It seems strange, but the world is running out of sand (see here; there’s also a fantastic book on the topic). The problem, in particular, is that sand is used in producing concrete, but only sand with grains that are shaped in a particular way will work.
Unfortunately, desert sand, which is plentiful, is weathered by the wind into a rounded shape that cannot be used for construction purposes. The kind of sand most commonly used for construction comes from a small number of places, and is increasingly rare (and hotly contested).
To turn granular sand into a useful building material, it is generally combined with cement (usually a limestone product) to produce concrete. In addition to using up vast quantities of rare sand, this also produces a lot of carbon dioxide (although there’s various work-arounds in development); construction is a significant source of this greenhouse gas.
What if we took a completely different approach to turning sand into a construction material though? One that can use any sand, even the most common of desert sands. One that does not require concrete at all.
What if, instead of combining sand with cement, we melt it, and then spray it from a nozzle?
This approach would be similar to experimental 3D printing construction methods that use concrete to form buildings, but the end result would be more durable (once cooled, this essentially would just be rock, and the molten material could also be combined with other minerals to increase hardness and tensile strength). It would also, as noted above, work with any type of sand, and would not need to use Portland cement.
Sand melts at a fairly high temperature (1,713 °C, or 3,115 °F). One challenge would be finding materials to make the spray nozzle out of so that it wouldn’t melt from the heat. A tungsten alloy might work for this purpose, or some sort of high temperature ceramic. Alternatively, the nozzle could be water-cooled.
Basically, what we’re suggesting here is to 3D print buildings out of lava!
Edit 1: Just to summarize: Portland cement accounts for 8% of global CO2 emissions. This method would cut down dramatically on that. It would also resolve sand shortages (since any sort of sand could be used). It likely also will wind up being cheaper (once R&D is done).
Edit 2: A friend pointed out that the end product will essentially be glass. Molten glass will need some sort of additive to ensure the right sort of viscosity while spraying it (otherwise it tends to be “sticky”). It likely will need other additives (as mentioned above) to increase tensile strength, change coloration etc. Perhaps Ti02?