Guido Biscontin

Advanced Byzantine cement based composites resisting earthquake stresses: the crushed brick/lime mortars of Justinian's Hagia Sophia

Abstract Structural studies to determine the earthquake worthiness of Hagia Sophia in Istanbul have proved that the monuments 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.

Characterization of binders employed in the manufacture of Venetian historical mortars

Abstract This research focuses on the characterization of historical mortars collected from a covered dockyard, called tezone 105, erected in the Arsenal of Venice during the XVI century. The mortars date back to different building phases. A stratigraphical analysis of tezone 105 has proposed a chronology of building interventions. The building phases recognized by the stratigraphical analysis belong to the original structure (XVI century) and to later interventions from XVI to XX century. Mortar samples are investigated by granulometric analysis, infrared spectroscopy (FT-IR), simultaneous thermal analysis (DSC/TG) and X-ray diffraction analysis (XRD) in order to identify the technology peculiar of each building phase. Mortar sampling was carried out on indoor masonry and foundation. Masonry mortars appeared to be characterized by the application of air-hardening binders, whereas foundation mortars were characterized by hydraulic binders.

Thermoanalytical research on traditional mortars in venice

Abstract The study of traditional mortars has recently been attracting considerable attention, in connection with both diagnosis and applications required for restoration. The mortar is only apparently a simple system; in reality the lime is often accompanied by hydraulic components. The inerts often interact with the binder and the technologies used in the application are very diversified. These situations make the study of the mixtures rather complex, as it is difficult to distinguish the neoformation compounds from the older ones. A basic approach is offered by granulometric analysis, allowing separation of the mortar into its components, in which the finer fraction is richer in binder. Some analyses on this fraction ( μ m) were performed to define the nature and quantity of the binder in the mortar. Samples were taken from various sites in Venice and were examined by calcimetry, TG-DTG and FTIR analysis. Moreover the investigation of this fraction by optical microscopy enabled us to distinguish the binder from the inert particles.

Characterization of the lumps in the mortars of historic masonry

The present work focuses on the investigation of mortar joints of historic masonries consisting traditionally of aerial binder and inerts which contain lumps. The presence of lumps, usually white in colour and of various dimensions, was often recorded inside these mixtures and does not appear to be random, as they are rather frequent, These lumps could confer some physicochemical properties to the mixture, that favour the overall compatibility of the system. For this purpose, various samples taken from historic Venetian masonry were examined by TG-DTG and FTIR analysis. Moreover SEM and fibre optical microscope observations were performed. The results indicate mainly the presence of completely carbonated lime and lead us to assume that the lumps arise from technologies based on the non-seasoning of the lime.

Interaction between clay and lime in “cocciopesto” mortars: a study by 29Si MAS spectroscopy

Abstract 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.

Hot lime technology imparting high strength to historic mortars

Abstract In previous works the mineralogical and physico-chemical properties of crushed brick-lime mortars in response to stresses, simulating earthquakes or dynamic soil structure interactions, were studied. It was proved that the effective mechanical properties of the mortars could be attributed to the alkali-silicate reactions occurring at the brick fragment-lime interface. Since the category of the pozzolanic mortars presents a wide spectrum, spanning from the crushed brick to various cementitious mortars, the idea was to study the effectiveness of other hydraulic mortars as well. The Symonos Petra Monastery at Mount Athos was selected for investigation as pilot monument, because in our previous works it was found to be scientifically sound. The mortars were analysed following a procedure correlating chemical and instrumental analysis to determine CaCo 3 CaOsil . TA, IR, SEM and EDX were performed and tensile strength and adhesion was measured. The amounts of Ca ++ and Mg ++ were determined by AAS. Old mortars, from the Arsenal tower (16th c.) present higher tensile strengths than traditional hydraulic lime mortars and are effective against dynamic stresses exerted onto the greater Serbomacedonian mass as well as against the intense marine environment. Fine ground magnesium-alumino-silicate dust of the montmorillonitic clays in the area could have been mixed in a ratio of 2 ( 1 5 ) of lime/‘pozzolanic’ or active clay admixtures/inert aggregates reacted with the in situ slaked lime, their hydraulic components augmenting considerably with Mg ++ . Hence Arsenal mortars present an intermediary between Roman and modern concrete for marine structures produced by hot lime technology.

Effects of condensed water on limestone surfaces in a marine environment

Abstract We have evaluated the effects of condensed water on limestone surfaces through a procedure that foresaw the cooling of the samples before their exposition to the open air, so that the condensation phenomena could occur easily. The effects of the condensed water were evaluated by measuring the weight change of the samples, through SEM observations and analysis of the 3-D profile, using laser profilometer. The results show the weak action of condensed water on the stone surface, particularly if compared with that of rain.

Chemico-Physical Interactions Among the Constituents of Historical Walls in Venice

Investigates the possible chemical interactions between the constituents of historic walls. In Venice, but also in the whole Mediterranean area, the cocciopesto (consisting of brick and powder fragments which traditionally confer hydraulic properties to the mortar) has been widely employed both for mortars and the so-called marmorino plasters. An examination of the brick-mortar interaction on historic buildings in Venice was carried out. The samples were chemically analyzed through x-ray photoelectron spectroscopy (XPS) and XPS-imaging techniques in order to ascertain the chemical composition of the interface layers. The results clearly indicate that a true physicochemical interaction between brick and lime is present in the historic materials. A calcium carbonate accumulation has been observed at the brick-mortar interface. -- AATA

Crushed brick / lime mortars of Justinian's Hagia Sophia

Structural studies to determine the earthquake worthiness of Hagia Sophia in Istanbul have proved that the monuments static and dynamic behaviour depends very strongly on the mechanical and chemical properties of these mortars and bricks used in its masonry. So, the cementitious nature of the mortars not only explains the fact that the monument still stands but also the very large static deformations which it has undergone. According to the analysis of the dynamic data, the strong motion data froma 4.8R magnitude earthquake about 120 km south of the building was used to determine the first three natural frequencies of the building. These results show a decrease of about 5-10 percent in the natural frequencies, as the amplitude of the accelerations increases and returns to their initial value, due to the non-linmear nature of the masonry. The above mentioned behaviour allows the structure to absorb energy without effecting its materrial properties, irreversibly. The properties of the mortars and bricks leaded to an extensive study. The results indicated mortars with considerable mechanical strength along with longevity. The model used proved to be resistant to the environmental pollution and to the presence of salt, while the gel phase as binder allows for greater energy absorption and the compatibility of the mortar to the original ones allows continuous stresses and strains. Hence, the recreation of the Hagia Sophia is attempted through a reverse engineering approach to simulate the historical mortars.

Tangible versus intangible in e-learning on cultural heritage : from online learning to on-site study of historic sites

The revolutionary development in digital theory and technology calls for non-trivial decisions in bridging between the virtual and real worlds. The field of conservation of cultural heritage thus provides various challenges, especially with regards to learning, study and investigation of tangible heritage through applications of intangible ICT technologies. This paper examines the interaction between e-learning, and the actual on-site learning and study of historic buildings and sites, with an emphasis on their visual characteristics. In this context, the paper presents some aspects of application of a methodology which allows basic documentation, monitoring and primary analysis of data on cultural (built) heritage sites by general public through educational process enabled by an e-learning platform.