B. Lubelli
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A study of the mechanism behind crystal lifting
Crystallization pressure of confined KAl(SO4)2⋅12H2O crystals
Journal article
(2026)
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Anton Tuluk, Erik de Ronde, Michael Steiger, Barbara Lubelli, Hugo Meekes, Elias Vlieg
Salt crystallization pressure is one of the main sources of weathering in porous building materials. In our work we study the origin of this phenomenon using single crystals of KAl(SO4)2⋅12H2O (potassium aluminium sulphate dodecahydrate) as model system. Crystals were grown immersed in a solution of a specific supersaturation (σ=10−80%). Evidence of crystallization pressure was the vertical lift of weights on top of the growing crystal, which was measured by in-situ displacement sensors. A clear supersaturation threshold of σ≃30% for a 0.5 N weight is required to initiate lifting in our model system. Above this value, the maximum displacement increases nonlinearly with σ and depends on crystal orientation, interfacial wettability, and applied load. Hydrophobic interfaces suppress crystal growth by limiting mass transport, whereas hydrophilic confinement supports continuous growth until the local supersaturation is exhausted. In saturated solutions, on the other hand, a load leads to dissolution. Based on the observations, we propose a mechanism for crystallization pressure for which the growth of the unloaded faces adjacent to the confined face is key. These results refine our understanding of crystallization pressure in confined spaces and can help explain and mitigate salt-induced damage in porous materials.
...
Salt crystallization pressure is one of the main sources of weathering in porous building materials. In our work we study the origin of this phenomenon using single crystals of KAl(SO4)2⋅12H2O (potassium aluminium sulphate dodecahydrate) as model system. Crystals were grown immersed in a solution of a specific supersaturation (σ=10−80%). Evidence of crystallization pressure was the vertical lift of weights on top of the growing crystal, which was measured by in-situ displacement sensors. A clear supersaturation threshold of σ≃30% for a 0.5 N weight is required to initiate lifting in our model system. Above this value, the maximum displacement increases nonlinearly with σ and depends on crystal orientation, interfacial wettability, and applied load. Hydrophobic interfaces suppress crystal growth by limiting mass transport, whereas hydrophilic confinement supports continuous growth until the local supersaturation is exhausted. In saturated solutions, on the other hand, a load leads to dissolution. Based on the observations, we propose a mechanism for crystallization pressure for which the growth of the unloaded faces adjacent to the confined face is key. These results refine our understanding of crystallization pressure in confined spaces and can help explain and mitigate salt-induced damage in porous materials.
Salt crystallization is one of the most common causes of decay in porous building materials. Plasters and renders, mainly due to their location at the surface of walls, where most often salt accumulation occurs, are particularly subjected to salt decay. Despite the relevance of the problem, there are no standard salt weathering tests for the assessment of the durability of plasters and renders against salt decay. This research proposes a salt weathering
procedure, based on an adaptation of the RILEM TC 271-ASC recommendation, and it validates it by applying it to three plaster types (based on hydrated lime, natural hydraulic lime and hydrated lime-cement). Combined stone/plaster specimens are prepared and contaminated with 10 % (weight salt/weight solution) sodium sulphate and sodium chloride solutions. The damage development is assessed by visual and photographic monitoring, gravimetric measurements of the material loss, assessment of salt distribution in the specimens, and SEM
observations supported by EDX mapping on thin sections. The results show that the test procedure is effective in causing damage in the tested plasters, within the time period of the test (about 4 months), and that damage increases with subsequent cycles. The decay severity and type differ depending on type of salt and/or of plaster.
Suggestions for further improvement of the procedure are provided. ...
procedure, based on an adaptation of the RILEM TC 271-ASC recommendation, and it validates it by applying it to three plaster types (based on hydrated lime, natural hydraulic lime and hydrated lime-cement). Combined stone/plaster specimens are prepared and contaminated with 10 % (weight salt/weight solution) sodium sulphate and sodium chloride solutions. The damage development is assessed by visual and photographic monitoring, gravimetric measurements of the material loss, assessment of salt distribution in the specimens, and SEM
observations supported by EDX mapping on thin sections. The results show that the test procedure is effective in causing damage in the tested plasters, within the time period of the test (about 4 months), and that damage increases with subsequent cycles. The decay severity and type differ depending on type of salt and/or of plaster.
Suggestions for further improvement of the procedure are provided. ...
Salt crystallization is one of the most common causes of decay in porous building materials. Plasters and renders, mainly due to their location at the surface of walls, where most often salt accumulation occurs, are particularly subjected to salt decay. Despite the relevance of the problem, there are no standard salt weathering tests for the assessment of the durability of plasters and renders against salt decay. This research proposes a salt weathering
procedure, based on an adaptation of the RILEM TC 271-ASC recommendation, and it validates it by applying it to three plaster types (based on hydrated lime, natural hydraulic lime and hydrated lime-cement). Combined stone/plaster specimens are prepared and contaminated with 10 % (weight salt/weight solution) sodium sulphate and sodium chloride solutions. The damage development is assessed by visual and photographic monitoring, gravimetric measurements of the material loss, assessment of salt distribution in the specimens, and SEM
observations supported by EDX mapping on thin sections. The results show that the test procedure is effective in causing damage in the tested plasters, within the time period of the test (about 4 months), and that damage increases with subsequent cycles. The decay severity and type differ depending on type of salt and/or of plaster.
Suggestions for further improvement of the procedure are provided.
procedure, based on an adaptation of the RILEM TC 271-ASC recommendation, and it validates it by applying it to three plaster types (based on hydrated lime, natural hydraulic lime and hydrated lime-cement). Combined stone/plaster specimens are prepared and contaminated with 10 % (weight salt/weight solution) sodium sulphate and sodium chloride solutions. The damage development is assessed by visual and photographic monitoring, gravimetric measurements of the material loss, assessment of salt distribution in the specimens, and SEM
observations supported by EDX mapping on thin sections. The results show that the test procedure is effective in causing damage in the tested plasters, within the time period of the test (about 4 months), and that damage increases with subsequent cycles. The decay severity and type differ depending on type of salt and/or of plaster.
Suggestions for further improvement of the procedure are provided.
Treatment of historic surfaces with water repellent and consolidation products
Choices for intervention
This research investigates how community participation can be enhanced to support the sustainable reconstruction of residential heritage in the Old City of Aleppo. In the aftermath of the Syrian war, reconstruction interventions on traditional courtyard houses have been affected by several issues, such as a lack of knowledge among junior architects and craftsmen (regarding houses’ conditions, relevant regulations, and residents’ needs), and limited residents’ participation in decision-making processes. Drawing on international experiences in similar post-war contexts that highlight the role of education and a participatory approach as critical components for sustainable reconstruction efforts. This research conducts a comparative analysis of several international capacity-building and co-creation initiatives to identify effective methods of stakeholder engagement. Building on these findings, the study proposes an education programme tailored to the socio-cultural and regulatory context of the Old City of Aleppo. The proposed programme integrates academic knowledge with community perspectives using validated teaching and participatory methods, such as photovoice, walkthrough, and lectures etc., within a co-creation framework. It aims to raise awareness, build capacity, and enable residents through participation in all phases of the programme: co-diagnostic, co-design, co-implementation and co-monitoring. This way, residents are empowered to play an active role in interventions on residential heritage and to align these interventions with their needs and current regulations. Thus, the research presents a scalable model for cultural and socially sustainable residential heritage reconstruction.
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This research investigates how community participation can be enhanced to support the sustainable reconstruction of residential heritage in the Old City of Aleppo. In the aftermath of the Syrian war, reconstruction interventions on traditional courtyard houses have been affected by several issues, such as a lack of knowledge among junior architects and craftsmen (regarding houses’ conditions, relevant regulations, and residents’ needs), and limited residents’ participation in decision-making processes. Drawing on international experiences in similar post-war contexts that highlight the role of education and a participatory approach as critical components for sustainable reconstruction efforts. This research conducts a comparative analysis of several international capacity-building and co-creation initiatives to identify effective methods of stakeholder engagement. Building on these findings, the study proposes an education programme tailored to the socio-cultural and regulatory context of the Old City of Aleppo. The proposed programme integrates academic knowledge with community perspectives using validated teaching and participatory methods, such as photovoice, walkthrough, and lectures etc., within a co-creation framework. It aims to raise awareness, build capacity, and enable residents through participation in all phases of the programme: co-diagnostic, co-design, co-implementation and co-monitoring. This way, residents are empowered to play an active role in interventions on residential heritage and to align these interventions with their needs and current regulations. Thus, the research presents a scalable model for cultural and socially sustainable residential heritage reconstruction.
Plasters and renders in historic buildings are often damaged by salt crystallization, because of their relatively low mechanical strength and their location at the surface of the wall, where evaporation and salt accumulation take place. Current solutions to provide plasters and renders with a better resistance with respect to salt decay are mostly based on the use of stronger binders, such as cement, or of water repellent additives. Unfortunately, both these solutions show often a low compatibility with the materials used in historic buildings.
In the past decade, research has been carried to improve the durability of plasters against salt damage by the use of crystallization inhibitors. Crystallization inhibitors are ions or molecules able to delay crystal nucleation and growth of the crystal by preferentially adsorbing on specific crystal faces. Sodium ferrocyanide (NaFeC) is a well-known inhibitor of sodium chloride. Past research has shown that NaFeC, is able to provide hydrated lime-based mortars with an improved resistance to salt decay? However, leaching of this water-soluble inhibitor may compromise its effect in time. Recently, encapsulation of NaFeC in chitosan-calcium alginate capsules was proven effective to control the release of the inhibitor in mortar. In this paper, the durability of a natural hydraulic lime plaster with encapsulated NaFeC crystallization inhibitor is discussed based on the results of laboratory accelerated salt weathering test and monitoring of test panels applied on site. ...
In the past decade, research has been carried to improve the durability of plasters against salt damage by the use of crystallization inhibitors. Crystallization inhibitors are ions or molecules able to delay crystal nucleation and growth of the crystal by preferentially adsorbing on specific crystal faces. Sodium ferrocyanide (NaFeC) is a well-known inhibitor of sodium chloride. Past research has shown that NaFeC, is able to provide hydrated lime-based mortars with an improved resistance to salt decay? However, leaching of this water-soluble inhibitor may compromise its effect in time. Recently, encapsulation of NaFeC in chitosan-calcium alginate capsules was proven effective to control the release of the inhibitor in mortar. In this paper, the durability of a natural hydraulic lime plaster with encapsulated NaFeC crystallization inhibitor is discussed based on the results of laboratory accelerated salt weathering test and monitoring of test panels applied on site. ...
Plasters and renders in historic buildings are often damaged by salt crystallization, because of their relatively low mechanical strength and their location at the surface of the wall, where evaporation and salt accumulation take place. Current solutions to provide plasters and renders with a better resistance with respect to salt decay are mostly based on the use of stronger binders, such as cement, or of water repellent additives. Unfortunately, both these solutions show often a low compatibility with the materials used in historic buildings.
In the past decade, research has been carried to improve the durability of plasters against salt damage by the use of crystallization inhibitors. Crystallization inhibitors are ions or molecules able to delay crystal nucleation and growth of the crystal by preferentially adsorbing on specific crystal faces. Sodium ferrocyanide (NaFeC) is a well-known inhibitor of sodium chloride. Past research has shown that NaFeC, is able to provide hydrated lime-based mortars with an improved resistance to salt decay? However, leaching of this water-soluble inhibitor may compromise its effect in time. Recently, encapsulation of NaFeC in chitosan-calcium alginate capsules was proven effective to control the release of the inhibitor in mortar. In this paper, the durability of a natural hydraulic lime plaster with encapsulated NaFeC crystallization inhibitor is discussed based on the results of laboratory accelerated salt weathering test and monitoring of test panels applied on site.
In the past decade, research has been carried to improve the durability of plasters against salt damage by the use of crystallization inhibitors. Crystallization inhibitors are ions or molecules able to delay crystal nucleation and growth of the crystal by preferentially adsorbing on specific crystal faces. Sodium ferrocyanide (NaFeC) is a well-known inhibitor of sodium chloride. Past research has shown that NaFeC, is able to provide hydrated lime-based mortars with an improved resistance to salt decay? However, leaching of this water-soluble inhibitor may compromise its effect in time. Recently, encapsulation of NaFeC in chitosan-calcium alginate capsules was proven effective to control the release of the inhibitor in mortar. In this paper, the durability of a natural hydraulic lime plaster with encapsulated NaFeC crystallization inhibitor is discussed based on the results of laboratory accelerated salt weathering test and monitoring of test panels applied on site.
The use of crystallization inhibitors for mitigation of salt decay in building materials was proposed for the first time about 20 years ago. Since then, research has been carried out to explore possible applications of crystallization inhibitors. This work discusses the potentials and limitations of mortars with mixed-in sodium-ferrocyanide, an inhibitor of sodium chloride crystallization, and provides an outlook for further developments.
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The use of crystallization inhibitors for mitigation of salt decay in building materials was proposed for the first time about 20 years ago. Since then, research has been carried out to explore possible applications of crystallization inhibitors. This work discusses the potentials and limitations of mortars with mixed-in sodium-ferrocyanide, an inhibitor of sodium chloride crystallization, and provides an outlook for further developments.
Salt (NaCl) weathering in mortar, can be mitigated by incorporating a crystallisation inhibitor (sodium ferrocyanide) during mortar preparation. However, the service-life of the inhibitor is limited, due to its susceptibility to leaching out of mortar. Encapsulating the inhibitor in chitosan-calcium alginate capsules has demonstrated controlled-release of the inhibitor and therefore, reduction in its leaching. Nevertheless, the addition of capsules may have a negative effect on mortar's properties and/or its salt-weathering resistance. In this research, natural hydraulic lime (NHL) and commercial cement-based mortars were prepared, with encapsulated inhibitor and with directly mixed-in inhibitor. Mechanical and physical properties of mortars were assessed experimentally. An accelerated NaCl-weathering test was performed to assess the durability of mortar to salt damage. The damage evolution was assessed visually and by quantifying material loss, efflorescence and leaching of the inhibitor. At the end of the test, crystal morphology inside the pores was examined using SEM. The results show that adding inhibitor, both in encapsulated and mixed-in form, had a negligible effect on the properties of NHL and cement-based mortars. Compared to the reference mortar without inhibitor, NHL-mortars with mixed-in inhibitor and encapsulated inhibitor had a better durability to salt damage, showing negligible material loss. The capsules facilitated controlled-release and reduced leaching of the inhibitor. In cement-based mortars including the reference, no damage was observed; still, the inhibitor was shown to be effective in modifying the salt crystal habit. The results show that encapsulation of the inhibitor can improve the service-life of the mortar without compromising its performance.
...
Salt (NaCl) weathering in mortar, can be mitigated by incorporating a crystallisation inhibitor (sodium ferrocyanide) during mortar preparation. However, the service-life of the inhibitor is limited, due to its susceptibility to leaching out of mortar. Encapsulating the inhibitor in chitosan-calcium alginate capsules has demonstrated controlled-release of the inhibitor and therefore, reduction in its leaching. Nevertheless, the addition of capsules may have a negative effect on mortar's properties and/or its salt-weathering resistance. In this research, natural hydraulic lime (NHL) and commercial cement-based mortars were prepared, with encapsulated inhibitor and with directly mixed-in inhibitor. Mechanical and physical properties of mortars were assessed experimentally. An accelerated NaCl-weathering test was performed to assess the durability of mortar to salt damage. The damage evolution was assessed visually and by quantifying material loss, efflorescence and leaching of the inhibitor. At the end of the test, crystal morphology inside the pores was examined using SEM. The results show that adding inhibitor, both in encapsulated and mixed-in form, had a negligible effect on the properties of NHL and cement-based mortars. Compared to the reference mortar without inhibitor, NHL-mortars with mixed-in inhibitor and encapsulated inhibitor had a better durability to salt damage, showing negligible material loss. The capsules facilitated controlled-release and reduced leaching of the inhibitor. In cement-based mortars including the reference, no damage was observed; still, the inhibitor was shown to be effective in modifying the salt crystal habit. The results show that encapsulation of the inhibitor can improve the service-life of the mortar without compromising its performance.
Crystallisation inhibitors, such as sodium ferrocyanide (NaFeCN), are highly effective in mitigating NaCl-induced weathering in lime-based mortars; however, direct addition of NaFeCN in lime-mortars increases its susceptibility to leaching and rapid depletion, thus compromising long-term performance. Here, we present hydrogel-capsules for the controlled-release of NaFeCN within hydraulic mortars for the prolonged prevention of salt weathering. Capsules were prepared by complexing chitosan and calcium-alginate in different ratios containing different concentrations of NaFeCN. The release of NaFeCN from these capsules was measured in (1) simulated lime-mortar solution (2) from mortar specimens incorporated with calcium alginate (CA) and chitosan-calcium-alginate (Cs-CA) capsules using ultraviolet–visible light spectrophotometry and Inductive Coupled Plasma-Optical Emission Spectroscopy. Mortars containing Cs-CA capsules exhibited controlled-release of NaFeCN with four times lower effective diffusion coefficient, compared to incorporating NaFeCN directly in mortar. Conversely, mortar containing CA capsules (without chitosan) released NaFeCN rapidly. Thus, chitosan’s presence in CA is necessary for tuning NaFeCN release and the reason may be attributed to chitosan’s role in reducing CA’s permeability and chitosan’s electrostatic-attraction to ferrocyanide anions, slowing diffusion of the latter. In conclusion, using Cs-CA capsules can control the release of NaFeCN within mortar, providing a steady NaFeCN supply to prolong mortar’s resistance against salt damage.
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Crystallisation inhibitors, such as sodium ferrocyanide (NaFeCN), are highly effective in mitigating NaCl-induced weathering in lime-based mortars; however, direct addition of NaFeCN in lime-mortars increases its susceptibility to leaching and rapid depletion, thus compromising long-term performance. Here, we present hydrogel-capsules for the controlled-release of NaFeCN within hydraulic mortars for the prolonged prevention of salt weathering. Capsules were prepared by complexing chitosan and calcium-alginate in different ratios containing different concentrations of NaFeCN. The release of NaFeCN from these capsules was measured in (1) simulated lime-mortar solution (2) from mortar specimens incorporated with calcium alginate (CA) and chitosan-calcium-alginate (Cs-CA) capsules using ultraviolet–visible light spectrophotometry and Inductive Coupled Plasma-Optical Emission Spectroscopy. Mortars containing Cs-CA capsules exhibited controlled-release of NaFeCN with four times lower effective diffusion coefficient, compared to incorporating NaFeCN directly in mortar. Conversely, mortar containing CA capsules (without chitosan) released NaFeCN rapidly. Thus, chitosan’s presence in CA is necessary for tuning NaFeCN release and the reason may be attributed to chitosan’s role in reducing CA’s permeability and chitosan’s electrostatic-attraction to ferrocyanide anions, slowing diffusion of the latter. In conclusion, using Cs-CA capsules can control the release of NaFeCN within mortar, providing a steady NaFeCN supply to prolong mortar’s resistance against salt damage.
The impregnation of the exterior surface of a masonry wall with a water repellent is a common intervention in (historic) building renovation and maintenance. Such treatments, whilst degrading at the surface with time under influence of ultra violet light, remain effective below the surface several decades after their application. During renovation works of masonry previously treated with a water repellent, the question arises whether it is necessary to repeat the hydrophobic treatment of the entire masonry after repointing. Opposing opinions exist with this regard, but no research clearly supporting one or the other. This research investigates for the first time the effect of hydrophobic treatment when applied on previously treated and repointed masonry walls. Small masonry walls were subjected to rain periods in the laboratory and their water uptake and drying behaviour were studied. Moreover, this laboratory research was followed by 30 months of outdoor exposition of the masonry specimens. The following cases were considered: (1) wall treated with water repellent, (2) wall treated with water repellent, followed by repointing but without new water repellent treatment, (3) wall treated with water repellent, followed by repointing and retreatment. This was done for three different types of pointing mortar: ordinary Portland cement and natural hydraulic lime with standard sand, and natural hydraulic lime with sand with one grain size. The results show that, after prolonged rain periods, the water uptake by repointed but not retreated masonry is comparable to that of untreated, non-hydrophobic masonry, whereas drying is considerably slower. This leads to a high saturation degree in repointed but not retreated masonry, which, in turn, increases the risk of damage to the masonry by e.g. frost. Therefore, retreating repointed hydrophobic masonry should definitively be considered.
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The impregnation of the exterior surface of a masonry wall with a water repellent is a common intervention in (historic) building renovation and maintenance. Such treatments, whilst degrading at the surface with time under influence of ultra violet light, remain effective below the surface several decades after their application. During renovation works of masonry previously treated with a water repellent, the question arises whether it is necessary to repeat the hydrophobic treatment of the entire masonry after repointing. Opposing opinions exist with this regard, but no research clearly supporting one or the other. This research investigates for the first time the effect of hydrophobic treatment when applied on previously treated and repointed masonry walls. Small masonry walls were subjected to rain periods in the laboratory and their water uptake and drying behaviour were studied. Moreover, this laboratory research was followed by 30 months of outdoor exposition of the masonry specimens. The following cases were considered: (1) wall treated with water repellent, (2) wall treated with water repellent, followed by repointing but without new water repellent treatment, (3) wall treated with water repellent, followed by repointing and retreatment. This was done for three different types of pointing mortar: ordinary Portland cement and natural hydraulic lime with standard sand, and natural hydraulic lime with sand with one grain size. The results show that, after prolonged rain periods, the water uptake by repointed but not retreated masonry is comparable to that of untreated, non-hydrophobic masonry, whereas drying is considerably slower. This leads to a high saturation degree in repointed but not retreated masonry, which, in turn, increases the risk of damage to the masonry by e.g. frost. Therefore, retreating repointed hydrophobic masonry should definitively be considered.
A model of the adaptive reuse process of heritage buildings
Validation on four cases in the Netherlands
Adaptive reuse (AR) of heritage buildings is a complex process involving many stakeholders with different ambitions. Recently, a theoretical model has been proposed to facilitate this process. However, the validation of this model and investigation of the nexus between process steps, methods/tools used by architects, and the effectiveness of projects are still lacking. This paper aims to validate the model by examining four AR projects in the Netherlands, considered effective as winners of a prestigious architectural prize. The research methods included literature reviews, case visits, and interviews with architects and other stakeholders. The model was refined, and methods/tools used by architects in the process steps were identified, highlighting their link with the effectiveness of results.
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Adaptive reuse (AR) of heritage buildings is a complex process involving many stakeholders with different ambitions. Recently, a theoretical model has been proposed to facilitate this process. However, the validation of this model and investigation of the nexus between process steps, methods/tools used by architects, and the effectiveness of projects are still lacking. This paper aims to validate the model by examining four AR projects in the Netherlands, considered effective as winners of a prestigious architectural prize. The research methods included literature reviews, case visits, and interviews with architects and other stakeholders. The model was refined, and methods/tools used by architects in the process steps were identified, highlighting their link with the effectiveness of results.
Recommendation of RILEM TC 271-ASC
New accelerated test procedure for the assessment of resistance of natural stone and fired-clay brick units against salt crystallization
Journal article
(2023)
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B. Lubelli, I. Rörig-Daalgard, More Authors..., A. M. Aguilar, M. Aškrabić, K. Beck, C. Bläuer, V. Cnudde, A. M. D’Altri, R. van Hees, A. Kamat
This recommendation is devoted to testing the resistance of natural stone and fired-clay brick units against salt crystallization. The procedure was developed by the RILEM TC 271-ASC to evaluate the durability of porous building materials against salt crystallization through a laboratory method that allows for accelerated testing without compromising the reliability of the results. The new procedure is designed to replicate salt damage caused by crystallization near the surface of materials as a result of capillary transport and evaporation. A new approach is proposed that considers the presence of two stages in the salt crystallization test. In the first, the accumulation stage, salts gradually accumulate on or near the surface of the material due to evaporation. In the second, the propagation stage, damage initiates and develops due to changes in moisture content and relative humidity that trigger salt dissolution and crystallization cycles. To achieve this, two types of salt were tested, namely sodium chloride and sodium sulphate, with each salt tested separately. A methodology for assessing the salt-induced damage is proposed, which includes visual and photographical observations and measurement of material loss. The procedure has been preliminarily validated in round robin tests.
...
This recommendation is devoted to testing the resistance of natural stone and fired-clay brick units against salt crystallization. The procedure was developed by the RILEM TC 271-ASC to evaluate the durability of porous building materials against salt crystallization through a laboratory method that allows for accelerated testing without compromising the reliability of the results. The new procedure is designed to replicate salt damage caused by crystallization near the surface of materials as a result of capillary transport and evaporation. A new approach is proposed that considers the presence of two stages in the salt crystallization test. In the first, the accumulation stage, salts gradually accumulate on or near the surface of the material due to evaporation. In the second, the propagation stage, damage initiates and develops due to changes in moisture content and relative humidity that trigger salt dissolution and crystallization cycles. To achieve this, two types of salt were tested, namely sodium chloride and sodium sulphate, with each salt tested separately. A methodology for assessing the salt-induced damage is proposed, which includes visual and photographical observations and measurement of material loss. The procedure has been preliminarily validated in round robin tests.
Salt weathering is one of the most recurrent damage processes affecting both the natural and the built environment. Due to the complexity of the process, numerical models are rarely applied in practice; accelerated weathering tests in laboratory are still the most common way to assess and forecast durability of (conservation and renovation) building materials.....
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Salt weathering is one of the most recurrent damage processes affecting both the natural and the built environment. Due to the complexity of the process, numerical models are rarely applied in practice; accelerated weathering tests in laboratory are still the most common way to assess and forecast durability of (conservation and renovation) building materials.....
Salt crystallization is a major cause of weathering of mortars, including plasters and renders. In the last decade, the use of mixed-in salt crystallization inhibitors in mortars has been proposed as a solution to improve the durability of this material with respect to salt decay. Laboratory characterization and accelerated weathering tests have shown encouraging results. However, data on the long-term behaviour of these mortars when applied on-site were missing until now .In this research the durability with respect to salt decay of a lime-based plaster and a salt accumulating plaster has been assessed. These plasters, with and without sodium ferrocyanide, a well-known inhibitor of sodium chloride crystallization, have been applied to an interior brick masonry wall with a high salt (sodium chloride) and moisture load and monitored for a period of 4 years. Monitoring included visual and photographic observations of the damage as well as measurements of the moisture and salt content and distribution, both in the wall and in the plaster. Moreover, the content and distribution of the inhibitor in the plaster after 4 year exposure was measured, to gain insight into the dissolution and transport of the inhibitor. The results of the research clearly show that the inhibitor is able to significantly reduce the occurrence of salt-induced decay in the lime-based plaster, in comparison to the plaster without inhibitor. No conclusions can be drawn in the case of the salt accumulating plaster, as no decay has developed yet in this case. Two issues related to leaching of the inhibitor and surface discolouration have emerged. These are discussed and possible solutions are proposed.
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Salt crystallization is a major cause of weathering of mortars, including plasters and renders. In the last decade, the use of mixed-in salt crystallization inhibitors in mortars has been proposed as a solution to improve the durability of this material with respect to salt decay. Laboratory characterization and accelerated weathering tests have shown encouraging results. However, data on the long-term behaviour of these mortars when applied on-site were missing until now .In this research the durability with respect to salt decay of a lime-based plaster and a salt accumulating plaster has been assessed. These plasters, with and without sodium ferrocyanide, a well-known inhibitor of sodium chloride crystallization, have been applied to an interior brick masonry wall with a high salt (sodium chloride) and moisture load and monitored for a period of 4 years. Monitoring included visual and photographic observations of the damage as well as measurements of the moisture and salt content and distribution, both in the wall and in the plaster. Moreover, the content and distribution of the inhibitor in the plaster after 4 year exposure was measured, to gain insight into the dissolution and transport of the inhibitor. The results of the research clearly show that the inhibitor is able to significantly reduce the occurrence of salt-induced decay in the lime-based plaster, in comparison to the plaster without inhibitor. No conclusions can be drawn in the case of the salt accumulating plaster, as no decay has developed yet in this case. Two issues related to leaching of the inhibitor and surface discolouration have emerged. These are discussed and possible solutions are proposed.
Walls overgrown with plants can have a positive impact on urban comfort and contribute to biodiversity in the city. In particular, quay walls, thanks to their close contact with water, have the potential to be ecologically engineered to encourage the growth of herbaceous plants. Different factors can affect growth of vegetation on walls. This research aims at experimentally investigating the effect of several variables, including quay wall design, building materials and environmental conditions, on receptivity of brick masonry quay walls for herbaceous plants. To this scope, ten quay walls (size 2 m × 2 m x 0.43 m), have been built and placed in a canal in the city of Breda (the Netherlands). The survival and growth of vegetation and the moisture content in the wall were monitored during a period of about 2 years. The results show that the presence of a layer of soil substrate with high capillary suction, positioned in between the masonry cladding and the concrete structure of the wall, has the most relevant positive effect on vegetation growth on the masonry. Mortar composition and irregularities of the wall surface influence bio-receptivity too, but to a less extent; orientation had only a limited effect. Moreover, the strategy of using a mechanically strong bedding mortar in combination with a weaker but more bio-receptive pointing mortar has proven successful at favouring growth of herbaceous plants, while providing sufficient strength to the masonry.
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Walls overgrown with plants can have a positive impact on urban comfort and contribute to biodiversity in the city. In particular, quay walls, thanks to their close contact with water, have the potential to be ecologically engineered to encourage the growth of herbaceous plants. Different factors can affect growth of vegetation on walls. This research aims at experimentally investigating the effect of several variables, including quay wall design, building materials and environmental conditions, on receptivity of brick masonry quay walls for herbaceous plants. To this scope, ten quay walls (size 2 m × 2 m x 0.43 m), have been built and placed in a canal in the city of Breda (the Netherlands). The survival and growth of vegetation and the moisture content in the wall were monitored during a period of about 2 years. The results show that the presence of a layer of soil substrate with high capillary suction, positioned in between the masonry cladding and the concrete structure of the wall, has the most relevant positive effect on vegetation growth on the masonry. Mortar composition and irregularities of the wall surface influence bio-receptivity too, but to a less extent; orientation had only a limited effect. Moreover, the strategy of using a mechanically strong bedding mortar in combination with a weaker but more bio-receptive pointing mortar has proven successful at favouring growth of herbaceous plants, while providing sufficient strength to the masonry.
Adaptive reuse (AR) of heritage buildings is common practice in The Netherlands and is becoming more and more common at the International level. While AR projects are generally considered positive actions towards preserving the qualities of heritage buildings, not all projects have similar (positive) impact. To propose a methodology for dealing with the AR of heritage buildings aiming for positive impact, the AR process has been studied. After a comprehensive systematic literature review, a theoretical model representing the steps of the AR process has been sketched (fig.1). This model depicts the ideal steps of architects in dealing with heritage buildings. To check whether these steps are actually followed, two effective AR projects, winners of the NRP golden phoenix prize, were studied namely ‘LocHal’ in Tilburg (fig.2) and ‘Energiehuis’ in Dordrecht (fig.3). During the research, the cases were visited, the published literature on the cases was reviewed, and architects and other stakeholders involved were interviewed. The interviews were based on the steps of the theoretical model but the model was not shown to the architects till the end of the interview. Finally feedback was asked from the architects if the model represented their actual steps and where they diverged. The analysis of the collected data confirmed that architects followed the steps reported in figure 1. However, the process was reported to be not linear, as suggested in the model, but to include several loops between some of the steps, mainly between steps 1, 2 , 3, 4, 5, and 6 (fig.4). Next to refining of the AR model, investigation of the case studies led to the identification of tools and methods used by architects, which have possibly positively influenced the effectiveness (positive impact) of the final result. Both case studies distinguished themselves, according to the NRP jury reports, because of their high ‘social value creation’. Involving end-users, other producers, and original users in different steps of the AR process has been identified as the main method used by the architects contributing to this positive impact.
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Adaptive reuse (AR) of heritage buildings is common practice in The Netherlands and is becoming more and more common at the International level. While AR projects are generally considered positive actions towards preserving the qualities of heritage buildings, not all projects have similar (positive) impact. To propose a methodology for dealing with the AR of heritage buildings aiming for positive impact, the AR process has been studied. After a comprehensive systematic literature review, a theoretical model representing the steps of the AR process has been sketched (fig.1). This model depicts the ideal steps of architects in dealing with heritage buildings. To check whether these steps are actually followed, two effective AR projects, winners of the NRP golden phoenix prize, were studied namely ‘LocHal’ in Tilburg (fig.2) and ‘Energiehuis’ in Dordrecht (fig.3). During the research, the cases were visited, the published literature on the cases was reviewed, and architects and other stakeholders involved were interviewed. The interviews were based on the steps of the theoretical model but the model was not shown to the architects till the end of the interview. Finally feedback was asked from the architects if the model represented their actual steps and where they diverged. The analysis of the collected data confirmed that architects followed the steps reported in figure 1. However, the process was reported to be not linear, as suggested in the model, but to include several loops between some of the steps, mainly between steps 1, 2 , 3, 4, 5, and 6 (fig.4). Next to refining of the AR model, investigation of the case studies led to the identification of tools and methods used by architects, which have possibly positively influenced the effectiveness (positive impact) of the final result. Both case studies distinguished themselves, according to the NRP jury reports, because of their high ‘social value creation’. Involving end-users, other producers, and original users in different steps of the AR process has been identified as the main method used by the architects contributing to this positive impact.
Sodium chloride (NaCl) is one of the most commonly occurring weathering agents, responsible for a progressive damage in mortar. Current solutions to mitigate salt damage in mortar, such as the use of mixed-in water repellent additives, have often exhibited low compatibility with the existing building fabric. In the last years, research has shown promising results in mitigating salt decay by making use of crystallisation inhibitors. Sodium ferrocyanide is one of the inhibitors that has proven to be particularly effective to reduce damage due to sodium chloride crystallisation. In this research the possibility of developing hydraulic mortars with mixed-in inhibitor (sodium ferrocyanide) for an improved resistance to sodium chloride crystallisation damage is investigated. As a first step, the interaction between the inhibitor and the hydraulic binder: natural hydraulic lime (NHL), was studied; the results are presented in this paper. Various concentrations of sodium ferrocyanide were tested (0%, 0.1% and 1% by binder weight). The effect of the inhibitor on several physical (hydration, water absorption, pore size distribution) and mechanical (compressive and flexural strength) properties was experimentally assessed, using several complementary methods and techniques. The results show that the addition of the sodium ferrocyanide does not affect the fresh and hardened properties of mortar. These results are promising and open new possibilities for the application of inhibitors to improve the durability of hydraulic mortars.
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Sodium chloride (NaCl) is one of the most commonly occurring weathering agents, responsible for a progressive damage in mortar. Current solutions to mitigate salt damage in mortar, such as the use of mixed-in water repellent additives, have often exhibited low compatibility with the existing building fabric. In the last years, research has shown promising results in mitigating salt decay by making use of crystallisation inhibitors. Sodium ferrocyanide is one of the inhibitors that has proven to be particularly effective to reduce damage due to sodium chloride crystallisation. In this research the possibility of developing hydraulic mortars with mixed-in inhibitor (sodium ferrocyanide) for an improved resistance to sodium chloride crystallisation damage is investigated. As a first step, the interaction between the inhibitor and the hydraulic binder: natural hydraulic lime (NHL), was studied; the results are presented in this paper. Various concentrations of sodium ferrocyanide were tested (0%, 0.1% and 1% by binder weight). The effect of the inhibitor on several physical (hydration, water absorption, pore size distribution) and mechanical (compressive and flexural strength) properties was experimentally assessed, using several complementary methods and techniques. The results show that the addition of the sodium ferrocyanide does not affect the fresh and hardened properties of mortar. These results are promising and open new possibilities for the application of inhibitors to improve the durability of hydraulic mortars.
This paper investigates the leaching behaviour of sodium ferrocyanide, a known crystallisation inhibitor of sodium chloride, which is added to mortars for mitigation of salt decay. Leaching and depletion of the inhibitor is a practical performance related issue that might over time, make the inhibitor less effective against salt decay. In this research, the inhibitor was added to natural hydraulic lime (NHL) mortars during the mixing stage. Leaching of the inhibitor from the hardened mortar was assessed experimentally in laboratory. Both diffusion- and advection-driven transport mechanisms were considered. Diffusion experiments were carried out in a tank leaching test setup. Capillary absorption and drying cycles were used as a driving force to study advection-driven transport. Quantification of the leached species was carried out using various analytical techniques, including UV-VIS spectroscopy, ICP-OES and ion chromatography. The results from the tank leaching test show a high effective diffusion coefficient of ferrocyanide ions, in the same order of magnitude as sodium chloride transport. The advection test shows accumulation of the inhibitor at the evaporative surface and depletion of the inhibitor in the inner layers with successive wet-dry cycles. Based on these results it can be inferred that the degree of inhibitor leaching is significant and needs to be minimised to prolong the positive effect of the inhibitor on mortar durability. Potential solutions to reduce inhibitor leaching are discussed.
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This paper investigates the leaching behaviour of sodium ferrocyanide, a known crystallisation inhibitor of sodium chloride, which is added to mortars for mitigation of salt decay. Leaching and depletion of the inhibitor is a practical performance related issue that might over time, make the inhibitor less effective against salt decay. In this research, the inhibitor was added to natural hydraulic lime (NHL) mortars during the mixing stage. Leaching of the inhibitor from the hardened mortar was assessed experimentally in laboratory. Both diffusion- and advection-driven transport mechanisms were considered. Diffusion experiments were carried out in a tank leaching test setup. Capillary absorption and drying cycles were used as a driving force to study advection-driven transport. Quantification of the leached species was carried out using various analytical techniques, including UV-VIS spectroscopy, ICP-OES and ion chromatography. The results from the tank leaching test show a high effective diffusion coefficient of ferrocyanide ions, in the same order of magnitude as sodium chloride transport. The advection test shows accumulation of the inhibitor at the evaporative surface and depletion of the inhibitor in the inner layers with successive wet-dry cycles. Based on these results it can be inferred that the degree of inhibitor leaching is significant and needs to be minimised to prolong the positive effect of the inhibitor on mortar durability. Potential solutions to reduce inhibitor leaching are discussed.
Reconstruction and recovery of historic cities after destruction due to conflict or natural disasters have gained increasing relevance in the last decades. The investigation of international examples of recovery after war or natural catastrophic events can provide knowledge for improving guidance and strategies for sustainable reconstruction/ intervention in similar cases in the future. This paper aims to identify and analyze the legal, administrative, social, and economic factors that can favor the reconstruction and recovery processes of the historic city and its residential neighborhoods. An extensive review of international examples and literature on guidance has been conducted to provide insight into best practices and potential solutions. As a result, a set of lessons learned that can be used to address post-conflict and post-disaster recovery and reconstruction in similar situations is given.
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Reconstruction and recovery of historic cities after destruction due to conflict or natural disasters have gained increasing relevance in the last decades. The investigation of international examples of recovery after war or natural catastrophic events can provide knowledge for improving guidance and strategies for sustainable reconstruction/ intervention in similar cases in the future. This paper aims to identify and analyze the legal, administrative, social, and economic factors that can favor the reconstruction and recovery processes of the historic city and its residential neighborhoods. An extensive review of international examples and literature on guidance has been conducted to provide insight into best practices and potential solutions. As a result, a set of lessons learned that can be used to address post-conflict and post-disaster recovery and reconstruction in similar situations is given.
Crystallisation due to commonly occurring salts like sodium chloride (NaCl) is a known cause of damage in the built environment. Use of crystallisation inhibitors is a potential solution to reduce salt decay in building materials. Researchers have reported lower damage when sodium ferrocyanide (NaFeCN), a known NaCl crystallisation inhibitor, is mixed in fresh mortar. However, the high solubility of NaFeCN in water could make it susceptible to leaching and thus diminish its effect over time.
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Crystallisation due to commonly occurring salts like sodium chloride (NaCl) is a known cause of damage in the built environment. Use of crystallisation inhibitors is a potential solution to reduce salt decay in building materials. Researchers have reported lower damage when sodium ferrocyanide (NaFeCN), a known NaCl crystallisation inhibitor, is mixed in fresh mortar. However, the high solubility of NaFeCN in water could make it susceptible to leaching and thus diminish its effect over time.