Porous Limestone Research Articles

Inelastic Compaction in High‐Porosity Limestone Monitored Using Acoustic Emissions

AbstractWe performed a systematic investigation of mechanical compaction and strain localization in Saint‐Maximin limestone, a quartz‐rich, high‐porosity (37%) limestone from France. Our new data show that the presence of a significant proportion of secondary mineral (i.e., quartz) did not impact the mechanical strength of the limestone in both the brittle faulting and cataclastic flow regimes, but that the presence of water exerted a significant weakening effect. In contrast to previously published studies on deformation in limestones, inelastic compaction in Saint‐Maximin limestone was accompanied by abundant acoustic emission (AE) activity. The location of AE hypocenters during triaxial experiments revealed the presence of compaction localization. Two failure modes were identified in agreement with microstructural analysis and X‐ray computed tomography imaging: compactive shear bands developed at low confinement and complex diffuse compaction bands formed at higher confinement. Microstructural observations on deformed samples suggest that the recorded AE activity associated with inelastic compaction, unusual for a porous limestone, could have been due to microcracking at the quartz grain interfaces. Similar to published data on high‐porosity macroporous limestones, the crushing of calcite grains was the dominant micromechanism of inelastic compaction in Saint‐Maximin limestone. New P wave velocity data show that the effect of microcracking was dominant near the yield point and resulted in a decrease in P wave velocity, while porosity reduction resulted in a significant increase in P wave velocity beyond a few percent of plastic volumetric strain. These new data highlight the complex interplay between mineralogy, rock microstructure, and strain localization in porous rocks.

Multifunctional TiO2-based hybrid coatings on limestone: Initial performances and durability over time

In the present work, the photocatalytic activity of different coatings containing titanium dioxide nanoparticles, both pure and in conjunction with metallic nanoparticles (silver and copper) to improve their photocatalysis and biocidal efficiency, was monitored over time. The nanoproducts were applied on travertine – a porous limestone – through spray-coating. An artificial accelerated ageing test – based on the prolonged exposure to ultraviolet light and the repeated application of stains – was used to simulate the extended use of the coatings on outdoor surfaces. Microscopical, aesthetical and physical macroscopic features, as well as self-cleaning and biocidal efficiencies of the coating-substrate system, were analysed assessing possible changes over time. The outcome of the research pointed out a good aesthetic compatibility with stone substrate (showing limited visual alteration) and high photocatalytic efficiency before ageing. Durability of self-cleaning and biocidal effects was also very clear while wettability of treated surfaces – especially without metallic nanoparticles – was the most altered characteristic of the coatings at the end of the ageing.

Nanostructured lime-based materials for the conservation of calcareous substrates

Nanostructured lime-based materials for the conservation of calcareous substrates

Stone weathering under Mediterranean semiarid climate in the fortress of Nueva Tabarca island (Spain)

The Nueva Tabarca fortress constitutes an exceptional example of baroque architectural heritage. However, the aggressiveness of the local environment and the low suitability of the used building stone cause their fast deterioration. The hydro-mechanical properties of the building stones, the characteristics of their porous system (open porosity and pore size distribution), the global climate of the island and the particular microenvironmental conditions of each studied monument explain the weathering process acting on the porous limestone of Nueva Tabarca.Results reveal that Halite crystallization and wind erosion are the main weathering agents. On the one hand, wind plays a critical weathering action because it controls the salt crystallization process, the abrasion by wind-blown particles, as well as the wind-driven rain impact. Different weathering forms are related to each erosion mechanism. On the other hand, the relative humidity in the island determines the agressiveness of the halite crystallization process. Salt damage activity was calculated quantifying not only the number of halite crystallization-dissolution transitions, but also the duration of the driest periods.Finally, a novel parameter (Equivalent Years, Yeq) is defined in order to quantify the representativeness of standarized artificial ageing tests. Yeq expresses the number of years of natural ageing required for achieving the same weathered state of rocks after laboratory procedures. A wide range of Yeq values are obtained for the studied rocks (from 8 to 165 years), showing a strong dependency with both the exposure time as well as the agressiveness of the environment.

Penetration depth and redistribution of an aqueous ammonium phosphate solution used for porous limestone consolidation by brushing and immersion

When consolidants are applied to porous stones, redistribution may occur inside the pore system after the treatment application, which influences their final penetration depth and performance. In this paper, the kinetics of redistribution were investigated for a 2-step hydroxyapatite-based consolidant, applied by brushing and immersion. The results of the study indicate that both the application method and the drying phase are crucial in determining the final penetration depth, the amount of hydroxyapatite that forms and the redistribution kinetics. In all cases, the limewater poultice applied during the second step of the treatment proved to be effective in removing soluble compounds.

The effects of the different curing conditions and the role of added aggregate in the strength of repair mortars

Four ready-mix commercial available repair mortars—that are used for porous limestone repair—were studied under different laboratory conditions. To have better compatibility with porous limestone, not only pure mortars but also mortars with 50 wt% of limestone aggregate was tested. The reason why limestone aggregate was added to mortar was to modify the strength and porosity. Samples kept under climate control, dry and humid conditions were tested to understand the influence of environmental conditions. The bulk density and uniaxial compressive strength of cubic specimens were measured 3, 7, 14, 28 and 90 days after casting. The microscopic analyses revealed that tested repair mortars contain Portland cement and also non-hydrated cement particles even after curing. The strength of mortars in time does not show similar changes; however, specimens kept under dry conditions show the lowest strength 90 days after casting. High humidity leads to lower strength than normal humidity for tested mortars, but there is one mortar with added limestone aggregate, which has higher strength under humid conditions. In general, adding 50% of porous limestone aggregate reduced the strength and increased the density of repair mortars kept in climate chamber. Limestone aggregate that has larger pores causes a shift in effective pore radii toward smaller pores of 50% limestone aggregate mortar mixtures compared to pure mortars, with one exception. Tests results indicate that these commercially available repair mortars, even though they are suggested to be used for porous limestone, behave very differently under different environmental conditions and that adding limestone aggregate do not shift properties of the mortars toward appropriate compatibility.

Self‐similar distributions of fluid velocity and stress heterogeneity in a dissolving porous limestone

AbstractIn a porous rock, the spatial distribution of the pore space induces a strong heterogeneity in fluid flow rates and in the stress distribution in the rock mass. If the rock microstructure evolves through time, for example, by dissolution, fluid flow and stress will evolve accordingly. Here we consider a core sample of porous limestone that has undergone several steps of dissolution. Based on 3‐D X‐ray tomography scans, we calculate numerically the coupled system of fluid flow in the pore space and stress in the solid. We determine how the flow field affects the stress distribution both at the pore wall surface and in the bulk of the solid matrix. We show that during dissolution, the heterogeneous stress evolves in a self‐similar manner as the porosity is increased. Conversely, the fluid velocity shows a stretched exponential distribution. The scalings of these common master distributions offer a unified description of the porosity evolution, pore flow, and the heterogeneity in stress for a rock with evolving microstructure. Moreover, the probability density functions of stress invariants (mechanical pressure or von Mises stress) display heavy tails toward large stresses. If these results can be extended to other kinds of rocks, they provide an additional explanation of the sensitivity to failure of porous rocks under slight changes of stress.

Dynamic simulation of coupled transmission processes and reaction mechanisms in porous calcined limestone

The particle reaction model and dynamic reaction characteristics of limestone over a wide particle size range from 0.15 to 10 mm were studied by thermogravimetric analysis and nitrogen adsorption‐desorption techniques. A clear boundary between the sintered porous product layer and the undecomposed part was found by field emission scanning electron microscopy (FESEM) analysis. A dynamic coupling model considering the effects of varied pore structure and transport resistances was established based on the appropriate particle reaction model, which allowed us to predict the decomposition ratio and reaction regimes in a broad range of particle sizes. The dynamic characteristics of pore size distribution and reaction mechanisms were discussed. Over the defined particle size range and calcination temperature range, the diffusion of gaseous product through porous product layer will become the rate determining factor as the ratio of (r0‐rc)/r0 corresponding to 25 % Damköhler number above 0.35.

Nanostructured lime-based materials for the conservation of calcareous substrates

Nanostructured lime-based materials for the conservation of calcareous substrates

Nanostructured lime-based materials for the conservation of calcareous substrates

Nanostructured lime-based materials for the conservation of calcareous substrates

THE SINKHOLE

5 8 Y T H E S I N K H O L E D E V I N J O H N S T O N Unclenched and half asleep – bloodstream tinged with melatonin, the hormonal expression of darkness – I lie still, listening to a soft persistent tapping at the baseboard, the little sounds that demand nothing, ordain nothing, explain nothing . . . A mouse worries a curl of wire. The house settles a hair’s breadth, ground giving way far below in a bed of porous limestone. And through the stone, a cavern meanders for a mile or so to Uhrig’s Cave, a dank saloon strung with lights, where the chorus sings, We sail the ocean blue. A stream of cold air, redolent of soil, leads on through a mushroom farm to swimming pools of wet clay, penates of brick, and bones of prehistoric peccaries. The entrances have long been lost in basements, behind furnaces, or sealed with highway rubble. These birdless regions now permit no tra≈c with the surface but for the secret course of water and low tones of a gallon jug. 5 9 R I see my mother’s ghost among the dead, sitting in silence near the blood. Not once has she glanced this way or spoken: does she not recognize her son? Thick drops beat against the glass. The ceiling plaster ticks, a sound as soft as a struck match or shutter click. As my head begins to settle, days flash behind my lids without sound – Lampyridae, the cold and shining ones. ...

A composite sphere assemblage model for porous oolitic rocks: Application to thermal conductivity

The present work is devoted to the determination of linear effective thermal conductivity of porous rocks characterized by an assemblage of grains (oolites) coated by a matrix. Two distinct classes of pores, i.e. micropores or intra oolitic pores (oolite porosity) and mesopores or inter oolitic pores (inter oolite porosity), are taken into account. The overall porosity is supposed to be connected and decomposed into oolite porosity and matrix porosity. Within the framework of Hashin composite sphere assemblage (CSA) models, a two-step homogenization method is developed. At the first homogenization step, pores are assembled into two layers by using self-consistent scheme (SCS). At the second step, the two porous layers constituting the oolites and the matrix are assembled by using generalized self-consistent scheme (GSCS) and referred to as three-phase model. Numerical results are presented for data representative of a porous oolitic limestone. It is shown that the influence of porosity on the overall thermal conductivity of such materials may be significant.

Coating’s influence on water vapour permeability of porous stones typically used in cultural heritage of Mediterranean area: Experimental tests and model controlling procedure

Abstract Water vapour flux into the porous microstructure represents a crucial factor capable of influencing the degradation of porous materials. This fact is of utmost importance especially considering materials installed in cultural heritage. The necessity to preserve stone artworks pushes to perform surface protective coatings that create an intermediate sacrificial layer between stone and the environment. High hydrophobicity and high permeability of water vapour must be one of the most important requirements of a protective film. These features depend upon the nature of coatings as well as the porous microstructures. In order to control coatings’ effects and their influence on final water vapour permeability ( δ ) properties, a new modelling procedure has been proposed. The study is conducted on a porous limestone, namely Pietra Leccese, which is being largely used for historical constructions in Mediterranean. The average experimental water vapour permeability δ exp is 4.83 × 10 −4 and 3.86 × 10 −4 (g/m d Pa) respectively for untreated and treated PL stone, while the average model prediction δ IFU is 4.87 × 10 −4 and 3.77 × 10 −4 (g/m d Pa) respectively for untreated and treated PL stone. The good agreement between experimental and calculated data shows that the proposed modelling procedure could represent a good tool for designing and controlling protection activity on cultural heritage.

Failure mechanisms of repair mortar stone interface assessed by pull-off strength tests

Adhesion strength between porous limestone and 8 repair mortars (4 commercial and 4 laboratory mixture) was tested. The composition of repair mortars was modified by adding aggregates, resulting in 1:3 and 1:5 binder/aggregate ratio. The limestone surface was either pre-treated (wetted) or dry. The pull-off strength was measured by using standard technique. The failure mechanism was also recorded. Three main failure types were identified depending on the location of the disintegration surface. The stone/mortar interface with pre-treatment had higher pull-off strength than the non pre-treated one. All mortars with higher aggregate content (1:5 binder aggregate ratio) showed lower adhesion strength, than the ones with lower aggregate content. The requirements for pull-off adhesion of concrete repair and historic stone repair are different, since for concrete strong bonding is required, while for stone failure at stone/mortar interface or within the repair mortar is a requisite.

Experimental investigation of factors affecting compressional and shear wave velocities in shale and limestone of Ewekoro formation of Southern Nigeria sedimentary basin

Compressional V p and shear V s velocities measurements were taken out on fluid-saturated shale and limestone obtained from the Ewekoro quarry of Southern Nigeria sedimentary basin at constant differential pressure of 50 MPa with porosities ranging from 0.32 to 0.53% and 0.01 to 0.35 for limestone and shale, respectively, while the volume of clay content C ranges from 0 to 60% and 0 to 40% for limestone and shale, respectively. Correlation coefficient for the velocities of both clean samples and those with clay minerals ranged from 0.972 to 1.000 and 0.971 to 1.000, respectively, with limestone having the lesser for both. A very small amount of clay, about 0.21 and 0.23, reduced the elastic modulus of limestone and shale, respectively. For water-saturated shaly samples, V s was more sensitive to porosity and clay content than V p . Consequently, velocity ratios V p /V s also showed a reasonable degree of correlations with clay content and porosity. For both limestone and shale studied, the presence of porosity is the most important parameter in reducing velocities followed by clay content due to the softening of its matrix. This study established that wave velocities are functions of porosity and clay content of porous shale and limestone of Ewekoro formations.

Simulation of dissolution in porous media in three dimensions with lattice Boltzmann, finite-volume, and surface-rescaling methods.

We present a pore-scale dissolution model for the simulation of reactive transport in complex porous media such as those encountered in carbon-storage injection processes. We couple a lattice Boltzmann model for flow calculation with a finite-volume method for solving chemical transport equations, and allow the computational grid to change as mineral surfaces are dissolved according to first-order reaction kinetics. We appraise this scheme for use with high Péclet number flows in three-dimensional geometries and show how the popular first-order convection scheme is affected by severe numerical diffusion when grid Péclet numbers exceed unity, and confirm that this can be overcome relatively easily by using a second-order method in conjunction with a flux-limiter function. We then propose a surface rescaling method which uses parabolic elements to counteract errors in surface area exposed by the Cartesian grid and avoid the use of more complex embedded surface methods when surface reaction kinetics are incorporated. Finally, we compute dissolution in an image of a real porous limestone rock sample injected with HCl for different Péclet numbers and obtain dissolution patterns in concordance with theory and experimental observation. A low injection flow rate was shown to lead to erosion of the pore space concentrated at the face of the rock, whereas a high flow rate leads to wormhole formation.

Shallow-generated damage within non-planar strike-slip fault zones: role of sedimentary rocks in slip accommodation, SW Holy Cross Mountains, Poland

We investigated exhumed damage zones of dextral strike-slip faults dissecting the south-western part of the Mesozoic cover of the Late Palaeozoic Holy Cross Mountains Fold Belt. Structural observations allow to examine the top 1–2 km of the fault zones that deformed asymmetrically with the most intense damage controlled by the non-planar geometry of the faults. The deformational style of fault zones and the roughness of slip surfaces on subsidiary faults within deflections of fault traces in the restraining and releasing bends were facilitated by rock fabric and porosity. High porous sandstones enhanced genesis of cataclastic shear bands within the damage zone and the smooth slip surfaces. Low porous limestones enhanced the formation of dilatant structures infilled with calcite within damage zones and rough slip surfaces. The complex structural pattern of damage zones records multiple episodes of slip and shows evidence of continuous seismic–aseismic modes of fault slip behaviour.

Optimization of nanolime solvent for the consolidation of coarse porous limestone

The potentialities of nanomaterials for applica- tion in the field of conservation have been widely investi- gated in the last two decades. Among nanomaterials, nanolimes, i.e., dispersions of lime nanoparticles in alco- hols are promising consolidating products for calcareous materials. Nanolimes are effective in recovering the very superficial loss of cohesion of decayed materials, but they do not always provide sufficient mass consolidation. This limitation is mainly related to the deposition of the nanoparticles nearby the surface of the material. Experi- mental research has been set up with the aim of improving the in-depth deposition of lime nanoparticles. Previous research by the authors has shown that nanolime deposition within a substrate can be controlled by adapting the nanolimes properties (kinetic stability and evaporation rate) to the moisture transport behavior of the substrate. Nanolime properties can be modified by the use of different solvents. In this research, nanolime dispersions have been further optimized for application on Maastricht limestone, a coarse porous limestone. Firstly, nanolimes were syn- thesized and dispersed in ethanol and/or water, both pure and mixed in different percentages. Subsequently, based on the kinetic stability of the nanolime dispersions, the most promising solvent mixtures were selected and applied on the limestone. The deposition of lime nanoparticles within the limestone was studied by phenolphthalein test, optical microscopy and scanning electron microscopy. The results confirm that nanolime dispersed in a mixture of ethanol (95 %) and water (5 %) can guarantee a better nanoparti- cles in-depth deposition within coarse porous substrates, when compared to dispersions in pure ethanol.

Experimental simulation of dissolution law and porosity evolution of carbonate rock

Experiments of acetic acid (initial 0.2%) with porous dolostone, fractured-porous-vuggy dolostone, porous limestone and fractured limestone were done in a continuous flow diagenesis simulation system to find out the controlling factor of dissolution and dissolution effect. The results show that the dissolution quantity of carbonate rock inversely proportional to temperature and directly proportional to pressure, and the temperature effect is greater than the pressure effect. Therefore, relatively shallow burial and lower temperature environment is more beneficial to the formation of large scale carbonate dissolution pores. Quantitative comparison of porosity volume and permeability variation, and evolution of pores inside the rock before and after the experiment show that pore structure has apparent control over the carbonate dissolution and pore evolution. After dissolution, porous dolomite with homogeneous pore distribution saw rise in pore volume (matrix pore volume) and permeability, and remained as pore type in terms of reservoir space; porous limestone, with significant heterogeneity in original pores and texture, saw significant increase in pore volume and permeability, but the increased pores were fracture type, so its reservoir space turned into fracture-pore type; dissolution increased the permeability of fracture-pore dolomite and fracture limestone remarkably by 2-3 orders of magnitude; and the pores increased were mainly along dissolution fractures, turning the reservoir space into fracture-cave type.

Effects of Fly Ash and Silica Fume on Permeability of Concrete Made With Porous Limestone and Non-Porous Aggregates

The research objective was to assess the permeability of concrete made with porous limestone and non-porous aggregates. Fifty-eight concrete mixes were made and tested to study the effects of fly ash, silica fume, and aggregate type on the permeability of concretes. Class F fly ash and silica fume were used at the levels of 10 to 50 %, and 5 to 20 % as cement replacement on weight basis, respectively. Nine different aggregates, seven in-states and two out-of-states, were collected to study the effects of aggregate type. The test results indicated that silica fume may cause considerable effects on both water and rapid chloride permeability of concrete, while the initial and prolonged moist curing was found essential for the fly ash concrete. In addition, the permeability of aggregate was positively affecting the permeability of concrete. The concretes mixed with aggregates of low permeability showed lower water permeability than those made with porous aggregates. The effect of the permeability of aggregate was also noticeable when the water cementitious material ratio (w/cm) of concrete was high. At lower w/cm ratio, the bond at the cement paste-aggregate interface reduced the effect of the permeability of aggregate.