Arcologies have been talked about on and off by architects, science fiction authors, and dreamers since Soleri’s City in the Image of Man first came off the printing presses. Looking at the scale of his drawings in the light of available building techniques leaves one asking how, exactly, we would accomplish such green buildings on a scale heretofore unknown in modern history.
One way to look at such green building concerns is through the lens of sustainability. If the building material in question is a metal, ceramic, or plastic, recyclability is a key concern- the building material also needs to be environmentally friendly from “cradle to grave” and require as little energy as possible to create or construct. Further, the nature of the constituent mass flows (carbon, mainly in the case of limestone) also plays a role, since such cycles make it easier to place those resources back into nature where they can do the most good.Given the sorry state of many of America's cities when population migration occurs, recycling is something we should definitely consider.
While recyclability is ideal, all materials are not equal in this regard. Some require far more energy to recycle than is required to acquire the raw materials in the first place, while some others are ideal for many uses.
Autoclaved Aerated Concrete is one such compound. In use in Europe and other areas, this compound adds aluminum to sand, lime, and cement in order to form a light, highly insulating structural material that can be cut to size on-site, requires no polluting compounds to make, and is easily recycled at the end of its life. While this material has not been qualified for use in the US due to earthquake resistance questions, it is hopeful that trends in energy prices and environmental impacts will cause consumers to take a serious look at this alternative to more traditional construction materials.