Mechanical Stresses Generated by Crystallization of Salts Inside Treated and Non-Treated Monumental Stones; Monitoring a
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MECHANICAL STRESSES GENERATED BY CRYSTALLIZATION OF SALTS INSIDE TREATED AND NON-TREATED MONUMENTAL STONES; MONITORING AND INTERPRETATION BY ACOUSTIC EMISSION / MICROSEISMIC ACTIVITY. R.M. ESBERT, M. MONTOTO, L.M. SUAREZ DEL RIO, V.G. RUIZ DE ARGANDORA AND C.M. GROSSI Dept. of Geology, Group of Petrophysics; University of Oviedo, 33080 Oviedo, Spain. ABSTRACT The crystallization of salts in building stones is one of the most common and severe deteriorating phenomencndeveloped on Historic Buildings. To evaluate their mechanical effects in treated and non-treated stones, experimental salt crystallization tests and the monitoring of the corresponding acoustic emission / microseismic activity, AE/MS, have been planned. Salt crystallization tests have therefore been performed on a high porosity (30%) limestone used in the building of the Cathedral of Murcia (Spain). Each test consisted of 11 and 20 cycles (for the non-treated and treated specimens, respectively) of immersion of specimens in salt solution (14% Na 2SO4 . 10H20) for 4 h., drying in an oven at 60 0 C for 14 h. and final cooling at room temperature for 6 h. The treated specimens were consolidated by total immersion in ethyl silicate -Tegovakon V- and protected with a water repellent, oligomeric polysiloxane -Tegosivin HL100-, (both from Th. Goldschmidt, FRG). The AE/MS, was monitored in the 100-300 KHz range. The preliminary results show a very different AE/MS behaviour between the non-treated and the treated specimens. INTRODUCTION The aim of this research is applying acoustic emission in the laboratory in order to detect the mechanical tensions induced by salt crystallization in the interior of the Murcia Cathedral stone. This alteration mechanism is frequently developed in monumental stones deteriorating them in a rather remarkable way whiL le it affects the durability of conservation treatments (mainly consolidation). Our research attemps also at establishing the differences in behaviour between the treated and non-treated stones. The Murcia Cathedral stone has been selected for the following reasons: - It is a calcareous stone having a low cohesion degree -it is poorly cemented and has an elevated porosity (n0=30%), and therefore it tends to dissagregation. In the monument this kind of deterioration is frequently found and hence the consolidation of the stone with any product that may increase its mechanical cohesion degree is a stage to be contemplated in its future conservation. - The Cathedral is placed in downtown Murcia, a city having a mild and relatively humid climate (60% R.H.) with sea-influenZ ce as well, implying the presence of sea-salots in the air mainly chlorides - and atmospheric pollutants (SO 2, C0 2 , dust, Mat. Res. Soc. Symp. Proc. Vol. 185. '1991 Materials Research Society
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