Study of early-age performance of cementitious backfills with alkali activated slag under internal sulfate attack

•Alkali activated slag (AAS) has been used in cemented paste backfill (CPB) applications.•A blend of two alkali activators (SS: sodium silicate, SH: sodium hydroxide) was considered.•Initial/final setting times of CPB-AAS tend to drop with growing sulfate content up to 5000 ppm.•The presence of sulfate can deteriorate the strength of AAS-CPB depending on activator type and age.•CPB with high SS/SH ratio reveals weaker resistance to internal sulfate attack due to their low pHs.