δ13C and δ18O Stable Isotope Analysis Applied to Detect Technological Variations and Weathering Processes of Ancient Lime and Hydraulic Mortars

Abstract

Samples of mortars were collected from lime and hydraulic mortars affected by environmental degradation. A total of 63 samples were obtained from Hellenistic, Late Roman and Byzantine historic constructions located at Kavala, Drama and Makrygialos in North Greece. Samples were collected in sections from the surface up to 6 cm deep using a drill-core material. The first sample was collected from the external layer, while the internal samples were collected each 1cm beeper from the previous, in order to monitor the moisture ingress. Isotopic data will make it possible to create an ideal Hellenistic and Byzantine mortar layer and to provide weathering gradients. The isotopic values comprise a range of δ13C and δ18O values from −17.1‰ to 1.2‰ and −25.9‰ to −2‰, respectively. The weathering process of Hellenistic and Byzantine are expressed, by the regression lines δ18Ocalcite matrix = 0.6 × δ13Ccalcite matrix − 1.9 and δ18Ocalcite matrix = 0.6 × δ13Ccalcite matrix − 2.0 for hydraulic and Lime mortars respectively. Pronounced isotopic shift to heavy or light δ13C and δ18O in the carbonate matrix was attributed to the primary source of CO2 (atmospheric versus biogenic) and H2O (evaporation of local primary water), in residual limestone and in secondary processes such as recrystallization of calcite with pore water and salts attack. Exogenic processes related to biological growth are responsible for further alterations of δ18O and δ13C in lime mortars. This study indicated that stable isotope analysis is an excellent tool to fingerprint the origin of carbonate, the environmental setting conditions of mortar, origin of CO2 and water during calcite formation and to determine the weathering depth and the potential secondary degradation mechanisms.

δ13C and δ18O Stable Isotope Analysis Applied to Indicate Sources of Water-Induced Degradation in Historic Monuments

“…Figure 3 shows the various sources of CO 2 and H 2 O (lines) and mechanisms (areas). Point CM indicates that precipitated calcite is formed directly by the absorption of atmospheric CO 2 in strong alkaline aqueous environment (Dotsika et al 2018); its values change to more enriched isotopic composition due to continuous enrichment of δ 13 C of CO 2 during calcite precipitation; area A indicates that precipitated calcite is formed from atmospheric CO 2 and contaminated by residual natural limestone; line 1A reflects that the primary source of water used for setting of the lime mortar is coming from heavy source, evaporation effect; area B indicates that precipitated calcite is formed from atmospheric CO 2 and heavy, evaporated water. Enrichment of C and O isotopes indicates recrystallisation of calcite with water of meteoric origin and atmospheric CO 2 ; area C shows the enrichment of δ 18 O of calcite due to the re-equilibrium with the silicate minerals; line 1B reflects that the primary source of water used for setting of the lime mortar is coming from light source, condensation effect; area D indicates that precipitated calcite is formed from atmospheric CO 2 and isotopically light local meteoric water or isotopically light re-condensed primary water; line 3 depicts the depletion of C and O isotopes indicating recrystallisation of calcite with light water and CO 2 of mixed origin (atmospheric and soil origin); and area E, depletion of C and O isotopes, indicates also human influence (surface treatment) and biological growth.…”

Preservation of Cultural Heritage and Resources Threatened by Climate Change

“…The SI encompass 10 open access papers presenting research studies based on the exploitation of a broad range of data deriving from preventive conservation monitoring [5][6][7] and climate or numerical modelling on material components for assessing environmental impact and climate change effects [8,9]. These papers are focused on a well-assorted sample of decay phenomena occurring on heritage materials, e.g., surface recession and biomass accumulation on limestone [10], depositions of pollutant on marble [11], salt weathering on inorganic building materials [12], and the weathering process on mortars [13]. Finally, one paper [14] is devoted to examining the perceptions of experts involved in the management of cultural heritage on adaptation to climate change risks.…”

“…The paper by Dotsika et al [13] analyze 63 samples of mortars collected from lime and hydraulic mortars affected by environmental degradation, obtained from Hellenistic, Late Roman, and Byzantine historic constructions located at Kavala, Drama, and Makrygialos in northern Greece. The analysis of isotopic data allowed the re-creation of an ideal Hellenistic and Byzantine mortar layer to study weathering gradients.…”

“…Correspondingly, with a combination of methods described in [10,11,13], i.e., material analysis, damage function application, and climate change scenarios, Menéndez [12] estimates the salt weathering induced by climate change on built cultural heritage in 41 locations in France. In the analysis of phase-change phenomena, the author uses not only the two most common salts held responsible for decay, i.e., sodium chloride and sodium sulfate, but also others like calcium sulfate or mixtures of chlorides, sulfates, and nitrates of sodium, calcium, magnesium, and potassium.…”

Historical and Scientific Investigations into the Use of Hydraulic Lime in Korea and Preventive Conservation of Historic Masonry Structures

“…The calcined limestone, i.e., quicklime, was ground into powder and immediately afterwards, a chemical analysis was performed to prevent hydration of the calcium oxide (CaO) with moisture in the air. The calcining process of pure limestone and the slaking process of quicklime can be represented chemically by Equations (1) and (2), respectively [1,34]:…”