A research has started aiming at evaluating the influence of aggressive environmental conditions (moisture, temperature and soluble salts presence) on the bond between various composites and masonry substrates already decayed. A series of on-site experimental tests was carried out on full-scale masonry models, built in open air in a polluted area and artificially exposed since years to capillary rise of a solution of water and salt, so to create salt crystallization cycles. The models are one-floor constructions built in either sandstone or softmud-brick masonry, representing a simple historic masonry structure. Composite strips were applied to the two masonry substrates in order to evaluate the bond at three levels, characterized by different conditions (wet, dry, alternate wet/dry) and crystallization exposure. The first results of the pull-off tests carried out after three months from composite application, are here discussed.

A methodology of investigation and diagnosis on the built patrimony of historic centres in seismic areas is presented with the aim of collecting an extensive knowledge on the structural typologies and behaviour of historic masonry buildings. This investigation is also the base for the prevention and/or repair of damages caused by earthquakes. Small historic centres or residential buildings in larger centres have been considered for long time as “minor architecture”, but they are meaningful testimonies of the local cultural heritage and express the evolution of a society and of its cultural identity. The results of the investigation carried out on different Italian historic centers, allowed also a critical review of the reliability of the analytical models and of the effectiveness of the repair techniques applied in the past decades. The guidelines emerging from the research results are here presented. A “minimal” diagnostic investigation program is also suggested, in order to support the designers in their projects and to set up appropriate mathematical models to study the vulnerability of the structures.

An experimental research on of masonry has been carried out. Thermal cycles and salt crystallization test were carried out on solid brick samples and small masonry assemblages, using bricks and mortars produced in Italy and in Poland. The specimens were strengthened with CFRP textiles or laminates in different configurations. To perform thermal accelerated ageing tests, specimens were subjected to a temperature variation ranging between −10 and +70 °C, applied cyclically. The procedure was validated during testing. The results showed the influence of the properties of the adhesive and of the strength of the brick in the failure of specimens. As for salt decay tests, a RILEM pre-standard procedure was followed to evaluate the resistance of tested materials to sulfates. Damage evolution was monitored by visual observation and by quantification, at each 4-week cycle, of material loss by a laser profilometer. The results showed the rising of salt from the uncovered surface as from the first week of observation, and also a concentration of stresses underneath the fibres. The pull-off test was chosen as reference test, in order to the loss of bond. The durability was also checked on reference unreinforced specimens. Pull off tests were carried out on the surviving specimens at the end of the tests. The results among the various series of specimens are compared. This costly repair technique can show adhesion problems due to humidity and high temperature.

In order to study the building technology of an old 19th century timber vault in the Palace of the Academy of Sciences in Torino, authors performed several diagnostic tests to detect the construction technique and the damages to this structure. The vault has the peculiarity of being a timber structure, made with a specific technology that is not easily visible from intrados and extrados. For this reason the interpretation of its mechanical behaviour must be based on the knowledge of its construction technology. The non destructive technique that provided the most interesting information was IR thermography. This technique provided valuable data about the timbering used to build the shell of the vault and enabled correct execution of other minor destructive tests, such as light sampling and stratigraphic investigation on the painted plaster.

An accurate diagnosis of the state of conservation of historic structures is based on an extensive experimental investigation and on an appropriate structural analysis. A methodology of investigation to be applied to Cultural Heritage (C.H.) buildings is presented by the authors, based on a long experience in the field. The investigation steps are described, from the collection of historical documents and the visual inspection to: the geometrical and crack pattern survey, the detailed masonry section and quality description through on site mechanical and physical tests and use of Non Destructive (ND) techniques to the material characterisation and the structural monitoring.

During the single and double flat jack tests applied on site to masonry walls, the measurement of displacements is carried out in order to determine the deformability properties (Young modulus, Poisson ratio). Traditionally displacement transducers (LVDTs, deformometers, etc.) or a removable extensometer applied to the masonry surface, are used to measure relative displacements at each stress increase. Nevertheless some known difficulties are present like: destructive positioning of the devices, difficulty in the measure of the maximum limit of pressure. Furthermore local anomalies due to the positioning of the transducers on small stones and bricks (in rubble walls) which can be submitted to local rotations and displacements during the loading cycles, can influence the test results and reliability.The proposed optical system allows the localization in a Cartesian coordinate system of fixed points within the interested area by using a high resolution video-camera and the analysis of captured frames. The developed software allows for the continuous acquisition of displacements referred to the fixed initial image of a high number of points on the chosen area.The system allows to fix absolute coordinates and to extrapolate information like displacement vectors of each measured point and also relative displacements between the most representative points of the interested area.

Conservation of historic buildings requires a deep knowledge of structures and materials, of their characteristics and eventual state of damage and their causes. Investigation procedures and strategies applied at different levels of complexity from monuments to historic buildings for several purposes are outlined with particular interest in ND techniques. The choice of the experimental should be carried out only after the clear identification of the problems affecting the structure. Furthermore, the complexity of the problem could require the complementary application of different procedures. The paper systematically describes the problems and the procedures applied in the investigations carried out on representative examples of several diffused historic masonry typologies: towers, churches, castles, palaces but also dwellings.

The durability of some commercial ready mix mortars used for repair of historic masonry to salt crystallisation was studied using the salt crystallisation test produced by a RILEM TC. The mortars were previously characterised by chemical and physical tests and some wallettes were made by the same type of bricks and the studied mortars. The specimens were submitted to the crystallisation test and their damage memorised by visual inspection and y the use of a profilometer. The results of the durability tests are reported and discussed with a comparison to the pore size and distribution of the mortars.

The literature concerning the chemical-physical decay and processes of decay of natural building stones subject to aggressive environments is very broad and substantially developed at both the macro and micro structural level. Whereas research carried out on the durability of masonry as a composite material and on the mutual influence of its components (mortar, brick or stone) is much less abundant or advanced and in the 1980’s it was even less developed. The results of research in recent decades have shown that in order to study and understand the decay phenomena due to salt crystallisation and freeze-thaw action, experimental accelerated ageing tests should be carried out on masonry specimens and not on single components. Since the end of the 1970s a Research Unit of the Polytechnic of Milan’s Department of Structural Engineering (DIS) has followed a systematic methodology for the study of damage caused to masonry by salt crystallisation. The decay of masonry is highly influenced not only by aggressive environments but also by the choice and combination of constituents within masonry. Within the DIS group research was initiated by G. Baronio and L. Binda in 1980 [Baronio et al. 1982]. During the initial phase of the research a crystallisation experiment was undertaken, on the basis of state diagrams of the most diffused and harmful salts to masonry components, from which a cyclic ageing test for single masonry components was developed; the experiment had two different aims: (i) ability to study the decay of slender elements such as columns and decorations by total immersion in a salt solution; (ii) study of decay in structural elements having large dimensions by capillary rise of salt solutions where solutions could not typically reach the core of the element. In these experimental studies the specimens were exposed to selected temperature and relative humidity conditions over specified periods of time following uptake of the solution causing decay. The conditioning cycles were repeated until damage to specimens reached a given level [Binda et al. 1985, 1987]. In this manner, the first accelerated ageing tests by capillary rise of salt solutions were proposed for brick and stone. 1 Department of Structural Engineering, Politecnico di Milano, Milano, ITALY, binda@stru.polimi.it 2 Department of Structural Engineering, Politecnico di Milano, Milano, ITALY, cardani@stru.polimi.it 3 Department of Structural Engineering, Politecnico di Milano, Milano, ITALY, garava@stru.polimi.it Luigia Binda, Giuliana Cardani and Elsa Garavaglia 2 XII DBMC, Porto, PORTUGAL, 2011 Several tests were carried out with different types of salts and different thermo-hygrometric conditions and as well, different duration of conditioning cycles (Fig. 1a, b) [Binda, Charola et al. 1985]. From these studies it was determined that sodium sulphate solution was the most aggressive to brick and stone masonry components over the shortest test duration. Salts Type of cycle NaCl MgSO Na2SO4 A. t1 = 2 h t2= 46 h (50% RH) B. t1 = 2 h t2= 94 h (50% RH) C. t1 = 2 h t2= 166 h (50% RH) D. t1 = 2 h t2 = 46 h (50% RH) t3 = 120 h (60° C) E. t1 = 2 h t2 = 46 h (50% RH) t3 = 120 h (100° C) a) b) Figure 1. (a)-Different thermo-hygrometric conditions used for different crystallisation cycles; (b)Percentage of damage refers to the external surface of brick specimens, due to different crystallisation cycles caused by various types of salt solution. A survey of surface decay on monuments located in Milan has been carried out in which photographs of the surface have been acquired every three to six months since 1981. The natural environment was also studied from which results acquired over 10 years by the Brera Observatory in Milan were evaluated and since 1990 the onsite micro-environment was also monitored near model masonry structures. The data compared with the equilibrium curve of sodium sulphate showed that the formation of its two phases, thenardite and mirabilite, could occur in Milan every month of the year and several times a month with an average duration of 48 hours. Since a non destructive technique was required to measure the on-going process of material decay, the research revealed that decay started from the external surface of the material and proceeded, cycle by cycle, toward the interior, the decay often manifesting itself as a delamination (Fig. 2a, b) [Binda et al.1987]. Furthermore it was found that the material characteristics below the decayed surface remained unaltered (Fig. 2c). Measurements of surface decay were first carried out with gauges applied to the external surface [Binda et al. 1992]. Thereafter, a laser profilometer was adopted as it was determined from studies to be the best tool to precisely measure decay over time (Fig. 3), [Binda et al. 1992]. a) b) c) Figure 2. (a)-Decay of historic masonry exposed to the synergetic effects of different decay actions; (b)-Fatigue damage behind brick external surface before delamination; (c) Penetration of decay is shown as only a few millimetres behind external surface damage. The mutual influence of masonry components on surface damage was first studied on masonry prisms damaged by salt crystallisation [Binda et al. 1985]. From these initial results the decision was then Decay of Historic Masonry Due to Salt Crystallization XII DBMC, Porto, PORTUGAL, 2011 3 taken to build full-scale models and subject these to the environmental conditions prevalent of a polluted area of Milan [Baronio et al. 1993]. In order to accelerate the damage process, a sodium sulphate solution was injected into the building foundation so that the ageing could occur by capillary rise of the solution to the masonry structure. The different types of decay caused to brick masonry by salt crystallisation were defined from work carried out within a European Community (EC) study [Van Balen at al. 1997] and thereafter collected in a “Damage Atlas”. A product of the same study was an expert system (MDDS) on the decay and diagnosis of brick masonry prepared with the aim of helping non expert professionals in the interpretation of decay mechanisms of masonry structures [Van Balen at al. 1997]. Currently, the laboratory crystallisation test that is carried out on masonry prisms forms part of a RILEM recommendation for testing as proposed by the TNO-Delft and the results have been calibrated in three EC studies in which other partners have also participated [RILEM 1998]. A more sophisticated device was introduced to measure surface decay: the laser profilometer. This device uses a laser beam that scans the surface of the materials and is thus able to characterise the variation in surface profile of a material. A suitable data acquisition system transforms these measurements to surface roughness profiles that in turn can be modified to describe the decay as a function of time and space (Fig. 3). The values of the chosen parameter measured over time can constitute the input data for a deterministic or probabilistic mathematical model in which material behaviour and durability of surface treatments in the presence of different soluble salts and exposed to salts of different concentration can be studied [Cardani et al. 2002]. The high degree of randomness associated with acquiring the material characteristics and their level of decay when subjected to natural ageing conditions suggests that the deterioration process may be defined, for example, by a function L(t,l); hence this is a stochastic process having random variables l and t, where l is the loss of material at the surface in time t (Fig. 4) [Garavaglia et al. 2002]. a) -22 -18 -14 -10 -6 -2 -230 -200 -170 -140 -110 -80 -50

After the earthquake that stroke the city of L’Aquila during the night of April 6th 2009, many historical buildings at the city centre were severly damaged. Nevertheless many others survived the seismic event with only local damages, showing a good mechanical behaviour against vertical and horizontal actions. In order to continue preserving these buildings, a careful investigation is necessary before applying any repair technique, new or traditional to understand the past design practices for building durable and safe structures. In order to understand the structural behaviour of the church of St. Biagio in L’aquila, an extensive diagnostic investigation based on non-destructive and minor destructive techniques was carried out by the authors. The paper describes mainly the applied methodology which can produce some guidelines to be followed in the future study of other Cultural Heritage (C. H.) buildings hit by the earthquake.

Within the framework of a European Commission project entitled Cultural HEritage against Flood (CHEF), a research was carried out in Milan on full-scale stone and brick masonry models by means of a simulated flood to investigate the effects of floods on historic and masonry buildings. The objective was to evaluate the post-flood moisture content and the drying process through non-destructive or minor-destructive techniques. Several non-destructive testing (NDT) were applied (thermography, sonic tests, radar) and were compared with the powder drilling test. Thermography and radar tests were the most useful; the attention is here more concentrated on radar tests which revealed interesting results. A high frequency GPR system was used to perform measurements on selected points of the models at selected intervals during the drying period. Radar velocity, radar amplitude in transmission and in reflection mode, radar waveform distortion and spectra were analyzed as a function of time after flooding and were compared to moisture content assessed by the powder drilling method. Measurements of radar velocity and radar waveform distortion were found meaningful and in agreement with the expected drying process.

After an investigation on the most recent floods occurred in Italy that damaged the Cultural Heritage masonry buildings, an experimental research started on-site on full-scale masonry models exposed to the environmental agents in Milan. The masonry materials used for the full-scale models were largely investigated in the past and the models were subjected to decay caused by the capillary rise and by the crystallization of sodium sulfate coming from the foundations. These walls can actually simulate the state of naturally contaminated walls before a flood and represent a construction where the main parameters are known. A flood has been simulated by adding water for several days to the walls of the full-scale models previously contaminated by salts, then the walls were left to naturally dry. The objective is to check the effectiveness of nondestructive (ND) techniques in detecting the presence of water and the drying process and also the influence of surface treatments presence. Radar tests, thermography tests, sonic tests, as well as the minor destructive powder drilling tests were applied successfully to evaluate the moisture distribution in the masonry after flooding and during natural drying.