Construction uses river sand or sand from crushed rocks, both of which are cubic (or at least angular) and free from contaminants, but they are in short supply and people are being murdered over it. Sea sand is also angular, but can react with other chemicals resulting in dangerous buildings. Sea sand can be dredged in order to extend coastlines, but this causes environmental damage. Desert sand is round and does not bind well, resulting in weak concrete. Recycled glass could be used, but needs preparing and is expensive.
Which leads me back to desert sand.
A few years ago Markus Kayser created the Solar Sinter Project, which used desert sand and focused sunlight to 3d print objects. This same technique could be used to convert desert sand in to rocks, that can crushed in to construction sand, the same way rocks are already and glass can be.
To calibrate this project, I set up #Measuring Extreme Temperatures