Making cement—the main ingredient in concrete—is estimated to be responsible for producing 8 percent of the world’s carbon dioxide emissions, at a rate of a ton of CO2 per ton of cement.
Various technologies have been developed that tout “net zero” concrete production or that capture CO2 emissions for use as an industrial feedstock.
Now the Massachusetts Institute of Technology has spun off Sublime Systems, a start-up making cement that meets construction industry performance standards and can do so not only by reducing CO2 emissions but, using a variation on its process, avoid creating any CO2 at all.
Conventional cement-making uses fossil fuels to heat limestone to about 2,550°F (1,400°C) to extract pure lime. Limestone is about half carbon dioxide by weight and that gas goes up the smokestack and into the atmosphere.
Instead of fire, the Sublime process uses electricity.
A current splits water molecules to create hydrogen and oxygen gasses, which also creates acidity at the unit’s negative terminal and alkalinity around the positive terminal.
A mineral containing calcium reacts with the acid at the negative terminal to make calcium ions, which have a negative charge and, therefore, migrate toward the positive terminal. In the positive terminal’s alkaline solution, the ions form solid calcium hydroxide, which is also known as builders lime.
The builders lime is a drop-in replacement for the lime used now in making cement. It can be mixed right in with silica, sand, and the other ingredients that make up cement.
This version of Sublime’s process does produce some CO2 but delivers it in a cold, compressed state ready to store.
Sublime also can pull calcium that appears as impurities in aluminum, iron, magnesium, silica, or other common materials. That version of the process produces no CO2 at all and, in addition, purifies the materials it takes the calcium from.
Whichever Sublime’s builders lime can then be mixed with the other ingredients that make cement.
Just as important, Sublime’s technology all happens at room temperature – no furnaces required.
The company has scaled up a demonstration plant able to turn out about 100 tons of cement annually.
The next goal is to drop the cost of the process so that Sublime’s cement competes on price with the conventional version. Sublime’s product now prices at $190 to $205 a ton, while the usual stuff costs around $130.
Sublime expects to be market-ready by the early 2030s.
TRENDPOST: Consumer pressure for all things green will continue to grow, creating a viable market for green building materials even if they are more expensive at first. That demand will generate a flow of investment into this and other new green building technologies.
By the next decade, green building materials will be a well-entrenched part of the market and on the way to dominance.