Natural consolidation of ancient historic buildings mortars submitted to humid and marine environment: a microscopic study

Abstract

Ancient historical buildings are important features of the history, culture and development of a country and its people. This study presents the results of chemical, physical and microstructural characterization performed on mortars in order to assess their durability and good performance in a marine and humid environment, The mortars are collected in two historical monuments in Lisbon region, the Santa Marta Fortress (SM) in the coast line Lisboa-Cascais (XVII century), and the Defence Wall of Lisbon (M), constructed and reconstructed during many centuries, but with zones dated from the roman period to which the analysed samples belong. This edification, approximately 2 km long, was, during centuries, the only defence of the city and is scarcely visible nowadays due to several constructions and changes carried out along the time. The microstrutural characterization was done by optical and scanning electronic microscopy to identify the binder and aggregate types, reaction products and porosity. The microstructural observation reveals that all mortars have the pores normally fulfilled with reaction products, etringite in the SM mortars and calcium carbonate and phosphate in M mortars. Moreover, reaction rims are evident around some aggregates, suggesting the occurrence of pozzolanic reactions between aggregates and the calcitic binder that creates neoformation products, such as calcium-silico-aluminates, which seems be, besides the pores filling, the responsible for the resistance and cohesion of these ancient mortars submitted to aggressive humid environments.