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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., Materials and Structures, 56 (5), ISSN:1359-5997, ISSN:1871-6873

The sustainable energy renovation of historical buildings is a challenge for all European countries. It is crucial for their conservation as well as for urban and rural development. Nonetheless, proposing adequate interventions requires appropriate investigation efforts. This paper presents a specific approach for performing the energy diagnosis of occupied historical buildings, developed under the contraints of several ongoing research projects. It is shown how photogrammetry and wireless sensor networks can be combined to produce rich datasets, while keeping disturbances for occupants at a minimum. Within this multi-disciplinary investigation program, the focus is also put on the production of input and validation data for implementing dynamic energy simulations. A case study is presented to illustrate the deployment of the proposed methodology. Only two site visits allowed to capture a large quantity of descriptive and performance information, which was valorized through clear protocols for sampling and formatting the data.

The sustainable energy renovation of historical buildings and listed heritage is a challenge for Belgium and other European countries. These are crucial for urban and rural development and for the future of old buildings. This is the context of the ‘P-RENEWAL’ research project. It aims to develop a methodological tool for retrofitting historical Walloon dwellings built before 1914, to enhance their heritage values while implementing relevant energy measures. The originality of this research is to consider energy, environmental and heritage aspects in a complementary way, in order to help designers achieving a goal of greater sustainability. According to the listed heritage administration, dwelling types built before 1914 represent approximately 25 % of the Walloon stock. This project is related to the research work carried out under the Task 59 of SHC ‘Renovating Historic Buildings Towards Zero Energy’. The methodology used to achieve the research objectives is articulated in various steps. First, a typological analysis of buildings from the interest era is completed. Then, based on on-site studies performed on representative case studies, the evaluations of heritage values and performance are conducted. Finally, dynamic energy models are run to support the proposition and validation of retrofitting strategies.

We employ laboratory X-ray micro-computed tomography (μCT) during climate-controlled salt weathering experiments to acquire data on the kinetics of drying and salt precipitation and the distribution of crystals within the pore space of Mšené sandstone. For that purpose, a custom-designed setup was built at the UGCT’s scanners of the Ghent University Centre for X-ray Tomography (UGCT) that allows to acquire 4D scans while drying. Samples were initially capillary saturated with a saturated NaCl-solution and subsequently dried at 20% RH and at 50% RH, at room temperature. These RH-values are representative for winter and summer conditions for the salt NaCl, which is not temperature sensitive. Different salt precipitation dynamics result in different drying kinetics at the two RH’s. These crystallization and transport dynamics can be directly linked as revealed by the 4D X-ray μCT datasets.

Rock alteration by salt crystallization is known since a long time ago. However, there are still controversies about the induced mechanism. This kind of alteration is considered the most important factor in historical monuments degradation. Currently, we ascribe the degradation to the capacity of salt to develop crystallization pressure. The crystallization pressure could reach several megapascal; exceeding stones mechanical resistance. This crystallization pressure concept arises from experimental studies carried out between the end of XIXth century and the middle of XXth but there are discrepancies between these notions and current theories about crystal growth. The goal of this study is to reproduce Corren and Taber's experiments under controlled experimental conditions. This work shows that, under supersaturated conditions, whatever the load, a KCl monocrystal grows along the unloaded directions and adopts a trapezoid-like shape with truncated edges. This is due to the heterogeneous constraint distribution and a vertical concentration gradient. Along the loaded direction, the crystal dissolves more or less according to the imposed load. The dissolution is not linear and presents two regimes. The first one is rapid and no linear, where the dissolution rate is a function of the contact surface between the load and the loaded face; the second one is slower and linear, where the dissolution rate is a function of the supersaturation of the solution. In no case, the monocrystal develops crystallization pressure. It seems unlikely that a crystal like KCl could damage stone by means of crystallization pressure., L'altération des pierres par les sels est un phénomène connu depuis l'antiquité. En revanche, le ou les mécanismes mis en jeu. Ce type d'altération est aujourd'hui considéré comme la principale cause de dégradation des monuments historiques. Actuellement, on attribue la dégradation à la capacité de ces phases minérales à développer une pression de cristallisation. Cette pression pourrait atteindre plusieurs mégapascals et dépasser la résistance mécanique des pierres. Ce concept de pression de cristallisation est né d'études expérimentales réalisées entre la fin de XIXème et le milieu du XXème siècle mais ces notions se concilient difficilement avec les principes de la croissance cristalline tels qu'ils sont connus actuellement. Cette étude a pour but de reproduire les expériences anciennes avec des monocristaux de KCl en contrôlant rigoureusement les paramètres environnementaux. Ce travail montre que, dans les conditions de sursaturation et de croissance, quelque soit la charge imposée, le cristal croit dans les directions non contraintes et adopte à la fin des expériences un faciès trapézoïdal à base tronquée. Ceci est dû à un gradient vertical de concentration et à une répartition non homogène de la contrainte au sein du cristal. Dans la direction de la contrainte le cristal se dissout plus ou moins selon la charge imposée. Cette dissolution n'est pas linéaire et présente deux régimes ; le premier, rapide et non linéaire est fonction de la surface de contact cristal/charge, le second plus lent et quasiment linéaire est fonction de la sursaturation de la solution. En aucun cas, le monocristal de KCl ne développe de pression de cristallisation. Il semble improbable qu'un cristal du type KCl puisse dégrader une pierre en exerçant par pression de cristallisation.

International audience; The "coffee-ring effect" [1] is an appealing problem as it is a frequent everyday observation, but the deposition of colloidal particles can also influence for instance printing and coating applications. Previous studies indicates that the deposition pattern of colloidal suspensions depends on contact line pinning [1], the presence of Marangoni flows [2], the thermal conductivity of the substrate [3], and the shape of the colloids [4]. Besides the coffee ring, in everyday life we are also very familiar with crystal deposits resulting from evaporation of drops of salt solutions such as calcium deposits on bathroom walls. Although the problem has been much studied for colloidal suspensions, for salts there are much less results. We experimentally study the effect of the combined wetting properties and thermal conductivity of the substrate on deposition of salt crystals from solutions. We use both Sodium Chloride and Calcium Sulfate solutions, and image the crystallization process and end deposits on various hydrophobic and hydrophilic surfaces. We observe for both salt solutions that the final deposition pattern is mostly very different from the coffee ring, and depends strongly on the wetting properties of the substrate rather than the thermal conductivity. [1] Deegan et al. Nature 1997, 389, 827-829 [2] H. Hu and R.G. Larson, J. Phys. Chem. B 2006, 110, 7090-7094 [3] Ristenpart et al. PRL 2007, 99, 234502 [4] Yunker et al. Nature 2011, 476, 308-311

International audience

ACL; International audience; The drying of porous media is of major importance for civil engineering, geophysics, petrophysics, and the conservation of stone artworks and buildings. More often than not, stones contain salts that can be mobilized by water (e.g., rain) and crystallize during drying. The drying speed is strongly influenced by the crystallization of the salts, but its dynamics remains incompletely understood. Here, we report that the mechanisms of salt precipitation, specifically the primary or secondary nucleation, and the crystal growth are the key factors that determine the drying behaviour of salt contaminated porous materials and the physical weathering generated by salt crystallization. When the same amount of water is used to dissolve the salt present in a stone, depending on whether this is done by a rapid saturation with liquid water or by a slow saturation using water vapor, different evaporation kinetics and salt weathering due to different crystallization pathways are observed. © 2015 AIP Publishing LLC.