Thermodynamic modeling of sulfate attack on carbonated Portland cement blended with blast furnace slag

Sulfate attack on concrete induces volumetric changes resulting in a severe damage to the structure. The structural deterioration can be coupled with carbonation in practice, while such coupled effect is relatively unknown. Herein, thermodynamic calculations are used to study the combined effect of sulfate attack and carbonation on slag-blended Portland cement. The results show that the resultant product of sulfate attack varies according to the cations being used. Gypsum and M-S-H are the major products when Mg2+ is present in the sulfate solution, while ettringite and gypsum are predominant in the presence of Na+. Higher levels of carbonation are found to accelerate the effects of sulfate attack, while slag replacement tends to lower the carbonation degree required for destabilization and precipitation of certain phases.