# A novel test protocol for assessing accelerated salt weathering effects on construction materials and natural rocks

Victor Okumko<sup>a</sup>, Bruno Leclere<sup>a</sup>, Hannelore Derluyn<sup>a,b |</sup>, David Grégoire<sup>a,c,* |</sup>

## ARTICLE INFO

### Keywords:

- Salt weathering

- Salt-induced damage

- Acoustic emission

- Digital image correlation

## ABSTRACT

Salt weathering poses significant challenges to the durability and integrity of construction materials across various engineering applications. This study introduces a novel accelerated salt weathering protocol designed for standardised laboratory testing, aimed at evaluating the effects of salt crystallisation on natural rocks and construction materials. The protocol was validated using three distinct materials: Flysch rocks, Vosges sandstone, and high-performance concrete. The core protocol features continuous partial immersion of cylindrical-shaped samples in a 3 molal sodium sulphate solution at 32 °C. At the same time, room temperature is maintained at 20 °C, providing well-defined boundary conditions for easy reproducibility and potential numerical modelling. Non-destructive monitoring techniques, including time-lapse photography coupled with Digital Image Correlation (DIC) and acoustic emission (AE) analysis, were integrated into the core protocol. In addition, post-mortem X-ray tomography and optical microscopy were used to characterise salt-induced crack patterns further. The Flysch rock samples exhibited significant external deterioration, with DIC analysis highlighting the influence of material heterogeneity in damage susceptibility. AE analysis captured internal damage progression and identified the onset of salt-induced deterioration in the Vosges sandstone samples, which displayed consistent responses to the weathering test protocol. The concrete samples, pre-cracked by mechanical loading to mimic on-site coastal erosion conditions, exhibited salt-induced crack propagation and development of new salt-induced cracks when tested under the weathering protocol. These findings demonstrate the protocol's effectiveness in evaluating salt-induced damage in construction materials, providing a reproducible framework that can be readily implemented in diverse testing environments to enhance durability assessment in engineering applications.

## 1. Introduction

Salt weathering presents a pervasive and persistent challenge to the durability of civil engineering infrastructure, construction materials and natural rocks. This destructive influence has been extensively studied across diverse environmental contexts [1–11]. Salt weathering is particularly impactful in coastal areas, where the combination of high salinity levels and fluctuating environmental conditions accelerates the degradation of structures [4,5,12–15].

The impact of salt weathering extends beyond historical monuments and cultural heritage sites to artworks and contemporary structures, where it contributes to the degradation of materials such as limestone, sandstone, and concrete [8,15–23]. For instance, rising damp driven by capillary suction of groundwater containing dissolved soluble salts

significantly contributes to the decay of historical buildings [24–26]. Additionally, salt weathering exacerbates coastal erosion by quarrying jointed rocks and weakening cliffs, leading to their potential collapse and damage to surrounding buildings, bridges and civil engineering infrastructure [5,12–15].

Understanding the underlying mechanisms of salt weathering is therefore essential for practical preservation and maintenance efforts. Mechanisms such as crystallisation pressure, thermal expansion, chemical weathering, and hydration pressure play pivotal roles in salt-induced deterioration [2,16,27–31]. Crystallisation pressure, in particular, arises when dissolved salts precipitate within porous materials, exerting significant pressures that can lead to cracking, spalling and damage [18,21,32–35].

Salts may infiltrate civil engineering infrastructures through various

<footnote><sup>a</sup> Universite de Pau et des Pays de l'Adour, CNRS, LFCR, Anglet, France</footnote>

<footnote><sup>b</sup> Universite de Pau et des Pays de l'Adour, CNRS, DMEX, Pau, France</footnote>

<footnote><sup>c</sup> Institut Universitaire de France (IUF), France</footnote>

<footnote>* Corresponding author at: Universite de Pau et des Pays de l'Adour, CNRS, LFCR, Anglet, France.
E-mail address: david.gregoire@univ-pau.fr (D. Grégoire).</footnote>
pathways, including groundwater ingress, seawater exposure, de-icing treatments, and aerosol deposition, among many others [5,10]. When salts are present in the form of a solution within porous structures and building materials, the damaging effects are often minimal until evaporation or drying of the solution occurs, causing salt crystallisation within the pores and generating mechanical stresses that result in physical damage [21,34,35].

Laboratory studies and testing play a crucial role in evaluating the susceptibility of construction materials to salt weathering. However, existing standardisation tests lack realism or comprehensiveness, hindering global acceptance by researchers and therefore limiting effective comparison of results for a detailed understanding of material behaviour under salt-induced conditions [36]. For example, the widely used European standard EN 12370–1999 [37] and International Union of Laboratories and Experts in Construction Materials, Systems, and Structures - RILEM protocols [38] provide foundational frameworks, but are not without limitations [36].

The European standard - EN 12370–1999 [37] outlines a method for determining the resistance of natural stones to salt crystallisation, primarily focusing on the durability assessment of stone materials. It prescribes cycles of total immersion of test specimens in a 14 % sodium sulphate solution at 20 °C for 2 h, followed by drying at 105 °C for 16 h and subsequent cooling to room temperature at 20 °C. While this standard provides an understanding of the behaviour of natural stones under certain conditions, its applicability is questioned due to the use of a highly concentrated sodium sulphate solution [36]. In some cases, researchers have adapted the standard by using water instead of fresh sodium sulphate during re-immersion cycles. These modifications, although aimed at improving the test’s applicability, create challenges in drawing direct comparisons across studies that employ slightly different versions of the adapted standards.

Similarly, the RILEM protocols [38], particularly RILEM MS-A.1, propose testing on representative samples of masonry (wallettes) for damage caused by sulphates and chlorides through capillary uptake. It involves partial immersion of the base of a wallette in a 10 wt% sodium sulphate or sodium chloride solution, unlike the European standard of total immersion, followed by regular solution additions to maintain levels. However, the evaluation of deformation at the surface of the wallette was prescribed for every 4 weeks, which is time-consuming, as mentioned by [36]. Furthermore, the RILEM MS-A.2 proposed testing on individual masonry units, involving repeated partial immersion cycles in sodium sulphate, followed by drying until damage. However, this approach also presents challenges of a lack of a well-defined standard for recording or evaluating damage [36].

Despite their shortcomings, these standards are commonly referenced in studies for evaluating rock, concrete and stone material durability [9,11,23,36,39]. Addressing the challenges of these standards necessitates more comprehensive and adaptable testing protocols that better reflect the wide range of conditions encountered in practical applications. In recent times, the RILEM TC 271-ASC Committee, in a bid to fulfil this need, has published a review of several existing test protocols and prescribed some recommendations in the assessment of damage and standardising accelerated salt weathering laboratory tests [36,40,41].

Non-destructive testing methods, such as visual inspection, acoustic emission (AE) analysis, and X-ray tomography, offer valuable tools for evaluating salt weathering in construction materials, and have been applied or recommended in several instances [8,10,36,39,41–46]. These techniques provide insights into both internal and surface damage, allowing researchers to assess the extent and progression of salt-induced deterioration. By developing innovative methodologies that integrate non-destructive testing techniques and consider the multifaceted nature of salt weathering mechanisms, researchers can enhance the reliability and relevance of laboratory testing for assessing material durability and informing preservation strategies. On the other hand, Digital Image Correlation (DIC) is now widely used to characterize deformation [47–49] or fracture of materials [50,51].

To complement these methodological advances, the materials selected for this study represent a range of natural rocks and construction materials in contexts susceptible to salt-induced damage. The chosen materials — Flysch rock, Vosges sandstone, and concrete — cover diverse geological and civil engineering settings. The Flysch rocks, acquired from cliffs at Socoa/Ciboure in southwestern France, exhibit a complex stratigraphy of sedimentary layers and are currently affected by ongoing coastal erosion, which poses challenges to nearby infrastructure such as the D912 coastal road, which was avoided by the Tour de France in 2023 due to local hazards caused by erosion. The concrete, specifically deployed as protective structures along the Saint-Jean-de-Luz bay area, such as the Artha breakwater, reflects how engineered materials respond under similar environmental stresses. The Vosges sandstone, extensively used in construction, was included to exemplify materials with diverse porosity, mineralogy, and mechanical properties. Collectively, these materials offer a comprehensive spectrum for assessing responses to the accelerated salt weathering protocol, emphasizing the interplay between geological complexity, engineering considerations, and material-specific durability, which is examined in this study.

This paper presents an innovative accelerated salt weathering laboratory protocol with simple boundary conditions, integrating non-destructive methods to comprehensively assess material responses. By incorporating combinations of time-lapse photography with DIC analysis, AE analysis, and X-ray tomography, the protocol offers a multifaceted approach to evaluate the impact of salt weathering on construction materials.

The following sections of this paper provide an overview of the materials used, the sample preparation process, and the design of the accelerated salt weathering protocol. Results, discussions, and conclusions derived from implementing the protocol will be presented to broaden the understanding of salt-induced damage in construction materials. Specifically, this study explores the varying responses of the different materials tested in the accelerated salt weathering protocol and emphasises how the integration of non-destructive testing techniques enriches the understanding of the phenomenon of salt-induced damage.

## 2. Materials and methods

### 2.1. Materials

Three representative construction materials were investigated to evaluate the applicability and reproducibility of the accelerated salt weathering protocol. Flysch rock from Socoa/Ciboure in southwestern France, Vosges sandstone from the Rothbach quarry in northeastern France, and high-performance concrete used in protective blocks of the Artha breakwater in the Saint-Jean-de-Luz bay area.

Significant portions of the Flysch rock representing the local stratified geological formation with alternating marly and siliceous layers were collected from the Socoa coastal cliffs. Its pronounced heterogeneity makes it suitable for assessing salt crystallisation effects in layered geomaterials.

Vosges sandstone, a pink quartz-feldspathic sandstone (composition provided in Table 1) primarily used as a local building and milling stone with an average porosity of about 22 %, was selected for its potential to facilitate rapid capillary fluid flow and expedite the possibility of salt-induced damage in the samples. Five cylindrical samples of 45 mm diameter and 100 mm height were prepared for testing. An additional

<table><caption>**Table 1**
Mineralogical composition and physical properties of Vosges Sandstone [52].</caption><thead><tr><td>Mineral</td><td>Percentage</td></tr></thead><tbody><tr><td>Quartz</td><td>65 %</td></tr><tr><td>Feldspars</td><td>25 %</td></tr><tr><td>Clay (micas, smectites and Kaolinite)</td><td>10 %</td></tr></tbody></table>
sample (VS-Prelim-001) of 25 mm diameter and 45 mm height was prepared with a natural notch and natural crack to further enhance capillary fluid flow, following procedures similar to the concrete sample preparation (Fig. 1).

High-performance concrete specimens were sourced from the same formulation as the 50-tonne protective blocks for the Artha dam (Fig. 2). The concrete was selected for two main purposes: first, to simulate the realistic conditions that the protective concrete blocks endure over time under tidal storms and wave impact; and second, to evaluate the effectiveness of the accelerated salt weathering test protocol in advancing pre-existing cracks and accelerating observation of salt-induced deterioration. Cylindrical specimens of 45 mm diameter and 100 mm height were prepared following a three-point bending test to introduce controlled cracks for accelerated salt ingress. A concrete mix designated for pavement use was also subjected to the accelerated salt weathering protocol as part of preliminary tests. Details regarding the pavement concrete formulation are provided in the work of [59].

All materials were oven-dried at 50 °C for at least 48 h after coring before testing to ensure consistent initial moisture conditions. Table 2 details all the samples used in the accelerated salt weathering tests.

## 2.2. Mechanical characterization

Mechanical properties were determined prior to the salt weathering tests to provide baseline reference values. Compressive strength tests were performed using a servo-hydraulic testing machine (HB250, Zwick/Roell) under displacement control. Young's modulus and Poisson's ratio were determined from stress-strain data in the linear elastic domain.

Mercury intrusion porosimetry was used to determine total porosity and pore size distribution of the Flysch rock and Vosges sandstone. Permeability was measured using a steady-state flow method under controlled differential pressure.

Three-point bending tests were performed on the concrete and the preliminary Vosges sandstone sample (VS-Prelim-001) using standard geometry and loading configuration to introduce controlled cracks prior to coring similar to the work of [54]. Cylindrical samples were then extracted along the notch orientation. For concrete, samples were cut to remove the notch region while retaining the pre-existing crack. In the sandstone sample, the notch was preserved to enhance capillary fluid

<figure><img src="image_1.png" /><figcaption>Fig. 1. Cylindrical Vosges sandstone samples prepared for salt weathering tests.</figcaption></figure>

flow during salt weathering experiments.

The complete results of the mechanical and microstructural characterisation, including compressive strength, elastic modulus, Poisson's ratio, permeability, and porosity values, are detailed in the Supplementary Data (Tables S1–S2).

## 2.3. Novel accelerated salt weathering test protocol

The design and development of the accelerated salt weathering protocol involved the use of sodium sulphate, a well-established choice in accelerated weathering tests due to its aggressive nature [2,16,29,55, 30,33–35,18,56–58,24,22]. The protocol was crafted with two primary considerations: [1] to promote the potential precipitation of mirabilite, widely recognized as the most deleterious phase of sodium sulphate, directly within the sample's porosity, and [2] to facilitate numerical validation by establishing easily reproducible boundary conditions to support future numerical simulations.

Key parameters influencing salt crystallisation including temperature conditions, relative humidity, and potential evaporation were meticulously considered to ensure consistent and reliable results. This rigorous approach ensured reproducible results for validation.

The core of the experimental protocol, as illustrated in Fig. 3, involved continuous partial immersion of the base of cylindrical-shaped test samples in 3 molal concentration of sodium sulphate solution at 32 ± 1 °C, while room temperature was maintained at a controlled 20 ± 1 °C. Samples were equilibrated in the laboratory at ambient conditions (25 ± 1 °C) prior to immersion. The solution was pre-heated to 32 ± 1 °C in the reservoir; thus, crystallisation occurs as the warmer solution cools within the pore network during capillary uptake, following the imposed temperature gradient. At 32 °C, the solution is undersaturated with respect to both mirabilite and thenardite (see Fig. 4), becoming supersaturated upon cooling to 20 °C, where the solubility of anhydrous sodium sulphate is about 1.4 molal. Hence, the 3 molal solution represents more than twice the solubility limit and for comparison, the EN 12370 standard prescribes a 14 wt% sodium sulphate decahydrate solution (≈ 6 wt% anhydrous sodium sulphate, ≈ 0.5 molal), which is roughly one-sixth of the concentration used in this work. This higher concentration ensures crystallisation within a single cycle and enables a more severe yet controlled salt-weathering environment.

The simple protocol design supports the hypothesis that upon rapid capillary uptake of the solution into the sample pores, a substantial temperature gradient is formed between the room (20 ± 1 °C) and solution within the sample pores (≈ 32 ± 1 °C). Over the course of the test, this gradient leads to cooling of the solution and prompt precipitation of mirabilite within the sample as illustrated in the sodium sulphate solubility diagram in Fig. 4. The simplicity of the setup and the controlled temperature and solution conditions make the protocol readily reproducible in other laboratories.

The protocol can be adapted to accommodate either full or limited solution supply, depending on desired experimental objectives, which makes it a versatile tool for investigating salt crystallisation across various conditions. Full solution supply promotes uniform absorption and complete saturation of the sample's porosity. Alternatively, a limited supply restricts capillary rise to specific areas of the sample, enabling targeted investigation of localised salt-induced damage. For the limited-supply tests, blank tests were conducted to determine the volume of solution necessary to reach the midpoint of each sample, calculated using $V = \varphi * \pi * r^2 * h$, where $\varphi$ represents the sample's porosity, r is the sample radius, and h is the desired capillary rise height. Although non-uniform absorption across the sample surface was not explicitly accounted for, this approach effectively limited the capillary rise to specific heights, allowing for focused study and analysis of localised crystallisation fronts and the associated damage.

Upon completion of each test, all samples underwent a uniform post-treatment procedure, with each sample gently rinsed in warm distilled water (≈ 50 °C) for approximately 3 min. The purpose of this step was to
<figure><img src="image_2.png" /><figcaption>**Fig. 2.** (Left: a) A newly casted 50-tonne concrete block, (Right: b) Ortho-photograph of western roundhead of the Artha dam, depicting some of the 50-tonne concrete blocks serving as a protective armour [53].</figcaption></figure>

<table><caption>**Table 2**
Sample materials and test samples for the salt weathering test.</caption><thead><tr><th>Sample Material</th><th>Sample description</th><th>Sample name</th><th>Sample dimensions (mm)<br>Height and diameter</th><th>Assessment Technique</th></tr></thead><tbody><tr><td rowspan="3">Flysch Rock</td><td rowspan="3">Target material displaying rhythmic alternations of heterogeneity</td><td>FR-001</td><td>53.89 mm, 21.68 mm</td><td rowspan="3">Time-lapse photography with Digital Image Correlation (DIC)</td></tr><tr><td>FR-002</td><td>≈ 45 mm, ≈ 25 mm</td></tr><tr><td>FR-003</td><td>≈ 40 mm, ≈ 20 mm</td></tr><tr><td rowspan="2">Concrete</td><td>Concrete used for protection of the Artha dam</td><td>Con-Artha-001<sup>a</sup></td><td>116 mm, 44.81 mm</td><td>Acoustic emission and X-ray tomography</td></tr><tr><td>Concrete used for pavements</td><td>Con-Pave-001<sup>a</sup></td><td>59.90 mm, 19.85 mm</td><td>Time-lapse photography</td></tr><tr><td rowspan="5">Vosges Sandstone</td><td rowspan="5">Layered heterogeneous sandstone with diffused porosity</td><td>VS-Prelim-001<sup>b</sup></td><td>≈ 45 mm, ≈ 25 mm</td><td rowspan="5">Acoustic emission and X-ray tomography</td></tr><tr><td>VS-001</td><td>99.15 mm, 44.47 mm</td></tr><tr><td>VS-002</td><td>≈ 100 mm, ≈ 45 mm</td></tr><tr><td>VS-003</td><td>99.24 mm, 44.51 mm</td></tr><tr><td>VS-004</td><td>99.97 mm, 44.89 mm</td></tr><tr><td></td><td></td><td>VS-005</td><td>99.92 mm, 44.93 mm</td><td></td></tr></tbody></table>

<figure><img src="image_3.png" /><figcaption>**Fig. 3.** Schematic representation of the experimental test protocol, showing partial immersion of cylindrical test samples in a 3 molal sodium sulphate solution at 32 °C.</figcaption></figure>

dissolve and remove residual superficial salts deposits and prevent post-test crystallisation during handling and microscopic inspection, rather than to achieve complete desalination in the pore network.

<figure><img src="image_4.png" /><figcaption>**Fig. 4.** Sodium sulphate solubility diagram. The diagram shows the liquid-phase region (above the solubility curve), the mirabilite stability field (Na₂SO₄·10H₂O, stable below ≈32.4 °C at high water activity), and the thenardite field (Na₂SO₄, stable at higher temperatures and lower relative humidity). The arrow indicates the experimental cooling path followed during capillary imbibition (reservoir ≈32 °C to ambient ≈20 °C), crossing from the liquid field into the mirabilite domain.</figcaption></figure>

<footnote>a Sample had a natural crack created by 3-point bending.</footnote>

<footnote>b Sample had a notch with a natural crack.</footnote>
Consequently, no conductivity control was applied as the internal salt content remained representative of the post-test condition. Samples requiring immediate internal inspection to verify capillary fronts or crystallisation were split using low-speed uniaxial compressive loading until splitting occurred, bypassing washing. When washing was performed, samples were cut with a saw to preserve structural integrity for subsequent internal deformation analysis.

### 2.3.1. Experimental setup and conditions

The experimental setup was designed to maintain stable test conditions and consisted of a custom-built climatic chamber, a double-boiler aluminium container, a plastic solution reservoir with elevated sample platform, cotton, parafilm, aluminium tape, hygrometers, and thermometers. The climatic chamber, as shown in Fig. 5, featured a main door with transparent glass for visual observation, a sealable aperture for cable connections, and a control panel. The chamber was mounted on an adjustable anti-vibration base with spring cylinders to minimize external vibrations, ensuring reliable Acoustic Emission (AE) measurements.

The double-boiler aluminium container, filled with tap water and wrapped with heating cables, maintained a constant temperature of 34 °C. The solution reservoir above the aluminium container held the sodium sulphate solution at approximately 32 °C. Preliminary tests optimized heating cable alignment and temperature control to achieve uniform solution temperature, and rock wool insulation further reduced fluctuations.

For limited supply experiments, a cotton pad was placed beneath the sample to maintain consistent contact with the solution. Parafilm was used to seal the plastic container, preventing evaporation and securing the samples in place. One layer of parafilm covered the container opening, leaving an opening for the sample. After the sample was inserted, a second layer of parafilm was applied to seal the narrow gap between the sample and the opening in the first layer, ensuring a tight fit and preventing evaporation from the gap. Temperature of the chamber and solution, as well as relative humidity (55 ± 0.01 %), were continuously monitored throughout the tests.

### 2.3.2. Assessment of material deformation

The effect of the accelerated salt weathering protocol was assessed using a combination of non-destructive testing techniques, including time-lapse photography, Acoustic Emission (AE) monitoring, and X-ray scanning, providing complementary insights into external and internal progression for a comprehensive characterization of the deterioration

<figure><img src="image_5.png" /><figcaption>**Fig. 5.** Custom-built climatic chamber set-up with an open climatic area, aluminium container, sample equipped with AE transducers, and in-chamber hygrometer and thermometer, all configured before testing.</figcaption></figure>

mechanisms and durability of the materials.

#### 2.3.2.1. Time-lapse photography.
Time-lapse photography captured high-resolution images of the samples at set intervals, typically every 30 s or 1 min, throughout the duration of the tests. The resulting images were analysed using IcaSoft software [59] for Digital Image Correlation (DIC), detecting surface displacement and crack formation, particularly in Flysch rock samples. The DIC analysis focused on the sample surfaces free of parafilm, preventing any bias in strain-field computation.

#### 2.3.2.2. Acoustic emission (AE) monitoring.
Acoustic Emission (AE) monitoring was integrated into the experimental protocol to continuously detect and localise acoustic events associated with microcracks and internal fracture events caused by salt crystallisation. The AE system similar to the work of [60] included an eight-channel MISTRAS system (PCI-DISP4) with six transducers assigned to a sample, arranged in two groups of three at upper and lower levels, offset at 60° between sets as shown in Fig. 6. The transducers were coupled to the sample using hybrid polymer sealant and calibrated using pencil lead breaks to validate localisation.

Acoustic events were recorded when signals exceeded 35 dB and reached at least four transducers. AE data, including the time, location, and amplitude were processed in MATLAB to visualise damage initiation and propagation within the sample.

### 2.3.3. Microscopy and X-ray scanning

Microscopy studies using a Keyence VHX-700 digital microscope and X-ray scanning using a ZEISS Xradia Versa 510 scanner at the DMEX Centre of X-ray Imaging (Pau, France) complemented AE monitoring by providing internal structural information. For both the concrete and Vosges sandstone samples, 1601 projection radiographs were acquired over a 360° rotation. Beam hardening was mitigated with ZEISS HE4 and HE2 filters. Geometrical magnification was 1.4, and the samples were positioned 72.3465 mm from the X-ray source and 29.0023 mm from the detector. Voltage was set to 160 kV for the concrete and 140 kV for the Vosges sandstone, with 0.4x optical lens yielding 49 µm pixel size.

For the concrete samples, pre-test and post-test scans were performed, whereas for the Vosges sandstone, scans were performed post-accelerated salt weathering. Radiographs were acquired with an exposure time of 1.25 s for concrete samples, and 1.15 s for Vosges sandstone. Each radiographic image was binned by a factor of 2 × 2, resulting in 1024 × 1024 pixels. To cover the entire height of the sample, overlapping scans were stitched together using the ZEISS software, and 3D absorption datasets reconstructed using standard filtered back-projection [61].

<figure><img src="image_6.png" /><figcaption>**Fig. 6.** (Left: a) Side and (Right: b) top view of the transducers affixed to a Vosges Sandstone sample.</figcaption></figure>
# 3. Results and discussion

The outcomes of this study are presented with a focus on individual samples and the assessment techniques employed, enabling a detailed examination of the salt weathering protocol's effectiveness. This section summarises key observations and outcomes, emphasising the correlation between the assessment techniques and the extent of damage induced by salt crystallisation.

## 3.1. Vosges sandstone samples: salt-induced deformations observed via time-lapse photography, AE analysis, and X-ray scanning

In the weathering test conducted on notched Vosges Sandstone sample VS-Prelim-001, significant external deterioration was observed after 12 h of continuous testing with an unlimited quantity of sodium sulphate solution. The deformation, as shown in Figs. 7a and 7b, was accompanied by notable efflorescence, signifying the presence of salt crystals on the external surfaces of the sample, particularly concentrated on the uppermost part. These visual changes, captured through time-lapse photography, served as an initial validation of the protocol's effectiveness.

In subsequent tests aimed at limiting capillary rise to half the height of the Vosges sandstone samples, controlled compressive pressure was applied immediately after the test, without washing, to assess the extent of capillary uptake, the presence of salt crystals, and potential internal deformation. Upon splitting samples VS-001 and VS-002 into semi-cylindrical halves, visible salt deposits were observed at the capillary front, confirming the location of salt crystallisation. These tests also revealed significant external deformation at the end of the accelerated salt weathering tests, and when compressive pressure was applied, further fractures developed horizontally, splitting the semi-cylindrical halves into upper and lower sections (refer to Supplementary Data - Fig. S3 a-b). This additional breakage is conceivably a result of changes in the mechanical properties caused by salt deposits within the capillary zone, which altered the material's strength and structural integrity. Similarly, examination of sample VS-003 under a Keyence VHX-700 digital microscope revealed salt crystallisation at the capillary front and the saturated capillary uptake region (Fig. 8), emphasizing the internal migration of the solution and its patterns of salt accumulation within the samples.

With the integration of the AE monitoring system, sample VS-004 was tested continuously for 4 days with limited quantities of sodium sulphate, revealing significant external deterioration, characterised by layered detachments. AE analysis recorded 1505 events, with the highest concentration of acoustic activity occurring after 18 h,

<figure><img src="image_7.png" /><figcaption>**Fig. 7.** Evidence of external deterioration accompanied with presence of salt crystals in Vosges Sandstone sample VS-Prelim-001 (a) before and (b) after the accelerated salt weathering test, with unlimited quantity of sodium sulphate solution.</figcaption></figure>

<figure><img src="image_8.png" /><figcaption>**Fig. 8.** Keyence VHX-700 microscope image showing region of salt crystallisation along the capillary front marked within the dotted lines and the area of sodium sulphate saturation beneath it within sample VS-003.</figcaption></figure>

indicative of the onset time of damage in the sample. Post-treatment examination showed distinct horizontal lines of deformation at approximately 30 mm and 50 mm from the sample base, a finding corroborated by X-ray scans (Fig. 9). AE data (Fig. 10) demonstrated clustering of acoustic events around microcracks and damaged regions, supporting to some extent the correlation between AE signals and localised damage.

Sample VS-005 was tested over a two-day period under the same conditions as Sample VS-004 with the aim of capturing the onset time of damage and recorded a total of 24 AE events. Despite exhibiting external layer detachment (Fig. 11a) similar to sample VS-004, no initial visible damage was evident when the sample was cut into halves (Fig. 11b). X-ray scans, however, revealed early-stage internal damage at the sample's edges (Fig. 11c), demonstrating the promising potential of advanced imaging techniques in capturing the entire phenomenon of salt-induced damage in porous materials. AE localisation indicated spiral damage zones within the capillary uptake area (Fig. 12), though the spatial accuracy of AE localisation could benefit from further refinement.

Despite fewer recorded AE events for sample VS-005, the timing of damage onset was consistent with sample VS-004, confirming a uniform response of the Vosges sandstone samples to salt crystallisation. Both samples exhibited a similar trend of AE events beginning around 18 h into testing (Fig. 13), suggesting a consistent response of the Vosges sandstone samples to the accelerated salt weathering protocol. This consistency underscores the potential of the AE system to capture crack initiation and salt-induced damage in porous materials, though improvements in acoustic event localisation are needed.
<figure><img src="image_9.png" /><figcaption>**Fig. 9.** Sample VS-004 after 4 days of testing: (a) external view showing layer detachment, (b) semi-cylindrical section displaying internal deformation, and (c) X-ray image corresponding to the location of internal deformation.</figcaption></figure>

<figure><img src="image_10.png" /><figcaption>**Fig. 10.** Localisation of acoustic events monitored in sample VS-004 during accelerated salt weathering test showing clustering of events in area correlating with observed damage.</figcaption></figure>

## 3.2. Flysch rock samples: observation of external deterioration via time-lapse photography accompanied by digital image correlation (DIC) analysis

Compressive tests performed on seven Flysch rock samples yielded a mean compressive strength of 117.7 ± 54.0 MPa, reflecting the pronounced heterogeneity of the formation. The large dispersion in strength values is consistent with the lithological variability of the Flysch sequence, structure, and texture. Deformation during loading followed pre-existing planes of weakness (Fig. 14a,b), replicating the fracture patterns observed in situ at the project site, where failure preferentially occurs along marl-rich horizons. These mechanically weaker zones

govern both crack propagation and fluid migration, providing the pathways through which salt solutions infiltrate during the weathering cycles. Consequently, the Flysch rock's heterogeneous fabric exerts a primary control on its susceptibility to crystallisation pressure and on the spatial variability of salt-induced damage discussed below. Detailed mechanical and porosity data supporting these observations are provided in the Supplementary Data.

Sample FR-001 underwent continuous testing for 4 days with an unlimited supply of sodium sulphate. External deformation was first noted after 2 days, with significant external deformation becoming apparent by day 3. These deformations were observed along the sample's inherent heterogeneity, suggesting that weaker zones within the
<figure><img src="image_11.png" /><figcaption>Fig. 11. Sample VS-005 after 2 days of testing: (a) external view showing layer detachment, (b) semi-cylindrical section with no visible damage, and (c) X-ray image indicating early-stage internal damage at the edges.</figcaption></figure>

<figure><img src="image_12.png" /><figcaption>Fig. 12. Localisation of acoustic events recorded in sample VS-005 during the accelerated salt weathering test, highlighting spiral record of acoustic events.</figcaption></figure>

rock mass are particularly the heterogeneous zones which were vulnerable to salt-induced damage, as shown in Fig. 15. DIC analysis further confirmed the presence of discontinuities at the deformation interfaces, highlighting the role of heterogeneity in the damage progression. These early findings hint at the critical influence of the rock's internal structure on its susceptibility to deterioration.

Building on these initial observations, Sample FR-002 was tested continuously for 6 days under similar conditions, displaying substantial external deformation. Damage initiation was first noted after day 2, with significant deformation observed on day 4, eventually leading to the sample's complete fracture. The role of heterogeneity in susceptibility to damage was more evident in this sample with indications of the timing of damage varying considerably. These findings strongly indicate that salt-induced crystallisation processes preferentially exploit the rock's

inherent weak points, further highlighting the heightened vulnerability of such heterogeneous materials. DIC analysis once again captured discontinuities at the deformation interfaces, as shown in Fig. 16.

Finally, Sample FR-003, subjected to 12 days of continuous testing under the same conditions, exhibited minor external deformation after 4 days, with more significant signs appearing by day 5. In comparison to FR-002, where significant damage was observed by day 4, Sample FR-003 showed a slower progression but ultimately split into two halves by the end of the test. Further demonstrating the cumulative impact of salt crystallisation and despite lighting challenges during image acquisition, DIC analysis confirmed that the damage followed the heterogeneity of the rock, as shown in Fig. 17. The extended testing period for this sample reinforces the notion that rock heterogeneity not only affects the onset timing of damage but also dictates the progression of damage
<figure><img src="image_13.png" /><figcaption>Fig. 13. Histogram of acoustic events monitored in samples VS-004 and VS 510 confirming consistency in the materials response to the accelerated salt weathering test after 18 h of testing.</figcaption></figure>

<figure><img src="image_14.png" /><figcaption>Fig. 14. (Left: a) Flysch rock sample prior to compressive testing, and (Right: b) after testing, showing deformation along weak heterogeneous zones.</figcaption></figure>

<figure><img src="image_15.png" /><figcaption>Fig. 15. Sample FR-001: (a) at the start of the accelerated salt weathering test showing zones of intrinsic heterogeneity, (b) after 4 days showing capillary rise and damage along the samples' intrinsic heterogeneity, and (c) associated displacement field from DIC analysis.</figcaption></figure>

over time.

Collectively, the findings from all three samples demonstrate the critical role of heterogeneity in salt-induced damage progression. The accelerated salt-weathering test protocol effectively induced observable external deformation across all samples, with the most significant deformations occurring in regions of inherent structural weakness. Time-lapse photography and DIC analysis proved highly effective in

capturing real-time data on crack propagation, particularly in areas characterised by heterogeneity. This approach not only revealed the susceptibility of flysch rocks to salt-induced damage but also provided an understanding of how these processes target weak zones, elucidating the underlying mechanisms of salt crystallisation and its detrimental effects on rock durability.
<figure><img src="image_16.png" /><figcaption>Fig. 16. Sample FR-002: (a) at the start of the accelerated salt weathering test, (b) after 6 days, and (c) associated displacement field from DIC analysis.</figcaption></figure>

<figure><img src="image_17.png" /><figcaption>Fig. 17. Sample FR-003: (a) at the start of the accelerated salt weathering test, (b) after 12 days, and (c) associated displacement field from DIC analysis.</figcaption></figure>

### 3.3. Concrete samples: observation of existing internal and external cracks, and crack propagation via time-lapse photography accompanied by DIC, acoustic emission (AE) analysis, and X-ray scanning

Concrete sample Con-Pave-001, intended for pavement applications, underwent a continuous 5-day testing period, monitored through time-lapse photography. This approach, similar to that used for the flysch rock samples, enabled the observation of external deformations. Detailed analysis of the time-lapse images revealed the progression of pre-existing natural cracks within the sample, with clear evidence of salt crystals (efflorescence) forming inside the natural crack. Digital Image Correlation (DIC) analysis, as shown in Fig. 18a-c, accurately captured the displacement field and discontinuities associated with crack propagation.

High-performance concrete sample Con-Artha-001 underwent a 20-day testing period during which a total of 989 acoustic events were recorded. The spatial distribution of the AE events, as visualised in Fig. 19, corroborated results obtained from the localisation software and to some extent, initial visual inspections of surface cracks. To further validate the spatial distribution inferred from the AE data and visual inspections, comparisons of the pre- and post-test X-ray images

confirmed crack development, showing strong agreement with the AE results. A simple phase segmentation of the post-test X-ray scan accompanied with the pre-test scan, as shown in Fig. 20, identified multiple cracks further highlighting the extent of internal damage. These findings reinforce the significant influence of salt crystallisation on the deterioration of the high-performance concrete, with the accelerated salt weathering test proving successful to initiate and propagate cracks, leading to substantial damage.

### 4. Conclusions

This study presents a novel accelerated salt weathering protocol and investigates its effectiveness on various construction materials, including Flysch rock, Vosges sandstone, and concrete. The experimental protocol successfully simulated accelerated salt weathering conditions, providing critical insights into the mechanisms of salt crystallisation, the influence of material heterogeneity in crack initiation, and the propagation of salt-induced damage in construction materials.

The results demonstrated significant external deterioration in the Flysch rock samples, with rock heterogeneity emerging as a key factor influencing damage susceptibility. Detailed crack propagation analysis
<figure><img src="image_18.png" /><figcaption>**Fig. 18.** Concrete sample Con-Pave-001: (a) at the start of the accelerated salt weathering test, with arrow indicating the extent of pre-existing natural crack, (b) after 5 days of continuous testing displaying salt crystals (efflorescence), with arrows indicating extent of visible crack propagation and (c) associated displacement field from DIC analysis showing discontinuity along the crack.</figcaption></figure>

<figure><img src="image_19.png" /><figcaption>**Fig. 19.** Concrete sample Con-Artha-001: (Left: a) after the accelerated salt weathering test and (Right: b) showing localisation of acoustic events recorded in the sample during the test.</figcaption></figure>

highlighted the evolution of cracks within the rocks, illustrating the variable mechanical responses to the weathering protocol. Observations on the Vosges sandstone samples revealed internal deterioration patterns, further supported by acoustic emission analysis, which provided insights into the onset of salt-induced damage. Comparisons between the sandstone samples confirmed a consistent response to the weathering protocol, demonstrating its reliability in evaluating the material's durability under these conditions.

Examination of the concrete samples revealed the propagation of

existing cracks and the development of new cracks under the accelerated salt weathering test. The combined use of time-lapse photography, Digital Image Correlation, Acoustic Emission analysis, and X-ray scanning significantly enhanced the understanding of crack propagation and damage progression.

Overall, this study establishes a reliable test protocol for assessing the effects of accelerated salt weathering on construction materials, contributing to a deeper understanding of durability of these materials in various engineering contexts. The experimental protocol was
<figure><img src="image_20.png" /><figcaption>Fig. 20. Pre- and post-X-ray image of sample Con-Artha-001 after 20 days of accelerated salt weathering test, with accompanying simple segmentation of the crack phase (including pores) showing extension of existing crack and development of multiple new cracks.</figcaption></figure>

intentionally designed to rely on standard laboratory resources, including temperature-controlled baths, optical imaging, and conventional DIC analysis tools. This practical configuration ensures that the proposed methodology can be reproduced in laboratories with varying levels of infrastructure, thereby broadening its accessibility and potential for comparative studies across different institutions. The findings enhance understanding of the critical role of salt distribution within capillary zones, the impact of material heterogeneity on damage progression, and the effectiveness of non-destructive techniques for monitoring salt-induced deterioration. These insights provide a framework for evaluating construction material performance, thereby informing strategies for improving infrastructure resilience against salt-induced degradation.

### CRediT authorship contribution statement

**Leclere Bruno Leclere:** Methodology, Investigation, Data curation. **OKUMKO Victor:** Writing – original draft, Methodology, Investigation, Data curation. **David Grégoire:** Writing – review & editing, Validation, Supervision, Methodology, Investigation, Funding acquisition, Formal analysis, Conceptualization. **Hannelore Derluyn:** Writing – review & editing, Validation, Supervision, Methodology, Investigation, Formal analysis, Conceptualization.

### Declaration of Competing Interest

The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Victor OKUMKO and Bruno LECLERE report financial support was provided by E2S UPPA Hub. David GREGOIRE reports financial support was provided by E2S UPPA Hub. Hannelore DERLUYN reports a relationship with European Research Council (ERC) that includes: funding grants. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

### Acknowledgments

This work was partially financed by FEDER funds (FSE 2014–2020) through the EZPONDA project and by the Investissement d'Avenir French program (ANR-16-IDEX-0002) under the framework of the E2S-UPPA Hub Newpores. H. Deluyn acknowledges the support from the European Research Council (ERC) under the European Union's Horizon

2020 research and innovation programme (grant agreement No 850853).

## Appendix A. Supporting information

Supplementary data associated with this article can be found in the online version at doi:10.1016/j.conbuildmat.2025.144881.

### Data availability

Data will be made available on request.

### References

[1] Goudie A.S., Viles H. Wiley.com. 1997 [cited 2024 Mar 2]. Salt Weathering Hazards. Available from: (https://www.wiley.com/en-us/Salt+Weathering+Hazards+p-9780471958420).

[2] C. Rodriguez-Navarro, E. Doehne, Salt weathering: influence of evaporation rate, supersaturation and crystallization pattern, Earth Surf. Process Land. 24 (3) (1999) 191–209.

[3] E. Doehne, Salt weathering: a selective review, Geol. Soc. Lond. Spec. Publ. 205 (1) (2002 Jan) 51–64.

[4] C. Cardell, T. Rivas, M. Mosquera, J.M. Birginie, A. Moropoulou, B. Prieto, et al., Patterns of damage in igneous and sedimentary rocks under conditions simulating sea-salt weathering, Earth Surf. Process Land. 28 (2003 Jan 9) 1–14.

[5] C. Cardell, F. Delalieux, K. Roumpopoulos, A. Moropoulou, F. Auger, R. Van Grieken, Salt-induced decay in calcareous stone monuments and buildings in a marine environment in SW France, Constr. Build. Mater. 17 (3) (2003 Apr 1) 165–179.

[6] A.V. Turkington, T.R. Paradise, Sandstone weathering: a century of research and innovation, Geomorphology 67 (1) (2005 Apr 1) 229–253.

[7] E. Ruiz-Agudo, F. Mees, P. Jacobs, C. Rodriguez-Navarro, The role of saline solution properties on porous limestone salt weathering by magnesium and sodium sulfates, Environ. Geol. 52 (2) (2007 Mar 1) 269–281.

[8] C. Noiriel, F. Renard, M.L. Doan, J.P. Gratier, Intense fracturing and fracture sealing induced by mineral growth in porous rocks, Chem. Geol. 269 (3) (2010 Jan 30) 197–209.

[9] T. Diaz Gonçalves, V. Brito, Alteration kinetics of natural stones due to sodium sulfate crystallization: can reality match experimental simulations? Environ. Earth Sci. 72 (2014) 1789–1799.

[10] B. Menéndez, V. Petránová, Effect of mixed vs single brine composition on salt weathering in porous carbonate building stones for different environmental conditions, Eng. Geol. 210 (2016 Aug 5) 124–139.

[11] F. Caruso, T. Wangler, R.J. Flatt, Easy illustration of salt damage in stone, J. Chem. Educ. 95 (9) (2018 Sep 11) 1615–1620.

[12] A.S. Trenhaile, Modeling the role of weathering in shore platform development, Geomorphology 94 (1) (2008 Feb 1) 24–39.

[13] J.A. Lawrence, R.N. Mortimore, K.J. Stone, J.P. Busby, Sea saltwater weakening of chalk and the impact on cliff instability, Geomorphology 191 (2013 Jun 1) 14–22.

[14] J.A. Lawrence, R. Spence, R.N. Mortimore, M. Eade, S.H. Bottrell, Coastal cliff rock mass weakening of Chalk and the impact of salt water, Proc. Inst. Civ. Eng. Geotech. Eng. 171 (6) (2018 Dec) 545–555.
[15] H. Morillas, F.F. de Mendonça Filho, H. Derluyn, M. Maguregui, D. Grégoire, J. M. Madariaga, Decay processes in buildings close to the sea induced by marine aerosol: Salt depositions inside construction materials, Sci. Total Environ. 721 (2020 Jun 15) 137687.

[16] G.W. Scherer, Crystallization in pores, Cem. Concr. Res 29 (8) (1999 Aug 1) 1347–1358.

[17] N. Thaulow, S. Sahu, Mechanism of concrete deterioration due to salt crystallization, Mater. Charact. 53 (2) (2004 Nov 1) 123–127.

[18] M. Angeli, J.P. Bigas, D. Benavente, B. Menéndez, R. Hébert, C. David, Salt crystallization in pores: quantification and estimation of damage, Environ. Geol. 52 (2) (2007 Mar 1) 205–213.

[19] M. Steiger, S. Asmussen, Crystallization of sodium sulfate phases in porous materials: the phase diagram Na₂SO₄·H₂O and the generation of stress, Geochim. Cosmochim. Acta 72 (17) (2008 Sep 1) 4291–4306.

[20] E. Molina, G. Cultrone, E. Sebastián, F.J. Alonso, Evaluation of stone durability using a combination of ultrasound, mechanical and accelerated aging tests, J. Geophys Eng. 10 (3) (2013 Jun 1) 035003.

[21] H. Derluyn, P. Moonen, J. Carmeliet, Deformation and damage due to drying-induced salt crystallization in porous limestone, J. Mech. Phys. Solids 63 (2014 Feb 1) 242–255.

[22] Leclere B. Damage induced by crystallisation in confined reservoir conditions [Internet] [phdthesis]. Université de Pau et des Pays de l'Adour; 2021 [cited 2024 Feb 22]. Available from: (https://theses.hal.science/tel-03194127).

[23] E. Ruiz-Agudo, A. Ibañez-Velasco, C. Ruiz-Agudo, S. Bonilla-Correa, K. Elert, C. Rodríguez-Navarro, Damage of porous building stone by sodium carbonate crystallization and the effect of crystallization modifiers, Constr. Build. Mater. 411 (2024 Jan 12) 134591.

[24] Derluyn H. Salt transport and crystallization in porous limestone: neutron-X-ray imaging and poremechanical modeling [Internet] [PhD Thesis], ETH Zurich; 2012 [cited 2024 Feb 22]. Available from: (https://www.research-collection.ethz.ch/bitstream/handle/20.500.11850/60428/1/eth-6248-01.pdf).

[25] A. Fragata, M. Rosário Veiga, A. Velosa, Substitution ventilated render systems for historic masonry: Salt crystallization tests evaluation, Constr. Build. Mater. 102 (2016 Jan 15) 592–600.

[26] A. Fragata, R. Veiga, A. Velosa, Performance of a salt-accumulating substitution lime render for salt laden historic masonry walls, Heritage 4 (4) (2021 Dec) 3879–3891.

[27] Winkler E.M., Singer P. Crystallization Pressure of Salts in Stone and Concrete [Internet]. 1972 [cited 2024 Feb 23]. Available from: (https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/83/11/3509/7485/Crystallization-Pressure-of-Salts-in-Stone-and).

[28] V. López-Acevedo, C. Viedma, V. Gonzalez, A. La Iglesia, Salt crystallization in porous construction materials. II. Mass transport and crystallization processes, J. Cryst. Growth 182 (1) (1997 Dec 1) 103–110.

[29] C. Rodriguez-Navarro, D. Doehne, E. Sebastian, How does sodium sulfate crystallize? Implications for the decay and testing of building materials, Cem. Concr. Res 30 (10) (2000 Oct 1) 1527–1534.

[30] R.J. Flatt, Salt damage in porous materials: how high supersaturations are generated, J. Cryst. Growth 242 (3) (2002 Jul 1) 435–454.

[31] C.M. Grossi, P. Brimblecombe, B. Menéndez, D. Benavente, I. Harris, M. Déqué, Climatology of salt transitions and implications for stone weathering, Sci. Total Environ. 409 (13) (2011 Jun 1) 2577–2585.

[32] A. La Iglesia, V. González, V. López-Acevedo, C. Viedma, Salt crystallization in porous construction materials I Estimation of crystallization pressure, J. Cryst. Growth 177 (1) (1997 May 2) 111–118.

[33] G.W. Scherer, Stress from crystallization of salt, Cem. Concr. Res. 34 (9) (2004 Sep 1) 1613–1624.

[34] M. Steiger, Crystal growth in porous materials—I: the crystallization pressure of large crystals, J. Cryst. Growth 282 (3) (2005 Sep 1) 455–469.

[35] M. Steiger, Crystal growth in porous materials—II: influence of crystal size on the crystallization pressure, J. Cryst. Growth 282 (3) (2005 Sep 1) 470–481.

[36] B. Lubelli, V. Cudde, T. Diaz-Goncalves, E. Franzoni, R.P.J. van Hees, I. Ioannou, et al., Towards a more effective and reliable salt crystallization test for porous building materials: state of the art, Mater. Struct. 51 (2) (2018 Apr 5) 55.

[37] European Committee for Standardization - British Standards Institution, Natural Stone Test Methods: Determination of Resistance to Salt Crystallization, British Standards Institution, 1999.

[38] RILEM Technical Committee 127-MS. RILEM TC 127-MS: tests for masonry materials and structures, Mater. Struct. 31 (1) (1998 Jan) 2–9.

[39] MacWilliam K. Aging Tests to Assess the Durability of Building Materials to Salt Crystallization - Towards a More Realistic and Effective Use of Sodium Sulfate. 2017 Jul 4 [cited 2024 Feb 24]; Available from: (https://dspace.cvtz.cz/handle/10467/73467).

[40] B. Lubelli, A.M. Aguilar, K. Beck, T. De Kock, J. Desarnaud, E. Franzoni, et al., A new accelerated salt weathering test by RILEM TC 271-ASC: preliminary round robin validation, Mater. Struct. 55 (9) (2022 Nov 15) 238.

[41] B. Lubelli, I. Rörig-Daalgard, A.M. Aguilar, M. Aškrabić, K. Beck, C. Bläuer, et al., 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, Mater. Struct. 56 (5) (2023 May 26) 101.

[42] C.M. Grossi, R.M. Esbert, L.M.S. del Rio, M. Montoto, M. Laurenzi-Tabasso, Acoustic emission monitoring to study sodium sulphate crystallization in monumental porous carbonate stones, Stud. Conserv. 42 (2) (1997 Jan 1) 115–125.

[43] C.M. Grossi, R.M. Esbert, L.M.S. del Rio, The application of the acoustic emission technique to stone decay by sodium sulphate in laboratory tests, Mater. Constr. 47 (245) (1997 Mar 30) 5–15.

[44] L. Golaski, P. Gebski, K. Ono, Diagnostics of reinforced concrete bridges by acoustic emission, J. Acoust. Emiss. (2002 Jan 1) 20.

[45] M. Holt, R. Harder, R. Winarski, V. Rose, Nanoscale hard X-ray microscopy methods for materials studies, Annu Rev. Mater. Res. 43 (1) (2013) 183–211.

[46] H. Derluyn, J. Dewanckele, M.N. Boone, V. Cudde, D. Derome, J. Carmeliet, Crystallization of hydrated and anhydrous salts in porous limestone resolved by synchrotron X-ray microtomography, Nucl. Instrum. Methods Phys. Res. Sect. B Beam Inter. Mater. 324 (2014 Apr 1) 102–112.

[47] M. Sutton, W. Wolters, W. Peters, W. Ranson, S. McNeill, Determination of displacements using an improved digital correlation method, Image Vis. Comput. 1 (3) (1983 Aug) 133–139, 1.

[48] M. Sutton, C. Mingqi, W. Peters, Y. Chao, S. McNeill, Application of an optimized digital correlation method to planar deformation analysis, Image Vis. Comput. 4 (3) (1986 Aug 1) 143–150.

[49] S. Touchal-Mguil, Une technique de corrélation d'images numériques: application à la détermination de courbes limites de formages et proposition d'un critère de striction, INSALYON Fr, 1997.

[50] D. Grégoire, H. Maigre, F. Morestin, New experimental techniques for dynamic crack localization, Eur. J. Comput. Mech. 18 (3-4) (2009 Jan) 255–283.

[51] D. Grégoire, O. Loh, A. Juster, H.D. Espinosa, In-situ AFM Experiments with Discontinuous DIC Applied to Damage Identification in Biomaterials, Exp. Mech. 51 (4) (2011 Apr) 591–607.

[52] W. De Boever, H. Derluyn, D. Van Loo, L. Van Hoorebeke, V. Cudde, Data-fusion of high resolution X-ray CT, SEM and EDS for 3D and pseudo-3D chemical and structural characterization of sandstone, Micro 74 (2015 Jul 1) 15–21.

[53] P.A. Poncet, B. Liquet, B. Larroque, D. D'Amico, D. Sous, S. Abadie, In-situ measurements of energetic depth-limited wave loading, Appl. Ocean Res 125 (2022 Aug) 103216.

[54] D. Grégoire, L. b Rojas-Solano, G. Pijaudier-Cabot, Failure and size effect for notched and unnotched concrete beams, Int J. Numer. Anal. Methods Geomech. 37 (10) (2013) 1434–1452.

[55] D. Benavente, del Cura M.A. García, A. Bernabéu, S. Ordónez, Quantification of salt weathering in porous stones using an experimental continuous partial immersion method, Eng. Geol. 59 (3) (2001 Apr 1) 313–325.

[56] M. Angeli, D. Benavente, J.P. Bigas, B. Menéndez, R. Hébert, C. David, Modification of the porous network by salt crystallization in experimentally weathered sedimentary stones, Mater. Struct. 41 (6) (2008 Jul 1) 1091–1108.

[57] H. Derluyn, T.A. Saidov, R.M. Espinosa-Marzal, L. Pel, G.W. Scherer, Sodium sulfate heptahydrate I: the growth of single crystals, J. Cryst. Growth 329 (1) (2011 Aug 15) 44–51.

[58] Steiger M., Charola A.E., Sterflinger K. Weathering and Deterioration. In: Siegesmund S., Snethlage R., editors. Stone in Architecture: Properties, Durability [Internet]. Berlin, Heidelberg: Springer; 2011 [cited 2024 Feb 23]. p. 227–316. Available from: https://doi.org/10.1007/978-3-642-14475-2_4.

[59] Morestin F. ICASoft digital image correlation software [Internet]. 2012 [cited 2024 Feb 2]. Available from: (https://lamcos.insa-lyon.fr/logiciels_icasoft.php?L=1).

[60] D. Grégoire, L. Verdon, V. Lefort, P. Grassl, J. Saliba, J.P. Regoin, et al., Mesoscale analysis of failure in quasi-brittle materials: comparison between lattice model and acoustic emission data, Int J. Numer. Anal. Methods Geomech. 39 (15) (2015) 1639–1664.

[61] L.A. Feldkamp, L.C. Davis, J.W. Kress, Practical cone-beam algorithm, JOSA A 1 (6) (1984 Jun) 612–619, 1.