While the high-tech trains have also captured the Chinese imagination of some day becoming an innovative powerhouse, the rail system serves a more prosaic purpose. As the high-speed rail is passenger-dedicated, that should open up freight capacity to ensure timely delivery of goods and commodities. The freight rail system in China is notoriously over-taxed and often has to defer to passenger transport as a matter of political priority. This creates bottlenecks and explains in part why so much Chinese coal is transported via trucks, occasionally causing epic traffic jams. When I was in Inner Mongolia this past November, I trailed an endless line of coal trucks for miles.
Yet there are legitimate critiques of whether the HSR system makes sound economic sense and whether the Chinese government can afford such a massive construction project. The pace of expanding the system -- the Beijing-Shanghai line, completed after a mere 2.5 years, is expected to commence operations this summer -- has led to questions over the quality and safety of what's being built. In particular, a little-known technical issue of the material used for the track foundations, apparently something called "fly ash." Here's what the South China Morning Post had to say:
The problem lies in the use of high-quality fly ash, a fine powder chemically identical to volcanic ash, collected from the chimneys of coal-fired power plants. When mixed with cement and gravel, it can give the tracks' concrete base a lifespan of 100 years.
According to a study by the First Survey and Design Institute of China Railways in 2008, coal-fired power plants on the mainland could produce enough high-quality fly ash for the construction of 100 kilometres of high-speed railway tracks a year.
But more than 1,500 kilometres of track have been laid annually for the past five years. This year 4,500 kilometres of track will be laid with the completion of the world's longest high-speed railway line, between Beijing and Shanghai. Fly ash required for that 1,318-kilometre line would be more than that produced by all the coal-fired power plants in the world...
...Professor Wang Lan , lead scientist at the Cement and New Building Materials Research Institute under the China Building Materials Academy, said that given poor quality control on the mainland, the use of low-quality fly ash, and other low-grade construction materials, was "almost inevitable" in high-speed railway construction.
Apparently, the Romans had used similar volcanic ash from Pozollana to fortify cement into a rock solid material for their infrastructure, according to Marco DiCapua of the Deptartment of Energy. He also writes:
The underlying concrete which is composed of water, cement, aggregate and fly ash i.e because of an excess (above 6%) of fine carbon particles, the concrete may not reach the compression strength that is specified in the design, or could disintegrate after a number of years in service. Or the excess carbon may interfere with the function of other additives. The strength is always an an issue, but even more so in critical applications like curved viaducts or other applications where some of the concrete may be subject to concentrated loads.
In another exchange with Loreal Heebink, an expert at the Energy and Environmental Research Center of the University of North Dakota, carbon content isn't the only issue:
Loss on ignition (LOI) is considered by industry to be one of the key quality measures for fly ash even though it may not be a direct indicator of fly ash performance or carbon content. LOI also does not provide any information on the form of carbon present in the fly ash, and the various carbon forms that have been identified in fly ash exhibit different reactivity. However, when significant levels of unburned carbon are present in or activated carbon (AC) is added to fly ash, LOI can provide a comparative indicator of the carbon present. Typical LOI limits range from 3% to 6%. Excessive LOI can have detrimental effects on wet and hardened concrete. LOI will not add to the cementitious and compressive properties of a concrete. Fly ashes with high LOI can absorb concrete chemical admixtures, such as air entrainment admixtures, resulting in a loss in air content in fresh wet concrete. Sufficient air content is critical for concrete durability in freeze-thaw conditions.
I am obviously not a technical expert on this, but it sounds like it could become an issue for China's current construction efforts. But how big of a problem is this ultimately? And what portion of the tracks being laid now contains lower quality ash? Will this require regular and expensive maintenance? Impossible to say, and I suspect even the Chinese government does not know for certain. Although the HSR system's safety record has been fine so far, it is an issue to be watched, and whether there will be more official acknowledgment of this potential problem.
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