Evaluation of Sulfate Resistance of Calcined Dolomite Activated Ground Granulated Blast Furnace Slag

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Aggressive environments significantly influence the durability and serviceability of hardened cement and concrete. This paper presents an evaluation of the resistance of ground-granulated blast-furnace slag (GGBS) activated with calcined dolomite, as a novel alkali activator, to 5% sodium sulfate attack and 5% magnesium sulfate attack. Two calcined dolomites, D800 and D1000, were prepared in the laboratory at 800°C and 1,000°C, respectively. The results demonstrated the good potential of using calcined dolomite activated slag in resisting sulfate attack. Immersion in Na2SO4 (aqueous) led to an increase in strength in both the D800 (D800S) and the portland cement CEM I 52.5 N (PCS) activated slag with a more pronounced effect in the former and a decrease in the D1000 (D1000S) activated slag. Conversely, calcined dolomite activated slag had less strength loss than PCS after MgSO4 attack. The products of sulfate attack and the deterioration processes are also analyzed by a range of tests, including pH, weight change, corroded depth, X-ray diffraction (XRD), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). After Na2SO4 attack, the main product on D800S and D1000S was gypsum with a larger amount in the latter. Gypsum, thaumasite, and M-S-H were the main products of D800S and D1000S after MgSO4 attack. The better resistance of D800S to sulfate attack was attributed to the absence of portlandite in the hydrated paste. Conversely, the presence of portlandite in D1000S led to the inhomogeneous sulfate ions inward progression; hence, the severe deterioration of the sample was observed.