Durability of phosphogypsum-based supersulfated cement mortar against external attack by sodium and magnesium sulfate

Supersulfated cements (SSCs) are composed primarily of blast furnace slag, calcium sulfate, and a small content of alkaline activator. SSC has been discussed in the literature because it has a low content of clinker and consequently low CO2 emissions. However, the current absence of durability studies is the main challenge for the large-scale implementation of SSC as a building material. The objective of this study was to investigate the behavior of phosphogypsum-based SSC mortar under sulfate attack. SSC mortars were submitted to MgSO4 and Na2SO4 solutions. Portland cements were also used as a comparison. SSC mortar showed good durability against sodium sulfate attack but presented an expansive behavior when exposed to magnesium sulfate. This behavior in the MgSO4 solution was attributed to the low portlandite reserve, which anticipated the attack of C-S-H. Besides, the non-formation of the brucite layer accelerated the entry of this type of sulfate.