Mitigation effect of glass powder on external sulfate attack and its relation to alkalinity of pore solution.

• Mortar bar incorporated with 30% glass powder exhibits good volume stability during external sulfate attack (ESA) test. • The pozzolanic reaction of glass powder significantly elevates the Na concentration and pH. • Elevated alkalinity of pore solution in sample with 30% glass powder leads to the dissolution of monosulfate. • The Pitzer model could give a reasonable estimation of the dissolution and/or precipitation trend of products formed during ESA test. Due to the presence of high alkali content, it is inferred that the improvement of sulfate attack resistance for blend with glass powder should not be solely ascribed to the refinement of microstructure. This study aims to explore the effect of glass powder on the pore solution and its relationship with the chemical sulfate attack process. Paste samples blended with 30 % wt. glass powder and quartz powder were prepared and subjected to a simulated external sulfate attack (ESA) test. To eliminate the effect of microstructure on sulfate ingress and alkali leaching, the pressed paste grains (after pore solution extraction) were immersed in test solution consisting of 5 % Na 2 SO 4 and extracted pore solutions during the ESA test. The evolution of the chemical composition of test solution and phase assemblage of pressed paste grains during the ESA test were quantitatively characterized. Results indicate that the improvement of sulfate attack resistance is related to the increase in alkalinity of pore solution. The high alkalinity of pore solution leads to the dissolution of monosulfate, which suppresses the formation of ettringite. The maintained high alkalinity reduces the saturation degree of ettringite, monosulfate and gypsum with respect to the pore solution, preventing it from precipitating even at a high sulfate ions concentration up to 0.5 M. This study highlights the effect of glass powder on alkalinity of pore solution and its relationship with stability of ESA products. [ABSTRACT FROM AUTHOR]