Why is this research needed?

Concrete has long been known for its ability to absorb CO2 via a naturally occurring carbonation process, which involves the reaction of atmospheric CO2 with the calcium and/or magnesium available in concrete to form thermodynamically stable carbonates. Given the scale of concrete production as the most consumed material on Earth, CO2 sequestration in concrete via carbonation has been considered to have great potential to reduce the carbon footprint of the giant concrete industry, which currently accounts for approximately 8% of total global CO2 emissions, with the projected demand for cement/concrete products set to grow continuously from its current level of 4.4 billion tons/annum to 5.5 billion tons by 2050.

The diffusion-controlled carbonation reactions occur extremely slowly in natural conditions, because of the low atmospheric CO2 concentration and high CO2 diffusion resistance in concrete, and that prolonged carbonation of hardened concrete needs to be avoided due to negative performance impact. This greatly limits the efficiency of CO2 utilisation in concrete manufacturing. Recently, accelerated carbonation curing (ACC) has emerged as a new technique to greatly increase the sequestration capacity and kinetics while improving the physio-mechanical properties of concrete.

In ACC, the concrete mixture is exposed to concentrated or pure CO2 to enhance CO2 penetration and accordingly accelerate the carbonation process. Various researchers have demonstrated that the use of ACC at ambient pressures, which serves as a CO2 utilisation step integrated into conventional concrete production, can reduce the carbon footprint of concrete industry by 4.6%. This means that the annual production of a medium-sized concrete producer will utilise ~24 tons of CO2, which amounts to 897 tons of CO2 avoided if taken with the 8% reduction in cement usage without compromising the strength of concrete. Researchers also found that ACC at high CO2 pressures can greatly increase the CO2 utilisation in concrete production to a massive level of 11% by the mass of cement used, while the compressive strength of the ACC-treated concrete can be increased by 200% compared to conventional concrete without ACC treatment.

Nevertheless, ACC needs to operate in a controlled environment, with the selection of curing conditions (e.g. CO2 pressure, concentration, and humidity) being vital to ensure the highest and fastest CO2 sequestration in concrete. Meanwhile, the carbonation resistance of freshly cast concrete increases sharply as the total porosity decreases, making it difficult to achieve high depth levels of carbonation within the suitable period of accelerated carbonation curing. Therefore, alternative ways need to be found to facilitate the ACC process.

What is this research investigating?

The project aims to develop CO2 carrier materials as an alternative technology to facilitate accelerated carbonation curing (ACC) for greatly improved operability and reduced cost. Accelerated carbonation curing has been considered as being a viable technology to help the net-zero transition of concrete industry but faces major challenges for deployment, due to issues with CO2 handing and lack of effective methods to facilitate effective CO2 diffusion in precast concrete during the vital early stages of curing. The objectives of the exploratory research include:

(i) To evaluate potential cost-effective candidate materials that can be used as the CO2 carriers for ACC applications
(ii) To examine effective methodologies to regulate the desorption rate of the best performing sorbent materials (in ambient conditions)
(iii) To characterise the CO2 release profiles of best-performing CO2 carrier material(s) under simulated conditions for carbonation reaction.
(iv) To use the results to produce carrier (~100 grams ) for simulated ACC tests.

The vital datasets to be obtained will help validate the technological concept, which underpins further research proposal(s) to advance the technology development.

What does the research hope to achieve?

The research project will generate new knowledge and engineering know-hows and patentable material and process technologies, which will be of direct interest or relevance not only to the research communities in areas of industrial CCS, direct air capture, and material chemistry, but also to the process industries, particularly the cement and concrete industry. The proposed research brings together the expertise from both industry and university.

In addition to patentable material and process concepts benefiting the UK industries, the research will also lead to high quality peer-reviewed publications in top international journals to help maintain or strengthen the UK’s international leadership in the vital areas of CCUS technologies.