B.A. Lubelli

Characterization and Damage of Brick Masonry

Clay brick is among the oldest used masonry materials. Given the technological evolutions since the industrial revolution, old bricks are much different from todays’ bricks. This chapter provides a review on the chemical, physical and mechanical properties of mortar, brick and masonry. In addition, a discussion on the possible causes of damage and the usage of expert systems in building diagnostics is also given.

The Effect of Environmental Conditions on Sodium Chloride Damage

Abstract Laboratory weathering tests are important in the field of restoration as they provide a means of estimating, in a relatively short time, the longer-term performance of conservation materials when applied in practice. Accelerated tests to simulate the damage caused to porous materials by soluble salts such as sodium sulphate are well known and highly effective. However, when using sodium chloride the existing test methods are not particularly successful. Research on case studies has shown that the environmental conditions play an important role in determining the occurrence of the decay. Therefore understanding the effect of the environmental conditions on the damage constitutes a first step in the development of an effective weathering test for sodium chloride. The research described in this paper studies the effect of environmental conditions on the decay due to sodium chloride with the ultimate aim of defining an effective laboratory test. The experiments have been performed on two plasters with very different physical, mechanical and mineralogical properties. Different techniques of analysis have been used: mercury intrusion porosimetry, optical polarized microscopy, environmental scanning electron microscopy, chemical analyses and X-ray diffraction. The results obtained highlighted which of the test conditions under evaluation were the most effective. Using this information, a new procedure for an effective accelerated salt weathering test using sodium chloride is proposed.

Application Protocol for the Consolidation of Calcareous Substrates by the Use of Nanolimes: From Laboratory Research to Practice

Abstract Calcareous materials such as limestone and lime-based mortars, widely used in the Built Heritage, are often subjected to degradation processes that can lead to loss of cohesion and material loss. Consolidation of these materials with liquid products via the surface is a common practice; however, the most used consolidation products (e. g. TEOS-based) show a poor physical-chemical compatibility with calcareous substrates. For application on calcareous materials, the so-called nanolimes, i. e. dispersions of lime nanoparticles in alcohols, are an alternative to TEOS-based products, thanks to their chemical compatibility with lime-based substrates. Nanolimes can help to recover a superficial loss of cohesion. However, their in-depth consolidation effect is not always satisfactory. Previous work has shown that a better deposition of lime nanoparticles in depth can be achieved by adapting the properties of the nanolime dispersion (kinetic stability and evaporation rate) to the moisture transport properties of the substrate, through optimization of the solvent. In this paper, freshly synthetized nanolimes were dispersed in pure ethanol and/or in binary mixture of ethanol (95 %) and water (5 %). These nanolimes were applied on Maastricht limestone and on a lime-based mortar by capillary absorption (method commonly used for laboratory tests) and by nebulization (method widely used in situ). The aim of this research is to fill the gap between laboratory tests and on site application, providing an application protocol for restorers and professionals in the field. The research shows that results obtained by application by capillary absorption do not always correspond to those obtained by nebulization. This fact should be considered when deciding on the use of a consolidation surface treatment in practice.

Effect of borax on the wetting properties and crystallization behavior of sodium sulfate

Borax has been identified as a possible crystallization modifier for sodium sulfate. Understanding the effect of borax on factors influencing transport and crystallization kinetics of sodium sulfate helps to clarify how this modifier might limit crystallization damage. It has been observed that the addition of borax to sodium sulfate solutions has no influence on the wetting properties (contact angle on glass, surface tension, or evaporation rate) and therefore will not influence solution transport. Additionally, the influence of borax on the crystallization kinetics of sodium sulfate was studied under controlled environmental conditions. This was carried out in mixtures in glass microcapillaries, and sequentially in droplets on glass plates. Under the here studied precipitation conditions, the addition of borax has no influence on the supersaturation ratio at the onset of crystallization, but it significantly affects the crystallization pattern of anhydrous sodium sulfate crystals (thenardite). Using RAMAN spectroscopy, two different hydrates of borax were identified after precipitation, depending on the initial concentration of the solution. Each hydrate has a different effect on the subsequent crystallization of sodium sulfate. The decahydrate polymorph of borax leads to the precipitation of hydrated sodium sulfate crystals (mirabilite) and the pentahydrate form favors the precipitation of the anhydrous sodium sulfate crystals (thenardite) with an altered crystal habit. Using X-ray diffraction, overdevelopment of the (111), (131), (222) and (153) faces of thenardite was identified. Additionally, the ratios between several peaks are reversed. These results confirm the deviation of the grown crystals of the equilibrium crystal shape of thenardite as observed with optical microscopy.

The Role Of The Pointing Mortar In The DamageDue To Salt Crystallisation

An accurate choice of a re-pointing mortar is fundamental for successful restoration work. Nevertheless many cases of failure show that the choice is not always sensible and that there is still a lack of knowledge on the compatibility of repair mortar for historic masonry. The new re-pointing mortar should be as durable as possible and possess physical, chemical and mechanical characteristics which are compatible with the ones of the existing masonry components. The use of an incompatible mortar can affect the moisture transport inside the masonry and consequently lead to a different drying behaviour of the various material: this can cause damage or speed up the decay process already present in the wall. The object of this paper is an experimental study carried out on two types of re-pointing mortar (cement and putty lime) applied to wallettes built with different combinations of bricks and bedding mortars. The specimens were subjected to a crystallisation test and the damage was surveyed. The drying behaviour was studied by NMR on little bricWmortar specimens to understand the moisture transport mechanism between the three components: brickibedding mortaripointing mortar. The aim was to find a relation benveen the drying behaviour and the damage due to salt crystallisation. From this research it results that damage is generally located where the evaporation is stronger. The influence of pointing mortar in the damage process due to salt crystallisation is verified: a coarse lime pointing allows evaporation so the damage consists in a superficial loss of cohesion of the material; a dense pointing slows down the evaporation and creates a discontinuity at the interface bedding mortarlpointing mortar resulting in the end in a loss of bond between the components of the wall.

Characterization of lime mortar additivated with crystallization modifiers

ABSTRACT Additivating mortars with crystallization modifiers is a novel approach to mitigate salt crystallization damage in historic masonry. Once verified the effectiveness of crystallization modifiers in bulk solution, the next step consists in verifying whether: (i) modifiers are still effective when mixed in mortar and going through the carbonation process and (ii) modifiers alter any mortar properties which might limit their application. This research addresses these issues for sodium ferrocyanide and borax, modifiers for sodium chloride, and sodium sulfate, respectively. Several experimental techniques have been applied to elucidate these questions. The results show that the selected modifiers are still able to alter the salt crystallization after going through the carbonation process of the mortar. Besides, no major effects of the modifiers on the fresh and hardened mortar properties were observed. It can therefore be concluded that there are no restraints for the future use of these crystallization modifiers in restoration mortars.

Desalination of Valuable Brick Masonry by Poulticing: Laboratory and in Situ Study / Entsalzen von wertvollem Mauerwerk mit Hilfe von Kompressen: Untersuchungen im Labor und vor Ort

The brick masonry masterpieces, located in the “masons tower” of the Waag building in Amsterdam, are suffering from severe salt crystallization damage. The damage is due to dissolution/crystallization cycles, induced by RH changes, of the hygroscopic salts present in the masonry. Taking into account the specific circumstances, desalination of the masonry masterpieces has been considered. By reducing the salt content in the outer centimetres of the masonry, the risk of crystallization/dissolution cycles can be limited and, consequently, the damage development will be slowed down. First, desalination experiments have been carried out in laboratory, on bricks similar to the ones present in the masterpieces. On the basis of the pore size distribution of the brick, desalination poultices have been selected. These poultices were based on kaolin or bentonite clay with and without the addition of cellulose and sand. The good efficiency obtained in desalination efficiency tests in laboratory encouraged the try out of the poultices on test panels on site. Measurements of the salt content in the wall, before and after desalination, showed that large part of the salts was extracted after only two applications, even up to a depth of 7cm.

Evaluation of Chemical Treatments against Rising Damp in a Long-term Site Test / Beurteilung chemischer Maßnahmen gegen aufsteigende Feuchtigkeit im Rahmen eines Langzeitversuchs

Rising damp is a well known phenomenon in ancient buildings. The creation of a horizontal barrier against capillary rise (damp proof course, DPC) by injection of chemical products in the wall is a diffused way of tackling rising damp problems. Chemical products may work well under controlled conditions in laboratory. Nevertheless, in practice, circumstances like lack of homogeneity of the substrate, high moisture and salt content may compromise the effectiveness of the treatment. In this research the effectiveness and durability of 4 chemical injection products (acrylamide, gelling silane, siloxane and siliconate) applied 16 years ago in test panels on different parts of the same wall, have been investigated by repeating sampling at the same locations and in the same way as performed in the past. Powder samples were taken from the wall, above and below the treated zone, and masonry cores were collected in the injection zone. As reference, an adjacent not treated area was sampled too. The efficiency of the treatment was evaluated by determining the moisture and salt content of the powder samples and by performing water absorption tests on the cores. Eventual differences in efficiency between mortar and brick were checked too. On the basis of the new and old results, the long term effectiveness of the treatments was assessed. Most of the treatments showed to have a limited effectiveness. Among the studied injection treatments, only one, siliconate, resulted in a significant reduction of the moisture content above the treated zone. In all cases the products were found to be more effective in the brick than in the mortar. No decrease of effectiveness of the products in time has been observed.

Veränderung des Trocknungsverhaltens von zwei Arten von Ziegelsteinen nach einer Anti-Graffiti Behandlung und daraus möglicherweise erwachsende Risiken / Change in Drying Behaviour of two Types of Bricks after Treatment with Anti-graffiti and Possible Risks

Anti-graffti coatings are often used to protect facades against unwanted graffiti. Despite the fact that anti-graffiti are widely used, their effect on the drying behaviour of materials is not well known. Product data sheets, as well as recommendations on their application, generally only consider their watcr vapour permeability without taking into account that the drying behaviour of a material is largely governed by liquid water transport. The paper reports a study carried out on six types of anti-graffiti coatings (permanent and sacrificial, water repellent and not) applied to two materials (fired-clay brick and calcium silicate brick). The effect of the anti-graffiti coatings on the drying behaviour of these materials was evaluated by means of drying tests performed at different RH. The obtained results are analysed as a function of product composition and the properties of the substrate materials, such as porosity and pore size distribution. The possible consequences of the application of the tested anti-grafhti coatings on common damage processes, such as frost and salt crystallization, are discussed.

Salt Damage and RH Changes: The Case of the Waag Building in Amsterdam / Salzschäden und Veränderungen der relativen Luftfeuchtigkeit: das Gebäude de Waag in Amsterdam, ein Fallbeispiel

Changes in the air MM can cause damage to building materials contaminated with hygroscopic saus, even in the absence of any other moishwe source. This phenomenon has been observed in the case of the iflag build ing in Amsterdam, affected by severe salt decay. The investigation, canied out by means of different tech niques (e.g. ESEM-EDX, IC and XRD), bas revealed the presence in the masomy of a large amount of hygroscopic saks (mainly sodium chloride and nitrates) and the absence of any moisture sources other than the RIT of the air. Besides, an adsorption experiment performed on sampks from the building has pointed out the hygroscopic moisture uptake of the salt mix even at low RH. These resuits, in combination with a moni toring of the interiorclimate for a period of about 1 year, have allowed to conchide that the damage obsen’ed is due to the frequent RK changes through the equilibrium where dissolution/ciystallization of the salt mix takes place, On the basis of these tindings en advice for the conservation of the building Was given