The evaluation of stone quality by means of non-destructive tests is of vital importance, especially when rock is used as a building material. Usually, however, only vp (P-wave velocity) is ...considered when rock properties such as strength, durability or decay level are assessed. In this paper, we propose a novel ultrasonic estimator based on wave energy: spatial attenuation (α
s). The benefits of this estimator were evaluated by comparison with five other ultrasonic parameters: compressional (v
P) and shear (v
S) wave velocities, velocity ratio (v
P/v
S), waveform energy and temporal attenuation.
The sensitivity of each ultrasonic parameter was compared by measuring 300 samples from ten different types of rock. Each type was selected according to its mineralogy (calcite and/or dolomite rock) and structural complexity (homogeneous, fractured, brecciated, foliated or laminated). Samples were subjected to weathering tests (thermal shock and salt crystallisation tests) in order to study the sensitivity of both ultrasonic parameters during fracture initiation, fracture growth and rock fabric disintegration.
Results show that although vp is the most widely used parameter, the information it yields is extremely imprecise. However, the new parameter α
s is highly sensitive to the petrographic characteristics of rocks as well as to the presence of individual defects (fractures, vugs or disintegrated areas). Moreover, the most significant aspect of α
s is that its values fall between two fixed limits: 0
dB/cm and 20
dB/cm. A rock with a α
s value close to 0
dB/cm is an unweathered, homogeneous and good-quality rock whilst a α
s value higher than 12
dB/cm indicates extreme decay, i.e. open fractures, developed vugs and/or disintegrated areas.
► This work introduces a new ultrasonic parameter that quantifies the wave energy. ► 300 samples with different degree of defects and weathering were tested. ► Sensitivity of s and vp for detecting defects and weathering rocks was analysed. ► The use of vp to evaluate the rock fabric and rock weathering is questioned. ► A new rock classification using s values is proposed.
In this paper, absolute water permeability is estimated from capillary imbibition and pore structure for 15 sedimentary rock types. They present a wide range of petrographic characteristics that ...provide degrees of connectivity, porosities, pore size distributions, water absorption coefficients by capillarity and water permeabilities. A statistical analysis shows strong correlations among the petrophysical parameters of the studied rocks. Several fundamental properties are fitted into different linear and multiple expressions where water permeability is expressed as a generalized function of the properties. Some practical aspects of these correlations are highlighted in order to use capillary imbibition tests to estimate permeability. The permeability–porosity relation is discussed in the context of the influence of pore connectivity and wettability. As a consequence, we propose a generalized model for permeability that includes information about water fluid rate (water absorption coefficient by capillarity), water properties (density and viscosity), wetting (interfacial tension and contact angle) and pore structure (pore radius and porosity). Its application is examined in terms of the type of pores that contribute to water transport and wettability. The results indicate that the threshold pore radius, in which water percolates through rock, achieves the best description of the pore system. The proposed equation is compared against Carman–Kozeny's and Katz–Thompson's equations. The proposed equation achieves very accurate predictions of the water permeability in the range of 0.01 to 1000mD.
•Permeability expressions are obtained using open porosity and capillary coefficients.•The permeability–porosity relationship shows two zones defined by a porosity of 10%.•A generalized model for predicting intrinsic permeability is proposed.•The analysis of wetting reveals incomplete water wetting in the studied rocks.
In this study, the deterioration effects of lichens and other lithobionts in a temperate mesothermal climate were explored. We examined samples of dolostone and limestone rocks with visible signs of ...biodeterioration taken from the exterior wall surfaces of four Romanesque churches in Segovia (Spain):
San Lorenzo,
San Martín,
San Millán and
La Vera Cruz. Biofilms developing on the lithic substrate were analyzed by scanning electron microscopy. The most common lichen species found in the samples were recorded. Fungal cultures were then obtained from these carbonate rocks and characterized by sequencing Internal Transcribed Spacers (ITS). Through scanning electron microscopy in back-scattered electron mode, fungi (lichenized and non-lichenized) were observed as the most frequent microorganisms occurring at sites showing signs of biodeterioration. The colonization process was especially conditioned by the porosity characteristics of the stone used in these buildings. While in dolostones, microorganisms mainly occupied spaces comprising the rock's intercrystalline porosity, in bioclastic dolomitized limestones, fungal colonization seemed to be more associated with moldic porosity. Microbial biofilms make close contact with the substrate, and thus probably cause significant deterioration of the underlying materials. We describe the different processes of stone alteration induced by fungal colonization and discuss the implications of these processes for the design of treatments to prevent biodeterioration.
The influence of both pore structure and strength on the estimation of stone durability is evaluated. Salt crystallisation may limit the durability of porous building stones because it can be ...considered as one of the most powerful weathering agents. Salt crystallisation produces stress over the pore surface. Consequently, stone durability is closely related to both pore structure and strength, which is the material resistance to crystallisation pressure. We propose a novel petrophysical durability estimator (PDE) as the ratio between parameters and estimators, which are based on pore structure and the strength of the material.
In this study, we have used stone parameters and estimators that have an influence on durability and depend only upon pore structure, i.e., connected porosity, water absorption, the water absorption coefficient, specific surface area (SSA), the saturation coefficient, the durability factor, the durability dimensional estimator (DDE) and others derived from porosity, such as microporosity and adjusted microporosity. We also used stone parameters and estimators with an influence on strength: flexural strength, uniaxial compressive strength, Young's dynamic modulus and compressional wave velocity. These parameters and estimators, and the proposed petrophysical estimator are compared with a salt weathering test. Our study shows that there is a very strong correlation between salt weathering and the proposed petrophysical estimator, whereas only moderate correlation exists with the estimators that depend on pore structure and strength. We conclude that the proposed estimator contains the information necessary to understand and estimate the durability of porous materials which have an impact on buildings, civil constructions and historical monuments.
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.
•Halite crystallization and wind erosion are reveled as the main weathering agents.•Salt damage depends on both the number and duration of halite transitions.•The location and orientation of monuments control the intensity of stone weathering.•Superficial resistance and porosity determine the durability of rocks.•The representativeness of artificial ageing tests is assessed by a new parameter.
The influence of rock fabric on physical weathering due to the salt crystallization of selected brecciated dolostones is discussed. These dual-porosity dolostones are representative of heterogeneous ...and anisotropic building rocks, and present highly complex and heterogeneous rock fabric features. The pore structure of the matrix and clasts is described in terms of porosity and pore size distribution, whereas the relative strength for each textural component is assessed using the Knoop hardness test. The whole characterisation process was carried out using the same samples as those used in the standard salt durability test (EN-12370), including connected porosity, the water saturation coefficient, fissure density, compressional wave velocity and waveform energy.
Results show the most important rock fabric elements to be considered are the matrix and clast properties and the nature of fissures. Firstly, a relatively weak matrix was the focus of major granular disintegration as it presents high porosity, low pore radius and reduced strength. Secondly, narrow micro-fissures appear to be important in the decay process due to the effectiveness of crystallization pressure generated by salt growth. On the contrary, macro-fissures do not contribute greatly to rock decay since they act as sinks to consume the high supersaturations caused by growth of large crystals. Additionally, an analysis of stress generated by crystallization was carried out based on the general situation of a lenticular crystal geometry. Finally, the relationships between whole petrophysical properties and durability were established using a principal component analysis. This analysis has clearly established that the durability of rocks affected by salt crystallization mechanisms diminishes in weaker and anisotropic rocks with high porosity and fissure density.
Young’s modulus is one of the most important mechanical parameters in building materials used to assess both the appropriateness of a material as well as its mechanical stability. The paper reports a ...study to predict the elastic modulus for ten carbonate rocks using the ultrasonic technique. The rocks varied from homogeneous limestones to rocks with abundant stylolite, veins and fissures and were subjected to both salt crystallization and thermal weathering tests in order to modify the number and features of their discontinuities. The dynamic and static elastic moduli were measured in both weathered and unweathered samples. The results confirmed the poor relationship between the static and dynamic moduli for the studied rocks. A new equation is proposed which uses both dynamic elastic modulus and spatial attenuation of compressive waves to provide an accurate prediction of static Young’s modulus. As spatial attenuation is highly sensitive to the presence of rock defects, the correlation is very useful for rocks with fractures, voids and/or which have suffered weathering.
Laboratory driven crystallisation of sodium sulphate and sodium chloride from concentrated solution in unsaturated porous stones has been performed. This contributes to a better understanding of the ...mechanisms by which salts crystallise and as a consequence limit the durability of porous materials which has an impact on buildings, civil constructions, and historical monuments. The identification of minerals in porous materials has been performed by scanning electron microscopy (SEM), Environmental Scanning Electron Microscopy (ESEM) and sequential profiles of X-ray diffraction (XRD) under temperature control of sample. The study of porous stones has been combined with experiments in capillary tubes. Data from SEM show that halite tends to precipitate on the surface of the stone with a similar distribution in all samples. However, the mirabilite–thenardite precipitation takes place preferably inside the stone and its depth from the surface and its relative concentration depends on the pore size distribution. In addition, mirabilite (Na
2SO
4·10H
2O) crystallises homogeneously, whereas thenardite (Na
2SO
4) and halite (NaCl) tend to nucleate heterogeneously. To explain the precipitation sequence from concentrated solutions in unsaturated porous materials, a detailed analysis of the thermodynamic equations has been carried out by establishing a simple model. The proposed model shows the influence of the pore structure both on the water activity and saturation degree of involved salts.
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•58.1% of calcite crystals have their c-axis perpendicularly oriented to foliation.•Higher microhardness is measured on surfaces parallel to the foliation.•Lower wettability and ...solubility are observed on surfaces parallel to the foliation.•Anisotropy is related to the CO32− organization in layers perpendicular to c-axis.•ESBD technique is revealed as a useful tool for crystal orientation analysis.
A single calcite crystal shows a pronounced anisotropy that can be transferred to the bulk stone, especially in the case of marbles. The aim of this paper is to analyse the effect of the preferential crystallographic orientation of the anisotropic calcite crystals on the surface properties of foliated marbles. Variations of microhardness, roughness, solubility and contact angle in rock surfaces are studied taking into account their relative position with respect the metamorphic foliation. Results show that more than 50% of the crystals have their c-axis oriented close to the normal of the axial foliation plane. This fact has a direct response on its surface properties: i) the microhardness in surface parallel to metamorphic foliation is a 14% higher than it is in the perpendicular surface; ii) contact angle of the water on the parallel faces is slightly lower than it is on the perpendicular one (42.75° and 53.25°, respectively); and iii) a lower chemical reactivity is estimated on parallel faces, which results in a lesser roughness of weathered surfaces. Results from this paper determine the optimal direction in which an ornamental piece should be cut in order to guarantee its maximum durability.
The Ruidera Lakes Natural Park, in Central Spain, contains a well-exposed Pleistocene to Recent freshwater carbonate (tufa) succession dominated by fluvial barrages and lacustrine deposits. The ...majority of exposed tufas are Holocene to Recent in age. Today, carbonate accumulation is currently manifested as active phytoherm barrage constructions, marginal lacustrine stromatolitic terraces, lacustrine lime muds (all produced mainly by precipitation) and sand-size detrital tufa. The depositional history of the Ruidera Park sites has been interpreted from natural outcrops, rotary drill and percussion auger cores. These reveal a long Quaternary record of microbially dominated barrage framework developments and associated lacustrine carbonates. These alternate with frost weathering deposits and detrital tufa episodes, especially during cooler conditions. U-series dating of several earlier tufa deposits within the park indicates four distinct episodes of tufa development at 190–250 ka B.P., 90–130 ka B.P., 30–40 ka B.P. and 16 ka B.P.–Present. The three oldest episodes appear to be related to cyclic tufa-building events associated with warm periods of Oxygen Isotope Stages (OIS): 7, 5 and 3. Growth under present conditions is slow and several barrages have been damaged by human activity and drought events.
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