Spray Grancrete over a frame of
Styrofoam, metal, wood-even woven sugarcane stalks-and in 20 minutes you have a waterproof, fire-resistant structure that has more than twice the strength of traditional concrete and can withstand extreme temperatures without cracking. A liquefied concrete-like mixture of sand, ash, magnesium oxide and potassium phosphate, Grancrete descends from a product developed to encase radioactive waste. And since it takes hours instead of weeks to build a home, it´s poised to provide low-cost, high-quality shelter to the estimated one billion people who lack it. $20.50 to coat 15 square feet
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.