I’ve mentioned concrete before as an emitter of CO2 during its production, but I was not aware of another of its shortcomings as a building material – consumer of sand. Julian Smith reports in NewScientist (17 February 2018, paywall) :
Riverbed mining downstream of the Karcham Wangtoo Dam on the Sutlej River.
Photo by Samir Mehta/International Rivers.Concrete is made mostly of sand and its chunkier cousin gravel, with a little cement and some water mixed in. Most recipes call for large, rough sand grains that bind together well. So, although there may be mountains of the stuff blowing around in the Sahara, for example, those grains are no good for most types of concrete – they are too small and polished round by the wind. The best sources of concrete-compatible sand are river beds, beaches and the near-shore seabed. Sand from the ocean floor works too, although it needs to be laboriously purged of salt and chlorine.
Sand mining in such places can ravage the environment. For instance, in the past few years sand pirates have harvested so much grainy booty from islands in Indonesia that at least 24 of them have disappeared. Much of the sand is shipped to the cramped island state of Singapore, where it is used in land reclamation projects. Meanwhile, there are fears of ecological catastrophe in Indonesia.
There are many more stories like this (see “Aggregate armageddon”) and they show we have a serious sand problem. But it is hard to know exactly how serious. Few countries publish how much sand they extract, in part because widespread off-the-books mining means most don’t know themselves. It is telling that the official import and export statistics for sand don’t cancel out.
Our sand crisis is a classic case of the tragedy of the commons, where unfettered access to a common resource leads to demand that overwhelms the supply. One logical solution, then, is to set up and enforce rules on how much sand can be mined – but that is easier said than done, especially in remote places. “The real solution is to decrease our need for sand,” says Peduzzi.
But, unfortunately, the article says nothing about returning to the old standby, wood, as I’ve mentioned on this blog before. Perhaps the author perceives the use of wood as being non-scalable in the face of a world where the phrase burgeoning population is still our present and future – not our past.
