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.
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...
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.
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:
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.