Cement is glue that binds sand and gravel together to form concrete. However, to manufacture it, a temperature of at least 1400°C (2552°F) is required, and the chemical reaction that produces cement also releases CO2. If the cement industry is a country, it will become the third largest producer of greenhouse gases on the planet.
In order to achieve the goals set by the Paris Agreement, countries around the world must reduce cement emissions by a quarter in the next 30 years, literally reimagining the walls around us.
This is how oil well cement currently cleans up its behavior, and how it becomes better in the future.
Last year, MIT researchers successfully demonstrated in the laboratory that electrolysis can be used instead of heat to make cement. This process breaks down water molecules into acid, which then dissolves limestone and triggers a chemical reaction. Unfortunately, this still produces carbon dioxide. However, unlike the dirty gas released when cooking cement, this carbon dioxide is pure enough to isolate it or use it for other purposes, such as soft drinks or liquid fuels.
What remains to be seen is the extent to which the process can be scaled up to run in actual cement plants.
Traditional cement production heats limestone and clay in a kiln to trigger a chemical reaction to release carbon dioxide, while geopolymer cement uses industrial waste products (such as coal ash) to accelerate the chemical reaction, which requires less heat. Although it can eliminate up to 80% of carbon dioxide emissions, its downside is its dependence on polluting industries. With the bankruptcy of coal-fired power plants, coal ash is not as good as it used to be-nor should it be now.
The North Carolina engineering company bioMASON raises bacteria, mixes them with sand, and waters them regularly until they harden into a solid surface made of coral-like calcium carbonate structures. The U.S. Air Force is very interested in any technology that does not involve the transportation of cement mixers to theaters. It is currently testing biocement for military runways, but it has not yet been put on the market.
Recycling concrete prevents this non-biodegradable material from occupying landfills, and the technology is simple: crush it and mix the result with fresh cement, or use it to produce new products such as pavement and gravel. The crusher requires energy, but when crushed, the previously unexposed part of the concrete will be exposed and absorb additional CO2 from the atmosphere through the carbonization process. Unfortunately, because the strength and durability of recycled concrete may change, it is not universally recognized.
California start-up Heliogen said that by precisely adjusting the angles of thousands of mirrors to reflect sunlight onto the furnace, it will quickly generate enough heat to make cement. So far, Heliogen’s experimental mirror array can only always reach a temperature of 1000°C-enough for the earliest steps of cement production, but not enough to go all the way. The technology will also be limited to cement plants that have enough land (and enough sunlight) for mirrors.
The injection of carbon injects CO2 into the wet concrete inside the cement mixer, where it chemically reacts and transforms into minerals, and is never released as a gas. This technology has been used in many places. Disadvantages: Since carbon dioxide is added to concrete, not to cement, it cannot reduce the emissions of cement production itself. The isolated gas is captured from other industrial sources such as fertilizer production.
Post time: Dec-16-2020