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The structure of historical “cocciopesto” mortars (utilized in Venice and more generally in the Mediterranean area) have been mimicked with samples of phyllosilicate rich (by 58%) clay heated at different temperatures (between 500 and 700 °C) and treated with lime over a 5-month seasoning period in the air (in the presence of CO2) or alternatively under N2 atmosphere (in the absence of CO2). The structural transformations have been detected with 29Si MAS NMR spectroscopy. Heating converts the crystalline Q3 phyllosilicates into the amorphous Q3am phase. The Q3am phase is partially converted by lime in the presence of CO2 into amorphous Q2am inosilicates, while the Q3 phase remains unchanged. In the absence of CO2, lime converts swiftly the Q3am phase (and more slowly the Q3 phase) into the crystalline Q2 inosilicates and Q1 sorosilicates. As the conditions encountered by historical “cocciopesto” mortars during their secular seasoning are better mimicked by clay treated with lime in the air, the hydraulic properties of the former material are temptatively attributed to the presence of the Q2am phase.

Structural studies to determine the earthquake worthiness of Hagia Sophia in Istanbul have proved that the monument's static and dynamic behavior depends very strongly on the mechanical, chemical and microstructural properties of the mortars and bricks used for the masonry. Hence, the classification of the crushed brick/lime mortars under the category of advanced cement-based composites is concluded, explaining the fact that the monument still stands, as well as the very large static deformations which it has undergone, since such mortars have a very long curing period. According to the analysis of the dynamic data, the first three natural frequencies of the building were determined. These results show a decrease of approximately 5–10% in the natural frequencies, as the amplitude of the accelerations increases and returns to their initial values, due to the non-linear nature of the masonry. The above-mentioned behavior allows the structure to absorb energy without affecting irreversibly its material properties. The determination of the mortar properties indicated that they are of considerable mechanical strength and longevity. The dated mortar samples examined proved to be resistant to continuous stresses and strains due to the presence of the amorphous hydraulic formations (CSH), investigated by transmission electron microscopy (TEM) at the crushed-brick powder/binder interfaces and at a sufficient content in the binding matrix, as proved by TG-DTA, which allowed for greater energy absorption without initiations of fractures, let alone the transition of the gel to a higher order of formation. Furthermore, the interpretation of the amorphous nature of the hydraulic formations of the crushed brick/lime mortars is attempted by the experimental validation of real chemical interaction between lime and clay and the characterization of the fundamental structural units of the calcium silicate hydrates, produced by mass spectroscopy.

In this study some results on the reactivity of silicatic consolidants employed for the conservation of valuable artistic and cultural porous materials are discussed. In particular, a colloidal suspension of silica made by particles with an average diameter of 10–15 nm, a sodium silicate and an ethyl silicate consolidant are studied. The chemical–physical characterization of xerogels achieved from the examined products were carried out determining the superficial area (BET method) and the average dimension of particles (SAXS) while the chemical structure of xerogels were investigated through NMR MAS spectroscopy of the 29 Si nucleus. The investigation on reactivity between silica and stone support was executed by mixing consolidants with calcite and quartz powder to simplify as much as possible the system otherwise very complex. On silica produced by the three examined consolidants structural differences are revealed and these diversities can be responsible for the dissimilar reactivity of the silicatic systems towards the stone, in particular with regard to the carbonatic component.

The study of the interaction between silica glass and saturated Ca(OH) 2 solutions can be a useful approach to resolve the problem of the adhesion between lime-sand mortar and clay bricks. Since it is reasonable that the silica–calcium hydroxide system well simulates a brick–mortar system, experimental observations concerning the interaction of silica glass and this strong basic solution should be of value for the comprehension of the chemical reactions that could take place at the mortar–brick interface, maybe affecting the adhesion between the two building materials. We demonstrated the effects of saturated Ca(OH) 2 solutions on commercial pure silica glass (fused silica) and on silica films obtained via a sol–gel process by means of dip-coating. Silica samples were dipped in the solutions at different temperatures (room temperature, 60 and 80 °C) and at different time intervals (1 and 21 h) and then they were analysed by means of surface techniques: X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS) and atomic force microscopy (AFM). It has been shown that Ca(OH) 2 reacts with the silica glass network. The experimental results clearly show a very different behaviour of sol–gel silica with respect to fused silica, probably because of their different nanostructure. Many problems concerning the interaction of silica and Ca(OH) 2 are still to be solved, but the results of this research strengthen the idea that adhesion between lime-sand mortar and clay bricks is caused not only by carbonation of calcium hydroxide contained in the mortar, but even by some chemical reactions involving the brick constituents and calcium hydroxide itself. The final products, calcium silicates, may induce a chemical continuity between lime-sand mortar and clay bricks.

Publisher Summary This chapter describes the method for the study of the effects of condensation on limestone surfaces. The results of condensation characterization in a lake environment indicate rather low pH values, in various cases lower than 6. The bicarbonate ion contents correspond to the pH. The ion concentration regarded as representative of both condensation and its effect on stone surfaces was evaluated. The evaluations were recorded by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) analyses. Initial results indicate effects related to the direct action of acidic substances, particularly dissolved carbon dioxide (CO2), leading to the recrystallization of calcite into smaller crystals. The results obtained from the condensation analysis in the Venice area indicate that it contains significant amounts of HCO3- ions, while other ions generally included in the “polluting” category (SO2 and NOx) are not present in particularly high concentrations. On the other hand, chloride ions (CI-) and sodium ions (Na+), which are characteristics of sea aerosol, were detected. Thus, the determination of pH is very important in indicating the intensity of the interaction between condensation and stone.

In the present study the possible chemical interactions among the constituents of historical walls have been investigated. In Venice but also in the whole mediterranean area the “cocciopesto” (constituted of powder and brick fragments which traditionally confer hydraulic properties to the mortar) has been widely employed both for mortars and the so called “marmorino” plasters. The work has been developed by examing the brick-mortar interaction on historical buildings in Venice. The samples were chemically analysed through XPS and XPSImaging techniques in order to ascertain the chemical composition of the interface layers. The results clearly indicate that a true chemico-physical interaction between brick and lime is present in the historical materials. A calcium carbonate accumulation has been observed at the brickmortar interface.

The hydrido-1,3-di- p -tolyltriazenido complex of platinum(II) trans -[Pt(PPh 3 ) 2 H( p -CH 3 C 6 H 4 NNNC 6 H 4 CH 3 - p )] reacts with CO, 2,6-Me 2 C 6 H 3 NC, PPh 3 and PhCCPh under mild conditions to yield platinum(0) complexes by reductive elimination of 1,3-di- p -tolyltriazene.

In the present study several cleaning procedures were taken into account: microblasting, ammonium carbonate, EDTA, etc. The various cleaning procedures were applied to Venetian Istria stone manufacture. The performance evaluation of the various procedures employed was accomplished by measuring the following significant parameters, before and after treatment: colour change through the CIELab method, surface morphology through a fiber optical microscope (MFO) and analysis of the different chemical action of the employed procedures.

Summarization: Samples of Istria stone were exposed in rain-washed conditions for 6 and 18 months, in the industrial and marine environment of Venice. To assess the initial stages of weathering, the exposed samples were analyzed by using X-ray photoelectron spectroscopy (XPS) and other analytical techniques, such as Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy coupled with energy dispersive X-ray analysis (SEM–EDS). Within a 6-month period, XPS revealed the deposition of sulfates, calcium silicates, carbonaceous particles, nitrogen compounds and organic compounds of lead, fluorine and chlorine. After an 18-month exposure period, the exposed surface exhibited pollutant compounds of sulfates, fluorine and nitrogen along with new-formed pollutant compounds of phosphorus and zinc. The appearance of silicon, aluminum and iron compounds indicates either dissolution of the argillaceous inclusions of the carbonate matrix or deposition of air-borne particles. The other applied analytical techniques evidence alteration features related more to morphological modification and less to chemical changes. Therefore, XPS revealing deposition of typical components of atmospheric pollution, as well as either deposition or dissolution of soil-derived and intrinsic elements evidences the initial weathering rate of exposed Istria stone to rain action. Παρουσιάστηκε στο: Journal of Cultural Heritage