A03_12

EFFECT OF LIME PRODUCTION AND PROCESSING METHODS ON THE PRESENCE OF GEOGENIC CARBON IN HISTORICAL MORTARS

Válek J¹, Kozlovcev P¹, Fialová A¹, Kotková K¹, Frankeová D¹, Světlík I², Pachnerová Brabcová K²

¹Institute of Theoretical and Applied Mechanics of the Czech Academy of Sciences, Prague, Czech Republic, ²Nuclear Physics Institute of the Czech Academy of Sciences, Prague, Czech Republic

The presence of geogenic carbon makes the radiocarbon dating of historical mortars a challenging task. Part of the geogenic carbon in mortars is commonly present due to the production and processing of lime binder. Lime burnt with wood in a traditional kiln was assessed for the presence of residual CO₂. Quicklime samples were taken from various locations in the kiln and thermal analysis was used to quantify the CO₂ residual levels. The quicklime obtained was slaked in excess of water and the presence of unburnt particles was investigated after sedimentation of the lime putty at three depth levels: top, middle and bottom. An optical microscope with Cathode Luminescence probe was used to qualitatively evaluate the presence of unburnt particles. In addition, the three putty specimens per lime sample were left to carbonate at laboratory conditions. After carbonation, the content of stable isotopes ¹³C and ¹⁸O was determined. This experimental procedure allows for description and estimation of the presence of geogenic carbon in quicklime produced in a wood-fired single batch kilns. It also shows the effectiveness of sedimentation treatment to reduce under-burnt lime particles. The comparative study of stable isotopes studies the possibility of evaluating a carbonated lime binder prior to its ¹⁴C analysis. The results suggest that the historical treatment of lime to produce a fine binder could potentially lead to mortar samples that are more suitable for radiocarbon dating than mortars produced directly from quicklime or dry slaked lime to hydrate.