, with many having only 30 or 40 years left on the state-granted lease, so even without the demolition cycle Chinese aren't really looking ahead more than a few decades anyway.
I'm not an expert on this and I may be mis-remembering something I read somewhere once, but I believe the Roman formula for concrete was quite a bit different. The reasons we don't use it in modern construction are: it takes a really long time to cure, and it's made with salt water, which might cause rebar to rust.
China had it's own historical cement recipe, including rice. Recently discovered it may have useful properties that can be reapplied today. http://phys.org/news194411869.html
>The Pantheon stands for a millennium, but 30-year-old concrete crumbling?
It took the wealth of a civilization to produce the Pantheon. We could make more durable buildings if we used stone, too, but do you really want to pay $10m for a house?
[1] http://ftalphaville.tumblr.com/post/100653486301/contextuali...
[2] http://pg.jrj.com.cn/acc/Res/CN_RES/INDUS/2014/2/19/c6835c29...