1. Educational Linkage Approach In Cultural Heritage Educational Toolkit Basic Course Teaching Material Topic 3.4 Phenomena and mechanisms of decay Decay and environment Module 3 Prof. Antonia Moropoulou - NTUA – National Technical University of Athens

2. Copyright ©ELAICH Beneficiaries 2009-2012 This material is an integral part of the “ELAICH – educational toolkit” and developed as part of the project ELAICH – Educational Linkage Approach in Cultural Heritage within the framework of EuroMed Cultural Heritage 4 Programme under grant agreement ENPI 150583. All rights reserved to the ELAICH Beneficiaries. This material, in its entirety only, may be used in "fair use" only as part of the ELAICH – educational toolkit for the educational purposes by non-profit educational establishments or in self-education, by any means at all times and on any downloads, copies and or, adaptations, clearly indicating “©ELAICH Beneficiaries 2009-2011” and making reference to these terms. Use of the material amounting to a distortion or mutilation of the material or is otherwise prejudicial to the honor or reputation of ELAICH Beneficiaries 2009-2011 is forbidden. Use of parts of the material is strictly forbidden. No part of this material may be: (1) used other than intended (2) copied, reproduced or distributed in any physical or electronic form (3) reproduced in any publication of any kind (4) used as part of any other teaching material in any framework; unless prior written permission of the ELAICH Beneficiaries has been obtained. Disclaimer This document has been produced with the financial assistance of the European Union. The contents of this document are the sole responsibility of the ELAICH Consortium and can under no circumstances be regarded as reflecting the position of the European Union. Educational Linkage Approach In Cultural Heritage

3. Prof. Antonia Moropoulou - NTUA – National Technical University of Athens Abstract The current presentation examines the impact of the environmental factors on building materials, the decay phenomena triggered and the interrelated structural pathology. Decay phenomena are classified to categories (mechanical – physical, chemical, biological) and are a function of various factors (intrinsic and extrinsic). As far as the study of decay is concerned, each case should be dealt individually, in the direction of revealing the specific mechanism acting in the interface materials / environment. The most common surface decay patterns are presented, with emphasis in gypsum formation, hard carbonate crust, salt crystallisation, degradation of joint mortars, incompatibility due to the use of inappropriate materials, mechanical and biological decay. Finally, the role of water in decay is examined, concerning the humidity sources and the water transport in porous means. Educational Linkage Approach In Cultural Heritage

4. Prof. Antonia Moropoulou - NTUA – National Technical University of Athens Content Educational Linkage Approach In Cultural Heritage Table of contents of this presentation 3.4.1. Decay phenomena 3.4.2. Decay factors 3.4.3. Approach to the study of decay 3.4.4. General categories of common surface decay patterns 3.4.5. Gypsum formation 3.4.6Development of the decay phenomena in depth 3.4.7. Capillary rise of salt solutions 3.4.8.Salt crystallisation 3.4.9. Degradation of joint mortars 3.4.10. Incompatible materials 3.4.11. Decay from mechanical factors 3.4.12.Decay from biological factors

5. Prof. Antonia Moropoulou – Topic 3.4: Phenomena and mechanisms of decay Educational Linkage Approach In Cultural Heritage Definition: Degradation over time of the material’s properties (physical, chemical, mechanical, etc.) and characteristics (mineralogical, texture), leading to their failure as a building component Classification: Mechanical or physical decay: Mechanical looseness of structures and separation of components due to compressive or tensile stresses within the material due to anisotropies or procedures which are related with the presence of soluble salts. An example of physical decay is the scaling of stone due to salts’ action. Chemical decay: It comprises the chemical reactions, happening in the material under environmental factors or due to thermodynamic instability of certain components of the material. An example of chemical decay is the effect of acid rain to building materials. Biological decay: It involves the effect of various organisms to the materials and is related with the above categories Development: Decay phenomena develop at the interfaces of materials / environment or materials / materials and are a function of intrinsic and extrinsic factors 3.4.1. Decay phenomena

6. Prof. Antonia Moropoulou – Topic 3.4: Phenomena and mechanisms of decay Educational Linkage Approach In Cultural Heritage Intrinsic decay factors Type of building materials: Stones, mortars, ceramics / glasses, metals, wood, advanced materials Properties of building materials: Mineralogical, physical, physico-chemical, chemical, mechanical Mass distribution: Macroscale, microscale Origin and processing technology Techniques and production technology History: Initial building phase, conservation interventions - reconstruction Compatibility with other materials Extrinsic decay factors General climate characteristics: Distribution, orientation, amplitude of environmental factors Microclimate: Orientation, location in the building, scale, surface morphology, type of attack by rain Atmosphere: Polluted, marine Water: Aerosol, rain, rising damp, condensation, salt crystallisation Biologic factors: Fauna and flora Usage of building: Building environment, interior environment Mechanical loadings: Temperature fluctuations, expansion of metal braces, salt crystallisation, frost, seismic vibrations, abrasion 3.4.1. Decay factors

7. Prof. Antonia Moropoulou – Topic 3.4: Phenomena and mechanisms of decay Educational Linkage Approach In Cultural Heritage 3.4.3. Approach to the study of decay The behavior of the materials in the environment is not generalised Each case should be dealt in the direction of revealing the specific active decay mechanism Macroscale Type of decay (morphology) Microscale -Kinetics of the phenomenon (decay rate) -Thermodynamics of the phenomenon (susceptibility to decay) LEVELS OF STUDY OF DECAY Correlation of decay and damage of materials Correlation of the mineralogical quality coefficient K and the modulus of elasticity E The modulus of elasticity, E, is a function of the mineralogical quality, K, of the material for every decay state Anisotropy of Endogenetic Rocks: Correlation Between Micropetrographic Index, Ultimate Strength and Modulus of Elasticity Ellipsoids Rodrigues, F. Peres & Aires-Barros, L. Lisbon Portugal 1971

8. Prof. Antonia Moropoulou – Topic 3.4: Phenomena and mechanisms of decay Educational Linkage Approach In Cultural Heritage 3.4.4. General categories of common surface decay patterns Cracks: Created due to material failure during the installation, earthquake stresses, temperature fluctuations, frost of external mechanical damage Granular disintegration: Created due to the stone fatigue from continuous expansion – contraction cycles. The cracks are becoming larger with acid rain attack “Sugaring”: Mainly appears on marbles. It is attributed to the granular disintigretation leading to selective detachment of grains altering the surface texture which appears as sugar grains. A. Moropoulou, K. Bisbikou, K. Torfs, R. Van Grieken, F. Zezza, F. Macri, “Origin and growth of weathering crusts on ancient marbles in industrial atmosphere” Atmospheric Environment 32 [6] 967-982 (1998) Scanning Electron Microscopy (SEM) Open microfractures (5-6μm) are evidenced with sub-efflorescences of gypsum Electron Probe MicroAnalysis (EPMA) Fe attain a maximum, while considerable S and Cl contents are detected Granular disintegration and detachment (Sanctuary of Demeter, Eleusis, Greece) Note: To analyse the sample composition in depth (EPMA), the sample was embedded in a resin and cut perpendicularly to the weathered crust

9. Prof. Antonia Moropoulou – Topic 3.4: Phenomena and mechanisms of decay Educational Linkage Approach In Cultural Heritage 3.4.4. General categories of common surface decay patterns Washed out surfaces: The result of successive wash out / dissolution of calcite by the acid rain which leads to the loss of authentic material. Usually it is accompanied with microcracks and delaminations, rough surfaces in unprotected surfaces Scanning Electron Microscopy Intercrystalline decohesion: calcite crystals covered by quartz and recrystallized calcite with various particle formations of Cu, Fe, Si, Al, Mg, Na, Ni, K, Mn, Cr and Ti Washed-out surfaces (Sanctuary of Demeter, Eleusis, Greece) A. Moropoulou, K. Bisbikou, K. Torfs, R. Van Grieken, F. Zezza, F. Macri, “Origin and growth of weathering crusts on ancient marbles in industrial atmosphere” Atmospheric Environment 32 [6] 967-982 (1998) Electron Probe MicroAnalysis (EPMA) Cu attain a maximum

10. Prof. Antonia Moropoulou – Topic 3.4: Phenomena and mechanisms of decay Educational Linkage Approach In Cultural Heritage 3.4.4. General categories of common surface decay patterns Washed out surfaces (cont.): Schematic representation of the processes involved A. Moropoulou, K. Bisbikou, K. Torfs, R. Van Grieken, F. Zezza, F. Macri, “Origin and growth of weathering crusts on ancient marbles in industrial atmosphere” Atmospheric Environment 32 [6] 967-982 (1998)

11. Prof. Antonia Moropoulou – Topic 3.4: Phenomena and mechanisms of decay Educational Linkage Approach In Cultural Heritage 3.4.4. General categories of common surface decay patterns Carbonate crusts (usually white): Due to the successive dissolution of calcite by the acid rain where the environmental conditions (temperature, relative humidity, et al.) allow the production of re-crystallised calcite CaCO 3 (s) + H 2 O (l) + CO 2 (g)  Ca(HCO 3 ) 2 (aq) Black crusts: They are a result of gypsum formation in the calcite surface and of the absorption of black smoke particles, Η/C and other particles of atmospheric origin that act as active catalysts in the transformation of calcite into gypsum. Its surfaces are protected from direct washout from rain water Scanning Electron Microscopy Secondary calcite is observed at white areas in contact with water and crystals of gypsum at the (water sheltered) dark ones Electron Probe MicroAnalysis (EPMA) Cu attain a maximum A. Moropoulou, K. Bisbikou, K. Torfs, R. Van Grieken, F. Zezza, F. Macri, “Origin and growth of weathering crusts on ancient marbles in industrial atmosphere” Atmospheric Environment 32 [6] 967-982 (1998) Black crusts (Sanctuary of Demeter, Eleusis, Greece)

12. Prof. Antonia Moropoulou – Topic 3.4: Phenomena and mechanisms of decay Educational Linkage Approach In Cultural Heritage 3.4.4. General categories of common surface decay patterns Black crusts (cont.): Schematic representation of the processes involved A. Moropoulou, K. Bisbikou, K. Torfs, R. Van Grieken, F. Zezza, F. Macri, “Origin and growth of weathering crusts on ancient marbles in industrial atmosphere” Atmospheric Environment 32 [6] 967-982 (1998) Parthenon, Acropolis of Athens, Photo courtesy of A. Moropoulou Sanctuary of Demeter, Eleusis, Photo courtesy of A. Moropoulou

13. Prof. Antonia Moropoulou – Topic 3.4: Phenomena and mechanisms of decay Educational Linkage Approach In Cultural Heritage 3.4.4. General categories of common surface decay patterns Black grey crusts: They are rich in iron oxides and hydroxides (intense brown - grey or / and orange – brown hue) which are often shielded behind an homogeneous and compact layer of alumino – silicates, successive dissolution of calcite from acid rain which due to environmental conditions (temperature, relative humidity) leads to the formation of re-crystallised calcite Scanning Electron Microscopy A calcitic microcrystalline matrix shields carbonaceous particles and amorphous deposits Electron Probe MicroAnalysis (EPMA) The amorphous deposits are rich in S A. Moropoulou, K. Bisbikou, K. Torfs, R. Van Grieken, F. Zezza, F. Macri, “Origin and growth of weathering crusts on ancient marbles in industrial atmosphere” Atmospheric Environment 32 [6] 967-982 (1998) Black grey crusts strongly bonded to the surface (Sanctuary of Demeter, Eleusis, Greece)

14. Prof. Antonia Moropoulou – Topic 3.4: Phenomena and mechanisms of decay Educational Linkage Approach In Cultural Heritage 3.4.4. General categories of common surface decay patterns Black grey crusts (cont.): Schematic representation of the processes involved A. Moropoulou, K. Bisbikou, K. Torfs, R. Van Grieken, F. Zezza, F. Macri, “Origin and growth of weathering crusts on ancient marbles in industrial atmosphere” Atmospheric Environment 32 [6] 967-982 (1998)

15. Prof. Antonia Moropoulou – Topic 3.4: Phenomena and mechanisms of decay Educational Linkage Approach In Cultural Heritage Rusty yellow crust (patina): It is formed by the diffusion of iron ions present in marble from the interior to the exterior surface and their oxidation, giving an orange – brown hue 3.4.4. General categories of common surface decay patterns Electron Probe MicroAnalysis (EPMA) Dissolution of calcite is taking place along with the deposition of Si and Al, and impregnation with Fe and Ti Rusty-yellow crusts at washed-out surfaces and where water-rebound phenomena occur (Sanctuary of Demeter, Eleusis, Greece) Schematic representation of the processes involved A. Moropoulou, K. Bisbikou, K. Torfs, R. Van Grieken, F. Zezza, F. Macri, “Origin and growth of weathering crusts on ancient marbles in industrial atmosphere” Atmospheric Environment 32 [6] 967-982 (1998)

16. Prof. Antonia Moropoulou – Topic 3.4: Phenomena and mechanisms of decay Educational Linkage Approach In Cultural Heritage Cementitious crusts: It is a hard crust of hydrous calcium silicate that covers the stone surface, while many cavities and cracks are developed 3.4.4. General categories of common surface decay patterns Pitting on marble surfaces covered by cementitious encrustations (E5) and at the other edge, a grey-yellow crust (E6) is formed continuing at a washed-out surface (E6B) (Sanctuary of Demeter, Eleusis, Greece) Scanning Electron Microscopy Amorphous and cementitious formations rich in alkalisilicate (Ca-Si) compounds, are coating the marble surface Electron Probe MicroAnalysis (EPMA) A. Moropoulou, K. Bisbikou, K. Torfs, R. Van Grieken, F. Zezza, F. Macri, “Origin and growth of weathering crusts on ancient marbles in industrial atmosphere” Atmospheric Environment 32 [6] 967-982 (1998)

17. Prof. Antonia Moropoulou – Topic 3.4: Phenomena and mechanisms of decay Educational Linkage Approach In Cultural Heritage 3.4.4. General categories of common surface decay patterns Cementitious crusts (cont.): Schematic representation of the processes involved A. Moropoulou, K. Bisbikou, K. Torfs, R. Van Grieken, F. Zezza, F. Macri, “Origin and growth of weathering crusts on ancient marbles in industrial atmosphere” Atmospheric Environment 32 [6] 967-982 (1998)

18. Prof. Antonia Moropoulou – Topic 3.4: Phenomena and mechanisms of decay Educational Linkage Approach In Cultural Heritage Oriented scratches: It refers to oriented scratches caused by previous incompatible conservation interventions by metallic brushes and laps Dust depositions: Depositions loosely bound to alumino-silicate substrate Carbonaceous crusts: Formed due to the corrosion of limestones in natural environment Surface loss: Formed due to chemical dissolution or Aeolian decay Decay with grain or crystal detachment: Appears due to salt action or granular disaggregation Flaking: Appears due to salt attack, acid rain corrosion and temperature fluctuations Alveolar decay: It is developed due to the soluble salts action in porous stones and due to the acid rain corrosion or biological reactions on non porous stones Hard crust of soluble salts Biological crust: Development of micro-organisms depending on the microclimate Color alterations: Developed due to alterations of various mineral phases in the stone or by metal oxides 3.4.4. General categories of common surface decay patterns

19. Prof. Antonia Moropoulou – Topic 3.4: Phenomena and mechanisms of decay Educational Linkage Approach In Cultural Heritage 3.4.5. Gypsum formation Gypsum formation The continuous peeling of the weathered surface reveals fresh material that in turn, is exposed to the creation of gypsum layer reaction and subsequent peeling, with the result that the phenomenon develops in depth The deterioration of the gypsum layer at the surface of the pentelic marble removes the details from the face and body of the Caryatides statues. In order to avoid further deterioration, for their protection, the Caryatides were placed in the Acropolis Museum. Replicas replaced the original ones at the Erectheion.

20. Prof. Antonia Moropoulou – Topic 3.4: Phenomena and mechanisms of decay Educational Linkage Approach In Cultural Heritage 3.4.5. Gypsum formation Gypsum formation (cont.) Gypsum formation (when the surface is not in direct contact with water) on the surface of calcite, but because the gypsum layer is more soluble than the calcite, it detaches – dissolves with rain, leading to the loss of surface details  Heterogeneous oxidation of SO 2 in liquid phase that takes place in the atmosphere or on the stone surface Although the initial components and the final products are known, the intermediate stages of the reaction have not been revealed in detail, and various mechanisms have been proposed:

21. Prof. Antonia Moropoulou – Topic 3.4: Phenomena and mechanisms of decay Educational Linkage Approach In Cultural Heritage 3.4.5. Gypsum formation Gypsum formation (cont.)  Dry state deposition of SO 2 and direct attack of the stone Proposed gypsum formation model of calcium carbonate and marbles based on Wagner theory (electrochemical potential) Skoulikidis, Th., Papakonstantinou, E., "The mechanism of sulfation by atmospheric SO2 of limestones and marbles of the ancient monuments and statues. I. Observations in situ and measurements in the laboratory; activation energy", Br. Corros. J., Vol. 16, 63 (1981).

22. Prof. Antonia Moropoulou – Topic 3.4: Phenomena and mechanisms of decay Educational Linkage Approach In Cultural Heritage 3.4.6. Development of the decay phenomena in depth Hard carbonate crust Although it is hard, the carbonate crust is accompanied by the relaxation of the underlying layers, that, in combination with any biological crusts, joint mortars dissolution and the plant development can result in localized collapse of the masonry Medieval City of Rhodes Photo courtesy of N. Kaseris Schematic representation by A. Poziopoulos in «History and conservation problems of the Medieval City of Rhodes» Proceeding Scientific Meeting 27- 29 Nov. 1986, Publ. UNESCO – Hellenic Ministry Culture – Municipality of Rhodes pages 375 ISBN 9602141115 (1992) Masonry collapses due to hard carbonate crusts

23. Prof. Antonia Moropoulou – Topic 3.4: Phenomena and mechanisms of decay Educational Linkage Approach In Cultural Heritage 3.4.6. Development of the decay phenomena in depth Hard carbonate crust (cont.) CO 2 is dissolved in the rain water according to the following reaction: The carbonic acid, CO 2.H 2 O (physically dissolved CO 2 ), breaks according to the following reactions The weak acid solution that is produced during the dissolution of CO 2 in rain water dissolves the carbonic calcium and carbonic magnesium that exist in limestones, dolomitic marble, lime mortars and lime-based plasters, as soluble acidic carbonic products are created Th. Skoulikidis «Decay and conservation of building materials of monuments» University of Crete Press, pages ISBN: 9605240769 pages 341 (2000)

24. Prof. Antonia Moropoulou – Topic 3.4: Phenomena and mechanisms of decay Educational Linkage Approach In Cultural Heritage Correlation of concentration of soluble salts and porosity Photo courtesy of A. Moropoulou 3.4.7. Capillary rise of salt solutions - Salt crystallization Moropoulou, A., Theoulakis, P., Tsiourva, T., Kourteli, C., Labropoulos, K., “Salt and humidity impact on porous stone masonries in marine environment”, Materials Issues in Art and Archaeology IV, Vol. 352, ed. J.R. Druzik, P.B. Vandiver, Publ. Materials Research Society, Pittsburgh (1995) pp. 893-906 Bakolas, A., Biscontin, G., Moropoulou, A., Zendri, E., “Salt impact on brickwork along the canals of Venice”, Materials and Structures, 29 (1996) pp. 47-55

25. Prof. Antonia Moropoulou – Topic 3.4: Phenomena and mechanisms of decay Educational Linkage Approach In Cultural Heritage Humidity sources - Atmospheric precipitations - Condensation of atmospheric humidity - Capillary rise of ground water - Direct transport of water droplets from sea - From the use of water as a cleaning agent - From leakages of the sewerage and supply networks 3.4.7. The role of water in decay K. Labropoulos, A. Moropoulou “Application of innovative and new nanostructured materials for compatible solutions in Cultural Heritage rehabilitated buildings” Proceedings of Forum International techa 2010 L’innovation au service du Patrimoine, 20- 23 Sept. Grande Halle, Arles, France, pp 87-96 (2011) Interaction of water with building materials - Rising damp/salt migration/salt efflorescences - Air pollutants are transferred in the water through rain or condensation in order to form acid solutions - Many reactions in the surface and in the interior of the stone can take place only with the presence of water. These actions are critical for the corrosion of aluminum- silicate rocks - Cyclic freeze/thaw degradation - Biological actions happen only with the presence of humidity

26. Prof. Antonia Moropoulou – Topic 3.4: Phenomena and mechanisms of decay Educational Linkage Approach In Cultural Heritage Water transport in porous means The water transport takes place: - horizontally (i.e. humidity transport from the exterior of the masonry to the interior) - vertically (rising damp from the ground) θθ Water source Hydrophobic surface Hydrophobic capillary Hydrophilic surface Hydrophilic capillary Contact angle for hydrophobic and hydrophilic materials The role of porous structure Porosity is defined as the ratio (%) of the volume of voids, Vp, towards the total volume, V, of the sample Closed Dead end TelescopesInkhorns Canals 3.4.7. The role of water in decay Karoglou, M., Moropoulou, A., Maroulis, Z.B., Krokida, M.K., “Drying kinetics of some building materials”, Drying Technology, 23 (2005) pp. 305-315

27. Prof. Antonia Moropoulou – Topic 3.4: Phenomena and mechanisms of decay Educational Linkage Approach In Cultural Heritage It refers to the mechanical decay of porous stones and building materials, through the development of mechanical tensions in the interior of the materials (pores) from salt crystals and disruption of the material when these tensions surpass its strength. The main salt sources in masonries are rising damp (from the ground), neighboring materials, such as cement and usually the binding mortar itself If the evaporation takes place in the interior of the mass of the material, the decay appears in the form of alveolation. Medieval City of Rhodes 3.4.8. Salt crystallisation Collapse mechanism of a masonry due to alveolation Photo courtesy of A. Moropoulou Schematic representation by A. Poziopoulos in «History and conservation problems of the Medieval City of Rhodes» Proceeding Scientific Meeting 27-29 Nov. 1986, Publ. UNESCO – Hellenic Ministry Culture – Municipality of Rhodes pages 375 ISBN 9602141115 (1992) Photo courtesy of N. Kaseris

28. Prof. Antonia Moropoulou – Topic 3.4: Phenomena and mechanisms of decay Educational Linkage Approach In Cultural Heritage The main and potentially the most catastrophic decay factor for porous stones. Attacks all porous materials regardless of their chemical composition and amplifies the primary decay factors Crystallization conditions: - Supersaturated solution in pores - RH  RHeq where RH = relative humidity RHeq = relative humidity in equilibrium with saturated solution SEM micrographs of detailed views inside two pores of a stone chip sample. The upper right shows an X-ray spectrum which is recorded inside the pore pictured at the left. Salts efflorescence: Development and deposition of crystals at the exterior surface of the stone [Salt solution transfer rate to the exterior > Drying rate] Sub-efflorescence: Development of crystals in the interior (pores) of the stones with deposition of the salt solution within the pores [Salt solution transfer rate to the exterior < Drying rate] Dangerous, since it may lead to stress development at the pore walls, depending on the salt type, and size and distribution of the pores 3.4.8. Salt crystallisation P. Theoulakis, A. Moropoulou “Salt crystal growth as weathering mechanism of porous stone on historic masonry”, J. Porous Materials, 6 (1999) pp. 345-358

29. Prof. Antonia Moropoulou – Topic 3.4: Phenomena and mechanisms of decay Educational Linkage Approach In Cultural Heritage Development of crystals in pores Evaporation zones Ways of development of crystals during evaporation within the pores in the masonry Decay model due to salt crystallisation in the pores of biocalcarenite 3.4.8. Salt crystallisation P. Theoulakis, A. Moropoulou “Salt crystal growth as weathering mechanism of porous stone on historic masonry”, J. Porous Materials, 6 (1999) pp. 345-358

30. Prof. Antonia Moropoulou – Topic 3.4: Phenomena and mechanisms of decay Educational Linkage Approach In Cultural Heritage It can lead to collapse of the masonry in combination with lateral stresses. Significant concentration of the phenomenon takes place at approximately 1/3 of the height of the masonry, where most of the humidity (and thus the soluble salts) is present. Collapse mechanism of masonry 3.4.9. Degradation of joint mortars (Dissolution and salt damage) Photo Courtesy of N. Kaseris Schematic representation by A. Poziopoulos in «History and conservation problems of the Medieval City of Rhodes» Proceeding Scientific Meeting 27-29 Nov. 1986, Publ. UNESCO – Hellenic Ministry Culture – Municipality of Rhodes pages 375 ISBN 9602141115 (1992)

31. Prof. Antonia Moropoulou – Topic 3.4: Phenomena and mechanisms of decay Educational Linkage Approach In Cultural Heritage Cement restoration mortars: The use of cement as a restoration binder material in masonries enhances the alveolar weathering of the surrounding original material (pore stone) and leads to the creation of large craters, due to incompatibility of the two materials in terms of mechanical properties and microstructure Medieval City of Rhodes A. Moropoulou, M. Koui, P. Theoulakis, Ch. Kourteli, F. Zezza, F., “Digital Image Processing for the Environmental Impact Assessment on Architectural Surfaces”, J. Environmental Chemistry and Technology, 1 (1995) pp. 23-32 Incompatible microstructure: The replacement of the decayed pore stones with new pore stones of smaller porosity, enhances the decay phenomena in the surrounding original material at the interfaces between the two stones. 3.4.10. Incompatible materials

32. Prof. Antonia Moropoulou – Topic 3.4: Phenomena and mechanisms of decay Educational Linkage Approach In Cultural Heritage Temperature fluctuations: - Extreme temperature fluctuations (between day and night) or uneven temperature distributions in building materials - Different coefficients of thermal expansion and heat capacity of different phases and materials of a system of materials The explosion of the Parthenon on 26 September 1687. Dimetrical drawing by M. Korres Expansion of metal joints: The oxidation products that are created at the surface of the metal joint increase significantly the volume of the system metal – oxidation product This expansion creates high mechanical stresses that lead to the failure (fracture) of the material, when these stresses increase over the strength of the stone Fracture of marble due to weathering of the metal joints Parthenon, Acropolis of Athens Skoulikidis, Th., "Atmospheric corrosion of the reinforcements of reinforced concrete and of marbles of ancient monuments and statues" in Proceedings of the International Symposium on Atmospheric Corrosion, (Hollywood, Miami, Florida, 1980), 807-825 3.4.11. Decay from mechanical factors The great desctruction of the Parthenon occurred in 1687, during the Turko-Venetian war and Morosini's campaign in Athens. The explosion that occurred at that time destroyed a large part of the frieze of the long sides of the temple and caused irreparable damage to stones that remained in place as well as those that fell out

33. Prof. Antonia Moropoulou – Topic 3.4: Phenomena and mechanisms of decay Educational Linkage Approach In Cultural Heritage Frost decay: It refers to the development of mechanical tensions from the crystals of frost in the interior of the materials, which when exceeding the material strength, lead to cracking and degradation. The intensity of the decay depends on the climate conditions where the material is exposed, the permeability of the material to humidity and mechanical strength Seismic vibrations: Earthquakes can sustain significant damage to monuments and historic structures requiring complex technical solutions to avoid structural failure Daphni Monastery Damage sustained during the 1999 Athens earthquake – Metal buttresses to support the building from complete collapse Photo courtesy of A. Moropoulou 3.4.11. Decay from mechanical factors

34. Prof. Antonia Moropoulou – Topic 3.4: Phenomena and mechanisms of decay Educational Linkage Approach In Cultural Heritage Seismic vibrations: The dynamic fatigue of the building can lead to damage when the frequency of the dynamic loads ranges from 8 to 80 Hz, depending on the maximum velocities, vmax, attained (DIN 4150 – 1978) Ground accelerations Monument model response to seismic vibrations Fragility curves Damage occurs usually when vmax > 10 mm/sec DIN standard anticipates that : - strong buildings can withstand 5 < vmax < 30 mm/sec whereas - historic buildings or buildings 2 < vmax < 5 mm/sec 3.4.11. Decay from mechanical factors Cakmak, A.S., Moropoulou, A., Mullen, C.L., “Interdisciplinary Study of Dynamic Behaviour and Earthquake Response of Hagia Sophia”, Soil dynamics and earthquake engineering, 14, No 9 (1995) pp. 125-133

35. Prof. Antonia Moropoulou – Topic 3.4: Phenomena and mechanisms of decay Educational Linkage Approach In Cultural Heritage Implications of Biological Decay - Biological products alter aesthetic image of the building materials - Chemical reactions on the surface of the stone - Physical reactions on the surface of the material Plant development among the tessarae of the mosaic leads to its destruction, Delos, Greece Photo courtesy of K. Efthimiou E. Efthimiou “Characterization of historic plasters – fresco mortars and conservation proposal in the archaelogical site of Delos” Master Thesis, NTUA Interdepartmental Postgraduate Course “Protection of Monuments, Site and complexes”, NTUA, supervisor A. Moropoulou (2004) Medieval City of Rhodes Biological crust with black & grey color Photo courtesy of N. Kaseris 3.4.12. Decay from biological factors