Improving cement-based building materials to self-heal, last longer and offer even better and safer support for carbon storage facilities. Those are some of the solutions that Associate Professor Min Wu and his research group at the Department of Civil and Architectural Engineering at Aarhus University are working on.

“Cement-based materials such as concrete are the most used materials in buildings and infrastructure. The cement industry, and the built environment are currently among the highest CO₂ emitters. So, our focus is improving the materials and thereby contributing to reducing the total CO₂ footprint”, says Min Wu.

As a part of the department’s Structural Engineering section, much of Min Wu’s work aims to reduce the overall carbon footprint in the built environment through innovation of materials. One project is investigating whether solid wastes can be used to develop low-carbon or even carbon-negative cements.  This could potentially integrate two critical pillars of sustainability: waste management and carbon capture and utilization. Other projects look into enhancing the materials and extending the lifespan of concrete structures, for instance by developing novel self-healing cement.

Novel self-healing cement
One of the promising projects of that kind is focused on careful design of particle sizes of cement. If succeeding, this work might lead to more robust cement to be used in constructions such as sealing of CO₂ storage reservoirs ensuring long-term integrity.

Underground carbon storage, for instance using non-producing oil and gas reservoirs/wells, is essential to meet the demanding climate goal of “net-zero emissions” by 2050. When oil and gas wells are no longer in use, they need to be sealed upon abandonment. Some wells may be used for CO₂ storage, others are just sealed, and the seals must be 100 percent tight from the long-term perspective. This applies both if the wells are used for storing CO₂ or not, that there must be no leakage of any fluids, including CO₂, oil, gas and any other chemicals from the wells. Cement is the dominant sealing material, and the extreme underground conditions place great demands on the cement that is used for the giant plugs in the sealing.

“Unfortunately, cement is a brittle material, so it tends to crack. Cracking is an almost unavoidable problem; when we use cement – whenever we use cement, we have this cracking problem. It increases the risk of leaking in CO₂ storage reservoirs, when cracks present in the cement seals. Therefore, it would be very ideal to have cement, that can self-heal the cracks, that is a self-healing cement”, explains Min Wu.

Research into self-healing cement has been conducted for decades, and various strategies have been proposed. Simply speaking, almost all the strategies involve the introduction of foreign materials such as chemicals and bacteria to cement. The common problems include reduction in cement mechanical properties, the associated high cost and the complexity added to the application process, among others.  Consequently, large-scale application of self-healing cement has not yet been practically possible.
 

New concept without added materials

Instead, Min Wu and his research group have been searching for another solution to improving the self-healing ability of cement:

“Cement itself has some self-healing capability. But it’s quite limited – especially in modern cement. Through and only through careful design of the cement particle sizes, we developed a new technology, without extra costs, without adding any new materials, while the self-healing capacity of the cement is significantly improved. Moreover, there is no complexity added to the application process, meaning it can be easily applied using the business-as-usual techniques”, says Min Wu.

The new concept is being developed as a part of the research project “An Easy and Robust Self-healing Concept for Cement” which was sponsored by Danish Offshore Technology Centre (DTU Offshore). It is one of the several projects within developing new solutions for well abandonment and long-term safe CO₂ storage, that Min Wu’s research group has been working with over a number of years.

The concept of the new technology has so far been validated in laboratory. While scientific publications are on the way, the work now focuses on maturing the concept.

” The future for the concept is to further mature it to reach industrial application. This cement is not only for sealing the oil wells, but also basically useful for all buildings and structures including large infrastructures such as bridges, tunnels, or essentially anything built with cement and concrete. It would extend the lifetime of the structures, which reduces the need for maintenance and repair, and minimizes demolition and rebuilding. Apart from effectively helping decarbonize the carbon intensive construction industry, this could also save tremendous natural resources and money”, says Min Wu.

Link to:

Min Wu: https://cae.au.dk/om-instituttet/kontakt/medarbejdere/vis/person/mnwu@cae.au.dk

Publications by Structural Engineering: https://cae.au.dk/en/about-the-department/research-and-development-sections-civil-and-architectural-engineering-technical-sciences-aarhus-university/structural-engineering/translate-to-english-publications-by-structural-engineering