K. Bisbikou

Characterization of ancient, byzantine and later historic mortars by thermal and X-ray diffraction techniques☆

The characterization of mortar properties can be accomplished by the use of thermal analysis. DTA can be used to identify various component materials and observe the reactions associated with controlled heating of the mortar. This method reveals thermal transformations, which include dehydration, dehydroxylation, oxidation and decomposition. In addition, crystalline transitions can be observed, which are exothermic or endothermic in nature. With TGA, thermogravimetric analysis, the mass of the sample is monitored (weight loss) as a function of temperature. Weight losses at reaction temperatures near 750°C, indicate loss of CO2 not from pure CaCO3, but from recarbonated lime. The dehydroxylated clays acted as a “pozzolan” which imparts early strength to the mortar. However, a more complex phenomenon occurs in crushed brick mortar, since compounds of hydraulic type occur at the brick matrix interface also. The DTA and TG-DTG analyses identify the dehydration of calcium alumino-silicate phases, giving clear evidence of a cementitious mortar rather than one of pure lime. In the present work a spectrum of thermal and XRD analysis results from ancient, Byzantine, post-Byzantine and later historic mortars from Greece is presented and the relevant information concerning the characterization of traditional mortars is validated Generally, the CO2 bound to carbonates and the water bound to hydraulic components (in weight loss%) discern two groups of mortars, the typical lime and the hydraulic, respectively. The specific classification of mortars into groups with characteristic transformations indicated by weight loss against temperature, enables discernment of: typical lime, cementitious, with crushed brick, with portlandite, with gypsum, with modern cement or of hot lime technology, mortars. Mineralogical, microstructural, mechanical and technological data could provide further evaluation criteria.

Thermal analysis as a method of characterizing ancient ceramic technologies

Abstract Ceramic materials represent manufacturing techniques which were improved consistently during the course of time. The components of ceramic materials are the “fingerprint” of the stable and/or metastable solid phases formed during the firing; the production processes of antique ceramics and pottery can be derived from their assemblage. There are many recognizable phases and their association depends, more than on their chemistry, upon the mineralogy of the raw materials, their grain-size distribution, maximum heating temperature, heating ratio, duration of firing and kiln redox atmosphere. All these factors help in understanding the “course” of reactions. Heating also affects the contact between the fine-sized clayey matrix and mineral clast fragments, appearing in reaction rims, sometimes showing newly-formed phases. The temperature at which ancient ceramics and pottery were fired varies over a wide range (600–1300°C) depending on the type of clay used and the kiln available, although firing temperatures not above 300–400°C have also been suggested. Clay minerals, as the main material for production of ceramics and pottery, show some characteristic reactions (dehydroxylation, decomposition, transformation) in the course of firing (heating effects) and several thermoanalytical criteria can be used for reconstruction of former production conditions. In the present work DTA, TGA and XRD results from byzantine and medieval ceramics are examined and information derived on ceramic technologies concerning raw materials and production conditions is validated by SEM observations concerning the extent of vitrification, as well as by the microstructural data provided by porosimetric measurements.

Physico-chemical adhesion and cohesion bonds in joint mortars imparting durability to the historic structures

Abstract It is well known that even though historic mortars present low strength and elastic moduli they confer durability to the structures surviving today. The present work investigates the durability of historic mortars in relation to the production technologies employed. Thermal analysis allows for classification of historic mortars in both lime and hydraulic types. Mineralogical data, concerning fabrication and texture, along with thermal analysis provide criteria on specific classification, for: typical lime, crushed brick–lime, cementitious, rubble masonry, hot lime technology and gypsum mortars. The correlation of the measured tensile strength (fmt, k ) with the estimated CO 2 /structurally bound water ratio, indicates direct proportionality to the levels of the hydraulicity. Physico-chemical adhesion and cohesion bonds, studied by SEM-TEM/EDX, developed at the matrix and at the binder/aggregate interface, respectively, becomes the key factor in interpreting the considerable durability that the historic mortars confer to the structures as bearing elements.

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.

Cholesteric liquid crystals as weathering indicators for marble surfaces

Cholesteric liquid crystals have been used to study the weathered surfaces of marble from the Sanctuary of Demeter in Eleusis, near Athens. Previous investigations have shown that when a cholesteric phase is spread across the surface of the stone, the pitch of the mesophase is sensitive to the topography of the surface. The wavelength of the maximum in the reflected spectrum varies therefore with the microtexture of the surface. Small samples of surface stone from the temple which had been weathered in distinctive ways, were investigated in the laboratory. There appears to be a significant correlation between the optical reflectance spectra and the surface microtopography investigated by SEM, as indicated by computer aided analysis (Digital Image Processing). The results point to the development of an effective in situ method of monitoring the weathering of marble surfaces using cholesteric liquid crystals.

Properties And Technology Of The CrushedBrick Mortars Of Hagia Sophia

Within the framework of the collaboration between Princeton University, the National Technical University of Athens, and Bogazici University, the present work deals with material analyses of small samples taken from Hagia Sophia, a sixth century masonry edifice, in Istanbul, Turkey, coordinated with structural studies to provide insight to the structures ability to withstand seismic loads. The present work is based on the methods of X-ray diffraction analysis and thermogravimetric analysis performed both on the samples themselves and on their fractions after a physical separation. The results account for a possible technology of a pozzolanic mortar, where one part per volume lime was mixed with 3 parts of aggregate (crushed brick fragments, sea sand, and fine pozzolanic sand). However, up to now, analytical techniques cannot provide directly technology information, let alone on the physicochemical interactions among the constituents of historic walls, as in the case under study. Hence, a reverse engineering approach is needed to reveal traditional technologies for the production of restoration mortars, simulating byzantine technologies. Consequently, restoration mortars resembling the original ones should be provided instead of the modern cement mixtures.

Stability And Materials WeatheringConditions At The Symonos Petra MonasteryOf Mount Athos, Greece. PreliminaryApproach

The Monastery of Symonos Petra, located in Athos mountain (Greece) was built, the first, around 1257 AC by the Blessed Symon, burnt down in 1891 AC and partially rebuilt. Today, 100 years after its burning down, national interest is attracted on restoration and conservation of that valuable piece of Byzantine cultural heritage. In the present work stability and materials weathering conditions are under study. Materials characterization analysis, as well as a first macroscopic and microscopic estimation of weathering problems were performed. Samples of mortars, as the critical factor of the masonry strength, were studied, regarding their origin and resistance to weathering. The present study concerns the slope stability conditions of the rockmass where the monastery is built as well. It is a preliminary investigation, thus no definitive results can be formulated at this moment.