A. Moropoulou

Investigation of the technology of historic mortars

Abstract Historical evidence on the use of mortars to meet several needs has existed for millennia. With reference to the characteristic historical periods of the city of Rhodes, mortar sampling was performed on historical constructions, masonry and architectural surfaces. In the present work the different mortar technologies are investigated aiming to answer questions regarding their finality, i.e. whether their differences arise mainly from the various historical periods of construction or from the purposes they had to serve, imparting to the mortars the properties required by their function in the structure. Mineralogical, chemical, physical and mechanical investigations have been performed on characteristic samples after gradation. The exponentially declining function of the ratio CO 2 /H 2 O structurally bound to the CO 2 content shows a continuous evolution of the kinetics governing the various mechanisms of carbonation of the binder or the formation of hydraulic components during setting, hardening and ageing of the mortars. The grouping of mortars in well-distinct ‘hydraulic levels’ is ascribed to the physico-chemical cohesion and adhesion bonds developed at the matrix and matrix/aggregate interfaces, respectively, allowing for the mortars to either bear continuous stresses and strains as joint mortars or provide compact impermeable renderings which harden even more on contact with water. Hence, parameters determining the diversification of the resulting mortar/matrix types concern the raw materials employed as binding materials and the production processing.

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.

Physico-chemical study of Cretan ancient mortars

Mortars from monuments of various periods in Crete, from Minoan up to now, have been studied (concerning mineralogical and chemical composition, grain size distribution, raw materials, tensile strength) in order to assess their durability in a marine and humid environment. The lime technology and raw materials, irrespective of the various historic periods, diversify the final composites into mortars, such as: (a) lime, (b) hydraulic lime, (c) lime with crushed brick, and (d) lime with pozzolanic material. These present binders in quantities ranging from 22% (pozzolanic mortars) to 29% (lime mortars). Hydraulic compounds, such as calcium silicate/aluminate hydrates, and tensile strength are higher in the pozzolanic mortars followed by crushed brick lime, hydraulic lime, and lime mortars. High quantities of water-soluble salts identified in the lime mortars indicate their risk of disintegration. A calculation procedure is presented herein, based on the combination of mineralogical and chemical analyses that allows the determination of the binder/aggregate proportion.

Emissivity considerations in building thermography

Abstract In the last 25 years, there have been considerable efforts put into the use and development of infrared thermography on buildings and large structures. As a result, nowadays, there are systems that can be used effectively in outdoor and/or indoor building surveys; indication and monitoring of problems such as voids, detached areas, deposits of humidity, etc. However, the principal problem where infrared thermographic measurements are concerned is the emissivity—emittance of the material(s). Given that an infrared camera detects the radiation emitted by a material under investigation and renders this energy to a temperature—thermal image, the feature that describes the relation between the emitted radiation and the material’s temperature, is termed as emissivity. Emissivity is actually a surface property that states the ability of the investigated material to emit energy. Correct emissivity values could provide valuable information concerning the interpretation of thermal images obtained from thermographic surveys. There is a considerable amount of work that has been published on emissivity of different materials and under various circumstances (i.e. temperature, surface condition, wavelength). In this work, a review on emissivity measurement techniques and the importance of emissivity values on building diagnostics was materialised. Furthermore, the emissivity of selected building materials were determined at a variety of temperatures, in the mid and long wavelength regions of the infrared spectrum, using different approaches and were discussed and explained in terms of the approach used, the wavelength and temperature effects, as well as the materials surface state.

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.

Origin and growth of weathering crusts on ancient marbles in industrial atmosphere

Abstract The origin and growth of weathering crusts on the ancient marbles of ruins of the Sanctuary of Demeter in the industrial atmosphere of Eleusis in Greece have been investigated. A systematic mineralogical, petrographical and chemical examination of weathered stones and crusts was performed, both in situ and in the lab, on samples taken from different parts of the monument in relation to the surface characteristics as well as to the exposure to rain, sea-salt spray and wet and dry deposition of airborne pollutants and dust. In particular, the various material–environment interactions take place, are characterized by (a) disintegrated “washed-out” surfaces, where products are taken away through dissolution, (b) rusty yellow patinas rich in Fe and Cu, (c) firmly attached black crusts in contact with percolating water, where recrystallized calcite shields amorphous deposits rich in S, Si, Fe and carbonaceous particles, (d) black loose deposits in the water sheltered areas, consisting mainly of gypsum and fly ash particles and (e) cementitious crusts, coating and pitting the horizontal surfaces. Moreover, an interconnected evolution of various physicochemical processes is shown, characteristic of the origin and growth of various crusts, which are formed and classified accordingly.

The effects of limestone characteristics and calcination temperature to the reactivity of the quicklime

Abstract This study has examined the effects of limestone characteristics (microstructure and texture) and calcination temperature on the reactivity of the produced quicklime. Two types of limestone have been calcined at four selected temperatures (900°C, 1000°C, 1100°C, 1200°C), and the produced quicklime was slaked. Chemical, physical, and mineralogical analyses have been performed in limestone, quicklime, and slaked lime samples with the intention of studying the quicklime reactivity. Test results indicate that the lower the limestone calcination temperature, the more reactive the produced quicklime. The optimum calcination temperature is ∼900°C, which was the temperature performed in traditional limekilns. Concerning the quicklime, the reactivity is related to its microstructure, which is, in turn, related to microstructural characteristics of the limestone (texture, grain size, porosity). The most reliable factors for the estimation of quicklime reactivity are the specific surface area of the quicklime and the rate of temperature increase during the slaking process.

Correlation of physicochemical and mechanical properties of historical mortars and classification by multivariate statistics

Abstract This work uses multivariate statistics in an attempt to classify historical mortars in more or less distinct groups, depending on their physicochemical characteristics. Four types of mortars are studied: “typical lime,” “cementitious,” “crushed brick” and Portland cement. Fifty samples in total were analysed by thermal analyses (differential thermal analysis [DTA] and thermogravimetric analysis [TGA]), mercury intrusion porosimetry and mechanical strength tests. The results give us useful information on the understanding of the technology of historical mortars and planning syntheses for restoration ones. The inverse hydraulicity ratio (CO 2 /structurally bound water, SBW) is correlated to CO 2 content (%) as measured by thermal analysis. The tensile strength increases with the amount of hydrated phases and the mechanical properties of the aggregate and the binder. Medians, ranges and extremely rare values were determined for each property showing compact groups. These groups were discriminated by principal component analysis (PCA) giving a tool for characterisation of historical mortars.

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.

Oxidation and Resulting Mechanical Properties of Ni/8Y2O3-stabilized Zirconia Anode Substrate for Solid-oxide Fuel Cells

Ni/8 mol% Y 2 O 3 -stabilized zirconia cermets are used in thin-film electrolyte solid-oxide fuel cells as support substrates. Rapid oxidation of the metallic Ni can cause failure of the substrate and of the whole system. The rate of Ni oxidation in air and in an inert atmosphere containing water vapor was determined as a function of temperature between 500 and 950 °C. A logarithmic rate law describes the oxidation kinetics in air, whereas a linear rate law fits the first branch of the curve of the experimental data in a humidified inert atmosphere. The substrate exhibits no significant mechanical degradation after uniform oxidation under moderate conditions. However, the observed bending of the samples after oxidation in humidified argon, due to the nonuniform oxidation, can cause damage to fuel cell.