Historic Mortars Research Articles

Radiocarbon Dating of Magnesian Mortars: The Case of San Salvatore Church in Massino Visconti, Piedmont, Italy

This study presents a comprehensive analysis and radiocarbon dating of historical mortar and plaster samples from the San Salvatore—Massino Visconti complex in Piedmont, Northern Italy. Mortar samples and one charcoal sample were collected from various areas within the complex’s lower chapels. Samples were selected and characterized by means of a multi-analytical approach in order to draw inferences about their compositional, mineralogical, and microstructural features. The identification of hydromagnesite and magnesite in the mortar samples suggests the usage of magnesian binder mortar, potentially affecting radiocarbon dating due to its slower carbonation kinetics when compared to calcitic mortars. To mitigate this effect, a purification method was developed involving thermal treatment at 550 °C to isolate datable binding fractions. The results yielded reliable radiocarbon ages consistent with historical context, shedding light on construction materials dating from the 12th to 16th centuries. The study also challenges previous notions by demonstrating the feasibility of radiocarbon dating for magnesian mortars, opening new perspectives for dating such materials. These findings offer valuable insights into the construction history and material composition of the complex, corroborating historical information.

Analytical characterization of historical mortars from the Roman villa of Frielas (Loures, Portugal)

The analytical characterization of mortar samples from the Roman archaeological site of Frielas, located in Lisbon, Portugal; was carried out by means of X-diffraction (XRD), thermogravimetry (TGA-DTG), optical microscopy and scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM-EDS), acid attack and granulometric analysis. A total of eighteen mortar samples were collected from the different structures of the villa with different functional uses (render, filler, and floor). The results showed a similar composition of binder, while differences in aggregates allowed to establish several groups. Results were discussed as evidence of manufacturing techniques, production technologies, and provenance of possible raw materials. There was no prominent variation that can suggest a different chronology between the group of samples. Though, it is assumed that there might be some renovation, restoration, or partial rebuilding that occurred in the same period. In terms of production technology, proportions ruled by Vitruvius were not followed.

A new multi-analytical procedure for radiocarbon dating of historical mortars

The overarching challenge of this research is setting up a procedure to select the most appropriate fraction from complex, heterogeneous materials such as historic mortars in case of radiocarbon dating. At present, in the international community, there is not a unique and fully accepted way of mortar sample preparation to systematically obtain accurate results. With this contribution, we propose a strategy for selecting suitable mortar samples for radiocarbon dating of anthropogenic calcite in binder or lump. A four-step procedure is proposed: (I) good sampling strategies along with architectural and historical surveys; (II) mineralogical, petrographic, and chemical characterization of mortars to evaluate the feasibility of sample dating; (III) a non-destructive multi-analytical characterization of binder-rich portions to avoid geogenic calcite contamination; (IV) carbonate micro-sample preparation and accelerator mass spectrometer (AMS) measurements. The most innovative feature of the overall procedure relies on the fact that, in case of positive validation in step III, exactly the same material is treated and measured in step IV. The paper aims to apply this procedure to the ancient mortar of the Florentine historical building (Trebbio Castle), selecting micro-samples suitable for dating in natural hydraulic mortars. The discussion of the mortar dating results with the historical-archaeological hypotheses provided significant insights into the construction history of the building.

An Approach to Accurately Identifying Binders in Historic Mortars by the Combination of Microscopic and Microanalytical Techniques

Mortars are among the most important materials in building construction. They are generally obtained by mixing aggregates with an inorganic binder. The identification of mortar constituents, particularly the binder type in historic buildings, is one of the essential aspects of building conservation, considering that the new conservation materials must be chemically, mechanically, and physically compatible with the old masonries. Among other techniques used to characterise binders, those related to optical and electronic microscopy are particularly important. Microscopy and combined techniques may be the key to this identification since the classic mineralogical and chemical-based identification approaches are not conclusive enough in investigating the types of hydraulic binders in mortars. This work presents an analysis procedure to identify mortar binders by combining EDS microanalysis and petrography. Mortar samples of known composition were used as a reference for analyzing mortars from historic buildings. The proposed methodology made it possible to identify the type of binder or a mixture of binders based on the identification of the binder features by petrography together with analysis of the chemical composition of the paste by X-ray microanalysis under a scanning electron microscope.

Characterization of historic mortars and the effect of rice husk ash (RHA) on quicklime

Historic mortars are minerologically characterized for many reasons pertaining to traditional building conservation. In order to determine the binding material of the historic masonary building, this material must be sufficiently separated from the aggregate. In this study, the Cas mortar (Traditional gypsum-based construction mortar in Siirt, Türkiye) used in traditional Cas houses was characterised and compared with composite lime mortars prepared by substituting quicklime with 10 %, 15 % and 20 % rice husk ash (RHA). The mechanical properties of Cas mortar are much higher than those of lime mortars. However, when 20 % RHA was substituted for lime, it was found to significantly change the properties of the mortars, increasing the compressive and flexural strength by 68 % and 58 % respectively and improving the specific heat and many other properties. X-ray diffraction (XRD), thermogravimetric analysis (TGA) and differential thermal analysis (DTA) and Fourier transform infrared spectroscopy (FT-IR) analyses showed that the 63 μm sieved powder analysis was more accurate in determining the chemical characterisation of the historic mortars.

Characterisation and Contextualisation of Mortars from the 19th and First Half of the 20th Centuries in Muharraq, Bahrain

ABSTRACT Within the context of the restoration projects at the buildings of the Pearling Path in Muharraq (World Heritage Site), interdisciplinary research has been conducted to determine the composition and historical context of the various mortars present in these historic structures. Some previous analyses carried out on historic mortars indicated a predominant use of gypsum, although lime was also frequently identified. However, the lack of details about the analysed samples did not allow estimating the possible composition of the local traditional mortars through their dating or location. To understand the use of historic mortars, an in-depth historical research and data analysis were conducted. This focused on the chronological sequencing of the buildings’ construction which was combined with petrographic analysis performed on a group of samples. Their selection was based on a pre-classification made according to the dating and the visible appearance of the mortars. The new data also enabled fresh conclusions on previously published studies. The obtained result is a mineralogical characterisation of the mortars used in Muharraq during the 19th and the first half of the 20th centuries, supported by historical data, including information about the provenance, the application criteria, and an explanation of changes in material trends. This information will assist heritage professionals in gaining a deeper understanding of buildings from this period in Bahrain, enriching the knowledge of materials used in the region. It will enable them to predict the composition of historic mortars based on dating, location, and visible physical features such as colour, type of aggregates, and binder-to-aggregate ratio.

CHARACTERIZATION OF EARTH, LIME, AND GYPSUM MORTARS IN THE CONSTRUCTIONS OF THE 16TH, 17TH, AND 18TH CENTURIES

The historical mortars of three ecclesiastical assets of the Colonial Quito were analyzed, which by 1978 was declared as heritage by UNESCO. The emblematic works of Jesuits, Dominicans, and Franciscans, built between the 16th to 18th centuries have multiple constructive stages and interventions of which there is no technical record because of the historical and present space of worship, living and religious museum of Quito. The objective of the lining mortars characterization is to provide the clear information of the composition of the analyzed samples for better understand the constructive chronology of the churches and to determine which earth, lime, gypsum, etc. mortar was used frequently according to the epoch and religious order. A total of 48 samples of lining mortars of the interior and exterior of the temples were examined, with the protocols and norms on non-destructive essays suggested by the research team. The analysis comprising stereomicroscopy studies that were complemented with mineral characterization and quantitative analysis by X-ray diffraction, as well as polarized light optical microscopy and scanning electron microscopy with microanalysis of the samples, among others. The results in the laboratory allowed us to demonstrate the existence of earth mortars, lime and gypsum bastards, and gypsum mortars with carbonate aggregate, those elements have volcanic and metamorphic volcanic mineralogical composition, this allowed us to date into the constructive stages registered in the church. The results in the laboratory allowed us to demonstrate the existence of earth mortars, lime and gypsum bastards, and gypsum mortars with carbonate aggregate, those elements have volcanic and metamorphic volcanic mineralogical composition, this allowed us to date into the constructive stages registered in the church

Long-term mechanical properties of lime-pozzolan mortars: The role of amorphous Al2O3

Today, lime-pozzolan mortars are being used in the repair of historic buildings, replacing the lime-cement mortars that were previously used in this practice, but were incompatible with historic mortars. It has been observed in laboratory research and also in practice that some lime-pozzolan mortars can lose strength over time. The cause of this behaviour is not fully understood, but the main reason seems to be the instability and breakdown of the aluminate phases. In this paper, the role of amorphous Al2O3 content in pozzolans on the long-term mechanical properties of lime-pozzolan mortars is studied. Lime-pozzolan mortars with 40% replacement of lime with pozzolans with different contents of amorphous Al2O3 (metakaolin, pumice, pozzolanic earth, trass, zeolite) were prepared and the changes in strength, porosity and mineralogical composition of the mortars (determined by XRD and TG/DTA) over time were monitored. Mortars containing pozzolans with a high content of amorphous Al2O3 (over 30% by weight) showed a dramatic decrease in strength, changes in porosity and a decrease in the content of monocarboaluminate (C4AcH11) with a simultaneous increase in the content of vaterite and aragonite. The negative effects of carbonation of the aluminate phases are particularly evident in pozzolans with a high content of amorphous Al2O3.

Numerical study of humidity flux in historical mortars based in air lime mortar: Simulation and a case study

RESUMO A segurança estrutural de edifícios históricos exige uma análise estrutural avançada. A argamassa geralmente apresenta composição e comportamento estrutural complexos. Em diferentes partes do mundo, existe uma quantidade significativa de construções históricas utilizando argamassas de cal aérea. A umidade em estruturas de cal tem uma influência importante no comportamento e desempenho. Resultados experimentais de um programa de monitoramento da argamassa desenvolvido pela equipe envolvida neste trabalho foi usado como referência. Para simular este processo de secagem, é utilizado um software implementado pelo Método das Diferenças Finitas (MDF). O software foi utilizado para identificar os principais parâmetros do material. A estratégia de modelagem (MC 2010) foi primeiramente aplicada aos resultados experimentais de corpos de prova cilíndricos, em sequência, aos resultados experimentais de um molde prismático. O modelo foi capaz de replicar os dados experimentais, de forma satisfatória. Destaca-se a relativa simplicidade da modelagem. Quando comparado com materiais como o concreto, foram encontrados maiores valores para D1 e fboundary. Para os corpos de prova estudados, os resultados experimentais e numéricos indicaram gradiente de umidade reduzido. Esses resultados estão associados à alta porosidade. Em sequência, considerando o par de valores obtidos na simulação numérica, estuda-se uma estrutura simulando uma construção real.

Characterization of coating mortars from the warehouse of the former rheingantz factory in the Rio Grande, southern Brazil

The Rheingantz complex, dating from the 19th century, is composed of several elements, such as the factory, daycare center, and workers' house, and is located in the Rio Grande in Rio Grande do Sul, Southern Brazil. Currently, part of the complex is in the process of restoration. From this point of view, the great importance of the buildings for the conservation of the memory and cultural identity of the city and state suggests the study, of the historical mortars, in a pavilion, a former warehouse of the complex, lent to the Federal University of Rio Grande-FURG. The present paper aims to characterize the historical mortars of the pavilion's external coating. To identify the primary constituent materials, the mortars were characterized using tests suggested in the bibliography, such as X-ray diffraction (XRD), mechanical compressive strength, and water absorption. The characterization of the mortar samples showed that they are mainly composed of calcite and quartz, in a 1:5 ratio (binder: aggregate), and also have a significant presence of dolomite, which is indicative of a mortar substantially formed by dolomitic lime and sand. The results provided subsidies for the formulation of mortar suitable for restoration with characteristics similar to the original, providing mechanisms to reduce future pathological manifestations.

Durability tests on lime-based mortars from the historic built heritage of Catania (Eastern Sicily, Italy): An experimental study

Mortars, like any other natural and artificial stone materials, are subject to atmospheric weathering agents which affect their durability according to the intrinsic characteristics of the material, such as mineralogical composition, texture and pore structure.This paper aims to investigate the physical-chemical durability of lime-based mortars made with two different volcanic aggregates, locally known as azolo and ghiara, peculiar of the historic built heritage of Catania (Eastern Sicily, Italy). An experimental approach has been used, based on the reproduction in laboratory of historic mortars by using ancient recipes. The experimental samples have been characterized from a physical point of view and then subject to accelerated aging tests. Specifically, the samples have undergone: i) mineralogical investigations through X-ray diffraction (XRD); ii) thin section analysis by polarized optical microscopy; iii) pore structure analysis through mercury intrusion porosimetry (MIP); iii) water absorption by capillarity; iii) water vapor permeability test; iv) accelerated aging test by salt crystallization; v) decay by sulfur dioxide.Results obtained highlight that the higher microporosity which characterizes the ghiara mortars is certainly responsible for their greater water absorption by capillarity as well as for their lower resistance to salt crystallization and exposure to sulfur dioxide, with respect to azolo-based ones.

The Effectiveness of Spraying nTiO2 on Coating Mortars in Historical Buildings Aimed at Reducing Fungal Growth

In historic mortars, the main binder used are calcitic or dolomitic lime. However, these mortars are also susceptible to the biochemical action of fungi causing undesirable changes in those materials. Nanotechnology has been investigated as a strategy to mitigate the deterioration of the cultural heritage. Photocatalysis has proven effective as an agent of degradation of organic contamination by inhibiting the recolonization of substrates affected by biological growth. This study verifies the effectiveness of a nanometric photocatalyst (nTiO2-P25, 3% in deionized water) sprayed on the surface of simple lime–sand mortar (1:4 mass trace), typically used in historical buildings, against the growth of Aspergillus niger fungal isolates, inoculated with a 106 spore/mL suspension. The samples were exposed to the incidence of artificial radiation of UVA light with a wavelength of 285 nm to activate the nTiO2. We observed a reduction in fungal colonies, especially after four hours of exposure per day, reaching 100% in the staining reduction in one case. Another aspect observed was that the previous application of nTiO2 on the mortar samples caused alterations in the morphology of the A. niger fungus structures, evidence of a disturbance in the growth of the colonies or even their reduction over time.

THE NEED FOR A NEW APPROACH TO THE RADIOCARBON DATING OF HISTORIC MORTARS

ABSTRACTThis commentary aims at raising awareness and fostering a discussion on the need of a new approach to the radiocarbon (14C) dating of historic mortars. Over the last decades, important advancements have been made in the application of the 14C dating methods to lime mortar samples, including the use of lime lumps instead of generic pieces of mortar. However, a relevant number of results in disagreement with the chronological framework of the related archaeological cases are published every year without a clear understanding of the reasons for such results. This suggests that further developments to the methodology are needed. The commentary argues that to further develop this particular application of the 14C dating method, a new, more holistic approach is needed that moves away from the very “applied” approach that dominated the last decades and focuses more on the causes of contamination and the mechanism of the reactions involved. Two actions are suggested that can immediately improve our ability to critically assess the results obtained: the publication of a chemical and mineralogical characterization of the binding fraction for the dated mortars, and the publication of sampling depth for each dated sample.

Semi-quantitative measurement of calcium carbonate in historic gypsum mortars, using diffuse reflectance infrared Fourier transform spectroscopy

This paper uses Fourier transform infrared spectroscopy to semi-quantitatively measure the amount of calcium carbonate in historical gypsum mortars. 17 historical mortar samples related to Arch of Alishāh in Tabriz-Iran, belonging to the Ilkhanid period, were evaluated. The methodology used in this study was diffuse reflectance infrared Fourier transform spectroscopy [DRIFTS]. Gypsum mortars containing 0-6.5% calcite were prepared and analysed using an FTIR spectrometer. The calibration curve was prepared based on the band intensity ratio of 1485 cm-1 related to carbonate vibrations in calcite to 660 cm-1 corresponding to sulphate vibrations in gypsum. Calculating the amount of carbonate in all historical mortars shows the presence of about 0.12 to 1.08% carbonate in gypsum mortar. According to obtained results, it can be acknowledged that due to the meagre amount of carbonate in the mixture of mortars, the existing carbonate has entered the mortar as an impurity through soil or dissolved salts. This can indicate that, contrary to the initial idea about some of these mortars, lime and gypsum mixture was not used as the main component in the making these mortars.

Understanding the provenance and production process of historic mortars—a novel approach employing calcareous nannofossils

Limestones (CaCO3) have been an important source for masonry and mortars throughout approx. 10,000 years of human history. They are often composed of calcitic shells of minute marine algae, known as calcareous nannofossils. The 0.25–30-µm large calcitic skeletons of these primary producers have been well documented from various archaeological materials including building stones of masonry. Surprisingly, these tiny microfossils were recently also observed in medieval mortars and mortar-based materials, even though the carbonate-based source rocks of the mortars have been heated in kilns for quicklime production. Burning experiments of carbonate-rich sedimentary rocks, containing well-preserved and abundant calcareous nannofossils, documented a deteriorating preservation and a decrease of diversity and relative abundance of the nannofossils with increasing temperatures.Alongside the lime-based binder historic mortars often contain under- and overburnt lime lumps and carbonate-rich aggregates; the latter were added after the heating process. Lime lumps and aggregates offer additional, so far not yet fully understood information on the burning process. Here, calcareous nannofossils were studied in ultra-thin sections of historic mortars, resulting in the separate analysis of the binder, lime lumps and aggregates. The findings allow (i) a more precise provenance of the limestones and (ii) a more accurate reconstruction of the temperatures reached during historic quicklime production. Our study thus improves the provenance analysis approach of limestones and sheds light on historic technology of mortar production by using calcareous nannofossils.

RILEM TC 277-LHS report: How hot are hot-lime-mixed mortars? A review

It is believed that many historic mortars were made using hot-lime mixing techniques. They are back in use today, and their good qualities are often praised, including being more compatible and a better match with historic fabrics. This paper studies the methods of producing hot-lime mortars and putties. It discusses the variables that determine the properties of the resultant mortars such as slaking and calcination, and compares hot-lime mortars with their equivalent putties, and with factory-produced calcium lime and hydraulic lime mortars. The paper concludes that the most important variable that governs the properties of hot-lime mixed mortars is the quantity of water used for slaking, because it determines the temperature reached during slaking which makes the resultant Ca(OH)2 vary from a fairly large size to extremely small, hence producing mortars with different properties. Based on scientific and historic evidence, it is concluded that the best method for hot-lime mixing is dry-slaking (sand-slaking) with long storage, because it combines a high slaking temperature (that reduces particle size and increases the surface area of the hydrate), with gradual slaking (that lowers volume expansion and crack development) and long storage (to ensure complete slaking hence no expansion cracks). Many historic mortars were probably hot-lime mixed. However, it is practically impossible to recreate them today due to the different limestones, kilns, calcination regimes and slaking/storage methods used in the past. Hydraulic and magnesian quicklimes were used historically for hot-mixing. In contrast, most of the factory quicklimes used today are purer limes with higher free lime content and a greater reactivity. Therefore, a hot-lime mix made with a factory-produced quicklime may not be more authentic or compatible than a natural hydraulic lime –NHL– mortar designed to suit a specific fabric and application. To ensure quality mortars that can be consistently repeated, a hot-lime mixing specification should contain both the process and the materials including: type of slaking (dry/wet); amount of water used; mixing details and the time at which it takes place; storage time and at what stage does it occur. To control the slaking temperature, the right amount of water should be established (according to free lime content) by trial which will also inform on the amount of yield and hence allow proportioning. With careful site work and specification, high-quality, compatible mortars can be made with both NHLs and hot-lime mixing. However hot-lime mixing requires more time and logistics, closer care and a more complicated specification.

Scanning through multidisciplinary techniques and recreation of historic mortar: Case study of Rohtas Fort

Rohtas fort built by Sher Shah Suri is located in Jhelum district of Punjab province in Pakistan. It is a national heritage as well as a UNESCO world heritage site. With the passage of time, Rohtas fort had seen significant deterioration. One of the major deteriorations affecting Rohtas fort the most is the decay of the mortar, which results in stone loosening in the stone masonry walls. The objective of the study is to analyze the mortar samples taken from Rohtas fort and suggest a repair material, which is compatible with the old Mortar. This work was divided into two parts; the first one consisted of the characterization of the old mortar and the second part as design of a modern-day mortar made from similar ingredients. The old mortar was evaluated through a number of multidisciplinary techniques like density, porosity, compressive strength, microscopic examining, XRD, XRF and TGA. The analysis revealed that the old mortar consisted of hydrated lime, broken bricks, sand and clay. The hydrated lime: aggregates ratio was found out to be 1.156. The density, porosity and compressive strength of the old mortar was found as 1.6 g/cm3, 42% and 2.2 MPa. The presence of Calcium-Silicate-Hydrate (C-S-H) gel revealed pozzolanic activity due to brick particles. The modern mortar was prepared with the same ingredients, hydrated lime, local brick particles, local sand and local clay in the composition analogous to that of the old one. The particle size distribution of the aggregates was also kept same as that of the old mortar. The density, porosity and the compressive strength of the modern mortar was found to be 1.9 g/cm3, 35% and 3.5 MPa respectively at 28 days of age. Owing to pozzolanic character of the brick particles, and carbonation of the hydrated lime, the properties are expected to improve further.

A new approach on data extrapolation for mortar dating in the Zagreb Radiocarbon Laboratory

There is no unique way of mortar sample preparation that would always provide the true date. We propose a procedure of 14C age extrapolation from CO2 fractions obtained by sequential dissolution of mortar grain size 32 – 63 μm by phosphoric acid. The collection of CO2 fractions is deduced from kinetics of mortar-hydrolysis curve.The procedure was designed from data obtained from mortars prepared in laboratory and tested on mortar/plaster from three archaeological cases, with confirmed ages. The first fractions gave true result for historical mortars, but for laboratory ones only extrapolated values were true. When certain conditions regarding CO2 fraction collection were met, extrapolated values agreed with the first fractions for the historical mortars. Although the extrapolation procedure seems to eliminate the effect of dead carbon contamination, it is not effective against influence of delayed hardening or restoration.

Protection of Historical Mortars through Treatment with Suspensions of Nanoparticles

Mortars, which are very important elements for the integrity of historic monuments, consist mainly of calcium carbonate and silicates in different proportions. Chemical dissolution due to exposure in open air is very important for the degradation of mortars. Inorganic nanoparticles with chemical and crystallographic affinity with mortar components are expected to be effective structure stabilizers and agents offering resistance to chemical dissolution. In the present work, we have developed and applied suspensions of amorphous calcium carbonate (ACC), silicon oxide (am-SiO2) and composite nanoparticles by the precipitation of ACC on am-SiO2 and vice versa. The application of suspensions of the synthesized nanoparticles on three different historical mortars of Roman times (1st century AD), retarded their dissolution rate in solutions undersaturated with respect to calcite, in acid pH (6.50, 25 °C). All three test historic mortars, treated with suspensions of the nanoparticles prepared, showed high resistance towards dissolution at pH 6.50. The ability of the nanoparticles’ suspension to consolidate the damaged mortar was the key factor in deciding the corresponding effectiveness in the retardation of the rate of dissolution. The combination of ACC with am-SiO2 nanoparticles showed high efficiency for protection from the dissolution of calcite rich mortars.

Bio-Stimulated Surface Healing of Historical and Compatible Conservation Mortars.

The main focus of this research was the bio-stimulated healing of cracks in lime mortar samples (historical and newly designed). The investigation started from comprehensive characterisation of historical mortars, while in the next stage a compatible conservation mortar was designed and characterised, with special attention given to the contact zone formation between original and conservation mortars. The next step was the design of a bio-stimulating crack-sealing agent, a two-component liquid system: bacteria culture Sporosarcina pasteurii DSM 33 and nutrients. Both historical and conservation mortar samples were used in order to study their potentials for bio-stimulated surface-crack repair. The experiment lasted for 150 days, allowing the ureolytic bacteria Sporosarcina pasteurii DSM 33 to induce the precipitation of calcium carbonate into cracks and heal the damaged surface of the tested materials. The healing phenomenon was continuously monitored during a period of 150 days. Special attention was given to the evaluation of the morphology, chemical and structural characteristics of the deposits created in/on the surface cracks, monitored by optical microscopy, SEM, XRF and XRD analyses. The obtained results present valuable input for the application of the developed system in real environmental conditions as a solution for the future sustainable architectural conservation of traditionally prepared mortars.