Fernanda Cantone *, Enrico Ciliberto **, Enrico Greco **, Salvatore La Delfa **, Gabriella Murgana *

Transcription

1 Analytical characterization of plasters and stones coming from the 19 th century Palazzo Fragapane in Grammichele Fernanda Cantone *, Enrico Ciliberto **, Enrico Greco **, Salvatore La Delfa **, Gabriella Murgana * * Faculty of Architecture, University of Catania, Italy ** Department of Chemistry, University of Catania, Italy (sladelfa@unict.it, egreco@dmi.unict.it) Abstract Plaster and stone samples coming from the 19 th century Palazzo Fragapane in Grammichele (CT) were collected and characterized by using several microanalytical techniques such as X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray analysis (EDX), Fourier Transformed Infrared Spectroscopy (FT-IR). The Analytical investigations were addressed to investigate the microstructure and the composition of the different samples and to define the type and the level of the weathering in order to design the best procedures for the maintenance and conservation of the historical building. Keywords: Plaster, Stone materials, Physico-chemical characterization, Sicilian architecture Introduction A recovery interventation of a historic building belonging to the urban environment, left for a long time in a state of neglect or without any kind of maintenance, whatever is its architectural or artistic value, can not ignore the knowledge of the construction techniques, materials, real conditions and the types of weathering phenomena affecting the structure, Dezzi Bardeschi [1]. From this perspective, the diagnostic step, that is, all the techniques, the procedures and the time needed for obtaining chemical and physical data in order to know and characterize the raw materials of the building, is essential for developing appropriate answers and solutions to the problems raised during the planning phase of a conservation or maintenance intervention, Saisi [2]. In particular, the analyses of raw materials coming from the external surfaces of historic buildings, that is the study of plasters, expects a deep and careful diagnostic investigation, because nowdays, unlike in the past, the plaster is no longer considered a sacrificial material to be replaced cyclically in order to saveguard the underneath masonry, but it is an important material that have to be protected and preserved, Gasparoli [3]. Always, plaster has been one of the most common materials used in construction field, mainly thank to the cheapness and to the ease of application. In the last years great economic, organizational and research efforts have been accomplished for the recovery and the saveguard of monumental and architectural heritage existing in Italian cities and consisting 297

2 principally of historic buildings, churches and noble palaces. In that direction, this work was accomplished in order to analyse and characterize the stones and the plasters (internal and external surfaces) of the hystorical building Palazzo Fragapane in Grammichele (Catania), Cantone [4], by using several microanalytical techniques for allowing an easier planning of the maintenance and preservation interventations, by respecting the building value and by minimizing the loss of historical and cultural informations. Experimental data Sampling The sampling was performed after having prepared a detailed internally and externally mapping of the building. The samples were placed in appropriate vessels and transported immediately to the laboratory. The number and the description of the samples are reported in the Table 1, according to the Normal 3/80 and 12/83, Raccomandazioni Normal [5]. Table 1: The number of the samples and their description are reported in the table Sample 01 Stone sample coming from Corso Vittorio Emanuele facade (height 1.00 m) Sample 02 Stone sample coming from Corso Vittorio Emanuele facade (height 1.75 m) Sample 03 Stone sample coming from Corso Vittorio Emanuele facade (height 2.25 m) Sample 04 Crust layer sample coming from Piazza Carlo Maria Carafa facade (height 2.10 m) Sample 05 Crust layer sample coming from Piazza Carlo Maria Carafa facade (height 2.00 m) Sample 06 Sample 07 Sample 08 Sample 09 Degraded external plaster pieces coming from Piazza Carlo Maria Carafa facade External plaster pieces coming from Via Garibaldi facade External plaster layer coming from Via Garibaldi facade- first level Internal plaster layer (ghiara) coming from Via Garibaldi facade- first level Sample 10 Pink plaster coming from Via Garibaldi facade- first level (height 1.70 m) Sample 11 Sample 12 Sample 13 Internal mortar coming from room A; Via Garibaldi Corso Vittorio Emanuele corner Internal plaster coming from the roof of the room A; Via Garibaldi Corso Vittorio Emanuele corner Internal plaster coming from the roof of the room A; Via Garibaldi Corso Vittorio Emanuele corner 298

3 Instrumental measurements The microstructure and the composition of the different samples were investigated using analytical methods such as Optical Microscopy (OM), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray analysis (EDX) and Fourier Transformed Infrared spectroscopy (FTIR), Lewin Seymour [6] and Ciliberto[7]. Samples were imaged using a VP LEO 1550 SEM instrument with a field emission source and a controlled electron energy of 15 kev. The samples did not require any metal coating. The SEM system was equipped with EDX microanalysis. The microstructure was investigated using a Bruker-AXS D5005 XRD instrument. Infrared spectra of the powdered samples were recorded on a JASCO FTIR, collecting the spectra with 80 scans at 4 cm-1 resolution and using the KBr technique at room temperature. Results and discussion Samples 01, 02, 03 Samples 01, 02, and 03 were collected from different height of Corso Vittorio Emanuele façade. All the samples showed weathering (aveolization) phenomena. Fig. 1 reports the mapping of the façade and the alveolization weathering observed in the area where samples 01, 02 and 03 were sampled. Fig. 1: a) The mapping of Corso Vittorio Emanuele façade; b) the area were the samples 01, 02, 03 were collected. The values of the electrical conductivity measurements of all the samples were similar (sample 01: 183,0 µs*cm -1, sample 02: 168,5 µs*cm -1, sample ,2 µs*cm -1 ). XRD and FTIR data showed the presence of calcite and a little amount of gypsum, as shown respectively in Fig. 2. SEM/EDX spectra (Fig. 3) revealed the presence of calcium, magnesium and silicon peaks confirming the origins of the samples (calcarenite stone with the presence of calcite e dolomite). 299

4 Intensity Theta (deg) Fig. 2: XRD and FTIR of sample 02 showing the presence of calcite and a low amount of gypsum. Fig. 3: SEM/EDX spectra revealed that samples were originated from calcarenite stone. Samples 04, 05, 06 Samples 04, 05 and 06 were collected from Piazza Carlo Maria Carafà facade. The samples 04 and 05 derived from a thick scab visible in the facade (Fig. 4a). The electrical conductivity values of both samples were high and similar (sample 04: 426,9 µs*cm -1, sample 05: 645,1 µs*cm -1 ). SEM/EDX spectra (Fig. 4b) revealed the presence of calcium and sulphur peaks due to the high amount of gypsum phase inside the crust. XRD and FTIR data (Fig. 5) showed the presence of calcite, gypsum and quartz phases. Fig. 4: a) Thick crust present Piazza Carlo Maria Carafà façade; b) SEM/EDX spectra revealed that the scab was constituted by gypsum phase. 300

5 Intensity Theta (deg) Fig. 5: XRD and FTIR of sample 05 showing he presence of calcite, gypsum and quartz phases. Sample 06 was collected from a plaster layer: the electrical conductivity value was 160 us*cm -1 and MO, XRD and FTIR analyses highlighted the presence of gypsum and calcite phase as binding and quartz (sand) as aggregate. Samples 07, 08, 09, 10 Samples 07, 08, 09, 10 were pieces of plaster coming from Via Garibaldi facade (first level). While sample 07 and 08 were external plaster pieces without any visible weathering phenomena, sample 09 was a red coloured internal layer and sample 10 was an external pink coloured crust, scialbo. The amount of soluble salts found in the four samples is relatively low. The XRD and FTIR analyses (Fig. 6) accomplished for sample 07 and 08 showed the lack of gypsum and the presence of quartz and calcite phases. MO images of sample 09 are reported in Fig. 7. SEM/EDX analyses (Fig. 8) revealed that sample 09 was constituted of limestone clasts having aluminosilicate species as binding Intensity Theta (deg) Fig. 6: XRD and FTIR of sample 08 showing the lack of gypsum and the presence of quartz and calcite phases. Fig. 7: Optical Microscopy image for sample

6 Sample 10, coming from a pinky crust, was a limestone scialbo (Fig. 9a), as highlighted from MO image in Fig. 9b and from XRD and FTIR analyses showing the presence of calcite phase. Fig. 8: SEM/EDX analyses showed that sample 09 contained limestone clasts having aluminosilicate species as binding. Fig. 9 a) pinky crust called scialbo ; b) Optical Microscopy image for sample 10. Samples 11, 12, 13 Samples 11, 12 e 13 were collected in room A (Via Garibaldi-Corso Vittorio Emanuele corner). The Fig. 10 shows the planimetry of the first floor of the Palazzo Fragapane and the position of the room A. Sample 11 was collected from the mortar block used for the stones of the walls of room A and was constituted of calcite and quartz. Samples 12 and 13 were collected from the roof of room A. The XRD and FTIR analyses revealed high amounts of gypsum and low amounts of calcite, as observed through XRD and FTIR analyses. Fig. 10: Planimetry of the first floor of the Palazzo Fragapane and the position of the room A 302

7 Intensity Theta (deg) Fig. 11: XRD and FTIR of sample 13 showing the high amounts of gypsum and low amounts of calcite phases. ConclusionS Table 2 shows crystalline phases found in the samples analyzed by XRD while Table 3a shows the values of electrical conductivity for each sample. Table 2: Crystalline phases found by XRD Sample Calcite Dolomite Gypsum Quartz If a constant relation is considered between electrical conductivity values and soluble salt contents, that is, if we assume a constant relative composition of amounts of anions and cations, the data obtained can be expressed as a percentage amount of soluble salts contained in one gram of sample, as reported in Table 3b. The values give a good measurement of the amount of soluble salts in each sample analyzed. Table 3: a) Values of electrical conductivity of all samples; b) Theoretical % of the soluble salts in the samples TABLE A Electrical conductivity (µs cm-1) Sample Sample

8 Sample Sample Sample Sample Sample Sample Sample Sample Sample Sample Sample TABLE B Theoretical % of the soluble salts in the samples Sample Sample Sample Sample Sample Sample Sample Sample Sample Sample Sample Sample Sample The diagnostic investigations concerned both plaster samples, collected from facades o from internal rooms, and stone samples of Palazzo Fragapane. Samples 01, 02, 03 were collected from the stones of Corso Vittorio Emanuele facade. The three samples had comparable values of electrical conductivity. All the three samples contained calcite, although sample 1 also contained a little amount of gypsum. Gypsum phase was due to secondary crystallization phenomena originated from the infiltration of solutions of calcium and sulphate ions coming from the surrounding surfaces covered with gypsum scialbo. Samples 04 and 05 were collected from the thick crust visible on Piazza Carlo Maria Carafà facade. The values 304

9 of electrical conductivity showed the presence of high amounts of soluble salts. XRD and FTIR measurements revealed that the most common phases present were gypsum, calcite and quartz. All the data confirmed that the thick crust was originated from a scialbo layer, visibly distinguishable from the underlying layers that had different morphologies and colours. Sample 06, collected from Piazza Carlo Maria Carafà façade, too, consists essentially of calcite and gypsum as binder and quartz sand as inert. Samples 07, 08, 09, 10 are pieces of plasters sampled from Via Garibaldi facade (first leve). These plasters contained calcite as binder and quartz as aggregate. The amounts of soluble salts were relatively low due to the absence of gypsum. The sample 09 was an internal plaster: MO and SEM analyses allowed us to observe the limestone clasts having as aluminosilicate compounds as binder. This internal layer is ghiara material, while the visible red colour was originated from the presence of iron, as observed by EDX analysis. Samples 11, 12 and 13 were sampled from room A (Via Garibaldi and Corso Vittorio Emanuele corner first level). Sample 11 came from mortar block used for the stones of the walls and it was constituted of calcite and quartz. Samples 12 and 13 were collected from the roof of room A. The XRD and FTIR analyses revealed high amounts of gypsum and low amounts of calcite, as observed through XRD and FTIR analyses. These data explained the extremely high electrical conductivity values observed in sample 12 and 13. The analyses data showed that the presence of gypsum, which was widely used in some external plasters and in all internal plasters, is the most important problem for the weathering of Palazzo Fragapane. Therefore, subsequent maintenance and conservation interventations have to take into account the results of diagnostic investigation in order to write the restoration plan that saveguards the antique materials found in the historical building and to take off calcium and sulphate ions sources by using appropriate anti-salts products. References 1. M. Dezzi Bardeschi, La memoria del tempo, ovvero la permanenza e la mutazione, in Recuperare n.2, A. Saisi, Il ruolo delle indagini nella diagnostica strutturale, 3. P. Gasparoli, Le superfici esterne degli edifici. Degradi, criteri di progetto, tecniche di manutenzione. Allnea Editrice, Firenze, F. Cantone, G. Cantone, P. Carnazzo, A. Giuffrida, Recovery of built heritage in nineteenth century architecture. Fragapane Palace in Grammichele (CT), in Health and Creative Facilities, CIB W070 Conference in Facility Management, Heriot Watt University, Edimburgh, 2008 (pp.79-86). 5. Raccomandazioni NorMaL, Commissione UNI-NorMaL. 6. Z. Lewin Seymour, X-ray diffraction and scanning microscope analysis of conventional mortars, in Mortars, cements and grouts used in the conservation of historic buildings, Rome, 3-6 November 1981, (pp ). 7. E. Ciliberto, G. Spoto, Modern Analytical Methods in Art and Archaeology. Wiley&Sons Ltd, July 2000, ISBN X. 305