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Jan Olek - One of the best experts on this subject based on the ideXlab platform.

  • chemical sequence and kinetics of alkali Silica reaction part i experiments
    Journal of the American Ceramic Society, 2014
    Co-Authors: Jan Olek
    Abstract:

    The deterioration induced by alkali-Silica reaction (ASR) is initiated by complicated heterogeneous chemical reactions. This study describes the experimental results obtained from the model reactant experiments focused on the kinetics of physical and chemical changes in the reactive aggregate-simulated pore solution system undergoing ASR. Specifically, the study investigated the products formed by exposing reactive Silica Mineral (α-cristobalite) to two alkali solutions in the presence of solid calcium hydroxide [Ca(OH)2]. The experimental results showed that, as long as the Ca(OH)2 remains in the system, the dissolution of the Silica Mineral proceeds at a constant rate and the only reaction product formed is the tobermorite-type C–S–H. However, once the supply of Ca(OH)2 in the system is exhausted, the level of dissolved Silica ions starts to increase. At the same time, the previously formed C–S–H changes in composition by incorporating silicon and alkali ions from the solution. Continuous increase in the concentration of Silica leads to formation of the ASR gel as a result of interaction between Silica and alkali ions.

  • Chemical Sequence and Kinetics of Alkali‐Silica Reaction Part I. Experiments
    Journal of the American Ceramic Society, 2014
    Co-Authors: Taehwan Kim, Jan Olek
    Abstract:

    The deterioration induced by alkali-Silica reaction (ASR) is initiated by complicated heterogeneous chemical reactions. This study describes the experimental results obtained from the model reactant experiments focused on the kinetics of physical and chemical changes in the reactive aggregate-simulated pore solution system undergoing ASR. Specifically, the study investigated the products formed by exposing reactive Silica Mineral (α-cristobalite) to two alkali solutions in the presence of solid calcium hydroxide [Ca(OH)2]. The experimental results showed that, as long as the Ca(OH)2 remains in the system, the dissolution of the Silica Mineral proceeds at a constant rate and the only reaction product formed is the tobermorite-type C–S–H. However, once the supply of Ca(OH)2 in the system is exhausted, the level of dissolved Silica ions starts to increase. At the same time, the previously formed C–S–H changes in composition by incorporating silicon and alkali ions from the solution. Continuous increase in the concentration of Silica leads to formation of the ASR gel as a result of interaction between Silica and alkali ions.

  • Chemical Sequence and Kinetics of Alkali–Silica Reaction Part II. A Thermodynamic Model
    Journal of the American Ceramic Society, 2014
    Co-Authors: Taehwan Kim, Jan Olek
    Abstract:

    This manuscript describes development of a thermodynamic model for the chemical sequence of the alkali–Silica reaction (ASR) process in the model, closed reactive system consisting of mixture of reactive Silica Mineral, calcium hydroxide, and alkali hydroxide solution. The focus of the first part of the study is on formulating the kinetic rate law for Silica dissolution as a function of several factors, including pH, temperature, concentration of alkalis in solution, and type of the reactive Silica Mineral. This kinetic rate law was then incorporated into the commercial modeling software (Geochemist's Workbench®) in an attempt to simulate the chemical sequence of the ASR process. Once the proper input data and parameters were selected, the model generated reasonably accurate predictions of the distribution of species in the reacting system and captured distinct features of experimental data. In addition, this model suggested that the thermodynamic equilibrium condition among reactant (reactive Silica Mineral), products, and ionic species in the solution resulted in the threshold value of alkali concentration needed for the ASR to take place. Though the application of the proposed model is currently limited to the closed ASR system, the model may offer the possibility of the establishment of the unified theory which can bridge the gap between fundamental (chemical) mechanisms of ASR and the mechanical responses of concrete by providing the kinetic basis for the evolution of ASR process.

Sergey E Pashenko - One of the best experts on this subject based on the ideXlab platform.

Yuri Amelin - One of the best experts on this subject based on the ideXlab platform.

  • Origin, timing, and temperature of secondary calcite-Silica Mineral formation at Yucca Mountain, Nevada
    Geochimica et Cosmochimica Acta, 2003
    Co-Authors: Nicholas S.f Wilson, Jean S. Cline, Yuri Amelin
    Abstract:

    The origin of secondary calcite-Silica Minerals in primary and secondary porosity of the host Miocene tuffs at Yucca Mountain has been hotly debated during the last decade. Proponents of a high-level nuclear waste repository beneath Yucca Mountain have interpreted the secondary Minerals to have formed from cool, descending meteoric fluids in the vadose zone; critics, citing the presence of two-phase fluid inclusions, argued that the Minerals could only have formed in the phreatic zone from ascending hydrothermal fluids. Understanding the origin, temperature, and timing of these Minerals is critical in characterizing geologically recent fluid flux at the site, and has significant implications to whether waste should be stored at Yucca Mountain. Petrographic and paragenetic studies of 155 samples collected from the Exploratory Studies Facility (ESF) and repository block cross drift (ECRB) tunnels indicate that heterogeneously distributed calcite with lesser chalcedony, quartz, opal, and fluorite comprise the oldest secondary Minerals. These are typically overgrown by intermediate-aged calcite, often exhibiting distinctive bladed habits. The youngest event recorded across the site is the deposition of Mg-enriched (up to 1 wt%) and depleted, growth-zoned calcite intergrown with U-enriched opal. The cyclical variation in Mg enrichment and depletion is probably related to climate changes that have occurred during the last few million years. The distribution of secondary Minerals is consistent with precipitation in the vadose zone. Fluid inclusion petrography of sections from the 155 samples determined that 96% of the fluid inclusion assemblages (FIAs) contained liquid-only inclusions that formed at ambient temperatures (35°C). However, 50% of the samples (n 78) contained relatively rare FIA that contain both liquid-only and liquid plus vapor inclusions (herein termed two-phase FIAs) that formed at temperatures above 35°C. Virtually all of these two-phase FIAs occur in paragenetically old calcite; rare two-phase inclusion assemblages were also observed in early fluorite and quartz, and early-intermediate calcite. Homogenization temperatures ( trapping temperatures) across Yucca Mountain are generally 45 to 60°C, but higher temperatures reaching 83°C were recorded in calcite from the north portal and ramp of the ESF. Cooler temperatures of 35 to 45°C were recorded in the intensely fractured zone. Multiple populations of two-phase FIAs from lithophysal cavities in the ESF and ECRB cross drift indicate early fluid cooling with time from temperatures 45°C in early calcite, to 35 to 45°C in paragenetically younger calcite. Freezing point depressions range from 0.2 to 1.6°C, indicating trapping of a low salinity fluid. The majority of intermediate calcite and all outermost Mg-enriched calcite contains rare all-liquid inclusions and formed from ambient temperature (35°C) fluids. Carbon and oxygen isotope data reveal a consistent trend of decreasing 13 C (from 9.5 to 8.5‰) and increasing 18 O (from 5.2 to 22.1‰) values from paragenetically early calcite to Mg-enriched growth-zoned calcite. Depleted D values (131 to 90‰) of inclusion fluids from intermediate and the youngest Mg-enriched calcite indicate derivation from surface meteoric fluids. Recalculation of 18 OH2O values of 12 to 10‰ is consistent with derivation from paleometeoric fluids. Results of integrated U-Pb dating (opal and chalcedony) and fluid inclusion microthermometry indicate that two-phase FIAs that trapped fluids of 50°C are older than 6.29 0.30 Ma. Two-phase FIAs in parage- netically later calcite, which formed from fluids of 35 to 45°C, are older than 5.32 0.02 Ma. There is no evidence for trapping of fluids with elevated temperatures during the past 5.32 my. The youngest Mg-enriched calcite intergrown with opal began to precipitate between about 1.9 to 2.9 Ma and has continued to precipitate within the past half million years. The presence of liquid-only inclusions and the consistent occurrence of Mg-enriched calcite and opal as the youngest event indicate a minor, but chemically distinct, ambient temperature (35°C) fluid flux during the past 2 to 3 my. Copyright © 2003 Elsevier Science Ltd

Yuri Dublyansky - One of the best experts on this subject based on the ideXlab platform.

Nicholas S.f Wilson - One of the best experts on this subject based on the ideXlab platform.

  • Origin, timing, and temperature of secondary calcite-Silica Mineral formation at Yucca Mountain, Nevada
    Geochimica et Cosmochimica Acta, 2003
    Co-Authors: Nicholas S.f Wilson, Jean S. Cline, Yuri Amelin
    Abstract:

    The origin of secondary calcite-Silica Minerals in primary and secondary porosity of the host Miocene tuffs at Yucca Mountain has been hotly debated during the last decade. Proponents of a high-level nuclear waste repository beneath Yucca Mountain have interpreted the secondary Minerals to have formed from cool, descending meteoric fluids in the vadose zone; critics, citing the presence of two-phase fluid inclusions, argued that the Minerals could only have formed in the phreatic zone from ascending hydrothermal fluids. Understanding the origin, temperature, and timing of these Minerals is critical in characterizing geologically recent fluid flux at the site, and has significant implications to whether waste should be stored at Yucca Mountain. Petrographic and paragenetic studies of 155 samples collected from the Exploratory Studies Facility (ESF) and repository block cross drift (ECRB) tunnels indicate that heterogeneously distributed calcite with lesser chalcedony, quartz, opal, and fluorite comprise the oldest secondary Minerals. These are typically overgrown by intermediate-aged calcite, often exhibiting distinctive bladed habits. The youngest event recorded across the site is the deposition of Mg-enriched (up to 1 wt%) and depleted, growth-zoned calcite intergrown with U-enriched opal. The cyclical variation in Mg enrichment and depletion is probably related to climate changes that have occurred during the last few million years. The distribution of secondary Minerals is consistent with precipitation in the vadose zone. Fluid inclusion petrography of sections from the 155 samples determined that 96% of the fluid inclusion assemblages (FIAs) contained liquid-only inclusions that formed at ambient temperatures (35°C). However, 50% of the samples (n 78) contained relatively rare FIA that contain both liquid-only and liquid plus vapor inclusions (herein termed two-phase FIAs) that formed at temperatures above 35°C. Virtually all of these two-phase FIAs occur in paragenetically old calcite; rare two-phase inclusion assemblages were also observed in early fluorite and quartz, and early-intermediate calcite. Homogenization temperatures ( trapping temperatures) across Yucca Mountain are generally 45 to 60°C, but higher temperatures reaching 83°C were recorded in calcite from the north portal and ramp of the ESF. Cooler temperatures of 35 to 45°C were recorded in the intensely fractured zone. Multiple populations of two-phase FIAs from lithophysal cavities in the ESF and ECRB cross drift indicate early fluid cooling with time from temperatures 45°C in early calcite, to 35 to 45°C in paragenetically younger calcite. Freezing point depressions range from 0.2 to 1.6°C, indicating trapping of a low salinity fluid. The majority of intermediate calcite and all outermost Mg-enriched calcite contains rare all-liquid inclusions and formed from ambient temperature (35°C) fluids. Carbon and oxygen isotope data reveal a consistent trend of decreasing 13 C (from 9.5 to 8.5‰) and increasing 18 O (from 5.2 to 22.1‰) values from paragenetically early calcite to Mg-enriched growth-zoned calcite. Depleted D values (131 to 90‰) of inclusion fluids from intermediate and the youngest Mg-enriched calcite indicate derivation from surface meteoric fluids. Recalculation of 18 OH2O values of 12 to 10‰ is consistent with derivation from paleometeoric fluids. Results of integrated U-Pb dating (opal and chalcedony) and fluid inclusion microthermometry indicate that two-phase FIAs that trapped fluids of 50°C are older than 6.29 0.30 Ma. Two-phase FIAs in parage- netically later calcite, which formed from fluids of 35 to 45°C, are older than 5.32 0.02 Ma. There is no evidence for trapping of fluids with elevated temperatures during the past 5.32 my. The youngest Mg-enriched calcite intergrown with opal began to precipitate between about 1.9 to 2.9 Ma and has continued to precipitate within the past half million years. The presence of liquid-only inclusions and the consistent occurrence of Mg-enriched calcite and opal as the youngest event indicate a minor, but chemically distinct, ambient temperature (35°C) fluid flux during the past 2 to 3 my. Copyright © 2003 Elsevier Science Ltd