Читать книгу Monument Future - Siegfried Siegesmund - Страница 173

According to the United Nations’ Educational, Scientific and Cultural Organization (UNESCO), there are around 869 sites of cultural interest around the world (UNESCO 2019). They were selected for their historical relevance and uniqueness. All of them struggle with surrounding aggressive climate conditions that accelerate their deterioration. Currently, 53 of those sites are rated as being in imminent danger due to anthropogenic and natural factors (UNESCO 2019).

For example, the Fortifications on the Caribbean Side of Panama (Portobelo-San Lorenzo), part of the defensive colonial system built by the Spanish Crown to protect transatlantic trade, constitute a valuable example of 17th and 18th-century military architecture, whose integrity has been compromised by environmental factors, uncontrolled urban extension, development and the lack of maintenance and management. Dozens of structures have been destroyed in the past in the name of Civilization, or because of high deterioration and/or earthquakes. An example of this is the Noto Cathedral, Italy, a historic masonry building that suddenly collapsed in 1996 (Binda et al. 1999) 126producing during centuries a redistribution of stresses from the core of lime mortar concrete to the external cladding of stiff masonry. This is likely one of the causes of long-time damage of some ancient masonry towers. With these motivations, coupled processes of moisture diffusion, carbon dioxide diffusion and carbonation reaction are analyzed numerically. Due to the absence of models and data for lime mortar, one of the simplest models proposed for Portland cement concrete is adapted for this purpose. The results reveal the time scales of the processes involved and their dependence on wall thickness (size. Factors responsible for over-stressing and damaging the monuments and thus inhibiting their conservation are high levels of air pollution in the atmosphere, daily and seasonal cycles of temperature and humidity, sea spray (or salt spray), rising damp, atmospheric conditions (rainwater, wind and sunlight exposure (Kameni & Orosa 2016)).

During the process of restoration of cultural heritage buildings, it is usual to replace highly deteriorated stones and mortars with new ones. Unfortunately, often the choice of replacement materials is done without sufficient preliminary investigation of the properties of the existing materials. In order to come to a selection of replacement stones compatible with the existent ones, several material properties need to be taken into account, such as petrographic properties, mechanical strength, moisture transport behaviour, colour, texture etc., (Baronio G., et al. 2003), (Binda L. et al. 2003).

In the present research the study case of the Fortresses of Cartagena is reported. They are UNESCO Cultural heritage since 1984, nevertheless, UNESCO inspectors identified and high level of deterioration and lack of long-term maintenance plans, (UNESCO, 1984). The structure stands in front of the Caribbean Sea, in a tropical area, therefore, salt crystallization process was studied on the structure surface to define its role in the structure deterioration.

Quarry samples were taken from an ancient quarry in Cartagena (Tierrabomba Island) in the geological Formation called La Popa. La Popa Formation rests on the Bayunca Formation (of the Pliocene) and it was formed during the Upper Pleistocene. It is conformed by coral reefs formed on an underwater platform in an area with little contribution of terrigenous sediments, clear waters and temperatures between 21 °C and 25 °C. High porous limestones (> 30 %) with bulk density < 1,500 kg m^–3 are common in the area. Similar physical-mechanical characteristics were identified in the Cartagena’s Fortification from previous analysis, (Saba et al. 2019).

Therefore, structure and quarry samples were physical-chemical compared to assess the reliability to use them as a replacement of the deteriorated structure stones.