Sulphate resistance of one-part geopolymer synthesized by calcium carbide residue-sodium carbonate-activation of slag

One-part geopolymers attract wide interests due to their much lower CO2 emissions and similar practice as ordinary Portland cements (OPC), that is “just add water”, instead of mixing alkaline solution with precursors. To apply this type of new cementitious material in sulphate-rich environments, such as wastewater system and sewer network, we investigated the chemical and microstructure properties of one-part geopolymers synthesized by calcium carbide residue (CCR)-sodium carbonate-activated slag when they were exposed to sodium sulphate and magnesium sulphate solutions. We highlighted the main synthetic parameter of CCR dosage (from 2.5% to 10%) and its impact on kinetics of degradation, and meanwhile proposed the conceptual degradation mechanisms to clarify the influences of cation type (Na+ and Mg2+). We found that the relatively higher CCR dosages (7.5% and 10%) significantly accelerated the kinetics of degradation in Na2SO4 solution. The formation of ettringite depended mainly on the portlandite availability in the binders. In comparison with the Na2SO4 attack, all the mixtures were more susceptible to the MgSO4 attack, which could be explained by two mechanisms: the formation of gypsum via the reaction between SO42− with Ca2+, and the transformation of main binding gel phase C-A-S-H into non-cementitious and fibrous M-A-S-H.