5.1.6. CAC + Sustainability

A search with the keywords, calcium aluminate cement and Sustainability (CAC + Sustainability) in the Scopus database returned 17 results. The number of documents produced per year is presented in Figure 8f. This reveals almost zero production in the last 8 years.

M. Giroudon, et al. [73] analyze the deterioration mechanisms of different binders focusing on the impact of the binding nature on the medium (biochemical composition) during digestion. Binders with a favorable composition for chemically aggressive media were tested: slag cement (CEM III/B), CAC and alkaline metakaolin-based material (MKAA), and a reference binder: OPC (CEM I). Under the explored conditions, biodeterioration mainly led to carbonation of the cement pastes.

Alternative cementitious materials (MCAs) are receiving increasing attention worldwide, but there is a lack of knowledge about the resistance of these materials against the intrusion of harmful ions. Furthermore, current accelerated test methods that measure ion diffusion under an electric field are not reliable when comparing binders with very different pore solution chemistry. M.K. Moradllo and M.T. Law [74] solve these problems by using laboratory transmission X-ray microscopy (TXM) and micro-X-ray fluorescence

imaging (µXRF) to perform real-time measurements of ion diffusion in paste samples and mortar for five commercially available ACMs and a OPC. They compared the apparent rate of ion diffusion, quantified the change in the rate of ion diffusion over time, and gave an idea of ionic binding. It was found after 42 days of ion exposure that samples made with calcium aluminate cement had the lowest rate of ion penetration, while samples with activated alkali cement and calcium sulfoaluminate had the highest rate of ion penetration. Portland cement had an ion penetration level that was between these two. Furthermore, both alkali activated and calcium sulfoaluminate samples showed a decrease in penetration rate over time. These measurements are important to quantify the sustainability of MCAs, better justifying their uses where durability is a concern, and guiding to future durability tests for these promising materials.

It is well-known that cement production represents 1.65 billion metric tons of annual global CO<sup>2</sup> emissions [75], making it one of the largest contributors to global CO<sup>2</sup> emissions. One way to reduce CO<sup>2</sup> emissions associated with concrete construction is using alternative cementitious materials and binders (ACMs), such as calcium sulfoaluminate, calcium aluminate, and alkali activated binders. These materials often require lower production temperatures than OPCs and have lower calcium contents, reducing the emissions associated with the CO<sup>2</sup> released by calcium carbonate during calcination. Most ACMs are not new materials, but the past uses have been primarily limited to small-scale applications, such as pavement repairs, and there is little field experience regarding their long-term durability in heavily travelled structures, such as pavements and bridge decks. L.E. Burris, et al. [76] present promising results after the first year, of an effort by the U.S. Department of Transportation.
