From Tony Cooper, Green Party
Your reporter Fred Pearce has slipped from his normal standards of excellence (13 July, p 38). The magnesium-based cements that he describes are not a green panacea.
Pearce quotes John Harrison, a technologist from Hobart, Tasmania, who proposes an industry that takes magnesium carbonate ore and converts it into magnesium oxide cement. Buildings using the MgO cement would absorb carbon dioxide from the air, turning cities into CO2 sinks. But the cement can only reabsorb at most the same amount of CO2 after the structure has been built as was released during the manufacturing process. You can’t use it to make a city a real carbon sink. The fact that magnesium cements are expensive should be a warning flag. It may just be due to a lack of economies of scale, but it’s equally likely to be due to the nature of the whole industry, from ore extraction, refining, cement manufacture and transport at all stages. These activities cost money and also cause CO2 emissions. It is important that a full life-cycle environmental analysis be carried out before governments and environment agencies start actively encouraging a magnesium cement industry.
It could well be that MgO cement is significantly less of a climate hazard than traditional calcium-based cement. However, wood or locally produced materials of any kind could well be better, particularly for housing. Making cities eco-friendly is a challenging but achievable goal. Tangible steps forward would include filling them with as many and as diverse trees and other plants as possible, and, as Barcelona has done, insisting that all new buildings have solar panels on their roofs.
Ashtead, Surrey
