Abstract:
Historical mortars from sixteenth to seventeenth century military forts located at the mouth of the Tagus River in Lisbon have been characterized by polarized
light microscopy (PLM), thermal analysis (TG/DTA), X-ray diffractometry (XRD) and scanning electron microscopy + energy dispersive spectroscopy (SEM + EDS). The results indicate that the mortars used were all hydraulic lime-based. The presence of well-rounded lime lumps indicates a limited use of water during the lime hydration process. The detection of hydrated calcium
chloroaluminate and carboaluminate compounds mostly at binder-aggregate interfaces provides evidence for the onset
of pozzolanic reactions during mortar production as further confirmed by the presence of ceramic fragments in the
aggregate fractions intentionally added by the fort builders to increase the hydraulic properties of the mortars. The higher mechanical strength and greater resistance to degradation processes imparted by these pozzolanic compounds
could explain why, despite the extreme proximity of the investigated sites to the sea, salt weathering processes
do not appear to have significantly affected the studied mortars.
