When Life Gives You Carbon… Make a Factory for Producing Carbon-Negative Concrete• https://www.goodnewsnetwork.org by Andy Corbley
One of the most ubiquitous of human building materials, concrete is nevertheless one of the most carbon-intensive manufacturing methods in society.
Finnish materials researchers at VTT Technical Research Center said that they were aiming to create carbon-negative concrete "before they know how to do so."
One of the interesting things about concrete is that it reabsorbs carbon over the years, which can lead to the corrosion of steel reinforcements like rebar inside it.
Experimenting with different substitutes, they discovered that slag from blast furnace smelting could be combined with bio-ash to replace cement in concrete.
During smelting, when the ore containing iron or copper is exposed to high temperatures, impurities within it such as oxides of calcium, magnesium, silicon, iron, and aluminum, are separated from the molten metal and can be removed. Slag is the term for the collection of compounds that are removed.