Florian Mittermayr

Concrete under sulphate attack: an isotope study on sulphur sources.

The formation of secondary sulphate minerals such as thaumasite, ettringite and gypsum is a process causing severe damage to concrete constructions. A major key to understand the complex reactions, involving concrete deterioration is to decipher the cause of its appearance, including the sources of the involved elements. In the present study, sulphate attack on the concrete of two Austrian tunnels is investigated. The distribution of stable sulphur isotopes is successfully applied to decipher the source(s) of sulphur in the deteriorating sulphate-bearing minerals. Interestingly, δ34S values of sulphate in local groundwater and in the deteriorating minerals are mostly in the range from+14 to+27 ‰. These δ34S values match the isotope patterns of regional Permian and Triassic marine evaporites. Soot relicts from steam- and diesel-driven trains found in one of the tunnels show δ34S values from−3 to+5 ‰, and are therefore assumed to be of minor importance for sulphate attack on the concretes. In areas of pyrite-containing sedimentary rocks, the δ34S values of sulphate from damaged concrete range between−1 and+11 ‰. The latter range reflects the impact of sulphide oxidation on local groundwater sulphate.

Rapid screening of boron isotope ratios in nuclear shielding materials by LA-ICPMS – a comparison of two different instrumental setups

10B enriched resources are widely used in shielding materials such as boron-alloyed steels in nuclear reactors and storage containers. During production, quality control is an indispensable part of the process. In this study two methods for the rapid screening of 10B enriched special steel samples with a 10B isotopic fraction from 90 to 97% – taken from the production process – were developed and compared. We used both ns-LA-ICPMS and fs-LA-MC-ICPMS and evaluated the different instrumental setups for this application. Even though the micro-inhomogeneous boron distribution in the steel samples was determined by LA-ICPMS and EPMA no effect on the isotope ratios could be observed. Besides matrix- and isotope-ratio-matched standardization with in-house reference materials, a non-matrix- and non-isotope-ratio-matched calibration using NIST 610 glass SRM was applied successfully.

Deterioration of Concrete: Application of Stable Isotopes

Groundwater interaction causing concrete damage and drainage clogging is of great economic interest due to reduced service life and additional costs for remediation and maintenance. Although numerous studies are available, detailed understanding of the reactions leading to concrete deterioration is still lacking. By introducing multiproxy approaches for the water–cement aggregate system, new fundamental insights are gained. This includes trace element and isotope signatures supplementary to the main elemental compositions, mineralogy, and microstructure. Our results are obtained from samples that were taken from Austrian tunnels. Possible sources for CO3 2– in thaumasite or newly formed calcite are atmospheric CO2, aggregates, or carbonate from solutions. Results acquired by stable carbon isotopes (δ13CVPDB) indicate that dissolved inorganic carbon of infiltrating groundwater is the main carbonate source for thaumasite formation, as values are in the range of –7‰. Contrarily, calcite sinters that are formed by CO2 absorption show much more depleted values from –25‰ to –40‰, and carbonates from marine limestone aggregates are close to 0 ± 2‰. The sulfate source for thaumasite, namely, secondary ettringite and gypsum, can be deciphered by the δ34SVCDT values. The δ34SVCDT values of thaumasite, sulfate from interacting groundwater, and local host rock were analyzed. For a case study, the δ34SVCDT values of thaumasite and ground water were close to 20‰. Therefore sulfate in thaumasite is related to infiltrating groundwater and sulfate from oxidation of local sulfides, organic matter, or atmospheric influence can be ruled out. Moreover, interstitial solutions of deteriorated concrete were separated by a hydraulic press. Extracted solutions contain up to 65 g/L total dissolved solids (TDS) and are extremely enriched in Na+ and SO4 2–. Concentrations reach values of up to 17 and 30 g/L, respectively. The analyzed 2H/H and 18O/16O values of the squeezed interstitial solution display a strong enrichment of the heavy isotopes versus the local infiltrating solutions. As this trend is in accordance with respective enrichment of conservative trace elements, elevated TDS can be quantitatively related to the isotope fractionation during evaporation of the interstitial solution.

Advances in concrete materials for sewer systems affected by microbial induced concrete corrosion: A review

Microbial induced concrete corrosion (MICC) is recognized as one of the main degradation mechanisms of subsurface infrastructure worldwide, raising the demand for sustainable construction materials in corrosive environments. This review aims to summarize the key research progress acquired during the last decade regarding the understanding of MICC reaction mechanisms and the development of durable materials from an interdisciplinary perspective. Special focus was laid on aspects governing concrete - micoorganisms interaction since being the central process steering biogenic acid corrosion. The insufficient knowledge regarding the latter is proposed as a central reason for insufficient progress in tailored material development for aggressive wastewater systems. To date no cement-based material exists, suitable to withstand the aggressive conditions related to MICC over its entire service life. Research is in particular needed on the impact of physiochemical material parameters on microbial community structure, growth characteristics and limitations within individual concrete speciation. Herein an interdisciplinary approach is presented by combining results from material sciences, microbiology, mineralogy and hydrochemistry to stimulate the development of novel and sustainable materials and mitigation strategies for MICC. For instance, the application of antibacteriostatic agents is introduced as an effective instrument to limit microbial growth on concrete surfaces in aggressive sewer environments. Additionally, geopolymer concretes are introduced as highly resistent in acid environments, thus representing a possible green alternative to conventional cement-based construction materials.

Temporal and spatial variability of chemical and isotopic composition of soil solutions from cambisols - field study and experiments

The chemical and isotopic composition of soil solutions is highly relevant for environmental and forensic tasks. We investigated interstitial solutions from soil horizons of three cambisols in Styria (Austria). The soils consisted mainly of quartz, feldspar and clay minerals with a vertical variability. Two soil solution fractions from meso-, macro- and micropores (m) and micropores only (μ) were extracted at two subsequent hydraulic pressure steps corresponding to matrix potentials of up to pF 5.43 and from 5.43 to 5.73, respectively. While solute concentrations indicated diverse distribution in soil solution fractions m and μ, heavy stable hydrogen and oxygen isotopes of H2O (-92.5‰<δ2H<-34.4‰; -11.9‰<δ18O<-4.0‰, VSMOW) are clearly enriched in the μ versus m fractions. Principal component analysis on the hydrochemical data set indicates that the intensity of the overall silicate weathering is higher in autumn versus spring, whereas the anthropogenic impact on weathering behaves inversely. The anthropogenic impact is related to seasonal variability of nitrification of N-fertilizers. In consequence of evaluated signals for overall silicate weathering about three-fourths of the soil solutions sampled in autumn indicated elevated total dissolved solid concentration vs. those in spring accompanied with washing out solutes from the soil cover following precipitation events in autumn before sampling. Isotopic shift of soil solutions from the local meteoric water line in spring obviously followed an evaporation trend because of less precipitation and high evaporation before sampling. Experimentally simulated evaporation of soil samples confirmed the observed isotopic evaporation trend. Wetting experiments indicated the infiltration of water within minutes into the micropores of the soils. Exchange of water molecules between micro-, meso- and macropores is an almost instantaneous process and soil solutions in micropores are not as isolated from the soil water system as it was formerly suggested, e.g. for plant uptake. Highly dynamic and complex mechanisms in the gas-water-solid system of soils have to be considered for the application of elemental and isotope proxies related to environmental, forensic and agricultural tasks.

Scale-fragment formation impairing geothermal energy production: interacting H2S corrosion and CaCO3 crystal growth

BackgroundMineral precipitates (scaling) from deep saline thermal waters often constitute a major problem during geothermal energy production. The occurrence of scale-fragments accumulating and clogging pipes, filters, and heat exchangers is of particular concern regarding an efficient energy extraction.MethodsCarbonate scale-fragments from different sections of two geothermal power plants were collected and studied in a high-resolution scaling forensic approach comprising of microstructural characterization, elemental mapping, and stable carbon and oxygen isotope transects. The solid-phase analyses were evaluated in the context of natural environmental and technical (man-made) production conditions.Results and discussionOur results indicate an interaction of metal sulfide mineral layers mainly from H2S corrosion of the steel pipes and CaCO3 nucleation and crystal growth. A conceptual model of scale-fragment development addresses the relevance of two key interfaces: 1) the corrosion layer between the steel substrate and calcite scale and 2) the scale surface versus thermal fluid flow. The corrosion products constitute an attractive crystallization substrate of brittle and mechanically weak consistency. A rough carbonate scale surface tends to induce (micro) turbulences and increased flow resistance (frictional forces). These factors promote partial exfoliation, scale-fragment mobilization, and rapid clogging. This investigation highlights the potential of detailed petrographic and geochemical analyses of mineral precipitates for evaluating favorable versus unfavorable processes in geotechnical environmental settings.