Olivine — a magnesium iron silicate — added to cement has been eyed by engineers at Imperial College London as an ingredient for the manufacture of carbon-negative concrete.

To make this determination, the team of engineers experimented with cement mixing, which led to an approach for producing concrete in a more climate-friendly way.

Cement-making is considered one of the major contributors to the release of carbon dioxide (CO₂). This is due to the cement manufacturing steps wherein fossil fuels are used to heat products in the mix — including clay, water and calcined lime — and the step where limestone is heated to create clinker, which is a cement binder. During their experiments in the lab, the engineering team discovered a replacement for clinker that does not result in CO₂ emissions.

Photographs showing (a) raw as-received olivine, (d) dissolution of the olivine using H2SO4, (b) separation of silica gel from magnesium/iron sulfate using IPA, (c) APS and (e) HMC nesquehonite. Source: Royal Society Open Science (2024). DOI: 10.1098/rsos.231645

The researchers explained that adding products from olivine to the cement mix in lieu of the clinker produced a cement that is both stronger and more durable as well as more environmentally friendly.

This discovery was made by extracting silica and magnesium sulfate from olivine samples by dissolving them in sulfuric acid. CO₂ was then bubbled through a batch of the slurry that was subsequently produced, leading to the creation of a mineral called nesquehonite during cooling and eventually resulting in sequestration of the CO₂. At this stage, the nesquehonite was added to the cement mixture in addition to some concentration of clinker.

Depending on how much nesquehonite is added to the cement mixture, the engineers suggest that the process might be either carbon-neutral or carbon negative.

The team’s findings are detailed in the article, “Carbon capture and storage in low-carbon concrete using products derived from olivine,” which appears in the journal Royal Society Open Science.