Calcium sulfoaluminate based cements versus standard testing procedures

Cements containing calcium sulfoaluminate (CSA) have reported excellent characteristics at both early and later ages. However, there are a number of studies reporting poor durability when compared with Portland cement (PC). Durability tests are used as an indicator for service life, and thus the viability of a cement system relies on its performance in these tests. Test methods often assume a sufficient maturity based on extensively tested PC systems; however, slower hydrating binder assemblages and variable chemistries can be severely underestimated when tested at the default 28 days. For example, a belitic CSA (BCSA) cement tested at this time will fail to account for later-stage hydration products that can improve the durability of the system. Tests on the durability of BCSA cements beyond 28 days of curing are sparsely covered in the literature, although in each study the results have shown a marked improvement in durability performance – a characteristic paralleled by other slow-hydrating binders such as fly ash composite cements. The use of an equivalent cement hydration/maturity in testing protocols is proposed, which could be considered a baseline for subsequent improvements that can be made with regard to how alternative binder systems are tested. A call to action for the cement community is outlined to (a) understand what tests are actually testing at a chemical level, (b) develop a ‘cure test’ to assess maturity and (c) undertake round-robin testing.