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Martinez-Martinez J.,University of Alicante | Martinez-Martinez J.,Laboratorio Of Petrologia Aplicada | Benavente D.,University of Alicante | Benavente D.,Laboratorio Of Petrologia Aplicada | And 2 more authors.
Key Engineering Materials | Year: 2011

Both strength and elastic modulus of rocks are usually determined by compression testing at the mesoscopic scale (UNE-EN 1926; ASTMD 3148-96), and the values obtained are representative of homogeneous rocks. However, heterogeneous and texturally complex rocks show a broad dispersion range and their strength and elastic modulus depend on the presence of different textures and their mechanical properties. The aim of this study was to quantify the mechanical behaviour of these textures individually in order to understand the strength and elasticity of the whole rock. Four varieties of brecciated carbonates (limestones and dolostones) were studied. These rocks have a very complex fabric, presenting a dense network of fractures and clasts between fractures (mm-cm size). The fractures are completely filled with calcite cement, and clasts can have one or two different textures, each presenting differences in crystal size, mineralogy and porosity percentage and type. Samples measuring 4x4x4 mm were obtained in order to test each texture individually. These micro-samples were tested in a uniaxial compression press and the stress-strain curve was recorded. In addition, mean strength and Young's moduli were calculated for each texture. Results show that textures with a larger crystal size, lower porosity and intercrystalline porosity had the lowest strength and were the least elastic. © (2011) Trans Tech Publications, Switzerland.


Martinez-Martinez J.,Laboratorio Of Petrologia Aplicada | Martinez-Martinez J.,University of Alicante | Benavente D.,Laboratorio Of Petrologia Aplicada | Benavente D.,University of Alicante | And 4 more authors.
Construction and Building Materials | Year: 2013

This paper studies the resistance of rocks to freeze-thaw and their petrophysical evolution during weathering. Moreover, the accuracy of existing standards regarding frost durability is discussed. A long-term test was established with these purposes, in which 102 samples of six different dimension stone types were tested (carbonates). Samples were divided into five groups and each group was tested after 0, 12, 24, 48 and 96 freeze-thaw cycles. At the end of the cycles several properties were measured: volume loss, open porosity variation, visual damage, mechanical properties evolution (measuring strength and elastic modulus) and ultrasonic propagation (quantifying both P-wave velocity and spatial attenuation). The micro-textural evolution was also studied using SEM in polished samples. Results display that the rocks with the highest open porosity values (>10%) are the least durable. These rocks show a non-linear decay pattern, with long periods of apparent stability followed by rapid and catastrophic decay. Microscopic observation reveals that during the stable period, isolated microcracks appear from where new ones nucleate and grow as the test progresses. When a critical threshold is exceeded, microcracks turn into cracks and grow rapidly, causing rock breakdown after a low number of cycles. Most of the measured petrophysical parameters do not predict the ultimate breakdown of rocks. However, spatial attenuation of ultrasonic waves reveals as the most sensitive parameter, detecting the critical decay threshold of rocks and their imminent breakdown. Results suggest an important review of standardized durability tests since they do not reflect the reality of frost weathering of rocks: to increase the number of freeze-thaw cycles and to monitoring the weathering process of samples by means ultrasonic measurements. © 2012 Elsevier Ltd. All rights reserved.


Martinez-Martinez J.,Laboratorio Of Petrologia Aplicada | Martinez-Martinez J.,University of Alicante | Benavente D.,Laboratorio Of Petrologia Aplicada | Benavente D.,University of Alicante | And 2 more authors.
Engineering Geology | Year: 2011

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 (s). The benefits of this estimator were evaluated by comparison with five other ultrasonic parameters: compressional (vP) and shear (vS) wave velocities, velocity ratio (vP/vS), 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 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 s is that its values fall between two fixed limits: 0dB/cm and 20dB/cm. A rock with a s value close to 0dB/cm is an unweathered, homogeneous and good-quality rock whilst a s value higher than 12dB/cm indicates extreme decay, i.e. open fractures, developed vugs and/or disintegrated areas. © 2011 Elsevier B.V.


Martinez-Martinez J.,University of Alicante | Martinez-Martinez J.,Laboratorio Of Petrologia Aplicada | Benavente D.,University of Alicante | Benavente D.,Laboratorio Of Petrologia Aplicada | And 2 more authors.
Bulletin of Engineering Geology and the Environment | Year: 2012

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. © 2011 Springer-Verlag.


Fusi N.,University of Milan Bicocca | Martinez-Martinez J.,Laboratorio Of Petrologia Aplicada
Engineering Geology | Year: 2013

The combined use of Hg-impregnation and microCT scanning is a powerful tool for detecting structural and textural features in low porosity massive carbonate rocks. Hg-impregnation of carbonate rocks can improve extremely the quality and resolution of microCT images, because of the high density contrast between Hg and the surrounding rock. The success of the combined used of these two techniques depends mainly on two different rock characters:1) Shape of the pores and characteristics of the porous system. Ink-bottle shape pores and tortuous complex porous systems prevent Hg from flowing out of the sample at the end of Hg-porosimetry test, producing reliable microCT images of the porous system itself. On the other side low tortuous cylindrical pores allow Hg flowing out, resulting in not completely true microCT images.2) Effective rock porosity. Hg-impregnation of carbonate rocks with very low porosity (<. 1%) and tortuous or ink-bottle pores improves significantly the analysis and quantification of their porous system. On the contrary, for carbonate rock with higher porosity (>. 4%), although with ink-bottle pores, microCT images are undetectable, as the relatively high quantity of Hg entrapped in the sample creates artefacts (metal effect) that completely obliterate the rock structure. Intermediate porosity (about 2%) can behave either as low porosity (<. 1%) or as higher porosity (>. 4%) depending on pore shape. A prevalence of tortuous ink-bottle pores results in undetectable microCT images, due to widespread metal effect. A small amount of cylindrical pores, reducing the quantity of entrapped Hg, results in a good quality of microCT images.The resolution of the technique depends on the rock porous system. For low porosity (<. 1%) rock, due to high density contrast between Hg and rock, pores with radius one order of magnitude smaller than the voxel size are clearly imaged by microCT and pores with radius two order of magnitude smaller than the voxel size are still detectable. Hg-impregnated pores smaller than the voxel increase the voxel density, as a function of the relative volume of Hg and rock. As a consequence, pores smaller than the voxel size appear as large as the voxel itself and bigger pores appear larger than they really are (partial volume effect). Although Hg-impregnation improves 3D qualitative analysis of porous system and its relationships with rock texture, quantification of the porous system through segmentation of microCT images is strongly affected by intrinsic error in pore dimensions, caused by partial volume effect. Quantification error is a function of the shape of the porous system, being lower for rounded pores and higher for complex tortuous pore system. © 2013 Elsevier B.V.


Martinez-Martinez J.,University of Alicante | Martinez-Martinez J.,Laboratorio Of Petrologia Aplicada | Fusi N.,University of Milan Bicocca | Galiana-Merino J.J.,University of Alicante | And 3 more authors.
Engineering Geology | Year: 2016

This paper studies the fracturing process in low-porous rocks during uniaxial compressive tests considering the original defects and the new mechanical cracks in the material. For this purpose, five different kinds of rocks have been chosen with carbonate mineralogy and low porosity (lower than 2%). The characterization of the fracture damage is carried out using three different techniques: ultrasounds, mercury porosimetry and X-ray computed tomography. The proposed methodology allows quantifying the evolution of the porous system as well as studying the location of new cracks in the rock samples. Intercrystalline porosity (the smallest pores with pore radius<1μm) shows a limited development during loading, disappearing rapidly from the porosimetry curves and it is directly related to the initial plastic behaviour in the stress-strain patterns. However, the biggest pores (corresponding to the cracks) suffer a continuous enlargement until the unstable propagation of fractures. The measured crack initiation stress varies between 0.25σp and 0.50σp for marbles and between 0.50σp and 0.85σp for micrite limestone. The unstable propagation of cracks is assumed to occur very close to the peak strength. Crack propagation through the sample is completely independent of pre-existing defects (porous bands, stylolites, fractures and veins). The ultrasonic response in the time-domain is less sensitive to the fracture damage than the frequency-domain. P-wave velocity increases during loading test until the beginning of the unstable crack propagation. This increase is higher for marbles (between 15% and 30% from initial vp values) and lower for micrite limestones (between 5% and 10%). When the mechanical cracks propagate unstably, the velocity stops to increase and decreases only when rock damage is very high. Frequency analysis of the ultrasonic signals shows clear changes during the loading process. The spectrum of treated waveforms shows two main frequency peaks centred at low (~20kHz) and high (~35kHz) values. When new fractures appear and grow the amplitude of the high-frequency peak decreases, while that of the low-frequency peak increases. Besides, a slight frequency shift is observed towards higher frequencies. © 2015 Elsevier B.V.


Fernandez-Cortes A.,CSIC - National Museum of Natural Sciences | Sanchez-Moral S.,CSIC - National Museum of Natural Sciences | Canaveras J.C.,University of Alicante | Canaveras J.C.,Laboratorio Of Petrologia Aplicada | And 4 more authors.
Geodinamica Acta | Year: 2010

During an annual cycle the affect of microclimatic changes (of natural and anthropogenic origin) on the geochemical characteristics of seepage water and mineral precipitation rates was analyzed for two karstic caves which contrast in environmental stability and energy exchange with exterior. On the one hand, Castañar cave (Caceres, Spain) is an extremely controlled show cave with limited visitation showing a minimum exchange rate of energy with the external atmosphere and, secondly, Canelobre cave (Alicante, Spain), is a widely visited cave where the anthropogenic impact generates rapid and high-energy environmental changes. Mineral saturation state of seepage water of both caves is controlled by microclimatic variations, such as: 1) natural underground air renewal through the porous system of the upper soil and the network of host-rock fissures, or elso through the cave entrance, 2) cumulative disruptions in the pCO2 levels of cave air due to the presence of visitors, and 3) forced ventilation of the subterranean atmosphere due to the uncontrolled opening of cave entrances. The obtained results reinforce the significance of the microclimatic fluctuations on short time scales in the dynamics of the subterranean karst systems, in terms of rates of mineral precipitation and growth of speleothems, as well as their key role for cave conservation. © 2010 Lavoisier SAS. All rights reserved.


Garcia-Anton E.,CSIC - National Museum of Natural Sciences | Cuezva S.,Laboratorio Of Petrologia Aplicada | Fernandez-Cortes A.,CSIC - National Museum of Natural Sciences | Cuevas-Gonzalez J.,CSIC - National Museum of Natural Sciences | And 4 more authors.
Spectroscopy Letters | Year: 2011

Phosphate stalactites found inside Canelobre cave (Southeast Spain) are here studied by hyperspectral Raman and cathodoluminescence (CL). Together with XRD and EDS analyses, we characterized the complex phosphate paragenesis present in these precipitates. Both resultant CL and Raman analyses point to a complex distribution of phosphate minerals that are difficult to interpret, as they contain a combination of alteration phosphates. As bands of a Raman spectrum relate directly to bond strengths and atomic masses, molecular groups such as the carbonate ion, the hydroxyl ion, and water of crystallization could be further studied in future research, along with better identification of the different phosphate mineral phases. Copyright © Taylor & Francis Group, LLC.


Fernandez-Cortes A.,CSIC - National Museum of Natural Sciences | Cuezva S.,CSIC - National Museum of Natural Sciences | Cuezva S.,Laboratorio Of Petrologia Aplicada | Garcia-Anton E.,CSIC - National Museum of Natural Sciences | And 2 more authors.
Spectroscopy Letters | Year: 2011

Spectra cathodoluminescence (CL) emissions of a stalactite from Castañar cave (west-central Spain) exhibit spatially resolved spectra patterns of Mn2+ and rare earth elements (REE3+). Although the REE3+ signal is smoothed in the speleothem background sample, the REE-enrichment in some growth layer derives from the presence of cerite, xenotime, monazite, and cerianite in the shale matrix. The spectra CL of both host rock and some calcite-aragonite layers show a wide range of spectral luminescence emissions attributed to REE3+, mainly Sm3+, Dy3+, and Ce3+. The high Mn2+-REE3+ anomalies in the inner calcite-aragonite layer could indicate its growth during a phase with stronger weathering of host rock and a more active dynamic hydrology. Copyright © Taylor & Francis Group, LLC.

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