Belitic calcium sulphoaluminate (BCSA) cements and the current durability standards: what are we testing?

The service life of concrete is often estimated using parameters attained from durability tests, as corrosion in concrete under natural exposure typically takes several decades. Standardised tests, such several of those outlined in EN 12390, are performed on specimens after 28 days of curing using conditions designed to accelerate natural effects. These tests were originally created for Portland cements (PCs), which at 28 days will have their major phases mostly hydrated, and thus have a durability representative of their lifespan. However, these tests can underestimate the potential of binder systems that chemically evolve beyond 28 days, such as belitic calcium sulphoaluminate (BCSA) cements, which are often reported to underperform under these procedures. BCSAs at 28 days curing would only fully consider the hydration of ye’elimite, which reacts rapidly, whereas belite typically starts to react much later. The hydration products of belite can contribute to the further filling of pores, lowering the porosity in the binder matrix and improving durability. Therefore, this study aims to review (i) the hydration of binders across time, specifically BCSA cements, (ii) reported durability results at these times, and (iii) assess how representative any results are of a hydrated binder. Furthermore, we aim to recommend alterations to testing that result in more representative data, such as incorporating ‘equivalent hydration’ into testing regimes.