When those futbol crazed Catalans aren't appealing for independence, they're apparently thinking up new ways to greenify construction by inventing something called green concrete. In this case, the 'green' in green concrete is literal, as fungus and algae grow inside it.
Biological concrete is a new riff on the conventional building material. Regular concrete gets some tweaks to its pH level, texture and porosity. In addition, the concrete has four different layers in it: there's a waterproofing layer keeps other structural elements from being contaminated by water, plus a structural layer that does exactly what you think it should. The third later, the biological layer, is the key, since this is where rainwater is stored for the fungi and algae to grow with. The fourth layer draws rainwater in, but prevents it from escaping. The growing fungus inside the concrete helps to insulate the building and also acts as a carbon capturing mechanism.
Biological concrete is the pet project of Sandra Manso, a graduate student at Barcelona University. The product is already patented, and a local company is looking into monetizing its development. It remains to be seen if the project turns out to be as profitable as it is interesting.