Historic Mortars

Sophisticated analysing proceedings have been used in the past to assess the composition of hardened mortars. Chemical and mechanical tests combined with microscopic investigations seem to provide all the information required for the design of repair mortars which physically and visually are appropriate for restoration purposes. Lime putty and hydrated lime of varying quality meanwhile are currently available. Nevertheless, the results are not always convincing. The limit of the analysing techniques has become evident in conservation practise. Knowledge of how mortars have been fabricated, mixed, stored and applied is as important as the chemical composition. The authors have therefore collected information on the fabrication, compositions and use of mortars revealed by an examination of written historic sources.

The microstructural investigation of prehistoric mortars selected from various archaeological sites of Cyprus demonstrated that the discovery of lime and gypsum technology had occurred on the island during the Neolithic period. This technology was already known in the Near East since earlier periods (Epi-Paleolithic period). Lime mortars were widely disseminated during the Chalcolithic period, whereas the use of gypsum mortars was rather limited on the island during all of the prehistoric periods. The discovery of crushed-brick lime mortars during the Late Bronze Age constitutes an innovation and can be associated with the overall prosperity of the era. The use of these mortars seems to have occurred simultaneously with the Mycenaean world. The selection of the raw materials for the preparation of mortars was based on the geology of each area. The absence of volcanic rocks in Cyprus led to the use of bricks as additives in the preparation of hydraulic mortars.

This paper presents the XRD, XRF and porosimetry analyses and SEM-EDX observations of nine mortars: three Egyptian plasters (New Kingdom, fifteenth to eleventh century B.C.) and six Meroitic mortars (first century AD) collected on temples, palaces and pyramids in archaeological sites located between the Third and Fourth Cataract. The two first Egyptian samples were mainly composed of gypsum plaster. The third one and a bedding mortar collected on a Meroitic pyramid were composed of siliceous sand bound by about 30% kaolinite-rich clay. A coating mortar collected on another Meroitic pyramid, probably highly lixiviated, had a similar composition with only 11% clay. The other Meroitic samples appeared as conventional fully carbonated lime-sand mortars. The compositions of the decorative surface layers varied from clay to lime or lime-and-gypsum, in the form of painting or applied as fresco. This extreme diversity of compositions observed is particularly interesting from an archaeological point of view. The knowledge of the various techniques used enables us to have a better understanding of foreign influences on building workers in ancient North Sudan.

Roman hydraulic maritime concretes of the central Italian coast have pumiceous volcanic ash, or

pulvis Puteolanus

, from the Bay of Naples as mortar pozzolan. Petrographic and mineralogical analyses of cement microstructures in relict lime, tuff, and pumice clasts suggest that pozzolanic reaction at high pH produced gel-like calcium-aluminum-silica-hydrate cements. Orthorhombic 11 Å-tobermorite, with unit cell dimensions a = 5.591(1)Å, b = 3.695(1)Å, c = 22.86(1)Å, developed in the residual cores of portlandite clasts and in certain pumiceous clasts, as well. Ettringite and calcium-chloroaluminate formed in discrete, perimetral microstructures and in the cementitious matrix. Phillipsite and chabazite cements may reflect later dissolution of alkali-rich volcanic glass at pH 9–10. The cement systems have remained stable for 2,000 years, during partial to full immersion in seawater. Vitruvius’

De architectura

and other ancient texts describe the raw materials of the concretes, preparation of lime, and construction of submerged wooden forms. Information concerning the materials, formulations, and installations of the concretes was apparently spread by movement of central Italian engineers around the Mediterranean but also, perhaps, by the circulation of sub-literary engineering manuals. Further analytical investigations will determine the diverse chemical processes that produced the cement microstructures, and why the harbour constructions have endured for two millennia.

From the mid-eighteenth century extensive research in Sweden and in present day Finland focused on the development of mortars with hydraulic properties, the results mainly published by the Royal Swedish Academy of Science. The aim was to replace imported Italian pozzolan and Dutch trass with a pozzolan produced in Sweden. Several products based on burned alum shale were developed. Cambrian alum shales with a high content of bitumen were fired without additional fuel to produce pozzolanic shale ash. The bituminous alum shale was used directly as a fuel in the lime burning process from the late eighteenth century. The alum shale mortars have a red-brown colour due to the high content of iron oxides. The mortars are hard, strong and generally have a good durability, both as masonry mortars and renders. Microscopic analysis shows that often only a skeleton remains of the shale particles and that large parts of the particles are consumed by the pozzolanic reaction. The field of application was initially restricted to structures in contact with water, such as locks in canals and harbours, but conventional building construction was also an early application.

Starting in the late eighteenth century, the age of industrialisation brought about a number of new binder systems of hydraulic nature meant to answer the demand for improved mortar strength even at moist conditions. Such mortars form an important part of today’s architectural heritage and are therefore frequently encountered, either as primary materials or as historic restoration mortars, when historic objects are studied in the course of restoration. This paper deals with the basic features of a selection of those cementing materials which were “novel” at their time: Sorel cements, iron hammer scale mortars, and natural Roman as well as early Portland cements. The analytical approach followed is based on light and scanning electron microscopy, believed to provide primary tools to identify the mortars and to understand some of their key properties. Sorel cement mortars were studied at examples of flooring and stone repair mortars, respectively. Both were frequently encountered applications of this binder prepared from a mixture of caustic magnesia and magnesium chloride. In both types of mortar, the binder appears composed mainly of magnesium oxychloride hydrates, whereas the matrix porosity varies from highly porous to dense. The aggregates range in composition from wood fibres to stone fragments, reflecting the capacity of Sorel cement to yield strong mortars with almost any kind of filler. Hammer scale mortars were prepared by adding files of metallic or oxidic iron to lime and sand. They were used for fillings or joints in masonry where they developed significant levels of hardness and strength. The observations by microscopy show that migration of rust products from the iron scales into the surrounding lime matrix is a key factor contribution to the high strength properties of such mortars. Nineteenth century Roman cements were produced from argillaceous limestone at temperatures as low as about 900°C. In their mineralogical composition they differ significantly from NHL and Portland cements. Consequently, Roman cements follow a specific path of hydration, generally yielding highly porous mortars of considerable strength. Whilst light microscopy is a good tool to identify Roman cement mortars by the abundant presence of binder-related particles, the SEM observations help understand their properties, as the calcium silicate hydrates formed in a Roman cement paste are of a coarse nature with card-house-like intergrowth. Early Portland cement mortars produced in the second half of the nineteenth century form the last group of materials addressed in this contribution. By the coarse size of their clinkers they can be easily identified in thin sections, however the lower amount of alite, as compared to modern Portland cements, is obvious. This observation is discussed in terms of lower temperatures of calcination as compared to modern successors.

Reaction rims of natural hydraulic relicts in historic mortars were investigated using a novel technology; a FTIR-spectrometer equipped with a focal plane array detector enabling in ATR-mode IR imaging with a spatial resolution of 1.0 μm. IR spectra show two regions with main absorption bands at 1,280–1,580 cm

−1

and 900–1,120 cm

−1

. Bands at 1,450 and 1,396 cm

−1

correspond to the asymmetric stretching of CO

3

2−

, indicating two different forms of CaCO

3

; the 900–1,120 cm

−1

group of bands is assigned to Si-O stretching vibrations indicating C–S–H phases. The ratio of the integral absorbance of these two main regions of absorption bands shows an inhomogeneous spatial distribution in the reaction rim. From this variation we conclude that the reaction rims consist of areas containing both calcite and aragonite in addition to C–S–H phases and areas containing aragonite and C–S–H phases, the latter with a lower Ca/Si ratio and a higher degree of polymerization. SiO

2

gel is present in both areas.

The binders of joint mortars, renders and plasters used during several construction phases in the history of the Benedictine monastery in Riesa have been identified as dolomitic lime. Magnesite and/or hydromagnesite could be determined as the magnesium bearing carbonate phases beside calcite in the binder. Most of the mortars contain carbonate lumps, partially with altered silicate mineral inclusions, that represent remnants of the original structure of the late Palaeozoic dolomites which were used as the local raw material for lime production over the centuries. Low contents of aluminous silicates in the limestone might have contributed to the formation of hydraulic components. Hydrotalcite has been determined by XRD in some of the samples investigated.

Natural hydraulic limes were used in ancient times and are still produced today. A comparison of the chemistry and mineralogy of currently available NHL2 and NHL5 limes indicate that there are no clear differences except for the amount of ‘undefined material’, mainly comprising an amorphous phase. The chemical composition of these different limes is nearly identical. However, the classification of ancient hydraulic limes is mainly based on their chemistry, obtained from the analysis of ancient mortar binders. Moreover, it is shown that the phase composition of these limes evolves with time, making their classification uncertain and difficult.

The use of gypsum plaster for the interior coating of walls and ceilings in the Portuguese architecture was particularly expressive in the period between the eighteenth and the twentieth century. However, information about this important heritage is almost nonexistent, which is leading to a rapid loss of important patrimony. In this paper the results of the characterisation of five gypsum plaster samples from the second half of the nineteenth century belonging to the

Arabian Room

of the

Bolsa Palace

, located in Oporto, North of Portugal, are presented and discussed. XRD and TGA-DTA techniques were used to establish the mineralogical composition, and the relative proportions of the binders. Optical microscopy and FESEM-EDS observations were performed both in fractured and polished surfaces in order to determine the stratigraphy and the composition of individual layers. The results of this characterisation work showed that the plasters used were mainly composed of gypsum and hydrated lime in different proportions – a feature that was correlated with the application techniques of the decorative elements analysed – and allowed the determining of the restoration interventions they had already been submitted to. Some physical properties like the dynamic modulus of elasticity and capillary absorption were also determined, and a correlation between the results obtained was established with previous studies performed by the authors.

Since 2001 the authors have been involved with the archaeologists of the Fondazioni Lerici, Politecnico di Milano, in the preservation of some Hindu temples in Mỹ Sơn, Vietnam. The characterisation of the brick- masonry materials was carried out at the Politecnico di Milano. Especially interesting was the successful study of the natural resin used to bond externally the bricks in the masonry; this allowed the formulation of a new compatible resin to be used for the conservation project. In the masonry internal leaf, the joint material, based on clay, was substituted by a new hydrated lime and powdered bricks mortar. The results of the research presented here allowed the direct application of the new materials in the conservation project of G1, G3, and G5 of group G.

Mortars from two medieval bridges (Charles Bridge in Prague and a bridge in Roudnice) and two Roman bridges (Ponte di Augusto in Narni and a bridge in Sardinia) were analysed using various techniques to obtain their chemical and physical characteristics. The analysis of binder quality was based on thermogravimetric analysis, using a methodology which enables the hydraulicity of the mortar to be expressed by the CO

2

/H

2

O ratio. The mechanical tests were performed on non-standard mortar specimens. The ratio binder/aggregate was determined dissolving the binder by an acid, and a sieving analysis was applied to the separated aggregate. The material characteristics of mortars from historic bridges were compared with each other, taking into account the requirements for mortar strength according to construction function and degree of exposure.

The

Santíssimo Sacramento

Convent in the Alcântara quarter of Lisbon is one of the most important ecclesiastical structures of the

Filipino Period

(1580–1640), showing an innovative architectural layout. An intervention aiming at the repair and restoration of the interior plasters of the Santíssimo Sacramento Church was performed in 2009 and 2010. To support the restoration plan, a physical, mechanical and chemical-mineralogical characterisation of the internal plasters of the church was carried out. In this paper the main results are presented, such as various types of plasters, mortars, stuccos and pigments; and also the nature of the main anomalies were identified and characterized. The results obtained contributed to the identification of the main decorative programs characterized by the use of different materials and techniques. The mortars are in very good condition, being composed of aerial calcitic lime with quartzitic and basaltic aggregates. The stuccos are comprised by gypsum and non-hydraulic lime, while the decorative layers features lime with some precious pigments, such as ultramarine (

lapislazzuli

) and gold-foil gildings. The plaster conservation and restoration works were performed with compatible repair materials selected according to the physical-chemical characterisation and on the evaluation of the conservation state.

It would be assumed that a survey of a masonry structure would result in the production of an objective report. This situation cannot necessarily be guaranteed as the experience and understanding of masonry deteriorology and repair will vary from practitioner to practitioner. The difference in reporting will clearly determine alterative starting positions for the repair works, with divergence in the project potentially occurring when philosophical tenets are applied. The selection of repairs can be significantly influenced by the different professional’s philosophical perspectives that can be broadly categorised as, purist, pragmatist and cynic. These perspectives may direct the approach to repair, placing emphasis of the intervention towards what is of greatest perceived value to the practitioner; for example, honesty over aesthetic integrity and vice versa. This paper investigates how and why projects may start at a subjective point (although perceived as being relatively objective) and be prone to further divergence when building conservation philosophies are applied. This situation would go some way in explaining why two professionals would be confronted with the same structure, yet the outcome of the finished repair project could be significantly different.

In interventions on historic renders and plasters, the first step is to decide upon the strategy: repair or substitution, based on an evaluation of the cultural value of the render or plaster, of the building itself and on a careful diagnosis of the typology of defects, their quantity and reparability. New renders or repaired renders should fulfil the main functions they are required to, especially protection and aesthetic functions. Compatible materials should always be used. Compatibility is needed for durability, not of the render, but of the wall as a whole, and also for preserving the documentary and symbolic value of the building as well as its image. Compatibility is defined in relation to the substrate and the existing mortars. Therefore tests need to be carried out on the old materials and on possible solutions, to compare characteristics and assist in the selection of the best. It is acceptable to begin using non-destructive or slightly destructive

in-situ

tests, because with them it is possible to collect useful information quickly and without destruction of the historic renders. Simple mechanical and physical tests can be carried out on the old mortars and a few chemical tests can also be performed, with portable equipment. If rigorous and complete tests are needed, some samples can be collected and tested in the laboratory, using methods adapted to non-regular, possibly friable specimens. The characteristics of the mortars to use can be established, based on the results obtained, in order to fulfil both functionality and compatibility. However, sometimes it is not possible to obtain enough data about old materials, especially concerning masonry as a whole, which is more difficult to test than mortars. For this situation, some general requirements have been established, based on previous work carried out on Portuguese historic masonry buildings, which can be used without risk of damaging existing materials. Decisions concerning the materials to use, especially binder materials, should also take into account the climatic and environmental conditions. Appropriate application techniques, workmanship and curing conditions are indispensable in achieving good aesthetic, physical and mechanical results. Therefore it is important to know what conditions are available for the application phase. An effective knowledge of the historic materials and of the possible compatible solutions, of their characteristics and problems, is essential; tests are an important tool but the interpretation of their results in order to take useful decisions is a complex task, requiring a multidisciplinary team efficiently coordinated.

This contribution faces the problem of choosing, preparing and applying render mortars to be used in restoration and repair of historic buildings. The results obtained in this work clearly show that some industrial “dry mortar” products, even if they are not based on slaked lime binders, can be compatible with traditional, lime based ones, with regard to mechanical and physical properties and, therefore, should have a comparable behaviour.

Stone repair mortars used on the cathedral of Berne (Switzerland) have been refined from existing recipes. These hydraulic mortars without any organic additions are prepared on the building site. They are applied as two different layers, a coarser ground layer (KMtl) and a finer surface layer (DMtl) which imitates the stone material. The investigations were undertaken to understand the overall good practical experiences with these materials, and to anticipate the long term performance of this mortar system under the rough exposure conditions on the cathedral. Laboratory investigations included, petrophysical measurements and thin section analysis, of the individual materials but also on the system of DMtl-KMtl-stone. The investigations suggest that the mortars used are in many ways well adapted to the sandstones on the monument, and that the diverse application methods only provoke small differences in the resulting mortars at an early stage. But only in-situ observations will be able to show whether these small differences will lead to problems after long exposure to the elements.

In the French Alps, near Grenoble, in the middle of the nineteenth century, natural cements were massively used to produce “cast stone” (concrete block) and to simulate natural yellowish to reddish cut stone. In a first project, several historic concrete buildings were studied, and a major decay mechanism was identified: erosion, leading to the loss of the original fake stone appearance. Today, due to a lack of appropriate repair materials, grey Portland cement-based mortars and paintings are used, leading to a complete loss of the original aspect. Therefore, the aim of this second study was to develop and test compatible repair materials to conserve the cultural heritage of this region. Based on the results of the first project, specifications concerning the composition and main properties of compatible repair materials were established. Then, four mortars were selected, two of them being specifically formulated. In a second step, the intrinsic properties of those mortars were characterised, and finally, their mortar/concrete compatibility was assessed.

In this paper a comparison is made between two views on solving rain penetration problems in solid historic fired clay brick masonry. The first one aims at protecting the masonry against rain penetration (“rain coat” concept). In the second approach the penetration of rain in the masonry is accepted and the measures taken are focused on improving the

capillary

moisture transport in the masonry and on the application of materials with favourable drying characteristics and/or the enhancement of the drying conditions (“breathing” concept). It is shown that the often preferred protection approach may result into deterioration of the rain penetration problem instead of diminishing it. Also is shown that the second approach generally leads to a significant drying of the walls, thus providing a sound solution for rain penetration problems in solid historic fired clay brick masonry.

An experiment was carried out in order to understand the influence of hot mixing on the properties of hardened mortars in comparison with mortars made of lime hydrate and lime putty. Lime from the same quarry and producer was used in the form of lime hydrate, lime putty and quicklime. Two types of quicklime were used, varying in their calcination conditions and also their reactivity. Standard specimens of 40 × 40 × 160 mm were cast and evaluated after curing. Mechanical (compressive and flexural strength) and physical properties (open porosity, bulk density, capillary absorption) were determined on the specimens of hardened mortars. Thin sections of the mortars were prepared and evaluated using polarising microscopy in order to describe the structure of mortar including the presence of binder related particles. The produced hot mixed mortars had hardened properties comparable with the lime putty and lime hydrate mortars. Due to the micro-cracks in the binding matrix the hot mixed mortars showed higher porosity and capillary absorption. The heterogeneity of the hot mixed mortars was a result of the preparation technology.

An experiment was conducted to determine how the slaking characteristics of quicklime produced from the calcination of selected limestones relates to calcination time. The experiment also permitted the determination of the optimum calcination time by determining when each limestone was under or over burnt (as indicated by minimum water reactivity values). Four limestones, three from Scotland Dornie, Parkmore, Trearne and one from England- Ham Hill, were calcined at 900°C for a range of times between 2 and 5 h. The limestones used include both granoblastic metamorphic and bioclastic-micritic limestones with variable silicate contents. The resulting quicklimes were tested for reactivity by recording temperature rise and rate of temperature rise during slaking. Sieve analysis of the residue after slaking was performed on some samples. The Dornie limestone was the most reactive with an optimum calcination time of 4 h, Ham Hill was the second most reactive with an optimum calcination time of 3.5 h, Trearne followed at 4 h and the least reactive was the Parkmore sample with an optimum calcination time of 4.5 h. Dornie, Ham Hill and Trearne limestones underwent complete calcination with a weight loss greater than 40%. The experiment showed that the determination of the optimum calcination time through the examination of water reactivity was possible.

Roman cement was extensively used to decorate façades during the nineteenth and at the beginning of the twentieth century. Interest in this material has revived recently for the conservation of architectural Cultural Heritage, using new production sources. This article gives preliminary results on the characterisation of the raw materials and the main reactive phases (using XRD, SEM, selective dissolution and isothermal calorimetry) of a Roman cement recently produced from the Lilienfeld marlstone (Austria), compared with a commercial Roman cement (Vicat, France). The mineralogical composition of the two cements differs strongly due to the presence of sulphate minerals in the marlstone and on the temperature of calcination. Isothermal calorimetry and

in-situ

XRD carried out on cement pastes allow the identification of the AFm and AFt type phases as early age hydration products responsible for the flash setting typical to Roman cements. The alumina rich composition and the polymorphs of dicalcium silicates is strongly different in the Lilienfeld cement. This influences their reactivity at the later ages.

The development of strength in conservation mortars is of particular significance for new synthesized lime-based mixtures in terms of practical application, performance requirements and renovation cost of built monuments. In this work, the effect of relative humidity (RH%) on the strength characteristics of lime-natural pozzolan mortars was studied in three groups of specimens cured at different humidity conditions (45, 65 and 95 RH%). The development of compressive strength of the specimens was determined at preset time periods, from 7 days to 1 year. At the same time periods, the setting products and the microstructure of the mortars were monitored by thermal analysis (DTA/TG) and scanning electron microscopy (SEM/EDX). The results highlight the beneficial effect of elevated humidity on the strength of lime-pozzolan mortars and at the same time some issues related to the reliability and reproducibility of laboratory work in the field are addressed.

The influence of slaked limes (calcium hydroxide) on the fresh mortar properties varies according to morphological and chemical characteristics of the raw material. Until now there have been no sufficient scientific results to describe the parameters of calcium hydroxide that modify the plasticity in mortar systems. The aim of the investigations carried out here is to determine these plasticity regulating parameters. Therefore, several calcium hydroxides from different manufacturers have been analysed. The analyses included characterisation of raw materials and detailed investigations of differently slaked lime and lime putty at different times. Chemical and morphological principles of plasticity have been identified. Furthermore, these results have been evaluated by correlation of pilot plant experiments with defined lime mortars regarding their workability. The resulting material parameters responsible for plasticity are pointed out and distinguished between parameters relevant for plasticity values and those for plasticity development after extended soaking time.

This article deals with the phenomenon of the early water transport between fresh mortar and a dry brick. Two bricks with different transport parameters were considered in combination with two different mortars: a lime hydrate mortar and a cement mortar. Water transport was monitored during the first hour after contact using X-ray imaging and simulated using a commercial control volume (CVM) software tool. Such simulations are made possible by a newly developed method to measure transport parameters of fresh mortars. The amount of water leaving the mortar in 1 h depends mostly on two parameters of the mortar: initial and residual water content. The rate of flow across the interface shows a complex behaviour and is larger for cement mortar and for strongly absorbing brick. The accuracy of simulations is somewhat limited by the importance of over-capillary effects in the bricks near the interface. It appears that this over-capillary water is partly distributed over the brick, and partly reabsorbed by the mortar.

In the restoration or repair of old buildings, the correct estimation of the stress-strain-relationship of the existing structure is an important task. Masonry stiffness is crucial to the load bearing behaviour of a structure. When detailed investigations are lacking, it is common practise to evaluate the masonry stiffness from the compressive strength by standardised empirical relations established for various types of modern masonry. This paper illustrates the danger of this approach in two case studies. The first example is a stone bridge upon the Main at Ochsenfurt. The thickness of the mortar joints in this construction allowed the sampling of mortars suitable for the direct testing of the stress-strain relationship under uniaxial compression. Thus it was possible to calculate the masonry stiffness from the measured elastic modulus of stone and mortar. It became evident that a first rough estimation according to the building standard would not have been safe. In a second case study dealing with masonry pillars it is shown that the quality of mortar samples are influenced by the position of mortar in the masonry section.

This paper aims at improving the quality of lime mortar masonry by understanding the mechanics of mortars and masonry and their interaction. It investigates how the mortar’s compressive and flexural strengths impact the compressive and bond strength of clay brick masonry bound with calcium lime (CL) and natural hydraulic lime (NHL) mortars. It concludes that the strength of the bond has a greater impact on the compressive strength of masonry than the mortar’s strength. The masonry compressive strength increased proportionally to the strength of the bond up to 6 months. A regression analysis, giving a second order equation with coefficient of determination (R

2

) of 0.918, demonstrates a strong and predictable relationship between bond strength and masonry compressive strength. It was noted that CL90s mortar masonry reaching a high bond value was stronger than that built with a stronger mortar but displaying a poorer bond. Finally, the mechanics of lime mortars and their masonry are similar. The predominantly elastic behaviour of the mortars of higher hydraulic strength compares well with the elastic and brittle behaviour of their masonry, with either little (NHL2) or non-existent plasticity (NHL3.5 and 5); in contrast, the CL90 mortar and masonry exhibit a plastic behaviour.

This paper builds on previous work investigating the flexural bond strength, initial shear strength and compressive strength of fired clay brickwork built using hydraulic lime mortars. It has been shown that whilst flexural bond strength and initial shear strength of the brickwork generally increased with mortar strength, flexural bond strength was significantly impaired by both low and high brick water absorption. This paper describes a study of the pore size distribution of the surfaces of brick and mortar at the brick/mortar interface using Mercury Intrusion Porosimetry. The paper identifies critical pore sizes at the brick surface which would appear to govern resultant bond strength.

Grouting of historical masonries has been a widely used technique for regaining their integrity or strengthening them. Since cement-based grouts proved very strong, and in some cases destructive for these old masonries, grouts based on a lime-pozzolan binding system have been developed by researchers as an alternative, meeting compatibility issues required for repair interventions. In this paper, a number of grout compositions based on lime and other traditional binders are studied, with and without additions of limestone filler and nanoparticles of silica. In some, a small quantity of white cement (15 wt.%) was incorporated into the system. Apart from the different constituents of the binding system, the addition of admixtures was used for improving the properties of grouts. Rheological properties, such as fluidity, volume stability and penetrability of the grouts, were measured in the fresh state. Mechanical properties of dried grouts and grouted sand were checked. Volume changes due to drying shrinkage of grouts were recorded after demoulding and up to 28 days. The microstructure of the dried grouts of the control mixture and of that with silica nanoparticles was examined by stereoscope, image analysis, and DTA-TG methodology.

Most of the historical masonry buildings in Slovenia were built out of local stone or stone and brick with lime-based mortars. An efficient technique for improving the mechanical properties of stone or stone-brick walls is grout injection. In order to evaluate the quality and compatibility of commercially available injection grouts with materials present in historical masonry buildings, several types of hydraulic lime-pozzolana, lime-cement and cement grouts were tested. Chemical, physical and mechanical criteria to select optimal grout mixture for strengthening of historical masonry buildings were proposed, by which tested grouts were classified in three quality classes A, B and C. Only two commercial lime-cement grouts and one cement grout were able to meet the set requirements and were qualified in class B as medium quality grout (one lime-cement grout) or in class C as low quality grouts. Therefore, the design of hydrated lime-based grouts was carried out in continuation of our study, in order to obtain a grout that is highly compatible with the historical masonry in Slovenia. Among available limes, hydrated lime in powdered state and lime putty were used. Ground granulated blast furnace slag (GGBS), volcanic tuff, and limestone powder were used as mineral additives. It was found that the added combination of limestone powder and supplementary cementitious material (GGBS or tuff) has a beneficial influence on the properties of designed grout compositions.

Non-destructive or micro-destructive

in situ

tests are very relevant to the physical characterisation of materials used in historical buildings. “

Controlled penetration

,” “

sphere shock

” and “

sonic methods

” can be used to evaluate the mechanical resistance of mortars and renders or to monitor the hardening process after their application. Used to evaluate surface hardness,

micro-drilling

(DRMS) is a very sensitive technique, and its use in this field is expected to contribute to more precise results. However, the diversity of the composition of mortars and the systematic presence of abrasive components are limiting factors for the use of this method in this field. In this study, several mortars with different composition and hardness are compared using drilling resistance as the comparative parameter. The mortars were applied on-site aiming at their use in real situations. Extracted mortar samples were tested in the laboratory using resistance drilling which was complemented by additional methods currently used for

in situ

characterisation of these materials. The results highlight the need for an integrated perspective of laboratory and on-site information.

Compressive strength, porosity and two “

in situ

” techniques (ultrasonic velocity and rebound hardness test) are used for the characterisation of several aerial, hydraulic lime-based and cement-based mortars. Prismatic specimens and mortars applied as a brick render are used for the characterisation. A comparative analysis of the “

in situ

” test results and compressive strength is performed and the relationship between porosity and ultrasound velocity is analysed. A satisfactory relationship between the porosity and ultrasound velocity values is found and this indicates the possibility of estimating porosity from ultrasound velocity. The relationship between ultrasound velocity, rebound values and compressive strength emphasizes the potential of the “

in situ

” test methods for characterisation of mechanical properties of mortars.

The micro-structural evolution of a lime-pozzolan system, during hydration, was studied by

1

H Nuclear Magnetic Resonance (NMR). The hydration process was monitored for a period of 1 year by

1

H NMR spin-lattice relaxation measurements, performed in a portable magnet. The development of the hydration was also examined by scanning electron microscopy (SEM), X-ray diffraction (XRD), mercury intrusion porosimetry (MIP), infrared spectroscopy (FT-IR) and thermal analysis (DTA/TG) and compared with the NMR results. The results indicated that

1

H NMR provides valuable information on the hydration process of lime-pozzolan mortars in a non-invasive way, as it was possible to monitor the development of the hydration phases through the resulted microstructure, in real-time.

Non-standard tests are carried out on specimens made of materials extracted from historical objects, and they typically have non-standard dimensions. Assessments of strengthening effects are also usually studied on non-standard specimens purposely designed and made of materials modelled on the historic materials. The tests themselves are destructive, as engineers prefer destructive tests on a real material for a better understanding of the real material’s behaviour. Destructive tests provide a better opportunity to acquire data for numerical modelling and for following the gradients of qualities, namely after consolidation interventions. The tests include compression tests, bending tests, shear tests, and a series of tests on specific specimens designed for studies of consolidation effects.