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Water takes part in most if not all of the degradation processes experienced by cement-based materials during their service-life. The effect of pure water usually is not of primary concern as it involves very lengthy degradation diffusion controlled processes; aqueous solutions are more aggressive, promoting increased solubility of matrix components and microstructure modification due to leaching. The ability to monitor such changes nondestructively presents a number of challenges as, often, conventional characterisation techniques require sample preparation likely to modify the properties of interest. In this study, ultrasonic pulse velocity profiles have provided a nondestructive means of monitoring microstructural changes during aggressive leaching of blastfurnace slag cement mortars with ammonium nitrate solutions. These data are compared with corresponding analyses by destructive techniques including mercury intrusion porosimetry (MIP), water porosity measurements, X-ray diffraction (XRD) and scanning electron microscopy (SEM). By analysing degraded ultrasonic velocity profiles it has been possible to calculate degraded depths in the samples, which correlate well with those results obtained by conventional methods.