CMMI-EPSRC RENACEM: Response to CO2 exposure of concrete with natural supplementary cementitious materials

Concrete can traditionally be thought of a mixture of mineral aggregates, water, and Portland cement. However, modern concrete mixtures are much more complex, also containing chemical admixtures and supplementary cementitious materials (SCMs) to enhance properties in the fluid and hardened states. SCMs are widely used in the US, UK and internationally to replace a portion of the Portland cement, improving concrete long term durability, reducing cost, and reducing CO2 emissions associated with concrete production.

The most commonly used SCMs are waste-derived, including coal combustion ashes and blast furnace slags from iron-making. However, changes in industrial processes (e.g. co-firing of coal with biomass, use of renewable energy, structural changes in the global iron industry) and increasing demand for SCMs are leading to a shortage of high quality, conventional SCMs. The use of widely-available natural SCMs, such as calcined clays and volcanic minerals, is rising dramatically, as their chemistry and mineralogy are more homogeneous, aiding in quality control compared to waste-derived SCMs. Standardization is advancing in the US and the UK to enable broader use of these materials, but the fundamental science of their use needs further investigation.

Natural SCMs, like waste-derived ones, generally have positive impacts on concrete durability, cost, and environmental footprint. However, one concern with all SCMs is that they often increase the vulnerability of concrete to carbonation. Carbonation occurs when CO2 enters the material, chemically reacting and reducing pH, leading to corrosion of steel reinforcement as well as changes in the integrity of the cementitious matrix. In concretes with natural SCMs, the mechanisms governing carbonation and related degradation are largely unknown. Considering that the field is pushing toward use of increasing volumes of natural SCM use in concrete (so-called LC3 systems), understanding the contribution of natural SCMs toward carbonation degradation is critical for future proof this technology. Furthermore, it is possible that manipulating the composition of the systems to reduce or prevent carbonation is possible, but has not previously been explored.

RENACEM is a joint US-UK collaboration between leading infrastructure materials researchers to elucidate the fundamental science explaining the long-term performance of concretes produced with natural SCMs. We will understand the chemical interactions between concretes and atmospheric CO2, and its transport, to identify meaningful methodologies to be used for their assessment. This will underpin the adoption of new methods for testing carbonation of concretes with natural SCMs and prediction models.

The costs associated with degradation of infrastructure, in the US and the UK, are vast; in both nations roughly 50% of the annual infrastructure budget is allocated to maintenance, repair and replacement. With the projected new infrastructure spending by 2025 ($1000B in the US; £480B in the UK), it is imperative to improve and predict the resilience of construction materials. A critical threat to concrete is CO2, which is now present in the atmosphere at record concentrations. Increasing presence of CO2 in the environment makes concrete structures more vulnerable to degradation due to carbonation; this problem is coupled with the increase in use of concrete mixtures that contain high-volume SCMs that are even more vulnerable.

The research proposed in this program has potential broad societal impact, reducing the monetary costs associated with infrastructure and building repair and reducing the risk of life-threatening failures due to deterioration and collapse of structures. The research programme establishes a strong and unique international network for research on cement-based materials encompassing materials characterization, design and synthesis, property development, accelerated degradation testing, innovative sensing, and thermodynamic and kinetic modelling. This diverse and multifaceted approach, bringing together experts from three universities in two countries, also builds upon existing collaborative relationships the researchers have with universities around the world on similar topics. For example, Prof. Juenger and Katz have collaborative relationships with researchers in Chile, Mexico, and Brazil already. The UK researchers have strong collaborations across the EU, Brazil, China, Colombia, and Australia, while the connection of team members to RILEM activities brings truly global reach. Strengthening the global research network facilitates solutions with broad, global impacts and improves the likelihood of acceptance of new materials and methodologies by standardization agencies, including those influential bodies (ACI, ASTM, BSI and others) for which the PIs and co-PIs are senior committee members. The industrial partnerships also established with this project also contribute to this effort.

Strengthening the global research network also provides an educational opportunity for students that broadens their research experience and improves their competitiveness in the global job market. The students and postdoctoral researchers involved in this research will learn how to work with a cross-institutional team of researchers, giving them valuable skills they can apply in today's increasingly global workplace. Further, the students will be able to learn from and participate in programmes available at the three applying universities that enhance education.