3.2 Evaluation In Situ of the State of Deterioration of Monumental Stones by Non-Destructive Sonic Techniques

Modesto Montoto San Miguel,
Chair Dept. of Geology, Univ. of Oviedo
Rosa Maria Esbert Alemany
(Faculty and Technical Staff)
Jose Ordaz Gargallo
Lope Calleja Escudero
Vincente Gomez Ruiz de Argandona
Luis Miguel Suarez del Rio
Javier Alonso Rey
Carlos de Llanos Gonzalez
Beatriz Perez Garcia
(Graduate Students)
Nicolas Manuel Martinez Alvarez
Carlota Maria Grossi Sampedro
Beatriz Menendez Villar
Antonio Martinez Hernando
Luis Valdeon Menendez
Rosa Maria Marcos Fierro
Mercedes Vazquez Llorens
Angel Martinez Nistal
Period of Activity: 6/87 to 12/89

Project Abstract
Bibliographic retrieval has been carried out, and statistics on papers presented in the international congresses and symposiums on the deterioration of monumental stones during the last twelve years were presented in the first progress report. Future work will be restricted to sandstone and granite, and will include acoustic emission/microseismic activity as a new nondestructive procedure. Authorization has been received to study the Monasterio de Ripoll and the Monasterio de El Escorial.

Primary and Secondary Publications
Montoto, M., "Evaluation In-Situ of the State of Deterioration of Monumental Stones by Non-Destructive Sonic Techniques: Monastery of San Lorenzo El Real De El Escorial (Madrid, Spain)," Final Report, Department of Geology-Group of Petrophysics, University of Oviedo, Oviedo, Spain, July 1989.

ABSTRACT-This report summarizes the petrophysical interpretation, by means of ultrasonic studies, of the deterioration process affecting the granodiorite rock of the Monastery of El Escorial along the period of time the rock has been placed in the site.

Aging tests for reproducing the deterioration process and corresponding ultrasonic monitoring in the laboratory have been designed. Three types of aging tests have been selected: salt crystallization, thermal cycling, and freeze-thawing. The ultrasonic parameters used in this study were: wave amplitude, wave energy, wave duration, number of counts, and the velocity of longitudinal waves (Vp). From laboratory tests, an inverse relationship can be found between the ultrasonic parameters and the degree of artificial deterioration. The acoustic parameter best displaying this relation is the energy and the most aggressive aging test is the freeze-thawing one.

In situ tests have been programmed based on the laboratory results. Measurements were made in different rock masonry at selected stations representative of all the forms of deterioration in the monument. A quality index was assigned to each of the measurement stations according to their deterioration state. The relationship between this index and the acoustic parameters is statistically analyzed; three deterioration groups have been obtained. For in situ tests, an inverse relationship between the rock deterioration degrees and the acoustic parameters is found. The energy is the best acoustic variable to define the deterioration groups and classify each of the measurement stations in one of the groups.

Montoto, M., L. M. Suarez del Rio, and A. Rodriguez Rey, "Métodos no Destructivos para la Caracterización de los Materiales Rocosos," 1er Seminario sobre Estudio, Diagnosis y Tratamiento de la Erosión Lítica en los Monumentos, Granada, Spain, April 27-30, 1987.

ABSTRACT-By using nondestructive techniques (NDT), rock types used in the construction of historic monuments can be characterized. Among NDT's the most notable methods are those that are based in the analysis of elastic waves, induced or spontaneous, that travel along their empty spaces, fractures, and/or detached facing slabs. These ultrasonic procedures have been extensively studied, disseminated, and commercialized; therefore, many of them, due to their portability, are more easily applicable in practical professional problem areas. At the same time, using ultrasonic techniques, the tensile status of the material can be appraised and possible unstable mechanics determined. This is carried out by the analysis of the elastic waves that spontaneously free all solids subjected to stress. This passive ultrasonic procedure, acoustic emission, or microseismic activity, AE/MA microseismic activity, can be combined with other active injections of ultrasound in the materials in order to determine and map fissures and inhomogeneities.

Calleja, L., M. Montoto, B. Perez-Garcia, L. M. Suarez del Rio, A. Martinez Hernando, and B. Menendez Villar, "An Ultrasonic Method to Analyze the Progress of Weathering During Salt Crystallization Laboratory Cycles," International Symposium, The Conservation of Monuments in the Mediterranean Basin, Bari, Italy, June 7-10, 1989.

ABSTRACT-A nondestructive ultrasonic procedure to study deterioration during laboratory aging tests is described. Salt crystallization aging tests were carried out on a sandstone, similar to that used in the Santa Maria de Ripoll Monastery (Gerona, Spain). Before, during, and after tests, steady ultrasonic signals from an ultrasonic pulse generator were passed through cubic samples of rock and, after traveling through the samples, the amplitude, duration, energy, and count number of the elastic waves were received and processed. Preliminary results show an inverse relationship between the acoustic variables and the observed degree of deterioration of the rock samples.

Montoto, M., L. Calleja, B. Perez Garcia, L. M. Suarez del Rio, V. G. Ruiz de Argandona, R. M. Esbert, and C. M. Grossi, "A Non-Destructive Ultrasonic Procedure to Evaluate In Situ the Relative Deterioration State of Monumental Stones: Preliminary Results," European Symposium, Science, Technology, and European Cultural Heritage, Bologna, Italy, June 13-16, 1989.

ABSTRACT-To evaluate in situ the relative deterioration of monumental stones, a nondestructive ultrasonic procedure has been in development: ultrasonic waves are introduced into the rock and processed to evaluate the ultrasonic parameters of velocity (Vp) velocity, amplitude, duration, energy, and count number.

The procedure was applied to two Spanish Monasteries, one built with granodiorite (El Escorial, Madrid, the results of which are included here) and the other built with sandstone (Sta. Maria de Ripoll, Gerona).

Laboratory aging tests, involving monitoring of the above-mentioned ultrasonic parameters, were performed as a basis for interpreting the in situ measurements. The energy seems to be most sensitive as an indicator of the state of rock deterioration, so the value obtained for a masonry block in the monument can be used to classify the rock into one of preset deterioration groups.

Perez Garcia, B., M. Montoto, L. Calleja, N. Martinez Alvarez, and J. Ordaz, "An Acousto- ultrasonic Method for Evaluating the Deterioration Degree of Monumental Stones," Ultrasonics International 89 Conference, Madrid, Spain, July 3-7, 1989.

ABSTRACT-An ultrasonic procedure is being developed for evaluating the relative deterioration of monumental stones. This method consists of the injection of ultrasonic signals and the processing and analysis of the signals after traveling through the rock. The selected ultrasonic parameters are: velocity of longitudinal waves, amplitude, duration , energy, and count number. Specimens of sandstone similar to one of the types used in the building of the Monastery of Santa Maria de Ripoll (Gerona, Spain) have been subjected to laboratory aging and monitoring of the variation of the above-mentioned ultrasonic parameters.

Rodriguez-Rey, A., G. A. D. Briggs, T. A. Field, and M. Montoto, "Acoustic Microscopy of Rocks," Journal of Microscopy, Vol. 160, Pt. 1, October 1990, pp. 21-29.

ABSTRACT-Acoustic images of two common rocks, granodiorite and limestone, are studied to explore the kind of geological information that they can provide. Rayleigh waves which travel in rock specimens confined to within a depth of a wavelength or so from the surface are mainly affected in their propagation by crystal anisotropy and surface discontinuities. Therefore, acoustic microscopy makes possible a detailed identification of intragranular structures in the rock-forming minerals (very fine cracks, grain and subgrain boundaries,etc.); these features may appear more sharply than in transmitted polarized light microsopy or in scanning electron microscopy. In particular the acoustic images are very effective in microfractographic studies because they can show not only the finest cracks, even those much less than a wavelength wide, but also their position in relation to the grain and subgrain structure.

Rodriguez, A., "Applications of Scanning Acoustic Microscopy to the Study of Rock Materials," Seminar, University of Oxford, Department of Metallurgy and Science of Materials, December 1, 1987.

ABSTRACT-None available.

Briggs, G. A. D., C. M. W. Daft, A. F. Fagan, T. A. Field, C. W. Lawrence, M. Montoto, S. D. Peck, A. Rodriguez-Rey, and C. B. Scruby, "Acoustic Microscopy of Old and New Materials," Acoustical Imaging, Vol. 17, ed. J. Kushibiki, N. Chubachi and S. Himizu, Plenum Press, 1989, pp. xiii-791.

ABSTRACT-None available.

Montoto, M., L. Calleja, B. Perez, and R. M. Esbert, "Evaluation In Situ of the State of Deterioration of Monumental Stones by Non-Destructive Ultrasonic Techniques," Materials Issues in Art and Archaeology, Vol. 185, 1991, Proccedings of the Materials Research Society, Spring Meeting, San Francisco, California, April 16-20, 1990, pp. 273-284.

ABSTRACT-A nondestructive ultrasonic procedure is under development for evaluating in situ the relative deterioration of monumental stones.Ultrasonic waves are injected into the rock and, after traveling through the rock, are registered, processed, and petrophysically interpreted. The procedure is being applied to two Spanish Monasteries, one built with a granitic rock (El Escorial, Madrid), and the other built with sandstone (Sta. Maria de Ripoll, Gerona).

The methodology implies: in situ categorization of the observable deterioration forms, sampling in the quarries, laboratory aging tests and continuous ultrasonic monitoring, in situ data acquisition, evaluation of the ultrasonic parameters by signal processing, and stepwise discriminant analysis. All that information is petrophysically interpreted for an approximate assignation of the in situ studied masonry blocks to the categorized deterioration degree.

Final in situ results from the Monastery of El Escorial are presented here. Among the studied ultrasonic parameters, "energy" is the most useful of all of them and velocity the least.

Esbert, R. M., M. Montoto, L. M. Suarez del Rio, V. G. R. de Argandona, and C. Grossi, "Mechanical Stresses Generated by Crystallization of Salts Inside Treated and Non- Treated Monumental Stones: Monitoring and Interpretation by Acoustic Emission/ Microseismic Activity," Materials Issues in Art and Archaeology II, Vol. 185, 1991, Proceedings of the Materials Research Society, Spring Meeting, San Francisco, California, April 16-20, 1990, pp. 285-296,.

ABSTRACT-The crystallization of salts into building stones is one of the most common and severe deteriorating phenomenon developed on historic buildings. To evaluate their mechanical effects on treated and nontreated stones, laboratory aging tests and their corresponding monitoring of the acoustic emission/microseismic activity, AE/MS, have been planned.

Therefore, salt crystallization tests have been performed on a high-porosity, 30%, limestone. limestone.; Each test consisted of fifteen cycles of immersion of specimens in salt solution (14% Na2SO4.10H2O) for 4 hours, drying in an oven at 60 C for 14 hours, and final cooling at room temperature for 6 hours. The treated specimens were consolidated by total immersion in ethyl silicate-Tegovakon V and protected with a water repellent, oligomeric polysiloxane- Tegosivin HL-100.

The AE/MS was monitored in the 100-300 KHz range. The preliminary results show a very different AE/MS behavior between nontreated and treated specimens; the AE/MS rate peaks of the former being more frequent and smaller.

Montoto, M., "Acoustic Emission in Stone Conservation," 5th Conference on Acoustic Emission/Microseismic Activity in Geologic Structures and Materials, Pennsylvania State University, June 11-13, 1991.

ABSTRACT-The acoustic emission/microseismic activity could represent a very valuable tool during the relevant stages of diagnosis and monitoring involved in stone conservation programs. The most relevant applications in this field are summarized; further research on some aspects not yet studied is suggested. In general, four main possible areas of application can be considered regarding AE/MS and stone conservation: (a) Stability of the rock foundation of the Monument, (b) Stability of the Monument as an architectural object, (c) State of the stress and characterization of the rock masonry and, (d) Evaluation of the treatments applied to the stones after a conservation program.