Calcium sulfoaluminate based cements versus standard testing procedures

Calcium sulfoaluminate (CSA)-containing cements have reported excellent characteristics across both early and later ages; however, there are a number of studies that display poor durability when compared to 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, such as acid attacks or those seen in EN 12390, often assume a sufficient maturity based on the extensively tested PC system; however, slower hydrating binder assemblages and variable chemistries can be severely underestimated when tested at the default 28 days. For example, a belitic calcium sulfoaluminate cement (BCSA) tested at this time will fail to account for later-stage hydration products that can improve the durability of the system. Testing the durability of BCSAs beyond 28 days of curing has sparse literature, although in each case 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 title paper proposes the use of equivalent cement hydration/maturity in testing protocols and could be considered a baseline for subsequent improvements that can be made in how we test alternative binder systems. A call to action for the cement community is outlined to i.) understand what tests are actually testing at a chemical level, ii.) develop a "cure test" to assess maturity, and iii.) undertake round-robin testing.