Carbon Negative Concrete Can Mitigate Climate Change

Concrete production, where cement is its primary component, is one of the most carbon-intensive industries. Cement is the source of around 8 % of carbon emissions worldwide.

The staggering amounts of GHG emissions stemming from the sheer scale of its production and demands make the cement and concrete industry so carbon-intensive. Concrete is everywhere and is a common feature in this modern age.   

But what if a technology allows cement production to absorb more carbon than it releases?  

The AsiaPacific Infrastructure article reports an innovation being developed by Solidia Technologies that can do this – making concrete become a carbon sink and building carbon-negative roads. According to the article, every ton of cement produced releases a ton of CO₂ into the atmosphere.

The article explains: “By changing the chemistry of cement, Solidia both lowers emissions at the cement plant and consumes CO₂ in the production of concrete. Our cement reacts with CO₂ instead of water. During curing, the chemical reaction with our cement breaks apart the CO₂ molecules and captures the carbon to make limestone that glues the concrete together.”

With precast concrete, the technology can reduce CO₂ emissions by up to 70% during production, including the CO2 absorption during curing. With ready-mixed cement, chemistry is again applied with the help of waste CO2, turning them into chemicals like oxalic acid to react with the cement and “pack” up to 4 times of carbon into it.  

Applying this type of cement to road pavements can create carbon-negative roads. The article says every kilometre of the road will absorb amounts of carbon dioxide that 100 thousand trees can.

Concrete has been known to absorb CO2 for decades and is the subject of many studies, according to a Portland Cement Association (PCA) paper. The process of carbon absorption of concrete is called carbonation.

Concrete in many forms, like buildings, pavements and even underground concrete structures like foundations and piping, can still absorb CO2 from the air in the soil or dissolve carbon dioxide. Even crushed concrete is used as aggregate in pavement construction, and recycled or secondary uses do the same.

The article explains,

“Carbon dioxide slowly absorbs into a concrete structure from the source of the carbon dioxide (usually the air around it), and the depth at which this absorption has resulted in a significant pH change is usually referred to as the carbonation front. Usually, applications with reinforcing material that might be affected by a change in pH are designed so that the carbonation front does not reach these materials over its intended life. So, carbonation depth or carbonation front really only refers to this specific phenomenon related to pH. These studies on carbonation depths are very useful, though. Usually, the carbonation front will move more quickly with adequate levels of moisture, higher porosity, and higher ambient CO₂ levels and with certain concrete mixes. Therefore we assume that applications with similar conditions will have absorbed more carbon dioxide than other applications in a shorter period of time.”

Cement industries and manufacturers can use this knowledge to improve the carbon footprint of concrete before, during its primary life,  and even up to its secondary application. And where lower Ph is not an issue, processes, mixes and additives that increase absorption of CO2 should be encouraged, especially since climate change is a significant problem we face today.  Innovations and knowledge like this can be maximised to mitigate GHG emissions and prevent the consequences of climate change.