Rendre compatible les techniques traditionnelles et les modernes ...

Rendre compatible les techniques traditionnelles et les modernesCompatibilizar técnicas tradicionales y modernasCombining traditional and modern techniquesReproduction of hydraulic lime mortarsbased on the traditional productiontechnology of ancient mortarsfrom CyprusI. Ioannou, M. Philokyprou, G. Papadouris, K. KyriakouIoannis Ioannou is a lecturer at the Department of Civil and EnvironmentalEngineering of the University of Cyprus. His research interestslie in the field of traditional building materials technology. His workfocuses on the characterisation of mortars, stone and brick. He isparticularly interested in water-mediated processes affecting theweathering of masonry materials and methods for the protection andrestoration of cultural heritage monuments.Address:75 Kallipoleos Str., P.O. Box 20537, 1678 Nicosia, CyprusE-mail:ioannis@ucy.ac.cyTelephone:+357 22 89 2257IntroductionUntil the beginning of the 19 th century, mud, air hardening lime,hydraulic lime and lime mixed with natural or artificial pozzolanas (e.g.crushed brick) were the most popular binders and renders used inthe construction of buildings. After the discovery of Portland cementin 1824, the latter and its derivatives became the dominant bindingand rendering materials in the building industry, mostly due to thestandardisation of their production [1]. As a result, during the lastcentury, there has been a gradual replacement of traditional mortarsby highly hydraulic cement-based mortars.The uncontrolled use of cement-based mortars for restoration purposesresulted, in many cases, in extensive damage to cultural heritage,mainly because of their incompatibility with the traditional material [2-8]. Cement is hard, rigid and impermeable. It also contains significantamounts of soluble salts which can be harmful to historic buildings.These salts not only produce non-aesthetic efflorescences uponcrystallisation on the façade of a building, but they can also developlarge damaging pressures when they crystallise behind the surfaces ofmasonry materials.Reported damage cases, together with the principle of “authenticity”,defined in the ICOMOS Venice Charter [9], resulted in a renewedinterest in the use of (hydraulic) lime mortars in the field of restoration.In the research study described in this paper, a physicochemicalcharacterisation of ancient mortar samples from Cyprus wasundertaken in order to find out the provenance of their raw materialsand to determine their composition and properties. An experimentalstudy was also carried out to design compatible mortars for restorationand conservation purposes.Materials and MethodsMortar sampling was performed on excavations, monuments andtraditional buildings. Part of each sample was ground and used for X-ray diffraction (XRD) and X-ray florescence (XRF) analyses to identifymineral constituents and to determine quantitatively the major oxidespresent in the mortars. A slice was used for the preparation of a thinsection which was used for petrographic examination of the mortars.A scanning electron microscope (SEM), equipped with an EnergyDispersive X-ray (EDX) microanalyser, was also used to examine themicrostructure and texture of the mortars, while a significant group of15 samples underwent thermal analyses (DTA/TG) to determine theirhydraulicity. The most important physical properties of the ancientmortars (i.e. vacuum saturation porosity and capillary absorptioncoefficient) were also measured using water as the wetting liquid.The analytical study of ancient mortar samples was followed by thelaboratory preparation and testing of experimental mortars withsimilar compositions. The laboratory mixes were prepared using awater/binder (w/b) ratio enabling the mortar to achieve a constantflow of 165 ± 10 mm. The proportion of binder (lime and ceramicpowder) to aggregates was equal to 1:3 w/w. This was selected as theproper mixture ratio for restoration syntheses since it is matching withtechnologies of homologous mortars found in ancient monuments ofthe wider Mediterranean area [6, 10-11].In all experimental samples, the aggregates comprised siliceous andcalcareous sands. The mixing of the aggregates and binder with tapwater was mechanical and always uniform. Compaction of the sampleswas carried out in accordance to EN 196-1:1995 [12]. It was consideredcritical to use the same batch preparation for all specimens to avoid anydifferences which might occur from batch to batch. Such differenceshave been shown to exist for hydraulic mortars in previous studies [13].The samples were prepared using standardised prismatic steel moulds ofdimensions 40 x 40 x 160 mm. After casting, the moulds containing thespecimens were covered with a glass plate to prevent loss of water byevaporation. Specimens were removed from the moulds after 7 days andthey were kept covered with a wet burlap until testing. The performanceefficiency of the experimental mortars was evaluated by a series of testsdesigned to measure their physical and mechanical properties.Results and DiscussionCharacterisation of ancient mortarsLaboratory examination of the ancient mortars under a stereoscoperevealed in most samples the presence of small (angular, sub-angularand rounded) reddish inclusions in a compact (fine-grained) matrix(Fig. 1). These inclusions were identified by SEM/EDX analysis as regionsof silica-alumina composition (i.e. clay brick ceramic).Petrographic observations provided evidence that the mortars mostlyconsisted of fine to medium aggregates of quartz, feldspars, pyroxeneand plagioclase. Carbonate compounds and broken shells were alsoobserved in some samples.Microscopic observations also provided ample evidence of productsof boundary reactions. Reaction rims were observed at the interfacebetween the binding matrix and the ceramic fragments. These weredispersed in the form of veins along the matrix, filling the vacancies and552