Marco Lezzerini

The mortar of the “Leaning Tower” of Pisa the product of a medieval technique for preparing high-strength mortars

Thirty mortar samples from the “Leaning Tower” of Pisa were examined. The specimens include mortars from both the first (1173-1178) and second (1272-1278) stages of Towers construction. The mineralogical, petrographical, chemical and physical data collected on the bulk mortar and its binder show that the famous “Leaning Tower” of Pisa was built through the constant use of a high-quality hydraulic mortar (average compressive strength about 16 N/mm2; average binder SiO2 content about 29%) as the binding agent for the “infill” masonry. Although a great deal of variability exists in the values of each measured property, even amongst samples from the same stage of construction, the averaged values for the foundations and the above-ground structures erected during the two distinct construction stages are highly uniform. The most conspicuous differences lie in the sand content and granulometry, which are respectively greatest and coarsest on the foundation mortars. Chemical and mineralogical data suggest that the Tower mortar was prepared by mixing slaked lime, obtained from an almost pure limestone, with sand from Arno and Serchio Rivers alluvium and a diatomaceous earth, probably quarried at Mt. Amiata, about 180 km to the south of Pisa. It is estimated that the construction of the Tower from the foundations to the top of the 7th storey (the belfry, added to the main structure only around 1365, is not considered here) required the use of about 1400 tons of slaked lime (assuming 60% water content), 1350 tons of sand and 400 tons of diatomite.

On the binder of some ancient mortars

SummaryAbout 90 samples of mortars from historical buildings in Pisa have been analysed and compared with some samples of ancient mortars characterized by pozzolanic aggregates. Chemical (XRF), mineralogical (XRD) and petrographical (optical microscopy) data have been collected on bulk samples. An X-ray energy-dispersive system (EDS) attached to a SEM was used to determine the chemical compositions of binder, clots and pozzolanic grains (whenever present). The binder components which could not be directly assessed (CO2, H2O+) have been indirectly derived through a computation method.Data collected suggest that the main stock of analysed samples (i.e., mortars from Pisa monuments) contains two principal types of binder: the first type corresponds to a common carbonated lime; the second type is a hydraulic lime, where the carbonate component is associated with an important silicate fraction, which constitutes 13 to 89 wt% of the total binder (on average 47%). This hydraulic type had a widespread application in the construction of ancient monuments in Pisa; for example, it was constantly employed in the building of the famous “Leaning Tower”. This study shows that the silicate fraction of such hydraulic mortar, which is amorphous to X-ray diffraction, is made up by a hydrated calcium alumino-silicate having a very low Al2O3/SiO2 ratio (on average 0.125). On the basis of chemical and optical characteristics of hydraulic mortar binders from Pisa and the results of laboratory tests, as well as through comparison with the characteristics of ancient hydraulic mortars having pozzolanic aggregates, it is concluded that such mortars were prepared most likely by mixing slaked lime with a reactive, highly siliceous material such as a diatomaceous earth.ZusammenfassungEtwa 90 Mörtelproben von historischen Gebäuden in Pisa wurden analysiert und mit Proben von antiken Mörteln, die durch pozzolanische Aggregate charakterisert sind, verglichen. Chemische (XRF), mineralogische (XRD) und petrographische (optische Mikroskopie) Daten wurden an den Gesamtproben ermittelt. Ein an ein SEM angeschlossenes energiedispersives System (EDS) wurde für die Bestimmung der chemischen Zusammensetzung des Bindemittels, der Mörtelklümpchen und der pozzolanischen Körner (sofern vorhanden) verwendet. Die Komponenten des Bindemittels, die nicht direkt gemessen werden konnten (CO2, H2O+) wurden indirekt durch ein Berechnungsverfahren ermittelt.Die gesammelten Daten belegen, dass die meisten untersuchten Proben (i.e. Mörtel von Monumenten aus Pisa) zwei Typen von Bindemittel enthalten: Der erste Typ entspricht einem gewöhnlichen karbonatisierten Kalk. Der zweite Typ ist ein hydraulischer Kalk, in dem die Karbonatkomponente mit einer mengenmäßig bedeutenden Silikatfraktion assoziiert ist, die 13–89 Gew.% des gesamten Bindemittels ausmachen kann (durchschnittlich 47%). Dieser zweite Typ wurde häufig beim Bau alter Monumente in Pisa verwendet, z.B. wurde er ständig beim Bau des Schiefen Turms herangezogen. Diese Studie zeigt, dass die Silikatfraktion dieses hydraulischen Mörtels, die röntgenamorph ist, aus einem hydratisierten Aluminosilikat mit einem niedrigen Al2O3/SiO2 Verhältnis (im Durchschnitt 0.125) besteht.Auf Basis der chemischen und optischen Charakteristika des hydraulischen Mörtel, die pozzolanische Aggregate führen, schließen wir, dass diese Mörtel höchstwahrschein lich durch Mischung von Löschkalk mit sehr reaktivem, silikatischen Material, wie etwa Diatomeenerde hergestellt wurden.

Hydric dilatation of ignimbritic stones used in the church of Santa Maria di Otti(Oschiri, northern Sardinia, Italy)

In the historical buildings of eastern Logudoro (northern Sardinia), as well as in large areas of western Sardinia, ignimbritic rocks are widely used for ashlars and architectural elements as architraves, pedestals, shafts and capitals of columns. The decay processes affecting these rocks cause a progressive disintegration of the stone ashlars, with loss of material by exfoliation and flaking that determine a progressive retraction of the external profile of the facade with obliteration of the decorative elements. New data on the linear dilatation due to water absorption of these volcanic rocks are presented in this study in order to contribute to the evaluation of the impact of hydric dilatation in the stone degradation. The relationships among linear hydric dilatation of ignimbritic samples and petrographic and mineralogical characteristics as well as physical properties (texture, welding degree, porosity) indicate that three lithotypes with different behaviour in the water absorption can be distinguished in the ignimbrite rocks used as building stones in the church of Santa Maria di Otti (Oschiri, northern Sardinia, Italy). Although the linear hydric dilatation of the ignimbrites is moderate to low, we suggest that hydric dilatation may be an additional factor in enhancing the decay of the stones of the Santa Maria di Otti church.

Cultural Heritage Documentation and Conservation: Three-Dimensional (3D) Laser Scanning and Geographical Information System (GIS) Techniques for Thematic Mapping of Facade Stonework of St. Nicholas Church (Pisa, Italy)

ABSTRACT This article reports the mapping of the stones, including marbles and brick masonry, used for building the facade of the medieval Church of St. Nicholas (XI century ad), one of the most interesting churches in Pisa, due also to the nearby famous octagonal bell tower. Mapping of stone materials was performed using a computer-aided design (CAD)/geographical information system (GIS) software package for storing and processing spatial information of the ashlars, obtained using three-dimensional (3D) laser-scanning data, combined with high-resolution images, and stone-to-stone observations. Based on collected data, the facade of the Church of St. Nicholas appeared mostly composed of rocks belonging to the metamorphic Tuscan sequence, quartzites, and marbles from Mt. Pisano area. Other types of rocks were also observed, as black limestones quarried at some kilometers northwest from Pisa in the Monti d’Oltre Serchio area, white Apuan marbles and Macigno sandstones. Conversely, intarsia appeared mainly made up of serpentinite and, subordinately, red limestones laid in white Apuan and Mt. Pisano marbles.

Relationships between mineralogical composition, water absorption and hydric dilatation in the “Macigno” sandstones from Lunigiana (Massa, Tuscany)

Despite its good technical properties, the “Macigno” sandstone undergoes a typical process of decay when used outdoor, consisting prevalently in a flaking of the stone surface with detachment of rock fragments. In order to understand the causes of this decay, the relationships between mineralogy and physical rock properties were investigated. Twenty-six rock samples were collected from quarries situated near the villages of Fivizzano and Pontremoli (the Lunigiana area of northwestern Tuscany, Italy) and examined for their chemical (XRF), mineralogical (XRPD) and petrographic (optical microscopy) characteristics, as well as physical properties such as real and bulk densities, water absorption capacity and linear dilatation coefficient of water-saturated samples. The phyllosilicate minerals of the sandstone were studied on oriented aggregates of the <4 μm fractions by X-ray powder diffraction, and their chemical composition determined by EDS microprobe analyses. The cationic exchange capacity (C.E.C.) was measured on fifteen selected samples. The studied sandstones are fine- to coarse-grained, arkoses and lithic arkoses whose colour ranges from grey to yellowish. The normative carbonate fraction consists essentially of calcite; its amount is generally low (<1–10%), with the exception of three samples collected in the Turlago-Labiano quarry, which contained calcite concentrations of up to 14, 15 and 38%, respectively. The normative non-carbonate fraction is made up of quartz (19–34%), K-feldspars (7–13%), plagioclase (14–33%), mica-like minerals (4–10%) and chlorite s.l. (5–26%). Mica-like minerals include muscovite (illite), minor amounts of biotite and sporadic illite/smectite mixed-layers (I/S). Chlorite s.l. includes chlorite s.s. and chlorite/smectite mixed-layer phases (Chl/S). The content of the sandstone smectitic component, predominantly associated to Chl/S, ranges from 1 to 7 (wt.%). C.E.C. varies from 2.4 to 11.1 meq/100g. Water absorption capacity (wt.% of dry samples) as well as hydric dilatation of the stone upon water saturation increase with increasing smectite content, indicating that this swelling component may play an important role in the “Macigno” sandstones decay.

Corrensite and chlorite-rich Chl-S mixed layers in sandstones from the `Macigno' Formation (northwestern Tuscany, Italy)

Abstract Corrensite and chlorite-rich chlorite-smectite (Chl-S) mixed-layers occurring in the Macigno Formation of northwestern Tuscany were investigated by XRPD/SEM techniques. The samples from the Macigno outcrops were affected by metamorphism corresponding to the highdiagenesis/ low-anchizone transition boundary. The basal spacing of corrensite measured from 00l reflections on EG-Mg2+-saturated samples ranges from 30.97 to 31.18 Å with a coefficient of variation (CV) of 0.46-0.77%, consistent with the rational pattern of a 1:1 Chl-S periodic stacking sequence. X-ray patterns of heated K+-saturated specimens reveal the presence of two types of corrensite, probably with different interlayer charges on their respective smectite-like layers. The chlorite-rich Chl-S mixed layers coexisting with corrensite consist of R2 chlorite (0.70-0.75)/S and chlorite (0.90)/S with long-range ordering R ≥ 1. SEM observations show that corrensite and chlorite-rich Chl-S mixed-layers are closely mixed on a sub-micron scale. Some grains of corrensite and chlorite-rich Chl-S mixed-layers include zones (2-10 μm) of chlorite composition, as shown by microprobe analyses.

The volcanic rocks of Easter Island (Chile) and their use for the Moai sculptures

Easter Island (Chile) is a volcanic island made up entirely of volcanic rocks, which are represented by lava flows and domes as well as cinder and scoria pyroclastic cones, covering the entire compositional range from basalts to peralkaline rhyolites. Apart from representing a cultural heritage of worldwide importance, the megalithic Moai statues of Easter Island are an exquisite example of the utilisation of a variety of volcanic rocks in sculpture. This work illustrates the spectrum of volcanic litho-types available to the islanders through new chemical and petrographic data and presents chemical, mineralogical, petrographic and physical data on the rocks from the same volcanic deposits used for fashioning the megalithic sculptures. The stones used for the statues and their topknots are represented by volcanic rocks with different depositional mechanisms and chemical compositions. They include tuffs deposited in water, subaerial welded scoriae, lava flows and lava domes, with composi- tions ranging from basalt to trachyte. Despite such variations, they all share rather high total porosity, and are all easily workable stones. Their low apparent density seems to be the critical factor in enabling such large statues to be fashioned. The rest of the volcanic rocks on the island were unsuitable for building megalithic sculptures for various reasons: they are either too heavy, as is the case of the basaltic lavas, or too fragile, as the obsidian, or too loose, as the unconsolidated tuff and scoria cones. The rocks used for the platforms and altars are lavas whose compositions vary moderately, from basaltic to mugearitic, but which share similar physical and mechanical properties, well suited to building stable bases for the statues. The results of the study on the Rano Raraku tuff, employed in the great majority of the statues, show that it consists of a hyalotuff, in which volcanic glass was altered by interaction with sea water. The products of alteration vary in composition from nearly amorphous palagonite to crystalline smectite. The magma that erupted at Rano Raraku was originally mugearitic, and the high loss on ignition (LOI) and low alkali content of the rock, as well as its high clay content, are characteristics stemming from glass-sea water interactions during the deposit formation. The samples taken from the base, middle and top of the cone flank hosting the quarries show very similar composition of the bulk rock, the fresh glass and the palagonite products, suggesting homogeneous rock characteristics throughout the quarries.

Marbles from the Campiglia Marittima area (Tuscany, Italy)

The area surrounding the Tuscan municipality of Campiglia Marittima hosts widespread deposits of thermo-metamorphic marbles that were extensively used as a building and ornamental stones since the time of the Etruscans. The macroscopic characteristics of this class of marble, its chemical, mineralogical, petrographic features as well as the P-T conditions of metamorphic re-crystallisation, C and O stable isotope data and the main physical properties are presented in order to provide a solid basis for possible studies on the provenance and distribution of building stones from this terranes. With the aim to evaluate the effects of thermal stress on these marbles, apparent density and water absorption at atmospheric pressure were measured before and after thermal treatments. Based on a careful survey of the marbles used for building in the area, their uses and state of conservation have also been assessed.

Micro-Laser-Induced Breakdown Spectroscopy (Micro-LIBS) Study on Ancient Roman Mortars

The laser-induced breakdown spectroscopy (LIBS) technique was used for analyzing the composition of an ancient Roman mortar (5th century A.D.), exploiting an experimental setup which allows the determination of the compositions of binder and aggregate in few minutes, without the need for sample treatment. Four thousand LIBS spectra were acquired from an area of 10 mm2, with a 50 µm lateral resolution. The elements of interest in the mortar sample (H, C, O, Na, Mg, Al, Si, K, Ca, Ti, Mn, Fe) were detected and mapped. The collected data graphically shown as compositional images were interpreted using different statistical approaches for the determination of the chemical composition of the binder and aggregate fraction. The methods of false color imaging, blind separation, and self-organizing maps were applied and their results are discussed in this paper. In particular, the method based on the use of self-organizing maps gives well interpretable results in very short times, without any reduction in the dimensionality of the system.

Extracting Time-Resolved Information from Time-Integrated Laser-Induced Breakdown Spectra

Laser-induced breakdown spectroscopy (LIBS) data are characterized by a strong dependence on the acquisition time after the onset of the laser plasma. However, time-resolved broadband spectrometers are expensive and often not suitable for being used in portable LIBS instruments. In this paper we will show how the analysis of a series of LIBS spectra, taken at different delays after the laser pulse, allows the recovery of time-resolved spectral information. The comparison of such spectra is presented for the analysis of an aluminium alloy. The plasma parameters (electron temperature and number density) are evaluated, starting from the time-integrated and time-resolved spectra, respectively. The results are compared and discussed.