A. Bakolas

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.

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.

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.

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.

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.

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.