LITMIR.BIZ

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href="#ulink_6d5d2df8-a436-5299-8c57-1f9d443fb6ad">², Nicole Hernández-Romero², Cristina Tedeschi³, Edgar Quiñones-Bolaños¹

      IN: SIEGESMUND, S. & MIDDENDORF, B. (EDS.): MONUMENT FUTURE: DECAY AND CONSERVATION OF STONE.

       – PROCEEDINGS OF THE 14TH INTERNATIONAL CONGRESS ON THE DETERIORATION AND CONSERVATION OF STONE –

       VOLUME I AND VOLUME II. MITTELDEUTSCHER VERLAG 2020.

1 University of Cartagena, Research Group Esconpat, Faculty of Engineering, Cartagena, Colombia

2 Universidad Nacional de Colombia, Department of Civil and Agricultural Engineering, Bogotá, Colombia

3 Department of Civil and Environmental Engineering, Politecnico di Milano, Italy

      4 University of Cartagena, Research Group Environmental Modelling, Faculty of Engineering, Cartagena, Colombia

       Abstract

      The deterioration of historical structures is a topic of primary importance due to their historical, cultural and economic importance. Aggressive environments around structures can depend on anthropogenic factors such as NO₂, SO₂ gases among others, and environmental factors such as differential dilation, differential hydric dilation and crystallization. In the present study is proposed a physical-chemical characterization of the structure and quarry stone used for the replacement of deteriorated blocks of the defensive Wall of Cartagena, Colombia, UNESCO Cultural Heritage since 1984. X-ray and ionic chromatography identification were done in the structure stone. Furthermore, is proposed a Petrographical comparison between structure and quarry material as well as mechanical characterization of the quarry material.

      The structure is composed mainly by soft limestone. Similar physico-chemical characteristics were found through X-Ray and Petrographical comparison, while salt crystallization is found playing a secondary role in the structure deterioration.

       Introduction

      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.

       Materials and Methods

      5 structure samples were collected from the stone surface (5 mm depth). Additionally, thin sections were done on those samples following the ASTM C1721 – 15, (2015) standard using blue epoxydic resin. Thin sections were petrographical analysed with an Olympus CX 31 microscope with magnifications ranging from x5 to x100 for assessing the presence of bioclasts, type of cement, terrigenous, distribution and quantification of primary and secondary porosity. Each thin section has a dimension of 4.5 cm × 2.6 cm. Point counting technique was used in a mesh of 300 equidistant points.

      On these samples, ion analyses were carried out using Ion Chromatograph (IC). Powdered samples were dried at 60 °C until constant weight. Saline solubilisation was achieved by shaking 1 g of each dried sample in 100 ml of ultra-pure water. The 10 ml of obtained supernatants were filtered through a 0.2 µm PTFE membrane. The separation of cations Na+, Mg+, K+ was achieved by using a stationary-phase featuring a CS12A 250*4 mm column with a 10*4 mm guard (Dionex). As for anions Cl–, SO₄–, NO₃–, the stationary phase featured a AS9-HC 250 *4 mm column with a 10*4 mm guard (Dionex), (Nasraoui M. et al. 2009)the standard analytical equipment as ion chromatography (IC).

      80 cubes of 5.0 × 5.0 × 5.0 cm were selected in the original quarry of the structure for the physical-mechanical 127characterization. Specimens were Characterized following the Natural Stone Test Methods (UNI EN 1936:2007 Natural stone test methods – Determination of real density and apparent density, and of total and open porosity, 2007). Real Volume V_R (m³), Open Porosity P_o (%) and Apparent Density ρ_b (kg m^–3) were calculated, (1–3).

      Where m_d (g) is the Dry mass, m_s (g) Saturated mass, m_h (g) water immersion mass, ρ_rh water density at 20 °C, 998

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