Validation of non-destructive characterization of the structure and seismic damage propagation of plaster and texture in multi-leaf stone masonry walls of cultural-artistic value

Assessment of multi-leaf stone masonry in earthquake-prone areas is mostly related to the evaluation of its texture, morphology, leaf detachment and structural cracking due to previous seismic activity, as well as disintegration due to material deterioration. For the plastered masonry with heritage or artistic value (paintings, frescoes etc.), both the type of structure and the extent of damage should be characterized with minimal interference to the structure, which could be overcome solely by non-destructive testing (NDT). However, due to the complexity of plastered multi-leaf masonry structure, the performance of well-known NDT methods could be significantly worsened. Therefore, as a prerequisite for applying NDT on multi-leaf stone masonry in practice, a validation process should be carried out. In this study, complementary ground penetrating radar (GPR) and infrared (IR) thermography measurements on plastered laboratory three-leaf stone masonry walls were performed. Apart from assessing the wall texture and morphology with the type of connection between the leaves, detection of gradual plaster delamination and crack propagation while subjecting the walls to an in-plane cyclic shear test was taken into account. The results showed that GPR could successfully visualize header stones passing through the whole depth of the specimen. The masonry texture behind the plaster could be well resolved by both methods, although GPR near-field effects worsened its localisation. For the detection of plaster delamination, IR thermography outperformed GPR by detecting delamination as small as 2 mm as well as structural crack patterns, whereas GPR only detected delamination larger than 8 mm. It was shown that the performance of both methods for defect detection could be further improved by image fusion based on unsupervised clustering methods.     

Metrological definition and evaluation of some mechanical properties of post-medieval Neapolitan yellow tuff masonry

The knowledge of the morphological and mechanical properties of masonry walls is very important for the refurbishment of ancient buildings, particularly when the requirements of both structural safety and historical preservation must be fulfilled. The masonry is not of homogenous material: its mechanical properties depend on stones, mortar, and texture which are very variable due to their dependence on the historical periods and the geographical area of the erection. For this reason, a deep knowledge of masonries built in different sites and historical periods is essential in order to evaluate both the capacities of bearing vertical load and the seismic vulnerability of the masonry structure. Three fundamental typologies of tuff masonry have been defined: they are the characteristics of different historical periods from the XVI to the XX century. The models are in full-scale in order to reproduce the three defined chronotypes. Original tuff stones quarried in the corresponding historical period, mortars similar to the original ones, reproduced according to ancient documents and original constructive techniques have been used for the construction of the specimens. Compression tests performed in displacement control have been carried out on the masonry models in order to determine the maximum resistance of the material and the corresponding strain, the ultimate strain and corresponding residual strength. In this paper, the procedure used for making the specimens and for experimentally evaluating the mechanical properties of post-medieval Neapolitan yellow tuff masonry are illustrated and the obtained results, even in terms of plastic capacity of these kinds of masonry, are reported.     

Historical and probabilistic structural analysis of the Royal ditch aqueduct in the Alhambra (Granada)

The structural and historical analysis of the aqueduct of the Alhambra is presented. In the 13th century, Muhammad I built the palatial city of the Alhambra. To provide a water supply, Muhammad I built an irrigation ditch, known as the Royal ditch. The aqueduct was reconstructed in the 18th century in ashlar masonry to replace the original one. This work analyzes the history, geometric modeling, materials and stability of the aqueduct. Due to difficulties in testing and measuring the properties and loads, the Monte Carlo analysis technique is used to analyze stability, where the input parameters are defined as probabilistic distributions. Monte Carlo analysis provides the probability of risk of collapse defined by the geometric security coefficient obtained by means of the theory of limit analysis. Additionally, this technique is used to optimize the thickness of the arch.     

A nano to macroscale study on structure-mechanics relationships of archaeological oak

Mechanical properties of wood at different length scales of its hierarchical structure are governed by structural and compositional properties on smaller length scales. This opens up the possibility to use microstructural data for estimating mechanical properties, which are difficult to assess by conventional, destructive testing but are nevertheless of high relevance for conservation practice. Herein, we investigate such microstructure-mechanics relationships for a particular example, namely the load bearing archaeological oak of the Oseberg Viking ship, displayed at the Viking Ship Museum in Oslo, Norway. In order to identify the effects of degradation on the mechanical behavior and their relations to the microstructure, recent oak specimens of different geographical origin (Norway and Austria) are investigated as well. Wood exhibits a cellular structure. Its cell walls are composed of an amorphous polymer matrix consisting of lignin and hemicelluloses and embedded, stiff cellulose fibers. At the cell level, experimental studies comprised microscopic investigations of the cellular structure, chemical analyses of the composition of the cell walls, as well as nanoindentation tests on single cell walls. The same samples were also analyzed on the macroscopic level, where additionally mass density and annual ring data were measured together with ultrasonic stiffnesses. The chemical data clearly indicate deterioration in the archaeological oak, affecting mainly hemicelluloses and amorphous cellulose. At the cell wall scale, however, this does not necessarily lead to a weaker material behavior. The nanoindentation modulus, as a measure of the cell wall stiffness, was found to even increase. This is counterintuitive to our understanding of the effects of chemical degradation. It might be due to possible modification of lignin in the Oseberg oak, and thus have a stronger effect on the indentation modulus than the concurrent weakening of the interfaces between the load-carrying cellulose fibers and the connecting cell wall matrix when analyzing wood at the microscopic level. A similar effect is also observed for the transversal stiffness of macroscopic samples, which increases. In tension-dominated loading modes, however, the degradation of the interfaces is the dominant effect, resulting for example in a considerable reduction of the macroscopic stiffness in longitudinal direction. This underlines the utmost relevance of the loading condition on the remaining load-carrying capacity of degraded wood. On the macroscale, effects of the geographical origin (i.e. growth conditions) on ring characteristics of the oak tissues override the effects of degradation on the mechanical behavior. They have to be carefully extracted in order to come up with conclusions on the effect of degradation from macroscopic test results. The identified microstructure-mechanics relationships provide the basis for–in further research steps–building mathematical models describing the relations between microstructural characteristics and macroscopic mechanical properties and, thereon, for structural analyses of historical wooden objects.     

A procedure to assess the suitability of plaster to protect vernacular earthen architecture

As part of a working definition of a new code of practice, this paper develops a methodology to determine the suitability of plasters manufactured on-site to protect the earthen walls of vernacular architecture buildings. Given the diversity of raw earth construction types, ranging from massive earth to stone masonry with earth mortars, and the variability of the materials used, two on-site tests (a shrinkage test followed by a shear test) were proposed. Those tests, as well as additional tests, were performed with lime/sand, earth/sand and earth with plaster admixtures. Lime/sand plasters do not typically pose shrinkage issues, which is why more earth based specimens were tested than lime based specimens. An analysis of the on-site testing complemented with laboratory tests reveals an antagonistic control of the bond between earth plaster and earthen wall based on clay content: an increase in the plaster clay content leads to increased bending strength, which strengthens the plaster and increased shrinkage, which weakens the plaster-wall interface. The heterogeneity of the wall leads to a wide range of results; therefore, this study was conducted to validate the formulation of plasters by means of shrinkage and shear tests at five different points on the wall. The shrinkage test allows finding the earth plaster formulations. Among all the validated formulations, the mason chooses the best one thanks to two criteria: the best workability (which is variable according to masons) with the highest clay content as possible. Then, when the formulation is chosen, the shear test must be done to verify if the bond between the plaster and the wall is high enough. This series of tests allows masons to validate formulations that will ensure good mechanical resistance of the plasters that protect buildings of vernacular earthen architecture.     

A portable NMR device for the evaluation of water presence in building materials

The direct recording of the water presence in stone materials or in masonry provides information about their state of conservation and it can also indirectly reveal the effectiveness and durability of protection treatments or chemical interventions for rising damp reduction. Evaluating the humidity, i.e. the water content, of a building material is a problematic issue because the water is distributed in a large volume in different amounts. Usually these kinds of measures have been carried out with resistance/conductivity and thermographic systems, which are all affected by weaknesses and intrinsic restrictions. Thermographic investigations are affected by temperature differences and the evaporation–cooling effect. In the case of electric measures, the signal does not originate from the water present, but from the conductivity of the water itself, which is strictly connected to the presence of ion species that can modify it significantly. Moreover, interruptions, like air gaps or fractures, cancel the signal. For both methodologies the quantitative water evaluation is difficult. Although some minerals, like iron-based ones, could disturb the NMR measure, the signal is not influenced by the presence of most common soluble salts or pollutants in the solution (such as nitrates, chlorides or sulphates) and it is only generated by the number of water molecules present in the sensitive volume. In this paper the results, obtained in the laboratory with a portable NMR device, developed within the framework of the Eureka Project E!2214-MOUSE, are shown. The encouraging results obtained in this preliminary experiment, concern mainly the investigation of stone materials that have different porosimetric features and the calibration of the instrument under different working conditions. The experiments focused on the correlation between the content of water absorbed by capillarity and the NMR signal intensity obtained by this device. Different materials have been investigated, such as calcarenite and bricks. The experimental work will define a starting platform to successfully transfer the analytical procedure from the laboratory to in situ measurements.     

Mechanical behavior of leaning masonry Huzhu Pagoda

The paper has been developed in the framework of a larger research program, in which the University of Rome “Tor Vergata” (Italy) and the Yangzhou University (China) are jointly involved to study and preserve historic towers. The research aims to evaluate the risk of collapse of the Huzhu Pagoda in Songjiang County, a leaning tower built in the XI century. Mechanical properties of the masonry material have been obtained by experimental tests on small specimen and the mechanical behaviour of the structure has been evaluated via numerical models. The static analysis of this ancient pagoda constitute a prerequisite base for the evaluation of its structural behavior leading to a suitable maintenance program. The architectural characteristics and damage conditions of the pagoda are key parameters in the preparation of a complex analytical model. The pagoda leans more than six and half degrees, and exhibits some bad structural conditions. Static analysis is carried out via finite-element method in order to establish a reliable numerical model and assess the static risk.     

Historical plasters on light thin vaults: State of conservation assessment by a Hybrid ultrasonic method

Historical plasters on light thin vaults, usually made by mats of reeds nailed to an upper wooden framework, were used in several historical and monumental Italian buildings and churches built between the 16th and the 19th century and almost all of the historical Italian theatres built between the 18th and the 19th century to cover the theatre-hall and to improve its acoustic properties. The non-destructive inspection of these structures is very important, but traditional inspection techniques are usually limited in resolution, which may be a problem for detection of defects at a very early stage. The paper presents the development and application of a high-resolution inspection technique based on a hybrid ultrasonic method, where a contact emitter probe and a non-contact air-coupled receiver probe are used. Results show the effectiveness of the method on laboratory samples and propose an inspection procedure for in-field application.     

Study on some sorption properties of treated bentonites for their potential use as a moisture regulating system for the preservation of historical wooden elements

We report the first results of a research study aimed at developing a new strategy for the conservation of wooden structural elements present in historical buildings, based on moisture regulating systems. As has been happening for artefact preservation in museums, the idea is to develop systems based on the ability of some highly hygroscopic materials to moderate variations in relative humidity. These materials could adsorb and release moisture to reduce the extreme values of humidity in the micro-climate, for example between wooden beams and masonry. In order to experimentally verify this possibility using current, low cost and easy handling building materials, 5 bentonite samples were laboratory processed to improve their adsorbing properties by means of treatment with sodium carbonate at 3 concentrations: 2, 3 and 4% by weight. The effectiveness of ion exchange between sodium carbonate and bentonite was controlled by measuring the swelling volume of the bentonites. All the samples (n = 15) were tested for their hygroscopic properties. Adsorption isotherms were measured at 25 °C, using desiccators with silica gel, saturated salt solutions and bi-distilled water. A comparison between isotherms of one of the lower hygroscopic treated sample of bentonite and of a sample of wood and of a sample of brick and some numerical analyses with the Delphin code were made in order to evaluate the potential use of this bentonite as a moisture regulating system for the preservation of historical wooden elements. Results show that it seems to be possible to use bentonites as a moisture buffering material in order to reduce moisture content in wooden beams at least during their adsorption phase. It remains to investigate their desorption phase and their behaviour if they be in a saturation condition. Further studies are currently under way.     

Pore structure of historic and repair Roman cement mortars to establish their compatibility

Mercury porosimetry was applied to the study of pore structure of the historic Roman cement mortars representative of different locations in Europe and time periods as well as different application techniques from architectural castings to in situ formed renders and profiles. Three categories of pores were found to coexist in the mortars. The finest pores, with diameters below 0.1 μm, are present within the hardened aged Roman cement matrix. The larger ‘air’ pores, with diameters between 0.2–2 μm, are due to the evaporation of the excess unbound water and restricted hydration. Pores larger than 2 μm are rare and, in general, can be related to microcracking induced by shrinkage drying and mortar weathering. The mortars have rarely been found to develop a dense fine-porous microstructure characteristic of the ideal conditions of moist-curing; massive architectural castings being the only exception identified. The presence of larger ‘air’ pores was, in turn, almost universally observed. The investigations of the freshly prepared Roman cement mortars have revealed that the restricted hydration could be due to the exposure of the freshly laid surface to dry real-world external environments, a high water-to-cement ratio in the original mortars, or the drawing of water from the stucco mass due to insufficient pre-wetting of the porous masonry. The insufficient reactivity of historic cements, resulting from a high content of over-burned, non-reactive cement components or coarseness of the cement grains, could be another reason for yielding poorly hydrated mortars in the past. In general, Roman cement stuccoes are in an excellent state of preservation in spite of their usual exposure to polluted urban environments for more than a century. Therefore, the coexistence of Roman cement mortars of widely different pore structures has not brought about any problems of incompatibility which field observations could reveal. The Roman cement repair materials have been found to develop pore structures similar to those of historic mortars. Therefore, they are in broad terms compatible with historic masonry or stuccoes. However, the porosity and strength of the repair materials can be controlled by a careful manipulation of the water-to-cement ratio of the mix to adapt them better to the properties of the host material.     

Modelling and analysis of a basilica under earthquake loading

In this paper a basilica-type church is analysed in order to assess its structural behaviour and seismic vulnerability. For this purpose, an effective two-step procedure has been used, consisting of: (a) 3D static and dynamic linear analyses of the structural complex, and (b) 2D nonlinear push-over analysis of the single macro-elements. The results obtained through push-over analyses have been compared to the collapse loads derived from limit analysis, proving the ability of finite element (F.E.) nonlinear model to provide reliable simulation of the actual response of masonry elements. Then, the strength demand on each single structural macro-elements, resulting from the 3D linear analyses, has been compared to the macro-element ultimate strength capacity. The comparison demand vs. capacity has been carried out for all transversal and longitudinal macro-elements of the church, allowing a direct, though approximate, assessment of the seismic safety level of the church. The comparison demand vs. capacity confirms the susceptibility of this type of buildings to extensive damage and possibly to collapse, as frequently observed. The insertion of rigid diaphragms, which represents a widely used retrofit technique, has also been investigated; such intervention triggers concentration of strength demand in the stiffest macro-elements, so that the seismic capacity of the building is not necessarily increased.     

Numerical modelling of the structural behaviour of Buti’s bell tower

The paper describes the numerical techniques implemented in the finite-element code NOSA for structural analysis of masonry constructions. The code is then applied to the analysis of “Buti’s bell tower”, a medieval structure located on the Pisa mountains, under two different conditions: firstly, with the structure subjected to its own weight alone, and then while subjected to both its own weight and a horizontal load, which models an earthquake. The displacement and stress fields, as well as the distribution of cracking have been calculated with NOSA, and the numerical results analysed and compared to the actual distribution of fractures in the tower.     

Preventive thermographic diagnosis of historical buildings for consolidation

Conserving architectural heritage usually requires a multidisciplinary approach involving a variety of professionals and organizations. Since the evaluation of the state of conservation of historical buildings using destructive techniques should be avoided to prevent the integrity of the cultural heritage, the development of non-destructive and non-contact techniques is very important. InfraRed (IR) thermography is a non-destructive powerful tool for fast and accurate building diagnostics. In the investigation of historical structures, where a restoration or conservation treatment can cause irreversible damage to the structure, it is considered to be of most importance. A campaign of thermographic surveys were conducted on a large part of the historical cultural heritage of L’Aquila and its surroundings. In this paper we present the results of the study for the Church of Santa Maria ad Cryptas (XIII century), one of the most ancient buildings in the surroundings of L’Aquila and one of the best examples of Gothic art in Abruzzo, with the aim to evaluate the correspondence between the damage induced by the earthquake and the previous thermographic results, in order to validate the effectiveness of thermography and its role in preventive diagnosis.     

University Under Structural Reform: A Micro-Level Perspective

National governments in several countries have promoted and carried out different forms of mergers, consolidations and alliances within their higher education systems in order to increase efficiency, effectiveness and governmental control to ensure that the universities more directly serve the national and regional economic and social objectives. This article sets out to explore structural reforms between and within universities from a micro-level perspective by investigating how academics make sense of and respond to the structural reforms, and how these reforms shape academic cultures, work practices and identities. Drawing upon in-depth interviews with 31 Finnish academics working under structural rearrangements, five core meanings of structural reforms are discerned: structural development as part of a flood of changes, expanding bureaucracy, profiling, searching for partners and branding. The paper concludes that structural reforms along with other managerial transformations foster experiences of competition and polarization at the departmental and individual level of academia, involving redefining what it means to be a successful academic.     

Granite desalination using electromigration. Influence of type of granite and saline contaminant

We describe the results of electromigration desalination of two soluble salt-contaminated Galician granites. The efficacy of electromigration, which had not been previously applied to granite, was assessed for two types of granite contaminated with a 20% NaCl solution and seawater. Desalination effectiveness was evaluated as follows: (1) analysis of anode and cathode ion content during testing; (2) analysis of ions at different distances from the electrodes after testing; (3) pH assessment of the stone surfaces; and (4) evaluation of colour changes. Results were very satisfactory; by the end of testing, chloride was reduced by almost 100% in both the NaCl and seawater contaminated samples. Sulfate reduction was also significant, despite this ion's lower mobility. The granite pH values remained close to neutral and colour changes were minimal. The difference in effectiveness of the process for the two types of stone was associated with their dissimilar pore structure.     

Desalination of masonry structures: Fine tuning of pore size distribution of poultices to substrate properties

Desalination is a relatively new intervention in the field of conservation of architectural heritage. Especially the desalination of immovable objects, such as masonry structures, is still a trial-error practice. In the field, different desalination materials and methods are used, sometimes with unsatisfactory results. Better understanding of the desalination process is needed in order to support the conservator with clear guidelines for choosing a suitable desalination material and method. The research presented in this paper constitutes the first step towards the development of a modular system of poultices, which can be adapted, i.e. fine-tuned to different types of substrates. Starting point is to make use of advection, i.e. the transport of salt ions with water flow. This transport mechanism is faster than diffusion and the application on immovable objects is relatively easy. In order to optimize salt extraction, a poultice working by advection should have smaller pores than the substrate. Starting from this principle the pore sizes of different desalination materials (sand, cellulose, kaolin and bentonite) mixed in different proportions, have been measured. Interesting results were obtained, showing that the desalination materials commonly used in the field are often not the most suitable ones. On the basis of the results, recipes for poultices, adapted to a specific substrate, can be formulated.     

Computational fluid dynamics (CFD) modeling of microclimate for salts crystallization control and artworks conservation

Many deterioration processes are linked to unsuitable microclimatic condition in cultural buildings. One of the most diffused processes is soluble salts crystallization that can be accelerated in masonry structures within specific microclimatic values for different chemical compounds. In this paper, microclimate and efflorescence diffusion were monitored over a one-year period in the Crypt of the Cathedral of Lecce (South Italy). This allowed to relate the microclimate with the efflorescence variation over time. A three-dimensional computational fluid dynamics (CFD) model was then developed to detail the thermo-hygrometric parameters and airflow patterns responsible for salts crystallization and artworks deterioration. Two main conditions were reproduced; one to simulate the current microclimate, which simulations showed to be inadequate for conservation, and the other to search for a more appropriate solution. In both cases, summer and winter conditions were simulated and compared to find a microclimate able to ensure more suitable thermo-hygrometric intervals required by the constituting artworks materials. The results helped to suggest actions to improve maintenance of the Crypt.     

La Medusa by Caravaggio: characterisation of the painting technique and evaluation of the state of conservation

The oil painting “La Medusa” executed by Caravaggio at the end of the XVI century on a wooden shield, was investigated by integrated physical–chemical and analytical methodologies in order to obtain scientific data capable of elucidating the state of conservation and the painting technique. Optical (OM) and electronic (SEM-EDS) microscopy, micro-FT-IR spectroscopy, gas chromatography–mass spectrometry (GC–MS) and pyrolysis GC–MS were applied on two microfragments and some organic samples obtained by solvent extraction using the swab cleaning technique. The obtained results indicated that Caravaggio probably reused an old shield as a previous gypsum preparation layer has been detected under the original painting layers. He used white lead, natural earths, verdigris and lead–tin yellow type I mixed with drying oils to paint. The considerable amount of amorphous particles of copper chlorides found in the green pigment verdigris suggests that it could have been produced according to the ancient recipe of verde salsum described by Theophilus. Mordant gilding has been identified on the upper part of the shield that can be related to an abandoned experiment to give the painting a mirror-like reflecting effect. Three different varnishes layers have been detected above the painted surface. The original and restoration varnishes have been identified and they contain a mixture of drying oil, mastic and turpentine and some beeswax. Cleaning tests, performed with different organic solvents, suggest the use of isopropyl alcohol as cleaning agent because it is less efficient in comparison to others solvents; thus it ensures a careful and controlled removal of the varnishes.     

Continuous monitoring of wooden works of art using fiber Bragg grating sensors

In recent years the control and monitoring of works of art has gained more and more importance. In particular, works partially or totally realized with wood, such as polychrome sculptures, painted panels or Crucifixes, are highly sensitive and delicate and thus need a particular attention. The wooden support is, in fact, an essential element for the stability of pictorial layers: the color lies on a preparation, which in turn, is anchored to the wood. Wrong conservation methods, i.e. in an environmental climate that is not controlled, or intrinsic mechanical stresses, can warp such structures, and the effects can be irreversible and destructive to the painted layer. The use of fiber Bragg grating (FBG) sensors for the quasi-distributed, in situ measurement and continuous monitoring of deformations in painted wood panel is proposed. In order to demonstrate the applicability of FBG sensors to painted wood panels, a wooden support, made using the same 15th–16th century techniques, was prepared in the Opificio laboratories. A number of Bragg grating sensors were affixed in several critical points, on the back and front sides and on the strengthening cross-beams, in order to detect deformations in the panel dependent on the variations in the environmental relative humidity (RH). Measurements during the removal of the cross-beams are also reported. The results of measurements have shown the applicability of FBG sensors for the continuous in situ monitoring of valuable wooden objects and works of art.