Historic Mortars Research Articles

The characterization of historic mortars: A comparison between powder diffraction and synchrotron radiation based X-ray absorption and X-ray fluorescence spectroscopy

Three mortar samples from different construction phases of the Cathedral of Paderborn (Germany) between ~ and ~1220AC have been investigated using three different and partly complementary techniques: conventional X-ray diffraction (XRD), synchrotron radiation based X-ray fluorescence (SR-XRF), and X-ray absorption near edge structure (XANES) spectroscopy. Samples were sieved and then investigated according to size: smaller and larger than 75μm. For the small samples XRD detected CaCO3 (calcite) and SiO2 (quartz) as the most abundant compounds and Na(AlSi3O8) (albite) as a minor component. No compounds containing transition metals (e.g. Fe) were observed by XRD. XRF results indicate just a marginal enrichment of binder compounds in the small samples as compared to the large ones. By XRF, in all samples Fe was observed at a very high concentration together with Ti and Zn at high concentrations and some other metals with lower concentration indicating that these metals are in an amorphous form and thus “invisible” for XRD. XANES spectra confirm the XRD result that most Ca exists as calcite, however at least in one sample (the “youngest” one) where the S-concentration is quite high also Ca(SO4) was detected via Ca–K and S–K-XANES spectra. Fe–K-XANES spectra indicated that Fe exists in the mortar samples with valency +3 as Fe2O3. Most likely, the SiO2 grains are coated with iron oxides that have a high adsorption capability for trace metals explaining in this way the XRF detection of several metals at low concentration.

Lime mortar and sacrificial protection of heritage stonework

Microstructural characteristics of historic Scottish sandstone and lime mortar are reviewed against the physical principles underlying the function of a desalination poultice. The functional role of lime mortar as a permanent poultice enhancing the durability of heritage masonry is presented. The materials’ porosities and pore size distributions are characterised using mercury intrusion porosimetry and validated through scanning electron microscopy. Key findings include the respective predominant pore ranges exhibited by lime mortar (c. 500–2000 nm) and sandstone (c. 10 000–25 000 nm), which together interact to invoke stonework’s unique response to moisture. A technical understanding of this sacrificial protection to stonework afforded by lime mortar is imperative to avoid the use of inappropriate materials. Such incompatible materials upset the mechanisms underlying the functional role of the mortar, leading to damage of heritage stonework. The optimal example set down by historic limes appears to be best replicated by the specification of lime mortars with a high degree of carbonation set, to which much of the predominant 500–2000 nm pore range formation is attributable.

Flos Tectorii degradation of mortars: An example of synergistic action between soluble salts and biodeteriogens

Abstract The definition of Flos Tectorii, originally suggested by F.S. Brancato in the 1980s’ (Brancato, 1986), refers to a unique form of deterioration identified on both aerial and hydraulic mortars used in the external walls of historic and contemporary buildings. It is clearly recognizable due to the development of peculiar concentric (occasionally sub-circular) macroscopic forms. At present, there is still a lack of information about the full interpretation of this phenomenon regarding the interaction between the different physicochemical and biological factors that lead to this particular type of degradation. The present study was aimed to examine whether the specific mineralogical and textural characteristics of plasters can promote or hinder the development of Flos Tectorii and, at the same time, to explore if the presence of biodeteriogens is involved in it. The analytical results seem to suggest that the chemical and mineralogical composition of historic mortars does not significantly influence the advance of this phenomenon. At the same time, the isolation of some Actinobacteria suggests that they could act as biodeteriogens in the presence of hygroscopic soluble salts, leading to selective intergranular decohesion of the affected material. Anyhow, the biodeteriogenic role of microorganisms needs to be further investigated.

Chemical Analysis of Historic Lime Mortars: Role of Sample Preparation

The characterization of historic lime mortars is crucial for many cultural heritage conservation issues. In this work, the characterization of a historical lime mortar is described. Samples for chemical analysis were obtained after different milling times and using the RILEM acid digestion method on several replicates. Qualitative and quantitative determination of phases in the mortar and in the residues after acid attack and the potential presence of CaCO3 polymorphs, were accomplished with X-ray powder diffraction. Results suggest that representativeness of the sample and the homogenisation, although not always achievable in conservation practice, are strongly affecting results.

Micro-destructive cutting techniques for the characterization of natural limestone

In every restoration project, knowledge of the mechanical properties of the original materials is considered essential for engineers, not only for the structural assessment of the monument, but also for the selection of compatible restoration materials. In the case of mortars, however, direct or indirect determination of their mechanical properties is usually challenging, due to the limited size and number of available samples. Hence, alternative non- or micro-destructive techniques need to be exploited for the evaluation of the compressive and flexural strength of historic mortars. In this study, the micro-destructive scratching resistance test is used to assess the compressive and flexural strength of a variety of lime-based mortars, that were either designed and produced in the laboratory using different binders, aggregates and admixtures, or sampled in-situ. Sound linear correlations observed between the intrinsic specific energy, resulting from the scratching resistance test, and the compressive and flexural strength of the laboratory designed and produced mortars validate the potential of the scratch tool in assessing the aforementioned mechanical properties of lime-based mortars. This is further confirmed by results on historic mortar fragments. Therefore, the use of the novel micro-destructive scratch tool is recommended in cases where lime mortar sampling is limited, in order to provide reliable estimates for the mechanical properties of historic mortars.

Técnicas Constructivas en las torres-atalayas de Montefrío (Granada): La Torre de Las Cabrerizas

This article presents some of the results obtained from the archaeological excavations in the Cabrerizas Nasrid Watchtower in Montefrio, located within the north-west sector of the Nasrid Kingdom of Granada. It is studied the construction techniques from an Archaeology of Architecture perspective and analyzed historic mortars and plasters by different laboratory methods.

Technology of Medieval Mortars: An Investigation into the Use of Organic Additives

This work proposes a multi-analytical approach to determine the additives in historical mortars, the use of which is widely described in bibliographical sources, but has rarely been reported in the literature. A protocol to thoroughly analyse mortars was created (optical microscopy, X-ray diffraction, infrared spectroscopy, thermal analyses and gas chromatography – mass spectrometry). These techniques, which had already been carried out on samples from various sites from the Roman to the modern era, determined that additives had only been used in the mortars from the internal masonry at our sampling site: the medieval military shipyard of Amalfi (Italy). The investigations yielded information on the production technology, and FT–IR and GC–MS revealed a saccharide material-based additive in the mortars, of plant origin. The FT–IR spectra suggested the presence of a natural gum, which has been used since ancient times to strengthen the cohesion properties of mortars and their resistance to tensile stress.

Historical Mortars from the Fortified Upper Town of Eivissa (Balearic Islands, Spain)

Samples of mortars and stone of Portal de ses Taules from the Renaissance city walls of Eivissa (16th century) were characterized using thermal analysis— thermogravimetry and derivative thermogravimetry (DTG)—x-ray diffractometry, and scanning electron microscopy. The granulometric fraction of particle size <63 μm was selected as representative of the binder, while the fraction 0.5–1 mm was taken as representative of the aggregate in order to characterize mortar samples. The results show that local materials were used. Lime was the main component of most of the samples tested. Thermal analysis revealed the hydraulic nature of the lime mortars. High amounts of sodium chloride were found in the samples analysed.

Chemical Weathering of Lime Mortars from the Jahangir Tomb, Lahore-Pakistan

The effects of environmental pollution on cultural heritage have been widely studied in different parts of the world over the last few decades but not with the reference to Pakistan, although cultural heritage in this part of the world is deteriorating at an alarming rate. Determination of the deterioration processes and causes are the fundamental parameters for the preservation on scientific grounds of these cultural assets. This study investigates the effect of environmental pollution on the facades of the 17th century historic monuments of Jahangir Tomb in Lahore (Pakistan). For this purpose, samples were collected from weathered as well as from sound interior surfaces. The samples were characterized by XRF, XRD, SEM-EDS and stereomicroscopy/wet chemistry to understand the weathering mechanisms and products. Those are mainly comprised of sulphates, chlorides and nitrates along with high contents of soil particulates and biological colonization. Results show that chemical weathering is occurring at the mortar-atmosphere interface of the historic fabric, conjoining the petrographic characteristics of the mortars and enveloping atmospheric composition. This interaction is responsible for the current deterioration of the historic lime mortars.

Characterization of historical mortars from the bell tower of St. Nicholas church (Pisa, Italy)

The aim of this research is to characterize the binder and aggregate fractions of sixteen mortar samples from the bell tower of the St. Nicholas church at Pisa, using X-ray fluorescence (XRF), X-ray powder diffraction (XRPD), simultaneous thermogravimetric/differential scanning calorimetry analysis (TG/DSC), optical microscopy (OM) and electron microscopy equipped with a microanalysis system (SEM/EDS).The analytical procedure used for studying the mortars is based on TG/DSC analyses performed on the binder fractions, obtained by disaggregation of the mortar samples, and on micro-analytical data directly collected on the mortar binders combined with chemical, mineralogical (qualitative composition) and petrographic (modal composition) data measured on the bulk mortar samples.The collected data indicate that the examined samples are hydraulic lime mortars with natural river sands (average binder/aggregate ratio 1:1), except for two of them which are artificial pozzolanic mortars with cocciopesto. The most probable raw materials used to produce the mortars are the binding materials obtained by firing carbonate rocks locally available, cherty limestone and subordinately Mt. Pisano marble, and the Arno River sands or, more likely, natural admixtures of Arno and Serchio River sandy sediments.

A Multidisciplinary Approach for the Archaeometric Study of Pozzolanic Aggregate in Roman Mortars: The Case of Villa dei Quintili (Rome, Italy)

This contribution focuses on the study of historical mortars from a Roman archaeological site known as Villa dei Quintili, a monumental villa located in the south‐eastern part of Rome (Italy). The study was carried out on 38 mortar samples, collected from several edifices within the complex. A multi‐analytical approach, including polarized optical microscopy, scanning electron microscopy coupled with energy‐dispersive system and laser ablation inductively coupled plasma mass spectrometry, was used to analyse the pozzolanic material used for the preparation of mortars. Data obtained on both major and trace elements were compared with the compositions of Pozzolana Rossa, Pozzolana Nera and Pozzolanella samples from the Alban Hills volcanic district, collected from a historic quarry nearby, as well as with literature data. The results of such a multidisciplinary approach allowed us to recognize the use of all three pozzolan types for the aggregate fraction of examined mortars from the Villa dei Quintili.

Modeling of degradation processes in historical mortars

The aim of presented paper is modeling of degradation processes in historical mortars exposed to moisture impact during freezing. Internal damage caused by ice crystallization in pores is one of the most important factors limiting the service life of historical structures. Coupling the transport processes with the mechanical part will allow us to address the impact of moisture on the durability, strength and stiffness of mortars. This should be accomplished with the help of a complex thermo-hygro-mechanical model representing one of the prime objectives of this work. The proposed formulation is based on the extension of the classical poroelasticity models with the damage mechanics. An example of two-dimensional moisture transport in the environment with temperature below freezing point is presented to support the theoretical derivations.

Paper 5: Historic Mortars from the Coudenberg Archaeological Site: Characterization and Source of Raw Materials

The characterization of historic mortars by means of a concise methodology of material analyses can provide crucial information with regard to the origin of the raw materials and the ancient mortar technology. For the analysis of the historic mortars of the Coudenberg archaeological site, the methodology consists of optical and scanning electron microscopy, simultaneous thermal analysis, and an acidic treatment. These analyses were carried out on a total of seventeen samples lifted from various areas in the site, in function of the building chronology resulting from a historic built investigation. The type of binder and aggregate as well as their volumetric ratio were determined.Both binder and aggregate present distinctive features, which made it possible to identify the probable geological provenance of the raw materials. The observations are verified with available historical records regarding the construction of the main banqueting hall — the Aula Magna — and the use of raw materials such as limestone and sand for the production of lime and construction purposes.

Safety issues in cultural heritage management and critical infrastructures management

Safety issues in cultural heritage management and critical infrastructures management

Replicating the chemical composition of the binder for restoration of historic mortars as an optimization problem

The present study aims to show how the problem of reproducing, as closely as possible, binders of historic mortars by mixing raw materials which are commercially available, can be formulated as a linear optimization problem. The study points out that by mixing five standard raw materials (end-members) it is possible to obtain mortar binders with the almost same chemical compositions of those determined on the historic and archaeological mortar samples studied in some recent scientific papers. An advanced function of the Microsoft Excel spreadsheet, the Solver add-in, was used for the calculation of the right amount of each raw material to be mixed for producing the new binders. This approach could be useful to provide an optimal solution in the process of restoration of ancient monuments, where it is necessary to replace the historic mortars with new highly compatible repair mortars.

Erratum to: Magnesium sulphate salts on monuments in Saxony (Germany): regional geological and environmental causes

A record of mortar and salt analyses from the last 20 years on various monuments in Saxony demonstrates the close relation between the occurrence of magnesium sulphate salts and the use of dolomitic lime mortars in a regional frame. The regional distribution scheme of dolomitic lime in historic mortars depends on the geological setting of the territory, i.e. the natural occurrence of dolomite deposits. Sulphation of these mortars with the formation of magnesium sulphate and gypsum is mainly due to environmental pollution, as can be shown by sulphur stable isotope analyses. Exposure of the sulphated mortar surfaces to rain leads to the preferential dissolution and advective transport of the novel formed magnesium sulphate salts, which effloresce or subfloresce on the mortar surface or can be accumulated in the structure of adjoining porous building materials like natural stones. These processes may cause severe damages in mortars by the weakening of the binder and in porous stones by salt crystallisation of phases like epsomite and hexahydrite.

Finite element analysis and fragility curves for the evaluation of restoration mortars behavior regarding the earthquake protection of historic structures

The target of this study is the evaluation of repair mortar contribution to the dynamic behavior of Kaisariani Monastery in Athens, by using the tools of finite element analysis and fragility curves. Three types of mortars (concrete) are designed in order to simulate the Hagia Sophia historic mortar, by using different binding material: lime/metakaolin, hydraulic lime, lime/cement. In the developed model the mechanical characteristics of the designed mortars are used. In addition, fragility curves were developed and their results indicated that for the current situation of Kaisariani Monastery and for peak ground acceleration (PGA) value ≥0.24g, the probability of occurrence of serious damage is 59%. For PGA=0.36g an overall failure happened. For PGA=0.40 and by using restoration mortar up to 15% of the total bed joint the failure percentage reduces in the range of 12–30%. Better protection is reported for lime/cement mix design followed by hydraulic lime and lime/metakaolin.

Statistical analysis on ancient mortars: A case study of the Balivi Tower in Aosta (Italy)

This study proposes a first approach to the characterization of the composition and degradation products of historical mortars and their classification through chemometric analysis. This work also aimed at comparing the usefulness and applicability of analytical techniques that are commonly used for mortar examination. Calcimetry, Thermogravimetric Analysis (TGA) and Differential Thermal Analysis (DTA), Ionic Chromatography (IC) and Fourier Transform Infrared Spectroscopy (FT-IR) were used to analyse a number of samples collected from the quadrangular Tower of the Balivi Complex in Aosta (Italy). Cluster Analysis and Principal Components Analysis (PCA) were carried out on the analytical results, and the accordance and the relevance of the results were evaluated. The role of the variables on the samples description and their correlation were evaluated. The results showed the division of the samples into groups that were probably due to the presence of different mortar types manufactured in different periods. Furthermore, an irregular degradation pattern on the four facades and at different heights of the tower was highlighted.

Historical mortars dating from OSL signals of fine grain fraction enriched in quartz

In the last years the mortar dating through Optically Stimulated Luminescence (OSL) techniques has become a viable support for chronological estimations (date of construction or restoration episodes) of historical buildings. However, the dating of mortar has still open issues mainly regarding the assessment of the bleaching degree of quartz, the analysis of the OSL processes for this type of samples and the need to do appropriate tests for the most correct evaluation of the equivalent dose. This paper discusses the results obtained by OSL dating (blue diode stimulation) on the polymineral fine grain phase, enriched in quartz, extracted from lime mortar samples collected from different sites. Thermal transfer effects, through the behaviour of Equivalent Dose (ED) and recovery tests, degree and time of bleaching were studied. For each mortar sample the adjacent brick was collected; in some cases, sampling of the bricks bracketing a mortar layer was a possibility, thus obtaining a direct comparison with the standard thermoluminescence (TL) dating on the bricks. The results obtained show, for this set of samples, the possibility of dating the mortars through the use of the fine grain fraction provided of a suitable chemical-physical preparation procedure and the verification of the bleaching conditions.

X-ray powder diffraction clustering and quantitative phase analysis on historic mortars

This paper describes the application of cluster analysis to X-ray powder diffraction patterns (XRPD) to define homogeneous groups of mortar-based materials according to their mineralogical composition. For this purpose, the diffraction patterns of 110 samples of mortars from the Temple of Venus (Pompeii, southern Italy) were used to test the method. Rietveld refinement, for quantitative mineralogical phase analysis, was performed on the most representative sample of each cluster. The mineralogical grouping yielded by cluster analysis of XRPD data turned out to be consistent with the petrographic groups.