There’s an article in the current issue of New Scientist about this fantastic new type of concrete being made right here in ol’ Melbourne town.
It is essentially concrete without Portland cement. The stuff is called ‘e-crete’ (my goodness words with randomly added e’s at the beginning annoy me) and it is made by a company called Zeobond. Instead of regular cement it uses fly ash or mineralogical slags for the required bonding of the concrete. The problem with cement is that to make it you need to cook the hell out of limestone (calcium carbonate), which not only requires a huge amount of energy, but the chemical reaction that occurs when you cook the limestone results in not only the quicklime (calcium oxide) that you need for the cement, but carbon dioxide, which as well all know is a greenhouse gas.
Cement production worldwide accounts for about 4-5% of total man made greenhouse gas emissions. For each kilogram of cement produced, approximately 800 grams of carbon dioxide is released into the atmosphere with the majority of this, about 500 grams, coming from the actual chemical reaction itself and the rest from fossil fuels used to provide the heat to drive the reaction.
But the Zeobond stuff uses geopolymers (like fly ash) instead of Portland cement, which don’t release anywhere near the amount of carbon dioxide and don’t require heating either, hurrah!
Unfortunately you can’t specify this for a slab just yet. At the moment e-crete is only able to be used in non-structural applications. Still, it’s something to look out for in the (hopefully near) future.