Mineralogy, technical properties, deterioration and conservation strategies

The present thesis deals with the deterioration and durability of volcanic tuff rocks used as building stones in historical architecture and presents a combined approach on identifying the main parameters responsible for the severe damages that can be observed. A comprehensive study on a dataset of over 500 tuffs from the literature regarding the technical parameters of tuff, in combination with an in-depth study of their petrographical properties, allows for the correlation of individual parameters and to identify key parameters, that influence the weathering behavior of tuff stones. A better evaluation of the weathering behavior of tuff stones can consequently allow for a more precise estimation of their durability. The results demonstrate that pore radii distributions are a good estimator for durability, since micropores (< 0.1 µm) have a particularly strong influence on the weathering behavior of tuffs. Therefore, the important influence of the micropores on salt weathering in tuff rocks is stressed. In addition, the effective porosity and bulk density are identified as reliable estimators to predict the strength (UCS, TS) and durability of tuff rocks (UCS reduction). The hydric expansion of tuff rocks can exceed values multiple times higher than other rock types and is considered to be an important factor for the deterioration of tuffs. It is typically associated with the presence of swellable clay minerals and two types of swelling mechanisms are generally discussed: stepwise intracrystalline swelling and continuous osmotic swelling. A mechanism that can cause expansion in the absence of swellable clay minerals, which is characterized by interaction of surface forces, is the disjoining pressure. The identification of the primary mode of swelling is important for understanding and finally preventing the swelling damage in tuff stones. The swelling experiments show, that intracrystalline swelling is the predominant mechanism for clay swelling in the investigated tuffs. The osmotic swelling on the other hand has only a minor influence on the clay swelling. Therefore, with a clay mineral analyses at hand, the swelling experiments proved to be a useful tool to differentiate between both clay swelling mechanisms in tuff rocks. Also, the importance of the location of the clay minerals in the tuff rock needs to be stressed. We could confirm that even small amounts of swellable clay minerals can cause significant expansion of the material if they are located in critical spots in the rock fabric. The role of the disjoining pressure is still unclear. New analytical techniques have to be developed to quantify its role in moisture expansion of tuff rocks. In addition, the effects of two consolidation agents, tetraethoxysilane (TEOS) and tetramethoxysilane (TMOS), on a larger set of tuffs was evaluated by comparative analyses of petrophysical properties and weathering behavior before and after the treatments. The goal of this approach was to identify a general suitability of the consolidation treatments for different types of tuff. The application of tetramethoxysilane (TMOS) was also conducted with the aim of identifying if this consolidant can be absorbed more efficiently by tuffs with a high share of micropores, due to its smaller molecule size compared to TEOS. The investigation provided a variety of data that indicate, that TMOS may be a suitable candidate to overcome the bottlenecks in the pore space of tuffs, which limit the consolidation success of current products.2021-11-2

Biphasic NMR of Hyperpolarized Suspensions─Real-Time Monitoring of Solute-to-Solid Conversion to Watch Materials Grow

Nuclear magnetic resonance (NMR) spectroscopy is a key method for the determination of molecular structures. Due to its intrinsically high (i.e., atomistic) resolution and versatility, it has found numerous applications for investigating gases, liquids, and solids. However, liquid-state NMR has found little application for suspensions of solid particles as the resonances of such systems are excessively broadened, typically beyond the detection threshold. Herein, we propose a route to overcoming this critical limitation by enhancing the signals of particle suspensions by >3.000-fold using dissolution dynamic nuclear polarization (d-DNP) coupled with rapid solid precipitation. For the proof-of-concept series of experiments, we employed calcium phosphate (CaP) as a model system. By d-DNP, we boosted the signals of phosphate $^{31}$P spins before rapid CaP precipitation inside the NMR spectrometer, leading to the inclusion of the hyperpolarized phosphate into CaP-nucleated solid particles within milliseconds. With our approach, within only 1 s of acquisition time, we obtained spectra of biphasic systems, i.e., micrometer-sized dilute solid CaP particles coexisting with their solution-state precursors. Thus, this work is a step toward real-time characterization of the solid–solution equilibrium. Finally, integrating the hyperpolarized data with molecular dynamics simulations and electron microscopy enabled us to shed light on the CaP formation mechanism in atomistic detail

A numerical stability analysis for the Einstein-Vlasov system

We investigate stability issues for steady states of the spherically symmetric Einstein-Vlasov system numerically in Schwarzschild, maximal areal, and Eddington-Finkelstein coordinates. Across all coordinate systems we confirm the conjecture that the first binding energy maximum along a one-parameter family of steady states signals the onset of instability. Beyond this maximum perturbed solutions either collapse to a black hole, form heteroclinic orbits, or eventually fully disperse. Contrary to earlier research, we find that a negative binding energy does not necessarily correspond to fully dispersing solutions. We also comment on the so-called turning point principle from the viewpoint of our numerical results. The physical reliability of the latter is strengthened by obtaining consistent results in the three different coordinate systems and by the systematic use of dynamically accessible perturbations.Comment: 35 pages, 12 figure

Consolidation of volcanic tuffs with TEOS and TMOS: a systematic study

In this study, nine volcanic tuffs from Armenia, Germany and Mexico were treated with two commercially available consolidants on base of silicic acid ester, as well as different pretreatments with an anti-swelling agent and/or primer components. Prior to the treatment, the tuffs were analyzed regarding their petrography and mineralogy, with a greater focus on their clay mineral content. The effect of the consolidation was evaluated by comparative analyses of petrophysical properties and weathering behavior before and after the treatments. The main goals of this study were to identify a general suitability of different consolidating treatments for different types of tuff, evaluating tartaric acid as a primer component for tuff consolidation and to pursue the approach of finding a molecular answer for apparent tuff consolidation problematics, by testing a consolidation agent with smaller molecule sizes than current products on the market: tetramethoxysilane (TMOS).Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659Volkswagen Foundation http://dx.doi.org/10.13039/501100001663Deutsche Bundesstiftung Umwelt http://dx.doi.org/10.13039/100007636Deutscher Akademischer Austauschdienst http://dx.doi.org/10.13039/501100001655Georg-August-Universität Göttingen (1018

Key parameters of volcanic tuffs used as building stone: a statistical approach

Volcanic tuffs naturally show a strong heterogeneity in their petrography and petrophysical properties. The arrangement of the components in tuffs can create a very wide spectrum of porosities and fabrics, which in turn can lead to a highly differential weathering behavior. Considerable amounts of clay minerals and zeolites are common and can contribute to a high sensitivity to expansional processes and salt crystallization. Understanding the influence of the rock properties on material behavior and durability can help to make predictions on future material behavior and evaluate the suitability of the material for construction purposes. This study presents the petrographic and petrophysical data of 15 selected tuffs and 513 tuffs from the literature used as building stones. Regression analysis show if parameters are comparable and if key parameters can be identified. Key parameters can potentially be used for the estimation of the material behavior, without the use of expensive analytics or weathering simulations.deutsche forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659volkswagen foundation http://dx.doi.org/10.13039/501100001663deutsche bundesstiftung umwelt http://dx.doi.org/10.13039/100007636deutscher akademischer austauschdienst http://dx.doi.org/10.13039/501100001655georg-august school of science (gauss)Georg-August-Universität Göttingen (1018

Consolidation of volcanic tuffs with TEOS and TMOS: a systematic study

In this study, nine volcanic tuffs from Armenia, Germany and Mexico were treated with two commercially available consolidants on base of silicic acid ester, as well as different pretreatments with an anti-swelling agent and/or primer components. Prior to the treatment, the tuffs were analyzed regarding their petrography and mineralogy, with a greater focus on their clay mineral content. The effect of the consolidation was evaluated by comparative analyses of petrophysical properties and weathering behavior before and after the treatments. The main goals of this study were to identify a general suitability of different consolidating treatments for different types of tuff, evaluating tartaric acid as a primer component for tuff consolidation and to pursue the approach of finding a molecular answer for apparent tuff consolidation problematics, by testing a consolidation agent with smaller molecule sizes than current products on the market: tetramethoxysilane (TMOS)

Key parameters of volcanic tuffs used as building stone: a statistical approach

Volcanic tuffs naturally show a strong heterogeneity in their petrography and petrophysical properties. The arrangement of the components in tuffs can create a very wide spectrum of porosities and fabrics, which in turn can lead to a highly differential weathering behavior. Considerable amounts of clay minerals and zeolites are common and can contribute to a high sensitivity to expansional processes and salt crystallization. Understanding the influence of the rock properties on material behavior and durability can help to make predictions on future material behavior and evaluate the suitability of the material for construction purposes. This study presents the petrographic and petrophysical data of 15 selected tuffs and 513 tuffs from the literature used as building stones. Regression analysis show if parameters are comparable and if key parameters can be identified. Key parameters can potentially be used for the estimation of the material behavior, without the use of expensive analytics or weathering simulations

NMR ‐identification of the interaction between BRCA1 and the intrinsically disordered monomer of the Myc‐associated factor X

International audienceAbstract The breast cancer susceptibility 1 (BRCA1) protein plays a pivotal role in modulating the transcriptional activity of the vital intrinsically disordered transcription factor MYC. In this regard, mutations of BRCA1 and interruption of its regulatory activity are related to hereditary breast and ovarian cancer (HBOC). Interestingly, so far, MYC's main dimerization partner MAX (MYC‐associated factor X) has not been found to bind BRCA1 despite a high sequence similarity between both oncoproteins. Herein, we show that a potential reason for this discrepancy is the heterogeneous conformational space of MAX, which encloses a well‐documented folded coiled‐coil homodimer as well as a less common intrinsically disordered monomer state—contrary to MYC, which exists mostly as intrinsically disordered protein in the absence of any binding partner. We show that when the intrinsically disordered state of MAX is artificially overpopulated, the binding of MAX to BRCA1 can readily be observed. We characterize this interaction by nuclear magnetic resonance (NMR) spectroscopy chemical shift and relaxation measurements, complemented with ITC and SAXS data. Our results suggest that BRCA1 directly binds the MAX monomer to form a disordered complex. Though probed herein under biomimetic in‐vitro conditions, this finding can potentially stimulate new perspectives on the regulatory network around BRCA1 and its involvement in MYC:MAX regulation