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Phosphate treatments for conservation of stone have provided so far encouraging results in laboratory studies, as they exhibit good effectiveness, compatibility and durability to accelerated weathering tests. However, limited data are available about their long-term performance in real environment. Here, a systematic evaluation of phosphate consolidants after prolonged exposure in the field is reported for the first time. Naturally weathered marble specimens and a XVII century marble sculpture located in the Park of the Royal Palace in Versailles were treated by various formulations of the phosphate consolidant. Their conservation state was assessed before treatment by non-destructive methods (ultrasounds, color measurement, water absorption) and, in the case of the specimens, also by slightly destructive tests (SEM, FT-IR, MIP, IC). The conservation state of the specimens and the sculpture was further assessed right after treatment and then periodically monitored during exposure in the Versailles Park. Characterization after field exposure demonstrated that some formulations of the phosphate treatment are able to slow down marble deterioration, although it was not completely inhibited. Limited alterations in water absorption and aesthetic appearance confirmed the general compatibility of the phosphate treatment.

International audience; Ultrasonic techniques are increasingly used in various fields such as mining, geotechnical, civil engineering, because they are non-destructive and easy to apply. These techniques are usually employed both in situ and in laboratory conditions to characterize and determine the dynamic and physical properties of rocks. In cultural heritage, the characterization of marble statue by acoustic wave is a wellknown non-destructive method. This paper undertakes a study of the Carrara marble that composes the statues exposed in the Château de Versailles gardens, in order to better understand the processes of deterioration affecting them. For this, a plate of Carrara marble is artificially aged through heating/cooling thermal cycles performed on one face of the samples. A Rayleigh wave is generated by a 1 MHz central frequency contact transducer exited by a voltage pulse. A laser vibrometry method is used to detect the Rayleigh wave propagation on the depth sample. In order to understand how the degradation and nonhomogeneity and Rayleigh velocity vary through depth, Slant Stack (SS) transform was used. This analysis is a particular case of the Radon Transform (TR). The results show a uniform vibration behavior of non-degraded sample and highlight three zones with different state of degradation in the altered marble sample. The extraction of relevant parameters using this analysis is promising for the characterization of marble and following up its weathering.

Ultrasonic techniques are increasingly being used in various fields such as mining, geotechnical, civil engineering, because they are non-destructive and easy to apply. These techniques are usually employed both in situ and in laboratory to characterize and determine the dynamic and physical properties of rocks. In cultural heritage, the characterization of marble statue by acoustic wave is a well-known non-destructive method. This paper undertakes a study of the Carrara marble that composes the statues exposed in the Château de Versailles gardens, in order to better understand the processes of deterioration affecting them. For this, 10 cm side square plates of Carrara marble are artificially aged through heating/cooling thermal cycles performed on one face of the samples. Acoustic waves such as compressive, shear and Rayleigh are generated by 1 MHz central frequency contact transducers exited by a voltage pulse generator. A laser vibrometry detection method is used in the case of Rayleigh wave detection. The transmission measurements point out a strong decrease of the wave speed as well as a dramatic decrease of the maximum frequency transmitted in conjunction with the weathering. The velocity of ultrasonic waves depends on the physical and mechanical properties of the stone (such as density, porosity, elastic constants, and structure), Therefore, correlating the changes in these properties with the measured ultrasonic velocity helps to provide classification schemes for evaluating the degree of stone deterioration Kohler (1991). Some classical tests such as drilling resistance and water absorption (contact sponge method and water drop test) were also performed in order to complete the results obtained by ultrasonic velocity method.

In cultural heritage, statue marble characterization by acoustic waves is a well-known non-destructive method. Such investigations through the statues by time of flight method (TOF) point out sound speeds decrease with ageing. However for outdoor stored statues as the ones in the gardens of Chateau de Versailles, ageing affects mainly the surface of the Carrara marble. The present paper proposes an experimental study of the marble acoustic properties variations during accelerated laboratory ageing. The surface degradation of the marble is reproduced in laboratory for 29 mm thick marble samples by using heating/cooling thermal cycles on one face of a marble plate. Acoustic waves are generated by 1 MHz central frequency contact transducers excited by a voltage pulse placed on both sides of the plate. During the ageing and by using ad hoc transducers, the marble samples are characterized in transmission, along their volume by shear, compressional TOF measurements and along their surface by Rayleigh waves measurements. For Rayleigh waves, both TOF by transducers and laser vibrometry methods are used to detect the Rayleigh wave. The transmission measurements point out a deep decrease of the waves speeds in conjunction with a dramatic decrease of the maximum frequency transmitted. The marble acts as a low pass filter whose characteristic frequency cut decreases with ageing. This pattern occurs also for the Rayleigh wave surface measurements. The speed change in conjunction with the bandwidth translation is shown to be correlated to the material de-structuration during ageing. With a similar behavior but reversed in time, the same king of phenomena have been observed trough sol-gel materials during their structuration from liquid to solid state (Martinez, L. et all (2004). “Chirp-Z analysis for sol–gel transition monitoring”. Ultrasonics, 42(1), 507-510.). A model is proposed to interpret the acoustical measurements