An exhaustive monitoring of an internal sulphate attack of Portland cement-based materials is addressed. Four series of Portland cement mortars with different amounts of gypsum (0%-2% SO3 respect to the cement by mass) were monitored by means of physical and non-destructive tests, studying specimens with a low expansion rate to examine the sensitivity of the applied techniques. The expansion analysis has shown the progressive axial deformation as a function of time and gypsum content. In the mechanical analysis, lower values of R-c were attained as the gypsum content increased. Ultrasonic pulse velocity have closely predicted the stiffness of the specimens. The time-frequency attenuation extracted by means of optimal broadband signals presented different trends, showing clear differences for the most damaged series (2% SO3). Attenuation supplied interesting information about the hardening process and the microcracking effect due to a mortar expansion higher than 0.04%, as well as the analysis of the frequency frontiers and patterns in damage progression.
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