Suchergebnisse

Experimental tests in the cabinet carried out at the University of Oxford were financially supported by the European Commission under the Marie Curie program (FP7-PEOPLE-2012-IEF call, research project "NaturaLime"). This research has been supported by the Spanish Government (MICINN) (PID2020-116896RB-C21 and PID2020-116896RB-C22). ; This research focuses on the analysis of the influence of two secondary salt weathering processes on the durability of rocks exposed to marine environments: chemical dissolution of rock forming minerals and differential thermal expansion between halite and the hosting rock. These processes are scarcely treated in research compared to salt crystallisation. The methodology followed in this paper includes both in situ rock weathering monitoring and laboratory simulations. Four different calcite-bearing rocks (a marble, a microcrystalline limestone and two different calcarenites) were exposed during a year to a marine semiarid environment. Exposed samples show grain detachment, crystal edge corrosion, halite efflorescences and microfissuring. Crystal edge corrosion was also observed after the laboratory simulation during a brine immersion test. Calcite chemical dissolution causes a negligible porosity increase in all the studied rocks, but a significant modification of their pore size distribution. Laboratory simulations also demonstrate the deterioration of saltsaturated rocks during thermal cycles in climatic cabinet. Sharp differences between the linear thermal expansion of both a pure halite crystal and the different studied rocks justify the registered weight loss during the thermal cycles. The feedback between the chemical dissolution and differential thermal expansion, and the salt crystallisation of halite, contribute actively to the rock decay in marine environments. ; European Commission European Commission Joint Research Centre ; Spanish Government PID2020-116896RB-C21 PID2020-116896RB-C22

This research focuses on the analysis of the influence of two secondary salt weathering processes on the durability of rocks exposed to marine environments: chemical dissolution of rock forming minerals and differential thermal expansion between halite and the hosting rock. These processes are scarcely treated in research compared to salt crystallisation. The methodology followed in this paper includes both in situ rock weathering monitoring and laboratory simulations. Four different calcite-bearing rocks (a marble, a microcrystalline limestone and two different calcarenites) were exposed during a year to a marine semiarid environment. Exposed samples show grain detachment, crystal edge corrosion, halite efflorescences and microfissuring. Crystal edge corrosion was also observed after the laboratory simulation during a brine immersion test. Calcite chemical dissolution causes a negligible porosity increase in all the studied rocks, but a significant modification of their pore size distribution. Laboratory simulations also demonstrate the deterioration of salt-saturated rocks during thermal cycles in climatic cabinet. Sharp differences between the linear thermal expansion of both a pure halite crystal and the different studied rocks justify the registered weight loss during the thermal cycles. The feedback between the chemical dissolution and differential thermal expansion, and the salt crystallisation of halite, contribute actively to the rock decay in marine environments. ; Experimental tests in the cabinet carried out at the University of Oxford were financially supported by the European Commission under the Marie Curie program (FP7-PEOPLE-2012-IEF call, research project "NaturaLime"). This research has been supported by the Spanish Government (MICINN) (PID2020-116896RB-C21 and PID2020-116896RB-C22).

In this paper, we propose a new methodology for the automatic picking of P- and S- wave arrivals. The measurement of elastic wave velocities is crucial for characterisation of the elastic properties of rocks, as well as their physico-mechanical properties and durability. P-waves are easy to generate and acquire, whereas the acquisition and subsequent analysis of the S-waves present major difficulties in most investigations of rocks. In our proposed method the recorded signal is first pre-processed in the wavelet domain, removing low-frequency disturbances and filtering noise. The signal is then analysed in the time-domain to detect and characterise the first pulse and, subsequently, estimate the corresponding onset time. The automatic approach analyses all pulses detected in the output signal and selects the first pulse of the P or S wave relative to symmetry, amplitude and duration criteria. This triple check provides greater confidence in the obtained results. We record P- and S- waveforms through the transmission method for a broad range of sedimentary, igneous and metamorphic rocks used in buildings. Results are compared to manual picking, which is considered as a true or reference value. The recorded signals show that microstructural components of rocks have a strong influence on the output signal. Mineralogical composition, porosity and particle size affect the wave velocity, attenuation, wavelength and waveform, which in turn influences the manual picking of the onset time. The proposed methodology provides precise values of the onset time of P- and S- waves. The discrepancies between automatic and manual P- and S- wave picking are 0.7 and 4.4%, respectively. P-wave signals have a high signal-to-noise ratio and their arrival times are clear and easy to determine. However, the arrival time of S-waves presents significant problems, mainly for medium to coarse-grained rocks. In this case, the output signal is contaminated by P-waves and has a lower signal-to-noise ratio. Besides, propagation of the S-wave through the rock affects the frequency and waveform of the first pulse, which complicates manual picking of the onset time. The developed methodology distinguishes between the S-wave and the remaining P-waves contained in the transversal signal, independently of the skill and subjectivity of a human analyst. ; This work was supported by the Spanish Government [grant number RTI2018-099052-B-I00], Regional Government of Comunidad Valenciana (Spain) [grant number AICO/2016/098] and Madrid (Spain) [Top Heritage, grant number S2018/NMT-4372] and the University of Alicante [grant number GRE17-12]. Predoctoral fellowships were awarded to D. Crespo-Jimenez by the MEFP [FPU2017/04377 and BDNS 311327].

This paper combines ultrasonic parameters recorded from P- and S- waves and effective porosity to estimate uniaxial compressive strength, σC, and intrinsic permeability, k - two of the most crucial physical parameters used in stone conservation studies. The ultrasonic parameters have been chosen because they are sensitive to the microstructural properties of stones which influence both σC and k differently. Velocities of compressional or primary, Vp, and shear or secondary, Vs, elastic waves are related to porosity and the mineralogical composition; the waveform attenuation is related to the presence of vuggy macropores and pore and particle size; and the wavelength is related to the pore and particle size. Fifteen types of stones used in the Spanish built heritage were measured including calcarenites, sandstones, dolostones and travertines. Several simple and multiple predictive expressions for σC and k are fitted, which are quantified through the Pearson correlation coefficient, R. Curve fitting improves as the number of petrophysical parameters taken into account in the multiple linear regressions increases. The obtained Pearson's correlations values for σC are slightly higher than for k. The best correlation for σC (R = 0.921) and k (R = 0.903) is found when the predictive equation incorporates all of the elastic wave parameters obtained non-destructively, and the connected porosity. In general, effective porosity is statistically the most significant variable of the fitted regressions. The σC and k estimation from all the ultrasonic parameters, without considering connected porosity, shows a good correlation (R = 0.852 and 0.864, respectively). The addition of Vs to multiple regressions does not significantly improve the goodness of the fit. Consequently, the measurement of Vs is unnecessary as it is difficult and time-consuming. Finally, results also show that vuggy porosity (present in travertines) influences waveform attenuation and σC and k differently, relative to other microstructural properties; limiting the techniques use for stones with this type of porosity. Estimating σC and k using ultrasonic parameters exclusively is advantageous as the estimations can be obtained non-destructively using portable equipment, while also providing an acceptable goodness of fit. ; This work was supported by the Spanish Ministry of Science and Innovation (MCIN) [grant numbers RTI2018-099052-B-I00, PID2020-116896RB-C21 and PID2020-116896RB-C22] and Regional Government of Madrid (Spain) [Top Heritage, grant number S2018/NMT-4372]; a pre-doctoral research fellowship (FPU20/05157) awarded to N. Garcia-Martinez by the MCIN; and Ph.D. scholarship awarded to M. de Jongh by Historic Environment Scotland (Charity Number: SC045925).

The soils above caves represent a membrane that regulates the connection between the underground environment and the outside atmosphere. In this study, soils from two different field sites (Cueva de Altamira and Cueva del Rull in Spain) are investigated. Field results are analysed and linked to laboratory tests. Several laboratory experiments are performed to quantify CO2 diffusion coefficients and water infiltration rates in these soils under different degrees of soil water saturation and compaction. Tests confirm that the grain size distribution, organic matter content, mineral composition and water content of soils affect gas transport through the soil pore network. Both field and lab results reveal that Altamira soil has a coarser texture and therefore has higher CO2 diffusion coefficients, infiltration rates and hydraulic conductivity values than Rull soil. Rull soil contains a higher proportion of fine particles and organic matter, which explains the lower fluid transport coefficients. When soils are near saturation, fluid transport does not depend on the physical properties of soil but depends on the soil water content. In this state, liquid transport regulates the available space within the soil pores, which leads to a reduction in the gaseous diffusion coefficient of the soil. After rainfall episodes, the connection between the exterior atmosphere and underground cavities is hindered due to a rise in the soil water content, which is responsible for the closure of the overlying membrane. This study demonstrates that soil-produced CO2 reaches the underground atmosphere through diffusion processes that are controlled by the intrinsic properties of soil (porosity, grain size distribution, texture, mineralogy and organic matter content) and soil water content. ; This research was funded by the Spanish Ministry of Economy and Competitiveness projects CGL2011-25162 and CGL2013-43324-R and its programme Torres Quevedo (PTQ 13-06296). A pre-doctoral research fellowship (BES-2012-053468) was awarded to C. Pla for the project CGL2011-25162. Funding was also provided by the People Programme (Marie Curie Actions–Intra-European Fellowships, call 2013) of the European Union's Seventh Framework Programme (FP7/2007–2013) under the REA grant agreement n° 624204.