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Ce chapitre présente la problématique de l’impact de sels sur les matériaux de construction. Il discute l’origine des sels. Il illustre la diversité et la complexité des situations rencontrées liée à la présence possible de nombreux sels en solution. Il met l’accent sur les conditions environnementales et explore en quoi l’évolution des conditions environnementales, liée notamment au changement climatique, peut affecter l’impact de la présence des sels sur la durabilité des matériaux.

Colloid cyst are benign intracranial lesions located in the III ventricle in the region of the foramen of Monro. The majority present in the third and fourth decades of life and are rare under the age of ten. We report a case of an incidentally colloid cyst presented in a 2.5 -years-old girl who was managed conservatively; follow-up with MRI showed a progressive reduction in size. We review the four similar case previously reported.

Key evidence of human occupation in Africa during the Middle Palaeolithic (Middle Stone Age [MSA]) is available from the south and east of the continent, where semi-arid climate prevails. Rare evidence of MSA human occupation in the humid tropical region was recently reported from Equatorial Guinea. To identify if paleolithic human occupation occurred in the tropical forest, the stratigraphy of the recently discovered archaeological site “Mabewele I” was analyzed using a paleopedological approach. The properties evaluated along a vertical profile are: granulometry, magnetic susceptibility (K), free iron extractable with sodium dithionite (Fed), total organic carbon (TOC), chemical composition by X-ray fluorescence (XRF), X-ray diffraction mineralogy (XRD), ternary plot of the three main oxides (SiO2-Al2O3-Fe2O3), phytoliths and micromorphology. The predominant fraction is sand, with a significant clay content (> 30 %). The K and the Fed presented low values, as well as the TOC. XRF showed few variations along the sequence and XRD showed that the clays are mainly kaolinites, with a very low component of vermiculites. The phytoliths correspond to tropical vegetation with few changes in the vegetal composition between the deep and superficial zones. A charcoal from the lower part of the profile was dated between 12.57-12.24 ka cal BP, while the main artifact horizon was located at the bottom. The analytical results appear contradictory: on the one hand, there is evidence of intense chemical weathering under a humid tropical climate, but the clay cutans in the pores are very scarce and incipient and the iron nodules are mostly anorthic. This indicates that the sequence is composed of pedosediments associated with a high environmental dynamism, with short periods of erosion-sedimentation-pedogenesis. The results allow us to propose that humans inhabited the tropical forest during the MSA and that erosion-sedimentation processes could be related to anthropization processes.

Rock varnish is a thin layer (1-40 microns every 1000 years), dark-reddish in color (30% Mn and Fe oxides, 70% clay minerals), that coats a rock surfaces in the northern Mexican deserts. This accretion has been used as a canvas by ancestral human groups to record different types of motifs (zoomorphic, geometric and anthropomorphic) in the northern Mexican desert (Sonora and Chihuahua). These petroglyphs reflect the cultural and artistic nature of past inhabitants and the varnish preserves them through the millennia. Rock varnish coats a variety of rock types, and this paper explores differences in the chemical composition and interaction of varnish and the underlying rock. We studied varnish from three different sites: Samalayuca (Chihuahua); El Álamo (Sonora); and La Proveedora (Sonora). The analytical techniques of microscopy, X-Ray Diffraction (XRD) and Laser Breakdown Spectra (LIBS), reveals a similar chemical composition (Mn, Fe, Ca and Al mainly) that it does not depend on the lithodiversity or location (Samalayuca -sandstone-, El Álamo -sandstone- and La Proveedora -granite-). We observed differences in the contact between the varnish and the underlying rock. Varnish penetrate into decayed minerals such as plagioclase; thick accumulations can occur on hard minerals such as quartz. Like prior research, we find little important contribution of material from the underlying to its varnish coating and conclude its main component derives mostly from aeolian deposition.

International audience; In the present work, we investigate the mechanical weakening and deformation induced by water on a microporous carbonate rock, the Obourg Chalk from Mons Basin (Belgium), through conventional triaxial tests and injection tests. The injection tests were conducted by waterflooding critically loaded rock samples, initially in dry condition, in a way to minimize the variations in the effective pressures. Furthermore, the samples were instrumented with P-wave piezoelectric transducers to provide active ultrasonic monitoring while injecting. The results show a significant reduction in the mechanical strength of this chalk. Analysis of the mechanical tests and the associated deformation allows us to describe the mechanical behavior as a function of the confining pressure, which draws a brittle-ductile transition spanning from low to high confining pressure. The injection tests, moreover, revealed that the amount of water injected before triggering mechanical instability decreases exponentially with respect to the applied differential stress on the rock sample. The data, therefore, suggest that the failure might be controlled by a mechanical coupling between the water-invaded zone and the dry one. Since water-weakening plays an important role in several fields like oil industry, through secondary and tertiary recovery of hydrocarbons, Enhanced Geothermal Systems (EGS), as well as in the mechanical stability of underground cavities, the outcome of this work is of primary importance in mitigating any kind of problems related to these operations.

ObjectivesThe large number of infected patients requiring mechanical ventilation has led to the postponement of scheduled neurosurgical procedures during the first wave of the COVID-19 pandemic. The aims of this study were to investigate the factors that influence the decision to postpone scheduled neurosurgical procedures and to evaluate the effect of the restriction in scheduled surgery adopted to deal with the first outbreak of the COVID-19 pandemic in Spain on the outcome of patients awaiting surgery.DesignThis was an observational retrospective study.SettingsA tertiary-level multicentre study of neurosurgery activity between 1 March and 30 June 2020.ParticipantsA total of 680 patients awaiting any scheduled neurosurgical procedure were enrolled. 470 patients (69.1%) were awaiting surgery because of spine degenerative disease, 86 patients (12.6%) due to functional disorders, 58 patients (8.5%) due to brain or spine tumours, 25 patients (3.7%) due to cerebrospinal fluid (CSF) disorders and 17 patients (2.5%) due to cerebrovascular disease.Primary and secondary outcome measuresThe primary outcome was mortality due to any reason and any deterioration of the specific neurosurgical condition. Second, we analysed the rate of confirmed SARS-CoV-2 infection.ResultsMore than one-quarter of patients experienced clinical or radiological deterioration. The rate of worsening was higher among patients with functional (39.5%) or CSF disorders (40%). Two patients died (0.4%) during the waiting period, both because of a concurrent disease. We performed a multivariate logistic regression analysis to determine independent covariates associated with maintaining the surgical indication. We found that community SARS-CoV-2 incidence (OR=1.011, pConclusionsPatients awaiting neurosurgery experienced significant collateral damage even when they were considered for scheduled procedures.

Monitoring of fluid movements in the crust is one of the most discussed topics in oil & gas industry as well as in geothermal systems and CO2 storage, but still remains a challenge. The seismic method is one of the most common ways to detect the fluid migration. However, the use of ultrasonic monitoring at the sample scale in laboratory experiments persists as the most effective way to highlight large scale observations in which the boundary conditions are not well constrained.To unravel the fluid effect on P-wave and S-wave velocity, we performed mechanical experiments coupled with ultrasonic monitoring on Obourg chalk from Mons basin (Belgium). Water injection tests under critical loading, imbibition tests and evaporation tests provided a full spectrum of observations of fluid-induced wave alteration in term of propagation time and attenuation.The analysis of these experimental results showed that significant velocity dispersion and attenuation developed through variations in water saturation, and that these processes are linked to the presence of patches of water and air in the pore space.We used the White’s formulation to model the relaxation effects due to spherical pockets of air homogeneously distributed in a water-saturated medium. In this framework, the pressure induced by the passing wave, produces a fluid flow across the water-air boundary with consequent energy loss.This model reproduces both qualitatively and quantitatively the experimental results observed on the water injection tests. Indeed, it is shown that the progressive water saturation or desaturation of this chalk, generates a shift of the critical frequency (from the undrained relaxed towards unrelaxed regimes) which at some point matches the resonance frequency of the piezoelectric transducers used in the experimental setup (0.5 MHz). This phenomenon allowed us to get a continuous recording of the relaxation processes induced by saturation variations.The outcomes of this work can significantly improve the actual knowledge on coupled effects of waves and fluids which is a crucial aspect of fluid monitoring in the context of reservoir evaluation and production.

The RILEM TC ASC-271 is developing a new laboratory test to assess the durability of porous building materials to salt crystallisation. The test encompasses two phases: salt accumulation and damage propagation. This paper focuses on designing a procedure for the accumulation phase; this is considered successful when salts crystallise at the material's evaporative surface (common situation observed on site) without the occurrence of damage. Two procedures were developed and tested on two limestones with different porosity: (1) capillary absorption of a salt solution followed by drying, and (2) continuous capillary absorption. Sodium chloride or sodium sulphate solutions were used. Several methods for assessing the salt distribution were employed: ultrasonic pulse velocity, drilling/scratching resistance, hygroscopic moisture content, ion chromatography, scanning electron microscopy, and micro X-ray fluorescence. The results enabled the selection of the most effective protocol for the salt accumulation phase. ISSN:0950-0618

Since the performances of geological reservoirs are continuously changing during the production history, tools capable of characterizing these changes are becoming day by day of relevant importance. A time-lapse monitoring is an important and widely used way to explore the variations induced by the oil depletion. In an enhanced oil recovery scenario, the seismic survey method has been mostly used to monitor the remaining oil fraction with respect to the injected water, however no particular attention has been addressed to the effects generated by the water-rock interaction, which might induce deformation with no stress variation. Indeed, it is well known that water can induce important mechanical weakening in reservoir rocks.For that purpose, we performed injection tests on carbonate rocks in a conventional triaxial cell. An essential characteristic of these tests is the very low injection pressure, in order to minimize changes in the effective stresses and focus specifically on the rock - fluid interaction. The test consists in injecting water from the bottom in a critically loaded sample, initially in a dry state, until deformation is induced by the water-air substitution and failure is reached. While testing, the rock sample is instrumented with either 6 (at UCP, GEC lab) or 16 (at CSIRO, Geomechanics and Geophysics lab) P-wave transducers allowing us to perform an active ultrasonic survey with a narrow time intervals.The described methodology allowed us to monitor how P-wave attributes (amplitude, velocity and frequency), elastic moduli, as well as, permeability and injection rate change while water is flooding the sample increasing the water saturation, and damage is produced by the water – rock interaction. For instance, injecting water into a dry rock sample could produce several patterns of variations in the P-wave velocity, which we ascribed to 1) partial water saturation; 2) water-induced damage with no failure; 3) water-induced failure and, in some cases, 4) total water saturation. More experiments are planned to mimic real EOR operation, like injecting water in an oil-saturated rock sample, with acoustic monitoring as well.The outcome of this study indicates that combining multiple data sets from different sources is an effective tool for monitoring the exploitation of underground resources. This can certainly enhance our understanding of reservoir properties changing over time and target the attention toward the areas of greatest interest.

Carbonate rocks are well-known to be tremendously heterogeneous. They mainly consist of component particles (from biological and non-biological origin) embedded in a lime-mud matrix and/or in a cement (composed of even smaller particles). The size, shape, density and spatial arrangement of those particles, alongside with natural fractures and cracks (although those are certainly not exclusive to carbonate rocks), define a microstructural pattern that is known to have a great influence on rock physical properties. Thus, to understand carbonate rock systems at large scales (formation, reservoir …), geophysicists have to study them at the pore scale, hoping to resolve the so-called “upscalling” problem. With this in mind, unravelling and identifying the relations between physical properties and carbonate rock microstructures is paramount for a global comprehension of a carbonate rock system. Since the late nineties, several research groups and authors have worked on documenting and providing significant insights into the microstructural parameters controlling the physical response of several rock properties (porosity, permeability, electrical conductivity, elastic, seismic and mechanical properties …) in carbonates. This article proposes a review of this specialized literature, from the early and recent contributions in rock physics, with emphasis on the recent studies on carbonate rocks from the Paris basin.

Persepolis historical complex hosts palaces and tombs which are constructed by stone blocks. These stones suffer from various weathering. Hence, in this study, physico-mechanical properties of Persepolis stone are investigated in relation to some important weathering factors including freezing–thawing, thermal shock and salt crystallization. This study focused on role of the stone petrography on its durability against the weathering factors. Petrography studies showed that the stone is a nonporous-impermeable bioclastic-packstone which suffered significant diagenesis pressures and contain fractures filled by clay. Based on the obtained results, most of the observed deterioration for the stone is related to freezing–thawing cycles. The freezing–thawing cycles induced significant losses in the stone mechanical properties. Similar variations were recorded after the salt crystallization and thermal shock cycles, although the changes in the stone properties were not to the extent of freezing–thawing. Assessing values of decay constant (λ) and half-time (N1/2) obtained for the stone in relation to the ageing test cycles showed that freeze–thaw and thermal shock have more deteriorative effects on the stone durability than salt crystallization. It is suggested that porosity is the main factor that controls the Persepolis stone durability. Low permeability of the stone inhibits water percolation throughout the specimens, so their deterioration against salt crystallization is negligible. But in case of the freeze–thaw cycles, water uptake by clay minerals, which filled diagenesis fractures in the limestone, could be considered as the main factor for the observed deterioration during freezing–thawing. Also, effect of micro-cracks, caused by the thermal shock cycles, is the best explanation for reducing the mechanical properties of the stone.

To assess water-weakening effects in reservoir rocks, previous experimental studies have focused on changes in the failure envelopes derived from mechanical tests conducted on rocks fully saturated either with water or with inert fluids. So far, little attention has been paid to the mechanical behavior during fluid injection under conditions similar to enhanced oil recovery operations. We studied the effect of fluid injection on the mechanical behavior of the weakly consolidated Sherwood sandstone in laboratory experiments. Our specimens were instrumented with 16 ultrasonic P wave transducers for both passive and active acoustic monitoring during loading and fluid injection to record the acoustic signature of fluid migration in the pore space and the development of damage. Calibration triaxial tests were conducted on three samples saturated with air, water, or oil. In a second series of experiments, water and inert oil were injected into samples critically loaded up to 80% or 70% of the dry or oil-saturated compressive strength, respectively, to assess the impact of fluid migration on mechanical strength and elastic properties. The fluids were injected with a low back pressure to minimize effective stress variations during injection. Our observations show that creep takes place with a much higher strain rate for water injection compared to oil injection. The most remarkable difference is that water injection in both dry and oil-saturated samples triggers mechanical instability (macroscopic failure) within half an hour whereas oil injection does not after several hours. The analysis of X-ray computed tomography images of postmortem samples revealed that the mechanical instability was probably linked to loss of cohesion in the water-invaded region.

International audience; Fossil-bearing shale specimens that include sulfides in their compositions are chemically reactive and sometimes also mechanically fragile. This decay is often related to iron sulfate efflorescence resulting from the oxidation of sulfide compounds. The processes underlying these degradations are poorly known, thus impeding the elaboration of curative or preventive treatments. The present contribution aims to identify the origin of museum specimen alterations. It focuses on the Flouest collection housed at the Muséum national d’Histoire naturelle (MNHN, Paris, France) and originating from the Autun Basin (Saône-et-Loire,France; Permian). To evaluate the alteration of MNHN specimens, it appeared necessary to compare their composition with that of unaltered shale so as to identify chemical changes occurring during ageing. Therefore new material was collected in the Autun Basin, among others on the locality of Muse that corresponds to the same lithostratigraphic unit than that of the MNHN specimens. The present article focuseson the combined use of X-ray diffraction and Mössbauer spectrometry for characterizing the speciation and reactivity of iron within the shale matrix. Crystalline pyrite was evidenced by X-ray diffraction (XRD) on one sample only and elemental analysis showed that iron is present in large excess with respect to sulfur. Iron sulfide, if present, involves a minor fraction of iron. A more complete characterization of iron-bearing phases was achieved with Mössbauer measurements, showing that a great part of iron, between approx. 25% and 65%, corresponds to iron(II) incorporated in clay minerals (illite and vermiculite weredetected by XRD). Similar percentages of these iron(II) signatures were found for MNHN specimens and new shale samples, suggesting that iron(II) present in clays is not affected by ageing. This point is complementary highlighted by porosity and permeability measurements showing that the pore size distribution of the samples originating from Muse is mostly unimodal and narrow (average radius below 10 nm). As a result, the shale is poorly permeable to water and almost fully impermeable to oxygen. This might explain the poor reactivity of iron(II) during ageing. Iron(III)-bearing phases were also identified. On new shale samples, they exclusively involve clay minerals. On MNHN specimens, poorly crystallized iron(III) sulfates are additionally observed. The presence of iron(III) oxyhydroxides appeared unlikely. The change of iron speciation provoked by the alteration of the matrix also mainly corresponds to the emergence of more or less crystallized iron(III) sulfates probably formed though iron sulfide oxidation. These phase show ever remain in the inner part of shale and cannot account for the large efflorescence of iron(II) sulfates observed nearby the fossil.

International audience; El Gueria carbonate Formation (Ypresian) in Tunisia is a proven hydrocarbon reservoir. In the Gulf of Gabes, El Gueria reservoir consists mainly of a nummulitic limestone which is developed in an inner shelf environment. In order to characterize the depositional facies evolution and the petrophysical parameters, and to understand the origin of heterogeneity of El Gueria reservoir, we firstly conducted a sedimentological and a sequence stratigraphy study of this Formation in more than 10 wells especially in P1, then we established a detailed petrophysical study of El Gueria reservoir in P1, P3c and P7d cores. Based on lithostratigraphic and gamma ray correlations of an important number of wells in the study area, a detailed sedimentological study has been established. This latter shows that: (i): The Ypresien deposits are deposited in an inner shelf (El Gueria Formation) in the south and in an outer shelf (Boudabbous Formation) in the north of the study area with the form of horsts and grabens, (ii): 3 distinct members and 7 principal facies within El Gueria Formation have been distinguished. The coupling of data logging and data of the P1 core shows that the El Gueria deposits include 10 transgressive-regressive depositional sequences, while showing from bottom to top a broad regressive tendancy from a subtidal domain during the early Ypresian to an intertidal domain during the middle Ypresian reaching the supratidal environnement during the late Ypresian-early Lutetian. The petrophysical parameters (porosity and permeability) of El Gueria reservoir vary in time and space (laterally and vertically variation) following the deposit environment variation. Particularly, the porosity variation is controlled by eustatic cycles so that high porosities are linked with transgressive phases and low porosities with regressive phases. In addition, the vertical evolution of porosity through the El Gueria reservoir varies following the (i) deposit environments, (ii) type and morphology of nummulites such as large nummulites are more porous than small nummulites and nummilithoclastes (iii) matrix and cement such as micrite are more porous than sparite (iv) microfacies and diagenetic structures (Fractures, stylolithic seals …) such as the fractured wackstone are the most porous and permeable.

Salts are among the most active weathering agents acting in the degradation of cultural heritage, especially on stone and brick buildings. Most of the previous works on salt weathering studied only single salt composition despite the fact that in buildings a mixture of different salts is always present. This paper presents a methodology to estimate salt weathering from complex solution composition and meteorological data, temperature and relative humidity. The proposed method uses a thermodynamic model (ECOS-RUNSALT) to predict the variation of salt volume with changing environmental conditions. To illustrate how the developed method can be applied, two examples are presented. Firstly, the model has been applied to real measurements on a repairing mortar sample sampled from a building in the center of Paris. Secondly, the model has been applied to estimate salt damage produced by a theoretical salt composition in different locations of France. Possible applications in cultural heritage conservation are (i) the prediction of future behavior of cultural heritage building materials taking advantage of climatic models and (ii) a help to determine the optimal conditions to avoid, as much as possible, salt damage.

Sodium sulfates are well known to be the most damaging salts in building materials and rocks. Unfortunately, the crystallization processes of sodium sulfates are not completely understood. In addition, the metastable heptahydrate has long been neglected in scientific works on salt damage until recently. In this study, we use temperature monitoring and differential scanning calorimetry to detect and identify the crystallization of sodium sulfate hydrates (i.e., mirabilite and heptahydrate) upon cooling/heating a bulk solution. The presence of impurities seems to play a major role in the crystallization sequence and can explain the crystallization of mirabilite and ice close to −10 °C. The crystallization of heptahydrate does not seem to be sensitive to the presence of impurities and does not always occur prior to the crystallization of mirabilite as commonly observed. The heptahydrate and mirabilite show different and characteristic thermal signatures that enable to distinguish each other. The shape, the intensity and the duration of the peak of temperature due to the crystallization depict these differences. Therefore, the thermal signatures can be used in further experimental studies to estimate the role of the different sodium sulfate hydrates involved in the salt weathering of rocks.

Stone-mortar specimens manufactured with limestone and commercial stone-repair hydraulic mortars have been exposed to accelerated ageing tests, salt crystallisation (mixture of sodium chloride, sodium sulphate, calcium sulphate and potassium nitrate) and acid vapours exposure (sulphurous and nitric acid) besides, their corresponding control specimens were exposed to deionized water imbibition cycles and water vapour, respectively. Large amounts of soluble nitrates and minor amounts of sulphates precipitate on the surface of both stone and mortar materials after the acid test. This mainly affects the surface of the specimens rather than the stone-mortar interface. Whereas parallel fissures to the interface show up due to salt mixture crystals precipitation after the salt crystallisation test. A remarkable yellowing of the stone takes place after both tests. The mortar with closest properties to Euville limestone, with no phyllosilicates is the most resistant. It shows good mechanical properties but bad hydric interactions with the stone that could prove damaging in the long run. The mortar with the highest porosity and better hydric behavior but poor mechanical interaction with the stone is highly affected by the ageing tests, acting more as a sacrificial mortar rather than as a repair mortar., Thanks to Foundation des Sciences du Patrimoine/LabEx PATRIMA (2014–2015) for founding the project “Durabilité de l’interaction Mortier-Pierre dans le patrimoine architectural” (acronym: Dimppa) that allowed to carry out this research and the postdoctoral contract of Dr. Lopez-Arce.

International audience; The influence of different factors, brine composition, environmental conditions and pore structure, on salt weathering of porous carbonate building stones is investigated. The main goal of this study is to highlight the differences in weathering between single salts and a mixture of different salts. Two kinds of weathering mechanism are studied, the crystallization pressure and the deliquescence/recrystallization process. To achieve this purpose wetting and drying cycles and cycles varying relative humidity on samples containing salts were performed. The effect of total salt content with different salts and mixtures is simulated by weathering tests with solution of different compositions (NaCl, 6% in weight, Na2SO4·10H2O, 6% in weight, CaSO4 at saturation, and a mixture of them at total concentration of 6.2%). Weathering tests were performed at room temperature and 50 °C and under low and high relative humidity.The results show that the final weathering depends on a complex combination of three parameters: (i) environmental conditions, (ii) salt composition and (iii) petrophysical properties of stones, and general conclusions on the impact of each parameter can be drawn. An important result is that salt mixtures have a lesser impact on weathering during crystallization cycles: single salt brines, especially sodium sulphate, produce more weathering than complex brine compositions during wetting and drying cycles. Conversely during variations on RH, samples with salt mixtures suffer more damage than samples weathered with a brine of single salt composition.

International audience; Non-destructive techniques have always been used in the study of built cultural heritage because of the high cultural value of the concerned objects and the need to preserve them as intact as possible. In this chapter, different non-destructive techniques applied to the conservation of historical building are presented. The selected techniques concern the measurement of some physical properties of the building materials measured at the surface: water absorption, permeability, water content, cohesion, hardness and so on; the actual conditions of the building: stress state, deformation, crack growth and so on; and in-depth physical properties: mechanical properties, inner structure of walls, damp location and salt content. Some of these techniques are used for inspection of the building at a given time, whereas others can be applied for long periods of time to investigate the evolution of the building or of one of its parts (e.g., crack propagation) with time.

The physico-chemical compatibility of the most frequently used commercial stone-repair mortars applied to repair surface damage of a common limestone (Euville stone) employed in the basements of historic buildings from Paris was assessed. The characterization of anhydrous raw mortar materials, of stone and mortar samples collected from these buildings and laboratory specimens was carried out. The presence of chlorides and sulfates (gypsum and mixtures of calcium and sodium sulfates) with minor amounts of nitrates in mortar samples collected from the buildings suggest an origin of salts caused by contamination/pollution coming from past restoration products and environmental pollution. The mortar containing quartz, marble aggregates, portlandite and hydraulic components (CS, CS and CAS) with addition of aluminosilicate micro-spherical particles with cementitious properties, and no phyllosilicates, shows a better chemical compatibility with the stone. The mechanical properties of this mortar are also closer to those of the limestone. However, some differences in the hydric properties due to their different pore systems and aesthetic features should be improved in further restoration works., Thanks to Foundation des Sciences du Patrimoine/LabEx PATRIMA (2014-2015) for funding the project “Durabilité de l’interaction Mortier-Pierre dans le patrimoine architectural” (acronym: Dimppa) that allowed to carry out this research and the postdoctoral contract of Dr. Lopez-Arce.

Petrophysical properties were measured on oolitic limestone from the Oolithe Blanche formation (middle Jurassic) in the Paris Basin. Eighteen oriented blocks were collected from three outcrops regarding of the three main facies, oolitic shoal facies, tide dominated facies and prograding oolitic facies. We investigated the relationship between both compressional wave and electrical conductivity with different petrophysical properties such as porosity (water porosity and mercury porosity), permeability and capillarity imbibition. These have led us to relate the variations of petrophysical properties to several microstructural parameters, among them the microporous structure is the most important. Concerning P wave velocities, the general trend observed is as expected a decrease of velocities as the porosity increases but with a significant fluctuation of velocities for a given value of porosity. We have used two distinct effective medium approximations to describe the velocity variations: the self-consistent (SC) approximation and the cemented contact theory (CCT) but no unique model can simply explain our velocity behaviours. The main parameter that controls the P wave velocities is the distribution of microporosity inside oolites: for samples with velocities higher than 4 km/s the microporosity is mainly located in the rim of the ooids while for samples with velocity lower than 4 km/s the microporosity is homogeneous across the ooids. Acoustical fabrics, which are controlled by the facies, indicate that sedimentary textural components such as the amount of cement and arrangement of elements within the oolitic limestones (bioclasts, pellets and ooids) and their degree of connectivity may have some influences on the acoustic velocities. In contrast with acoustic properties, the electrical conductivity data are not so clustered by facies indicating that transport properties are more influenced by microstructural heterogeneities. One single Archie's law can well account for all the data sets but these sets also show a large range of tortuosity factor related to the microporosity arrangement inside oolites. Some good predictive permeability modeling were found using mercury injection spectra. Our investigations reveal that, the best way for fluids to flow is to pass through the microporosity in the oolites, and that permeability depends mainly of the connectivity of the ooids, which is certainly related to the facies.

International audience; The Paris Basin seems a suitable location for CO2 capture and storage given both the amount of CO2 produced and the availability of depleted fields and deep saline aquifers. This study investigates the petrophysical properties in relation to the sedimentary and diagenetic environment of the Oolithe Blanche Formation (Middle Jurassic), a deep saline aquifer considered a potential candidate for CO2 storage. Because of the scarcity of core data in the Paris Basin, our investigation was based on the study of field analogues in the south-east part of the Paris Basin. The Oolithe Blanche Formation (Bathonian) is 70-80 m thick. Eighteen oriented blocks were collected from three outcrops selected for the different sedimentological facies identified in the formation. Their petrophysical properties were measured: porosity, pore size distribution derived from mercury injection tests, permeability and capillary imbibition parameters. The sedimentary and diagenetic facies were defined by using optical microscopy coupled with image analysis on thin sections and SEM. The Oolithe Blanche Formation is composed of oolitic and bioclastic limestones, deposited in a shallow marine setting. Three main sedimentological facies were defined: the oolitic shoal facies, the tide dominated facies and the prograding oolitic facies. They exhibit subtle variations in composition and in the distribution of carbonate textures. Porosity, measured using the water saturation triple weight method, ranges from 6% to 34%. Permeability values are low, between 0.1 mD and 9 mD. The data from mercury intrusion porosimetry show that the distribution of the pore throat diameter is either unimodal (microporosity only) or bimodal (macro- and microporosity). Microporosity is intraparticle (intraooid) and macroporosity is interparticle and is related to dolo-dedolomitization. Variations of petrophysical parameters can be explained by the microstructure. Now, these latter results calibrated by studying field analogues must be extended to borehole data and core data to optimize our knowledge of the deep saline aquifer of the Oolithe Blanche Formation. Without such investigations, it will be impossible to estimate the suitability of this deep saline aquifer for CO2 storage.

The aim of this study is to evaluate how the ambient temperature and the salt concentration affect the salt decay of a sedimentary stone. Samples of a detritic limestone have suffered cycles of accelerated ageing at 5, room temperature (around 22 °C) and 50 °C with brines which had different sodium sulphate concentration. The weight of the samples and of the pieces fallen off during the cycles has been monitored. The results show that the damage is more important at 5 °C than at room temperature. The samples at 50 °C were intact at the end of the experiment. Second, the weathering patterns are different at different temperatures: fine crumbling at 5 °C; coarse crumbling and contour scaling at room temperature. The decay seems also to be of a different kind for each concentration at room temperature: crumbling at low concentration, contour scaling at high concentration. Crystallization seems to take place deeper inside the porous network of the stone when the concentration of salts in the brine is higher, that is to say when the brine viscosity is higher.

This paper presents the technological and typological study of the lithic assemblage recovered at Picamoixons during the field season carried out in 1993. Its technotypological features, the differential conservation of the assemblage, the spatial distribution of lithic remains and the radiometric dates allow us to divide the assemblage into two different sets and suggest that they belong to different chronological and cultural periods. The items included in the first one (CP) show a strong patina and should be included in the macrolithic Mesolithic, while the second one’s items (CNP) are not patinated and belong to the final part of upper Palaeolithic., En este artículo se presenta el análisis tecnológico y tipológico de la industria lítica recuperada en el año 1993 en el yacimiento de Picamoixons. Dadas sus características, su estado de conservación diferencial, su distribución espacial y las dataciones radiométricas disponibles, podemos concluir la existencia de dos conjuntos líticos pertenecientes a dos momentos cronológicos y culturales diferentes. El primero es el conjunto patinado (CP) que debería incluirse dentro del Mesolítico macrolítico, y el segundo conjunto es el no patinado (CNP) perteneciente a los momentos finales del Paleolítico superior.

Several methods are compared for the detection of moving capillary fronts in spontaneous imbibition experiments where water invades dry porous rocks. These methods are: (i) the continuous monitoring of the mass increase during imbibition, (ii) the imaging of the water front motion using X-ray CT scanning, (iii) the use of ultrasonic measurements allowing the detection of velocity, amplitude and spectral content of the propagating elastic waves, and (iv) the combined use of X-ray CT scanning and ultrasonic monitoring. It is shown that the properties of capillary fronts depend on the heterogeneity of the rocks, and that the information derived from each method on the dynamics of capillary motion can be significantly different. One important result from the direct comparison of the moving capillary front position and the P wave attributes is that the wave amplitude is strongly impacted before the capillary front reaches the sensors, in contrast with the velocity change which is concomitant with the fluid front arrival in the sensors plane.

International audience; Abstract Most buildings of architectural heritage in Paris and its surroundings are built with Lutetian limestone. Several historic buildings of the ‘Vexin Normand’ region show Lutetian limestone in the upper parts of their walls, while the lower parts are built with a chalk known as ‘Pierre de Vernon’. The ‘Pierre de Vernon’ appears up to the first metre, although in exceptional cases it can reach the middle height of a building. Commonly, chalks exhibit low durability due to their high porosity. However, ‘Pierre de Vernon’ is supposed to have greater durability than other chalks because of its historic use for basement construction. The objective of this research was to understand the use of the ‘Pierre de Vernon’ in the lower part of the constructions. A petrophysical characterization of Vernon chalk and Lutetian limestone was carried out, focusing mainly on the differences in porosity and water uptake. Salt crystallization tests were done to contrast their response to decay. Colour and roughness measurements and scanning electron microscope observations were performed. Results show that the different porous networks of these two limestones lead to a high contrast in their hydric properties and responses to decay, and the use of Vernon chalk in the lower sections of buildings has been found to be appropriate.

Crystallization of salts is recognized to be a major factor of the degradation of porous materials such as stone and concrete. On the theoretical side, there is now general acceptance about the thermodynamic origin of this phenomenon. However, on the experimental side, there are only scarce quantitative data. In this respect, the reference work par excellence is that of Correns (Discuss Faraday Soc 5:267–271, 1949) who shows a good correlation between calculated and measured crystallization pressures. However, concerns about both the thermodynamic derivation and the experimental conditions raise the question about why Correns could have obtained such a good correlation. This issue is discussed extensively in this paper which is organized as a commented translation of a former paper by Correns, co-authored by Steinborn, and that is much richer in experimental details.

International audience; The objective of this study is to understand and predict the alteration of porous rock by crystallization of salts. Samples of different rocks have been tested according to the EN 12370 standard test. Two parameters are proposed to evaluate the alteration of a rock during these tests. The alteration index AI represents the cycle in which the first damages occur. The alteration velocity AV represents the alteration rate at the end of the experiment, when the decay has become regular. These parameters can be estimated with the help of a microstructural study of the rocks. The most relevant intrinsic parameters of the stones for this estimation are capillary coefficient, evaporation coefficient, tensile strength and P-waves velocity. An evaluation of the alteration pattern is also proposed depending on the eventual heterogeneities and anisotropies of the rocks. The influence of the dimension and shape of the samples is also discussed.

Microstructural analysis of two undeformed sandstones, the Bentheim and Rothbach sandstones, supports the origin of the macroscopic anisotropies previously investigated (ultrasonic P-wave velocity, electrical conductivity and magnetic susceptibility). The shape and spatial distribution of both grains and voids were determined by computer image processing, measurement of magnetic anisotropy coupled with ferrofluids and stereological analysis. In addition, data on permeability measured in different directions are also provided for the two sandstones. The elastic models proposed in a previous paper are confirmed by the present study. In the Bentheim sandstone, the anisotropic behaviour was attributed to the non-spherical shape of the porosity, while in the Rothbach sandstone, an orientation-dependent cement radius at the intergranular contacts controls the observed anisotropy. The methods used for analysing the rock microstructure and its anisotropy are shown to be very useful and appropriate for detecting features such as pore or grain shape anisotropy, or the spatial distribution of grain contacts.

We present an overview of experimental results that we obtained in the last decade on the permeability evolution with stress and the analysis of stress-induced damage in sandstones. The goal of these studies was to get a fundamental knowledge on the interplay between deformation at the microscale level, fluid flow processes and the macroscopic rock properties. In a first part we present experimental data on the effect of stress on permeability, with emphasis on the influence of stress path and failure mode. In a second part, results from a microstructural study on the mechanics of deformation in Berea sandstone are shown. Although both studies have not been done on the same rock, some general conclusions are drawn on the influence of mechanical deformation on permeability with implications for field studies.

18 pages; International audience; The Oolithe Blanche Formation was studied in three quarries, located at the south-eastern edge of the Paris Basin (France). Heterogeneities in reservoir properties were assessed through a sedimentological, diagenetic and petrophysical study. The relationships between depositional settings, diagenesis and petrophysical properties were analysed using detailed petrographic studies, image analysis, Nano CTscans and petrophysical measurements. The carbonate reservoir pore network is mainly controlled by intraparticle microporosity which ensures the connectivity with interparticle meso- and macroporosity. Early cementation vs. early compaction processes (mainly grain interpenetration) may have considerable influence on fluid-flow properties and parameters such as permeability, acoustic velocities and tortuosity. Better reservoir properties are found when compaction processes begin before cementation. From statistical analyses, e.g. Principal Component Analysis and Linear Discriminant Analysis, a sedimentological/diagenetic and petrophysical model is proposed that is in a good agreement with the geological model developed from field work.

Confocal Scanning Laser Microscopy (CSLM) was used to characterise 3D crack networks in La Peyratte granite samples in which cracking was artificially induced either by heating samples at selected temperatures in order to induce thermal cracking, or by performing mechanical tests in order to develop stress-induced cracking at room temperature. Our goal was to recognise typical crack patterns associated with the different cracking mechanisms. We have taken advantage of the ability of CSLM to image thin slices within the rock sample in two different ways: first there are no overprojection problems for stereological studies, and second, one can obtain series of images at different depths from which the 3-D crack network can be reconstructed. Stereological analysis and 3D reconstructions revealed that thermally cracked and mechanically cracked samples differ in anisotropy of crack orientation distribution, with mechanically cracked samples characterised by strongly anisotropic crack networks.

The purpose of this work was to investigate the influence of cement on the mechanical behaviour of granular rocks. Following the technique described in den Brok et al. [den Brok, S. W. J., David, C. and Bernabe, Y., Preparation of synthetic sandstones with variable cementation for studying the physical properties of granular rocks. C. R. Acad. Sci., 1997, 325, 487–492], two blocks of synthetic sandstones with different cement content were prepared for mechanical testing under hydrostatic and triaxial conditions. The results of the mechanical tests show that the behaviour of the synthetic rocks compares well with that of natural sandstones. Increasing the amount of cement from 3 to 5% in volume had important consequences on the mechanical properties: the critical pressure, strength and elastic moduli were significantly increased and the brittle-to-ductile transition was shifted towards higher pressures. We compared our results to the models of Zhang et al. [Zhang, J., Wong, T. -F. and Davis, D. M., Micromechanics of pressure-induced grain crushing in porous rocks. J. Geophys. Res., 1990, 95, 341–352] and Wong et al. [Wong, T. -F., David, C. and Zhu, W., The transition from brittle faulting to cataclastic flow in porous sandstones: Mechanical deformation. J. Geophys. Res., 1997, 102, 3009–3025]. We conclude that Zhang et al.'s microstructural parameter φD (i.e. the product of porosity φ by grain size D) appeared to be a scaling parameter for both the failure envelopes and the critical pressure as defined in these models. Intuitively, the contact length L is expected to play a crucial role in the mechanical properties of granular materials. Accordingly, we made a statistical analysis of this microstructural parameter in our synthetic materials and in a suite of natural sandstones. A positive correlation with Young's modulus and a negative correlation with porosity were found. This last result gives a physical background for the use of parameter (φD) in theoretical models. We want to emphasize that working on synthetic sandstones allows for a better control of the structural parameters (grain size, sorting, cement content, etc.) which appear to be so important for the mechanical properties of granular rocks.

International audience; Gypsum is one of the most universally distributed salts in weathered materials but little is known about the influence of environmental conditions on the damage generated by gypsum in stones. To quantify the damage induced by gypsum crystallization acoustic emission techniques are employed to record the elastic energy released during salt crystallization cycles in a limestone. Different environmental conditions have been established during the cooling and drying periods in traditional salt crystallization cycles. During drying two different temperatures (50°C and 25°C) and relative humidity (low, 25% at 50°C and 65% at 25°C, and high, 99%) have been applied. The acoustic emission signals are filtered by a frequency analysis in order to eliminate signals corresponding to external noise or artifacts. Our experimental results show that acoustic emission activity is higher under high relative humidity conditions than under low relative humidity conditions, and also higher when drying at 50°C than at room temperature. Microscopic observations on the weathered samples indicated that under high relative humidity conditions and at room temperature gypsum crystallizes not on the sample surface, like in the other samples, but deeper in the inner part of the sample, in good agreement with previously published data. We show that using acoustic emissions as usually done in rock mechanics is also very useful in the study of stone decay and weathering processes in the laboratory.

The role played by the petrophysical characteristics of the rock matrix in the radioelement transfer phenomena through the geosphere is considered. The aim of this paper is to correlate information provided by the microcrack network, mineralogy and U-micromapping studies which can be used to quantify the extent of radioelement migration/retention in the granite. This study is part of an interdisciplinary research project on the El Berrocal site (Spain), which forms part of the R & D Programme “Management and Disposal of Radioactive Waste” of the Commission of the European Communities. The experimental procedure combines complementary microscopic techniques: polarizing light, fluorescence, confocal laser scanning, acoustic, scanning electron microscopy and uranium-induced fission-track micromapping. All of these techniques are applied for quantifying the rock matrix characteristics. Data on preferential fissure zones in relation to mineralogy, and the correlation between these data and uranium microdistribution are obtained. These results are discussed in terms of radionuclide mobility and can be used, with other information, for evaluating the retardation capacity of the crystalline rock matrix around a high-level radioactive waste repository.

The micromechanics of failure in Berea sandstone were investigated by characterizing quantitatively the evolution of damage under the optical and scanning electron microscopes. Three series of triaxial compression experiments were conducted at the fixed pore pressure of 10 MPa and confining pressures of 20, 50 and 260 MPa, respectively, corresponding to three different failure modes: shear localization with positive dilatancy, shear localization with relatively little dilatancy and distributed cataclastic flow. To distinguish the effect of non-hydrostatic stress from that of hydrostatic pressure, a fourth suite of hydrostatically loaded samples was also studied. Using stereological procedures, we characterized quantitatively the following damage parameters: microcrack density and its anisotropy, pore-size distribution, comminuted volume fraction and mineral damage index. In the brittle regime, shear localization did not develop until the post-failure stage, after the peak stress had been attained. The microcrack density data show that very little intragranular cracking occurred before the peak stress was attained. We infer that dilatancy and acoustic emission activity in the prefailure stage are primarily due to intergranular cracking, probably related to the shear rupture of lithified and cemented grain contacts. Near the peak stress, intragranular cracking initiates from grain contacts and this type of Hertzian fracture first develops in isolated clusters, and their subsequent coalescence results in shear localization in the post-failure stage. The very high density of intragranular microcracking and pronounced stress-induced anisotropy in the post-failure samples are the consequence of shear localization and compactive processes operative inside the shear band. In contrast, Hertzian fracture was a primary cause for shear-enhanced compaction and strain hardening throughout the cataclastic flow regime. Grain crushing and pore collapse seem to be most intense in weakly cemented regions. Finite element simulations show that the presence of cement at grain contacts alleviates the tensile stress concentration, thus inhibiting the onset of Hertzian fracture and grain crushing.