Imaging spontaneous imbibition in full Darcy‐scale samples at pore‐scale resolution by fast X‐ray tomography

Spontaneous imbibition is a process occurring in a porous medium which describes wetting phase replacing nonwetting phase spontaneously due to capillary forces. This process is conventionally investigated by standardized, well-established spontaneous imbibition tests. In these tests, for instance, a rock sample is surrounded by wetting fluid. The following cumulative production of nonwetting phase versus time is used as a qualitative measure for wettability. However, these test results are difficult to interpret, because many rocks do not show a homogeneous but a mixed wettability in which the wetting preference of a rock varies from location to location. Moreover, during the test the flow regime typically changes from countercurrent to cocurrent flow and no phase pressure or pressure drop can be recorded. To help interpretation, we complement Darcy-scale production curves with X-ray imaging to describe the differences in imbibition processes between water-wet and mixed-wet systems. We found that the formation of a spontaneous imbibition front occurs only for water-wet systems; mixed-wet systems show localized imbibition events only. The asymmetry of the front depends on the occurrence of preferred production sites, which influences interpretation. Fluid layers on the outside of mixed-wet samples increase connectivity of the drained phase and the effect of buoyancy on spontaneous imbibition. The wider implication of our study is the demonstration of the capability of benchtop laboratory equipment to image a full Darcy-scale experiment while at the same time obtaining pore-scale information, resolving the natural length and time scale of the underlying processes

Texture and mineralogy influence on durability: The Macigno sandstone

The behaviour of ornamental stones in response to environmental changes or interactions is crucial when dealing with the conservation of cultural heritage.Weathering factors affect each rock differently, depending on structure, mineralogy, and extraction and implementation techniques. This work focuses on the Macigno sandstone, a dimension stone often employed in Tuscany over the centuries. A thorough mineralogical (optical microscopy, scanning electron microscopy and X-ray powder diffraction) and petrophysical characterization (i.e. mercury intrusion porosimetry, X-ray computed tomography, hygroscopic adsorption behaviour, ultrasounds, image analysis and capillary uptake) was made of the sandstone type extracted in the area of Greve in Chianti. The lithotype shows mineralogical (i.e. presence of mixed-layer phyllosilicates) and microporosimetric features, leading to a high susceptibility to relative humidity variation. Moreover, the influence of swelling minerals is related to weathering due to saline solution. The joint application of petrographic and petrophysical techniques allows an understanding of the characteristic weathering pattern of exfoliation (i.e. detachment of multiple thin stone layers, centimetre scale, that are sub-parallel to the stone surface)

Understanding the microstructure of mortars for cultural heritage using X-ray CT and MIP

In this study, the microstructure of mock-up mortar specimens for a historic environment, composed of different mixtures, was studied using mercury intrusion porosity (MIP) and micro-computed tomography (\ub5CT), highlighting the advantages and drawbacks of both techniques. Po-rosity, sphericity, and pores size distribution were studied, evaluating changes according to mortar composition (aerial and hydraulic binders, quartz sand, and crushed limestone aggregate). The \ub5CT results were rendered using 3D visualization software, which provides complementary information for the interpretation of the data obtained using 3D data-analysis software. Moreover, \ub5CT contrib-utes to the interpretation of MIP results of mortars. On the other hand, MIP showed significant ink-bottle effects in lime and cement mortars samples that should be taken into account when interpret-ing the results. Moreover, the MIP results highlighted how gypsum mortar samples display a porosity distribution that is best studied using this technique. This multi-analytical approach provides important insights into the interpretation of the porosimetric data obtained. This is crucial in the characterization of mortars and provides key information for the study of building materials and cultural heritage conservation

Sedimentological study of cold-water coral mounds on Pen Duick Escarpment (Gulf of Cadiz): preliminary results of the MD169 cruise

Cold-water corals are widely distributed along the Moroccan margin in the Northeast Atlantic Ocean. Within the Gulf of Cadiz mud volcanoes, submarine ridges and steep fault escarpments occur, which favour the settlement of scleractinians and build up coral mounds. One of these sites is the Pen Duick Escarpment, situated in the El Arraiche mud volcano field, 35 km offshore the city of Larache. Pen Duick Escarpment is a 6 km long, SSE-NNW oriented, 80 to 125 m high wall with a southwest-facing slope of 8 to 12°. Up to now, 15 coral mounds were recognized on top of the escarpment with an average estimated elevation of 15 m. Although cold-water corals are a common feature on the adjacent cliffs, mud volcanoes and seafloor, no actual living coral has been observed.This study is based upon three on-mound gravity cores (Alpha, Beta and Gamma mound) acquired by R/V Marion Dufresne in 2008 (MD169). Each mound was cored at least twice to recover both a core for biogeochemical and microbial studies, and another core for sedimentological purposes, in order to link both processes. The sedimentological cores were analysed using different techniques (medical CT scanning, XRF, U/Th dating, stable isotopes, grain-size analysis) in order to obtain a holistic view on the build-up of a mound. The coring, together with present-day seabed observations, revealed the architectural importance of open coral rubble plates in the role of mound building. These graveyards act not only as sediment trap but also as microhabitat for a wide range of benthic organisms

Micro computed tomography images of capillary actions in rough and irregular granular materials

The present work investigates the effect of both surface roughness and particle morphology on the retention behaviour of granular materials via X-ray micro-computed tomography (\ub5CT) observations. X-ray \ub5CT images were taken on two types of spherical glass beads (i.e. smooth and rough) and two different sands (i.e. natural and roughened). Each sample was subjected to drainage and soaking paths consisting in a multiphase ‘static’ flow of potassium iodine (KI) brine (wetting phase) and dry air (non-wetting phase). Tomograms were obtained at different saturation states ranging from fully brine saturated to air dry conditions with 6.2 μm voxel size resolution. The data acquisition and pre-processing are here described while all data, a total of 48 tomograms, are made publicly available. The combined dataset offers new opportunities to study the influence of surface roughness and particle morphology on capillary actions as well as supporting validation of pore-scale models of multiphase flow in granular materials

Efficiency assessment of hybrid coatings for natural building stones : advanced and multi-scale laboratory investigation

The efficiency of a hybrid patented consolidant (PAASi) and two commercially available hybrid coatings (a consolidant named AlSiX and a hydrophobic product named WS3) properly modified was assessed on a calcarenite substrate. Test routines based on standard recommendations were first applied to evaluate the performances of the consolidant and protective treatments, while the investigation of additional aspects such as penetration depth and interaction with the substrate was achieved by a multi-scale approach based on classic intrusion methods (mercury intrusion porosimetry) and Drilling Resistance Measurement System (DRMS), combined with non-invasive imaging techniques (X-ray computed micro-tomography and neutron radiography) and small angle neutron scattering (SANS). A distinct interaction of the products with the pore network of the stone was quantified in the range 0.007–200 µm. Their effects on capillary water absorption were also visualized with neutron imaging. The suitability of the products on the selected substrate was discussed, highlighting also how the applied routine can support conservation material studies. The results indicated that the Al-Si-based product led to unwanted effects. Alternative application methods and/or curing procedures have to be explored to overtake these undesirable changes. On the contrary, the polyamidoamine-based product seemed to be more suitable for calcarenite substrates conservation. The performances of the hydrophobic coating, when used in combination with consolidants, were strictly influenced by the pre-consolidation of the substrate

Multi-scale laboratory routine in the efficacy assessment of conservative products for natural stones

The evaluation of conservative treatments’ efficacy on natural building stones are usually based on standard recommendation routines finalized to evaluate compatibility and harmfulness of products in turn of the substrate. However, the visualization and the quantification of products inside pore structure of natural stones is not immediate through standard tests, so that imaging and advanced techniques are recently proposed in material conservation field to improve knowledge on penetration depth, modification of pore-air interface at different scale and monitor dynamic absorption processes. Moreover, natural stones are usually characterized by complex structure, which changes due to conservative treatments have to be inspected at different scale (from micrometer to nanometer). In this prospective, the assessment of laboratory practices able to integrate multiscale methods and give back a complete overview on interaction between new conservative formulates and natural stones is of high interest. In this paper, we propose a methodological routine for efficacy assessment of conservative products, incorporating classical and innovative nondestructive techniques. Validation of the workflow has been verified on a high porous natural stone treated with new hybrid formulates appropriately customized for conservation issues. • The study intends to add new insights on problems related to consolidation of high porous carbonate stone, application methods in consolidating natural stones and methods to evaluate efficacy of new products.• A multi-scale laboratory investigation procedure is proposed by integrating standard and innovative nondestructive methods. Merits and limits of each applied method are discussed during validation.• The possibility to incorporate standard routines and/or substitute destructive testing with non-destructive ones seem to be a valid alternative to evaluate efficiency and monitor behavior of stones treated with consolidating products