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PHYSICS (578 journals)

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Journal Cover Physics and Chemistry of the Earth, Parts A/B/C
  [SJR: 0.611]   [H-I: 26]   [7 followers]  Follow
    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 1474-7065
   Published by Elsevier Homepage  [3042 journals]
  • Interaction of ordinary Portland cement and Opalinus Clay: Dual porosity
           modelling compared to experimental data
    • Authors: A. Jenni; T. Gimmi; P. Alt-Epping; U. Mäder; V. Cloet
      Pages: 22 - 37
      Abstract: Publication date: June 2017
      Source:Physics and Chemistry of the Earth, Parts A/B/C, Volume 99
      Author(s): A. Jenni, T. Gimmi, P. Alt-Epping, U. Mäder, V. Cloet
      Interactions between concrete and clays are driven by the strong chemical gradients in pore water and involve mineral reactions in both materials. In the context of a radioactive waste repository, these reactions may influence safety-relevant clay properties such as swelling pressure, permeability or radionuclide retention. Interfaces between ordinary Portland cement and Opalinus Clay show weaker, but more extensive chemical disturbance compared to a contact between low-pH cement and Opalinus Clay. As a consequence of chemical reactions porosity changes occur at cement-clay interfaces. These changes are stronger and may lead to complete pore clogging in the case of low-pH cements. The prediction of pore clogging by reactive transport simulations is very sensitive to the magnitude of diffusive solute fluxes, cement clinker chemistry, and phase reaction kinetics. For instance, the consideration of anion-depleted porosity in clays substantially influences overall diffusion and pore clogging at interfaces. A new concept of dual porosity modelling approximating Donnan equilibrium is developed and applied to an ordinary Portland cement – Opalinus Clay interface. The model predictions are compared with data from the cement-clay interaction (CI) field experiment in the Mt Terri underground rock laboratory (Switzerland), which represent 5 y of interaction. The main observations such as the decalcification of the cement at the interface, the Mg enrichment in the clay detached from the interface, and the S enrichment in the cement detached from the interface, are qualitatively predicted by the new model approach. The model results reveal multiple coupled processes that create the observed features. The quantitative agreement of modelled and measured data can be improved if uncertainties of key input parameters (tortuosities, reaction kinetics, especially of clay minerals) can be reduced.

      PubDate: 2017-06-17T07:08:10Z
      DOI: 10.1016/j.pce.2017.01.004
      Issue No: Vol. 99 (2017)
       
  • Interaction processes at the concrete-bentonite interface after 13 years
           of FEBEX-Plug operation. Part II: Bentonite contact
    • Authors: Raúl Fernández; Elena Torres; Ana I. Ruiz; Jaime Cuevas; María Cruz Alonso; José Luis García Calvo; Enrique Rodríguez; María Jesús Turrero
      Pages: 49 - 63
      Abstract: Publication date: June 2017
      Source:Physics and Chemistry of the Earth, Parts A/B/C, Volume 99
      Author(s): Raúl Fernández, Elena Torres, Ana I. Ruiz, Jaime Cuevas, María Cruz Alonso, José Luis García Calvo, Enrique Rodríguez, María Jesús Turrero
      The in situ FEBEX experiment performed at the URL in Grimsel (Swizerland) was dismantled after 18 years of operation. Interface samples between bentonite and a shotcreted concrete plug that was constructed in a second operational phase have been studied after 13 years of interaction. Mineralogical and geochemical characterization of samples have been performed by XRD, SEM-EDX, TG and FTIR techniques in addition to determinations of major ions by chemical analysis of aqueous extracts, δ18O and δ13C stable isotopes both in concrete paste and bentonite, and exchangeable cations in bentonite. Low mineralogical alteration impact was observed in bentonite that is only affected by a few millimeters. A large accumulation of Mg was observed at the bentonite side of the interface precipitating as silicates in various forms. In addition, heterogeneous carbonation was observed at the interface, but mostly affecting the concrete side. Migration of aqueous species occurred, being the most relevant the diffusion of chloride and sulfate from bentonite to concrete, in agreement with Part I of this study. Chloride advanced more into the concrete, while sulfates reacted to form ettringite, which has an evident alteration impact at the very interface (<0.5 mm rim) within the concrete. The ionic mobility has also redistributed the exchangeable cations in bentonite, increasing the content in Ca2+ and Na+, compensated by a decrease in Mg2+. The results presented in this paper complement those presented in Part I, focusing on the alteration of concrete by the bentonite and the granite groundwater.

      PubDate: 2017-06-17T07:08:10Z
      DOI: 10.1016/j.pce.2017.01.009
      Issue No: Vol. 99 (2017)
       
  • Modelling of cementitious backfill interactions with vitrified
           intermediate-level waste
    • Authors: Graham Baston; Timothy Heath; Fiona Hunter; Stephen Swanton
      Pages: 121 - 130
      Abstract: Publication date: June 2017
      Source:Physics and Chemistry of the Earth, Parts A/B/C, Volume 99
      Author(s): Graham Baston, Timothy Heath, Fiona Hunter, Stephen Swanton
      New types of wasteform are being considered for the geological disposal of radioactive intermediate-level waste (ILW) in the UK. These include vitrified ILW products arising from the application of thermal treatment processes. For disposal of such wasteforms in a geological disposal facility, a range of concepts are under consideration, including those with a high-pH cementitious backfill (the NRVB, Nirex Reference Vault Backfill). Alternatively, a cement-based material that buffers to a less alkaline pH could be used (an LPB, Low-pH Backfill). To assess the compatibility of these potential new wasteforms with cement-based disposal concepts, it is necessary to understand their impacts on the long-term evolution of the backfill. A scoping thermodynamic modelling study was undertaken to help understand the possible effects of these wasteforms on the performance of the backfill. The model primarily considers the interactions occurring between the vitirified waste, the porewater and the backfill, within a static and (in most cases) totally closed system. The approach was simplified by assuming equilibrium between the backfill and the corroded glass available at selected times, rather than involving detailed, reactive transport modelling. The aim was to provide an understanding of whether the impacts of the vitrified wastes on backfill performance are sufficient to compromise disposal in such environments. The calculations indicated that for NRVB, the overall alkaline buffering capacity of the backfill is not expected to be impaired by interactions with vitrified waste; rather the buffering will be to less alkaline pH values (above pH 9) but for a longer period. For the LPB, slightly lower pH values were predicted in some cases. The sorption capacities of the backfills are unlikely to be impaired by interactions with vitrified ILW. Indeed they may be increased, due to the additional C-S-H phase formation. The results of this study suggest that disposal of vitrified ILW in a cement-based disposal system with a high-pH backfill is a potentially viable disposal option.

      PubDate: 2017-06-17T07:08:10Z
      DOI: 10.1016/j.pce.2017.02.007
      Issue No: Vol. 99 (2017)
       
  • Reactive transport modelling of a high-pH infiltration test in concrete
    • Authors: M. Carme Chaparro; Josep M. Soler; Maarten W. Saaltink; Urs K. Mäder
      Pages: 131 - 141
      Abstract: Publication date: June 2017
      Source:Physics and Chemistry of the Earth, Parts A/B/C, Volume 99
      Author(s): M. Carme Chaparro, Josep M. Soler, Maarten W. Saaltink, Urs K. Mäder
      A laboratory-scale tracer test was carried out to characterize the transport properties of concrete from the Radioactive Waste Disposal Facility at El Cabril (Spain). A hyperalkaline solution (K-Ca-OH, pH = 13.2) was injected into a concrete sample under a high entry pressure in order to perform the experiment within a reasonable time span, obtaining a decrease of permeability by a factor of 1000. The concentrations of the tracers, major elements (Ca2+, SO 4 2 − , K+ and Na+) and pH were measured at the outlet of the concrete sample. A reactive transport model was built based on a double porosity conceptual model, which considers diffusion between a mobile zone, where water can flow, and an immobile zone without any advective transport. The numerical model assumed that all reactions took place in the immobile zone. The cement paste consists of C-S-H gel, portlandite, ettringite, calcite and gypsum, together with residual alite and belite. Two different models were compared, one with portlandite in equilibrium (high initial surface area) and another one with portlandite reaction controlled by kinetics (low initial surface area). Overall the results show dissolution of alite, belite, gypsum, quartz, C-S-H gel and ettringite and precipitation of portlandite and calcite. Permeability could have decreased due to mineral precipitation.

      PubDate: 2017-06-17T07:08:10Z
      DOI: 10.1016/j.pce.2017.01.010
      Issue No: Vol. 99 (2017)
       
  • Formation of magnesium silicate hydrates (M-S-H)
    • Authors: Ellina Bernard; Barbara Lothenbach; Daniel Rentsch; Isabelle Pochard; Alexandre Dauzères
      Pages: 142 - 157
      Abstract: Publication date: June 2017
      Source:Physics and Chemistry of the Earth, Parts A/B/C, Volume 99
      Author(s): Ellina Bernard, Barbara Lothenbach, Daniel Rentsch, Isabelle Pochard, Alexandre Dauzères
      The formation of magnesium silicate hydrates (M-S-H) with MgO to SiO2 ratios from 0.7 to 1.6 has been studied at 20, 50 and 70 °C. TGA and XRD data reveal that initially brucite and M-S-H are formed while amorphous silica is still present as indicated by FT-IR and 29Si MAS NMR experiments. In this first step M-S-H with Mg/Si ∼1 with pH values ∼9.4 is formed independently of the total Mg/Si. Investigations by FT-IR and 29Si MAS NMR detail that the structure of that initial M-S-H evolved with time and M-S-H formed with Mg/Si ranging from ∼0.8 to ∼1.3 after 2 years at 20 °C and after 1 year at 50 and 70 °C. This implies that the composition of synthetic M-S-H depends strongly on temperature and equilibration time. At 50 and 70 °C the M-S-H formation occurs faster although it is thermodynamically slightly less stable. The solubility of M-S-H, talc and antigorite after 1 year or longer shows comparable trends.

      PubDate: 2017-06-17T07:08:10Z
      DOI: 10.1016/j.pce.2017.02.005
      Issue No: Vol. 99 (2017)
       
  • Traditional Portland cement and MgO-based cement: a promising
           combination'
    • Authors: Monica Tonelli; Francesca Martini; Lucia Calucci; Marco Geppi; Silvia Borsacchi; Francesca Ridi
      Pages: 158 - 167
      Abstract: Publication date: June 2017
      Source:Physics and Chemistry of the Earth, Parts A/B/C, Volume 99
      Author(s): Monica Tonelli, Francesca Martini, Lucia Calucci, Marco Geppi, Silvia Borsacchi, Francesca Ridi
      MgO/SiO2 cements are materials potentially very useful for radioactive waste disposal, but knowledge about their physico-chemical properties is still lacking. In this paper we investigated the hydration kinetics of cementitious formulations prepared by mixing MgO/SiO2 and Portland cement in different proportions and the structural properties of the hydrated phases formed in the first month of hydration. In particular, the hydration kinetics was investigated by measuring the free water index on pastes by means of differential scanning calorimetry, while the structural characterization was carried out by combining thermal (DTA), diffractometric (XRD), and spectroscopic (FTIR, 29Si solid state NMR) techniques. It was found that calcium silicate hydrate (C-S-H) and magnesium silicate hydrate (M-S-H) gels mainly form as separate phases, their relative amount and structural characteristics depending on the composition of the hydrated mixture. Moreover, the composition of the mixtures strongly affects the kinetics of hydration and the pH of the aqueous phase in contact with the cementitious materials. The results here reported show that suitable mixtures of Portland cement and MgO/SiO2 could be used to modify the properties of hydrated phases with potential application in the storage of nuclear waste in clayey disposal.

      PubDate: 2017-06-17T07:08:10Z
      DOI: 10.1016/j.pce.2017.01.011
      Issue No: Vol. 99 (2017)
       
  • Advance in seismic site response: Usual practices and innovative methods
    • Authors: Francesco Panzera; Sebastiano D'Amico; Jan Burjanek; Marta Pischiutta
      Pages: 1 - 2
      Abstract: Publication date: April 2017
      Source:Physics and Chemistry of the Earth, Parts A/B/C, Volume 98
      Author(s): Francesco Panzera, Sebastiano D'Amico, Jan Burjanek, Marta Pischiutta


      PubDate: 2017-05-13T05:19:01Z
      DOI: 10.1016/j.pce.2017.04.005
      Issue No: Vol. 98 (2017)
       
  • From standard to fractional structural visco-elastodynamics: Application
           to seismic site response
    • Authors: C. Germoso; A. Fraile; E. Alarcon; J.V. Aguado; F. Chinesta
      Pages: 3 - 15
      Abstract: Publication date: April 2017
      Source:Physics and Chemistry of the Earth, Parts A/B/C, Volume 98
      Author(s): C. Germoso, A. Fraile, E. Alarcon, J.V. Aguado, F. Chinesta
      This paper revisits visco-elastodynamics from its most standard formulation to some more advanced description involving frequency-dependent damping (or viscosity), analyzing the effects of considering fractional derivatives for representing such viscous contributions. We will prove that such a choice results in richer models that can accommodate different constraints related to the dissipated power, response amplitude and phase angle. Moreover, the use of fractional derivatives allows to accommodate in parallel, within a generalized Kelvin-Voigt analog, many dashpots that contribute to increase the modeling flexibility for describing experimental findings. Finally, the effect of fractional damping in dynamic soil models will be addressed within a seismic site analyses framework.

      PubDate: 2017-05-13T05:19:01Z
      DOI: 10.1016/j.pce.2016.01.005
      Issue No: Vol. 98 (2017)
       
  • A comparative analysis of site-specific response spectral amplification
           models
    • Authors: Valerio Poggi; Benjamin Edwards; Donat Fäh
      Pages: 16 - 26
      Abstract: Publication date: April 2017
      Source:Physics and Chemistry of the Earth, Parts A/B/C, Volume 98
      Author(s): Valerio Poggi, Benjamin Edwards, Donat Fäh
      In the framework of the Seismic Hazard Harmonization in Europe (SHARE) project, the Swiss Seismological Service (SED) has performed an evaluation of two procedures developed to produce soil amplification models for 5% damped pseudo-spectral acceleration response spectra, each using different parameters to describe the soil properties. The goal of the work presented here is to evaluate the statistical consistency of the methods, with particular regard to their applicability to engineering practice. Additionally, we compare the results with those from a methodology internally developed by the SED, which is based on spectral modeling of ground motion using the quarter-wavelength approximation to parameterize soil conditions. Soil amplification is computed with respect to reference rock condition as defined for the probabilistic seismic hazard assessment performed during the SHARE project. For the comparison, a residual analysis was performed between the computed soil-amplification functions from the three different methodologies, over a number of selected sites spanning different soil classes and ground motion levels. The analysis of the average residuals of these functions is useful to highlight the main differences between the proposed approaches, with special regard to the impact of soil resonances and anelastic attenuation within different frequency bands. The assessment was performed on a group of 88 selected stations of the Japanese KiKNet strong-motion network, for which complete logs of the shear-wave velocity profiles are available, in addition to a significant number of earthquake recordings. In a first step, average residuals were computed. Subsequently, amplification variability related to soil classes was investigated. The target of this second step was to perform the comparison by separately analyzing the impact of different soil and velocity classes, according to a soil-classification scheme proposed by Aristotle University of Thessaloniki (AUTH). In this paper the main results of these investigations are summarized and, when applicable, an interpretation of our findings is given.

      PubDate: 2017-05-13T05:19:01Z
      DOI: 10.1016/j.pce.2016.09.001
      Issue No: Vol. 98 (2017)
       
  • Site amplification at the city scale in Basel (Switzerland) from
           geophysical site characterization and spectral modelling of recorded
           earthquakes
    • Authors: Clotaire Michel; Donat Fäh; Benjamin Edwards; Carlo Cauzzi
      Pages: 27 - 40
      Abstract: Publication date: April 2017
      Source:Physics and Chemistry of the Earth, Parts A/B/C, Volume 98
      Author(s): Clotaire Michel, Donat Fäh, Benjamin Edwards, Carlo Cauzzi
      Hazard assessment at the city scale requires a detailed characterization of the effect of surface geology on ground motion (site effects). Though this analysis is commonly achieved using geophysical site characterization and site response modelling, we propose here a complementary analysis based on amplification functions retrieved from Empirical Spectral Modelling (ESM) of earthquake recordings. We applied this method to the city of Basel (Switzerland) that benefits from a detailed microzonation and a dense Strong Motion Network with 21 modern free-field stations. We first verified the accuracy of ESM amplification functions for this region and used them to determine the bedrock interface at a site with a detailed velocity profile. While the interface between Upper and Lower Tertiary was, until now, considered responsible for the fundamental frequency of resonance in the Rhine Graben, we found that the bedrock interface in fact lies at the Mesozoic limestone. We also investigated the second peak of the H/V ratios that is clustered in a particular area of the basin where amplification is found to be different. We successfully used the ESM amplification functions to verify the microzonation of 2006 and would strongly advise the installation of strong motion stations where such studies are performed in the future. Outside the Rhine Graben, where shallow sediments are found, we propose an amplification functional form based on ESM and the fundamental frequency of resonance. Finally, we combined all our findings and generated amplification maps of the response spectrum at any period of interest for earthquake engineering. This map is proposed for a high resolution real-time implementation in ShakeMap and will be used for seismic loss assessment.
      Graphical abstract image

      PubDate: 2017-05-13T05:19:01Z
      DOI: 10.1016/j.pce.2016.07.005
      Issue No: Vol. 98 (2017)
       
  • Results from shallow geophysical investigations in the northwestern sector
           of the island of Malta
    • Authors: M. Pischiutta; F. Villani; S. D'Amico; M. Vassallo; F. Cara; D. Di Naccio; D. Farrugia; G. Di Giulio; S. Amoroso; L. Cantore; A. Mercuri; D. Famiani; P. Galea; A. Akinci; A. Rovelli
      Pages: 41 - 48
      Abstract: Publication date: April 2017
      Source:Physics and Chemistry of the Earth, Parts A/B/C, Volume 98
      Author(s): M. Pischiutta, F. Villani, S. D'Amico, M. Vassallo, F. Cara, D. Di Naccio, D. Farrugia, G. Di Giulio, S. Amoroso, L. Cantore, A. Mercuri, D. Famiani, P. Galea, A. Akinci, A. Rovelli
      We performed geophysical investigations in the northwestern sector of the island of Malta to reconstruct velocity-depth models and provide shear-wave velocity profiles. We have chosen two sites, one located in Rabat (Malta) and another in the Golden Bay area. We used both active (seismic and electrical 2D-tomography, Multichanel Analysis of Surface Waves – MASW) and passive (2D arrays and single-station measurements using ambient noise) geophysical methods. Consistently with previous studies performed in this part of Malta, we have found that both sites are characterized by site resonance in the frequency range 1–2 Hz as an effect of the local lithostratigraphic succession that shows an impedance contrast at about 60–90 m depth. This resonance effect can have important implications on both seismic hazard as well as seismic risk evaluation of the region since the amplified frequency range coincides with the resonance frequencies typical of 5–10 storey buildings which are very diffuse in the Maltese Islands, especially after intense recent urbanization. We also highlight the importance of performing seismic velocity measurements even at rock sites. As an example, the Golden Bay site would be classified as class “A” following the EuroCode EC8 when considering only the outcropping lithology represented by limestone rocks. Conversely the subsoil characterization provided by this study has revealed that this site falls in the EC8 class “B”, stressing the importance of direct geophysical measurements since the a-priori assignment to A-class could lead to wrong estimates in evaluating the site response.

      PubDate: 2017-05-13T05:19:01Z
      DOI: 10.1016/j.pce.2016.10.013
      Issue No: Vol. 98 (2017)
       
  • S-wave velocity measurement and the effect of basin geometry on site
           response, east San Francisco Bay area, California, USA
    • Authors: Koichi Hayashi; Mitchell Craig
      Pages: 49 - 61
      Abstract: Publication date: April 2017
      Source:Physics and Chemistry of the Earth, Parts A/B/C, Volume 98
      Author(s): Koichi Hayashi, Mitchell Craig
      We measured S-wave velocity profiles at eleven sites in the east San Francisco Bay area using surface wave methods. Data acquisition included multichannel analysis of surface waves using an active source (MASW), a passive surface-wave method using a linear array of geophones (Linear-MAM), and a two-station spatial autocorrelation method (2ST-SPAC) using long-period accelerometers. Maximum distance between stations ranged from several hundred meters to several kilometers, depending on the site. Minimum frequency ranged from 0.2 to 2 Hz, depending on the site, corresponding to maximum wavelengths of 10 to 1 km. Phase velocities obtained from three methods were combined into a single dispersion curve for each site. A nonlinear inversion was used to estimate S-wave velocity profiles to a depth of 200–2000 m, depending on the site. Resultant S-wave velocity profiles show significant differences among the sites. On the west side of the Hayward fault and the east side of the Calaveras fault, there is a low velocity layer at the surface, with S-wave velocity less than 700 m/s, to a depth of approximately 100 m. A thick intermediate velocity layer with S-wave velocity ranging from 700 to 1500 m/s lies beneath the low velocity layer. Bedrock with S-wave velocity greater than 1500 m/s was measured at depths greater than approximately 1700 m. Between the Hayward Fault and the Calaveras Fault, thicknesses of the low velocity layer and the intermediate velocity layer are less than 50 m and 200 m respectively, and depth to bedrock is less than 250 m. To evaluate the effect of a lateral change in bedrock depth on surface ground motion due to an earthquake, a representative S-wave velocity cross section perpendicular to the Hayward fault was constructed and theoretical amplification was calculated using a viscoelastic finite-difference method. Calculation results show that the low frequency (0.5–5 Hz) component of ground motion is locally amplified on the west side of the Hayward fault because of the effect of two-dimensional structure.

      PubDate: 2017-05-13T05:19:01Z
      DOI: 10.1016/j.pce.2016.07.001
      Issue No: Vol. 98 (2017)
       
  • Surface geology and morphologic effects on seismic site response: The
           study case of Lampedusa, Italy
    • Authors: F. Panzera; G. Lombardo; S. Sicali; S. D'Amico
      Pages: 62 - 72
      Abstract: Publication date: April 2017
      Source:Physics and Chemistry of the Earth, Parts A/B/C, Volume 98
      Author(s): F. Panzera, G. Lombardo, S. Sicali, S. D'Amico
      A joint Italo-Maltese research project (Costituzione di un Sistema Integrato di Protezione Civile Transfrontaliero Italo-Maltese, SIMIT) was financially supported by the European community with the aim to produce hazard maps in the area between the south-eastern Sicilian coast and the Sicily Channel including the islands of Lampedusa and Malta. In the frame of this project, the present study investigates the characteristics of the local seismic response in Lampedusa, a carbonate shelf belonging to the foreland domain at the northern edge of the African plate. Ninety-two ambient noise recordings were collected and processed through spectral ratio techniques. Polarization of the horizontal component of motion was also investigated in order to set into evidence possible directional effects. Results point out that in the central part of the island, where the most ancient and rigid terrains outcrop most of the spectral ratio plots show no particular site effects. On the other hand, nearby morphologic escarpments and fault lines, pronounced spectral ratio peaks in the frequency range 2.0–5.0 Hz are observed. These peaks, as highlighted by polarization analysis, are clearly directional with the largest amplification occurring with high angle (60°–90°) to the structures strike. Moreover, in sites located close to recent and soft deposits outcrops other significant seismic site effects at frequency higher than 5.0 Hz are identified. We can however assert that, rather than the surface lithology, the presence of cliff areas and tectonic structures strongly influence the local amplification of the ground motion and the occurrence of directional effects.

      PubDate: 2017-05-13T05:19:01Z
      DOI: 10.1016/j.pce.2016.08.006
      Issue No: Vol. 98 (2017)
       
  • Balancing water demand for the Heihe River Basin in Northwest China
    • Authors: Feng Wu; Yuping Bai; Yali Zhang; Zhihui Li
      Abstract: Publication date: Available online 11 July 2017
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Feng Wu, Yuping Bai, Yali Zhang, Zhihui Li
      Water resource crisis becomes the most serious threat to global economic sustainable development. Balancing water demand under the pressure of economic development is a new challenge faced by water resource managers. In this study, we investigated the mutual feedback mechanism between economic systems and eco-hydrological processes in the Heihe River Basin of China with a Water Economic Model (WEM). The WEM is built based on input-output table that embeds water-land resource factors and focuses on the interactive route between water resource and economic elements. On one hand, we investigated the routes and patterns of how eco-hydrological processes acted on economic systems in the upstream of Heihe River Basin, and analyzed how climate change disturbed the economic systems through its impacts on water yield. On the other hand, we explored the feedback of economic systems on eco-hydrological processes through land use interface. We determined the key parameters of simulation and designed the economic development scenarios for the Heihe River Basin. Based on the WEM, we simulated the change of water demand under urbanization and industrial transformation scenarios, supporting scientific basis for the water resource management and policy.

      PubDate: 2017-07-12T07:26:26Z
      DOI: 10.1016/j.pce.2017.07.002
       
  • Scenario analysis of land use change in Kabul River Basin – A river
           basin with rapid socio-economic changes in Afghanistan
    • Authors: Omaid Najmuddin; Xiangzheng Deng; Jia Siqi
      Abstract: Publication date: Available online 5 June 2017
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Omaid Najmuddin, Xiangzheng Deng, Jia Siqi
      Land use management has a great importance in socio-economic development of countries and regions. Recently, Afghanistan has, at one hand, experienced significant socio-economic changes through political and economic transformation and, on the other hand it is considered amongst vulnerable countries to climate and other natural changes. For this, understanding the interactions between socio-economic and natural changes with land use change under different development scenarios is crucial for sustainable land use management. Present research took Kabul River Basin (KRB) as a case study area and used Dynamic of Land System (DLS) model to simulate land use/cover for the years of 2020 and 2030. For this purpose, various socio-economic and bio-physical datasets were prepared and then integrated into the model under three different scenarios i.e. baseline, economic development, and environmental protection. The results indicated a significant land use change under all three scenarios. Cultivated land, grassland and built-up area will significantly increase under all three scenarios; while forest area, water area and unused land will significantly decrease under the economic development and baseline scenarios. While in the environmental protections scenario, the forest area will considerably increase, however, water area still showed a decreasing trend but it will be lesser as compared to the other two scenarios. By considering the above degradations, particularly under baseline and economic scenarios, it is suggested that the government needs to develop overall land use planning in KRB to achieve a rational exploitation of land resources and we hoped that the results of this study will help to target management decisions on rational land uses and effective environment protections of KRB.

      PubDate: 2017-07-12T07:26:26Z
      DOI: 10.1016/j.pce.2017.06.002
       
  • Impact Assessment of Climate Change on Poverty Reduction: A Global
           Perspective
    • Authors: Xiaoxue Zhou; Jiancheng Chen; Zhihui Li; Guofeng Wang; Fan Zhang
      Abstract: Publication date: Available online 23 June 2017
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Xiaoxue Zhou, Jiancheng Chen, Zhihui Li, Guofeng Wang, Fan Zhang
      Climate change and its impacts are the biggest environmental problems that the world is facing in recent decades. Climate-sensitive events have already been critical obstacles of poverty reduction and sustainable economic development. Assessing how climate change impacts on poverty reduction is of great significance to the comprehensive assessment of climate change impacts on social economy and the mitigation of the negative impacts. With geo-spatially referenced malnutrition and infant mortality data as a proxy for poverty, focusing on the aspects of agriculture and human well-being consist of physical health and personal autonomy. This study selects three countries, China, India and Senegal, to investigate the impacts of climate change on poverty reduction. Contrast to previous work what analyze climate changes’ impacts most concentrated on coastal urban areas, this paper is concentrating on the rural poor areas in different income group countries and on a contrastive analysis. The correlation analysis results show the same is that the indicators of climate change are in significant correlations with indicators of poverty and that of agriculture and human well-being in China, India and Senegal. However, China performs poorly in terms of personal autonomy, while the Senegal performs well, the correlations of forest area percentage (one indicator of climate change) with other variables in Senegal are absolutely opposite to that in China and India. We find the same influence factors have different effects on poverty reduction in these countries, the anti-poverty policies should be made according to local conditions.

      PubDate: 2017-07-03T07:20:23Z
      DOI: 10.1016/j.pce.2017.06.011
       
  • Characterization of soil salinization in typical estuarine area of the
           Jiaozhou Bay, China
    • Authors: Qifei Li; Min Xi; Qinggai Wang; Fanlong Kong; Yue Li
      Abstract: Publication date: Available online 23 June 2017
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Qifei Li, Min Xi, Qinggai Wang, Fanlong Kong, Yue Li
      In this study, the characteristics of soil salinization and the effects of main land use/land cover and other factors in typical estuarine area of the Jiaozhou Bay are investigated. Soil samples were collected in the parallel coastal zone, vertical coastal zone and longitudinal profile depth in the area to determine the soil salt content. The correlation analysis and principal component analysis are used to address the general characteristics of soil salinization in the study area. In the horizontal direction, there are moderate salinization, severe salinization and saline soil state. The farther from the sea (within 1.1 km), the lower the soil salinization degree. In the direction of longitudinal profile depth, there are severe salinization and saline soil state, and the soil salt content is accumulated in the surface and bottom. The Na+ and Cl- are the dominant cation and anion, respectively, the distributions of which are consistent with that of salt content. All the salinization indexes, except for soil pH, are of moderate/strong variability. The invasion of Spartina alterniflora results in the increase of soil salt content and salinization degree, the effects of which are mainly determined by the physiological characteristics and the growth years. The degree of soil salinization increased significantly in the aquaculture ponds, which is mainly caused by the use of chemicals. The correlation between soil salt content and Na+, Cl- is significant. From the results of principal component analysis, Na+, Cl-, Ca2+, Mg2+ and SO4 2- could be used as main diagnostic factors for salinization in typical estuarine area of the Jiaozhou Bay. The effects of NaCl and sulfate on salt content further affect the degree of salinization in the estuarine area.

      PubDate: 2017-07-03T07:20:23Z
      DOI: 10.1016/j.pce.2017.06.010
       
  • Sensitivity of the mayfly Adenophlebia auriculata (Ephemeroptera:
           Leptophlebiidae) to MgSO4 and Na2SO4
    • Authors: E.C. Vellemu; P.K. Mensah; N.J. Griffin; O.N. Odume
      Abstract: Publication date: Available online 22 June 2017
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): E.C. Vellemu, P.K. Mensah, N.J. Griffin, O.N. Odume
      Acid mine drainage (AMD) continues to deteriorate water quality in freshwater ecosystems. Sulphates, a major salt component in AMD, can exacerbate AMD effects in freshwater because salts are toxic to aquatic life in high concentrations. Sulphates are predominant in South African AMD impacted freshwater ecosystems. In this study, the sensitivity of nymphs of the mayfly Adenophlebia auriculata (Ephemeroptera: Leptophlebiidae) was investigated by exposing the organisms to magnesium sulphate (MgSO4) and sodium sulphate (Na2SO4) as models of mining salinisation in short-term (96 h) and long-term (240 h) in static system tests. Short-term and long-term lethal concentrations of each salt were estimated using regression analyses. The results indicated that A. auriculata was more sensitive to MgSO4 (LC50 = 3.81 g/L) than Na2SO4 (LC50 = 8.78 g/L) after short-term exposures. However, this species became sensitive to Na2SO4 (LC10 = 0.19 g/L) but tolerant to MgSO4 (LC10 = 0.35 g/L) after long-term exposures. These results suggest that the 0.25 g/L sulphate compliance limit for South Africa is inadequate to protect A. auriculata from Na2SO4 toxicity in the long-term, yet it overprotects this species from MgSO4 exposures in the short-term. The findings of this study are an important major step in understanding the ecological effects of AMD to aquatic life.

      PubDate: 2017-07-03T07:20:23Z
      DOI: 10.1016/j.pce.2017.06.009
       
  • Dynamic characteristics of soil respiration in Yellow River Delta
           wetlands, China
    • Authors: Xiao Wang; Xianxiang Luo Hongli Jia Hao Zheng
      Abstract: Publication date: Available online 21 June 2017
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Xiao Wang, Xianxiang Luo, Hongli Jia, Hao Zheng
      The stable soil carbon (C) pool in coastal wetlands, referred to as ‘‘blue C’’, which has been extensively damaged by climate change and soil degradation, is of importance to maintain global C cycle. Therefore, to investigate the dynamic characteristics of soil respiration rate and evaluate C budgets in coastal wetlands are urgently. In this study, the diurnal and seasonal variation of soil respiration rate in the reed wetland land (RL) and the bare wetland land (BL) was measured in situ with the dynamic gas-infrared CO2 method in for seasons, and the factors impacted on the dynamic characteristics of soil respiration were investigated. The results showed that the diurnal variation of soil respiration rate consistently presented a “U” curve pattern in April, July, and September, with the maximum values at 12:00 AM and the minimum values at 6:00 AM. In the same season, the diurnal soil respiration rate in RL was significantly greater than those in BL (P < 0.05). In April, July, and September, the mean diurnal soil respiration rate was 0.14, 0.42, and 0.39 umol m-2 s-1 in RL, 0.05, 0.22, 0.13, and 0.01 umol m-2 s-1 in BL, respectively. Soil surface temperature was the primary factor that influenced soil respiration, which was confirmed by the exponential positive correlation between the soil respiration rate and soil surface temperature in BL and RL (P < 0.05). In addition, the high salinity of soils suppressed soil respiration, confirming by the significantly negative correlation between soil respiration rate and the content of soluble salt (S). These results will be useful for understanding the mechanisms underlying soil respiration and elevating C sequestration potential in the coastal wetlands.

      PubDate: 2017-06-22T07:11:36Z
       
  • Can Potamonautids be used as umbrella invertebrate species for
           conservation: identifying opportunities and challenges related to
           community sustainable livelihoods
    • Authors: Mwazvita TB. Dalu; Ryan J. Wasserman; Tatenda Dalu
      Abstract: Publication date: Available online 20 June 2017
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Mwazvita TB. Dalu, Ryan J. Wasserman, Tatenda Dalu
      In this study, we assessed direct or indirect community livelihoods impacts on the preservation of Potamonautes spp., in the Eastern Highlands region of Zimbabwe and attempted to identify opportunities and constraints to conservation of crabs within the pre-existing livelihoods of community households. Random and snowball sampling methods were used to select households for informal open-ended interviews and participants for the focus group discussions. We found that increasing human populations, poverty, crab consumption, and illegal mining (i.e. resulting in water pollution, degradation of habitats) are threatening freshwater crabs in the Eastern Highlands. The combined and interacting influences of the above highlighted anthropogenic factors have resulted in Potamonautes crab population declines in populated areas. Potamonautes spp. crabs were, therefore, found to be largely restricted to upstream mountainous sites where human populations were less dense. Patterns of spatial overlap of rural population, higher poverty prevalence and crab abundance revealed in this study indicate priority areas of possible conflicts of interest, but also areas where benefits to both conservation and livelihoods can potentially be realised.
      Graphical abstract image

      PubDate: 2017-06-22T07:11:36Z
      DOI: 10.1016/j.pce.2017.06.007
       
  • Diffused impact of grassland degradation over space: A case study in
           Qinghai province
    • Authors: Pei Wang; Xiangzheng Deng Sijian Jiang
      Abstract: Publication date: Available online 16 June 2017
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Pei Wang, Xiangzheng Deng, Sijian Jiang
      Our study aims to simulate and detect the interregional association of livestock production induced by grassland degradation in Qinghai province by TERM (The Enormous Regional Model). The shock variable, grassland degradation, is set and calculated by using its proxy, change of grassland area. We conclude that grassland area is decreasing during 1990-2008 in Qinghai province, and the average reduction rate is 1.591%. And grassland degradation in Qinghai province has a marginal effect on the other regions in China. Livestock production of the other 30 provinces expands in the case of the exogenous shock, and this impact is greater with a variation above 0.05% in Inner Mongolia, Tibet, Ningxia province and so on than the other regions. Thus, construction of ecological projects like natural reserves in Qinghai province for ecosystem conservation and livestock grazing benefits interregional equity and shrink their differences.

      PubDate: 2017-06-17T07:08:10Z
       
  • Mechanisms and modelling of waste-cement and cement-host rock interactions
    • Abstract: Publication date: June 2017
      Source:Physics and Chemistry of the Earth, Parts A/B/C, Volume 99


      PubDate: 2017-06-17T07:08:10Z
       
  • Non-flood season neap tides in the Yangtze estuary offshore: flow mixing
           processes and its potential impacts on adjacent wetlands
    • Authors: Taoyuan Wei; Zhanghua Wang; Jing Chen; Maotian Li
      Abstract: Publication date: Available online 6 June 2017
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Taoyuan Wei, Zhanghua Wang, Jing Chen, Maotian Li
      How flow mixing process influences the wetlands of the Yangtze Estuary is still poorly understood. Hydrological fieldwork was conducted on five vessel-anchored sites (S1-S2; M1-M2-M3) near the major wetlands of the Yangtze Estuary offshore (121°57′-122°30′E, 30°50′-31°23′N) on May 8-11 2004, to examine the dynamics of neap tides in the non-flood season of the Yangtze (∼24, 700 m3s-1 at Datong) and their impacts on adjacent wetlands. Based on the measurement of the acoustic Doppler current profiler (aDcp), direct-reading current meter and optical backscattering sensor (OBS-3A), two flow patterns were revealed: 1) well mixing flow pattern caused by the turbulent tidal currents, and 2) weak mixing flow pattern resulted by the estuarine circulation in the North Port of the estuary. The characteristics of such different flow patterns were analyzed and resultant sediment dispersals were discussed in relation to the adjacent wetlands. It is suggested that the estuarine circulation might be the important process to nourish the eastern wetland of the Yangtze Estuary which has been neglected before.

      PubDate: 2017-06-07T07:00:24Z
      DOI: 10.1016/j.pce.2017.06.004
       
  • Phosphorus fraction and phosphate sorption-release characteristics of the
           wetland sediments in the Yellow River Delta
    • Authors: Yuan Cui; Rong Xiao; Ying Xie; Mingxiang Zhang
      Abstract: Publication date: Available online 5 June 2017
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Yuan Cui, Rong Xiao, Ying Xie, Mingxiang Zhang
      The aim of this study was to investigate phosphorus (P) fractions and phosphate sorption-release characteristics of the surface sediments regarding the wetland restoration in the Yellow River Delta (YRD). Sediments samples were collected from three typical sample plots: Phragmites australis community (p), Suaeda salsa community (s), and bare land (b) both in natural wetland (N) and restored wetland (R). The results showed that the mean content of TP was 541.58 mg/kg, and the rank order of P fractions were: inorganic phosphorus (IP) (65.6%) > residual phosphorus (RP) (24.9%) > organic phosphorus (OP) (9.5%). For sediments under the same land cover, TP and OP contents were significantly higher in natural wetlands than those in restored wetlands. This indicated that the restoration project really made a difference in TP content of sediments, and the decreased TP might result from decreased OP. For P kinetics sorption, a quick sorption mainly occurred within 0.5 h. The maximum phosphorus adsorption capacities (Q max) ranging from 139.40 mg/kg to 224.06 mg/kg and the bonding energy constant (K) ranging from 0.33 mg/L to 1.37 mg/L were both obtained using a Langmuir model. In addition, Q max, P release (P r) and P release rates (P rr) were in the order of Nb > Np > Ns > Rb > Rp > Rs, Np > Rp > Ns> Rs = Nb > Rb and Rp > Ns > Rs > Rb > Np > Nb, respectively. This indicated that sediments from natural wetland could adsorb more P as well as release more P into overlying water, moreover, more content of P were left in sediments comparing to restored wetland. Sediments from bare land were more likely to retain P as a pool because of the highest sorption capacity while lowest release potential. Our study showed that P sorption-release and the quick sorption processes were mainly affected by sediment moisture, amorphous iron and aluminum oxides (Feox and Alox). Besides, Q max was related to background value of sediments P. OP was the major P fraction adsorbed by sediments, and the P adsorbed by sediments was mainly adsorbed on Feox and Alox.

      PubDate: 2017-06-07T07:00:24Z
      DOI: 10.1016/j.pce.2017.06.005
       
  • Responses of the water-yield ecosystem service to climate and land use
           change in Sancha River Basin, China
    • Authors: Yanqing Lang; Wei Song; Ying Zhang
      Abstract: Publication date: Available online 5 June 2017
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Yanqing Lang, Wei Song, Ying Zhang
      Water supply is a key ecosystem service, directly influencing sustainable development of the social economy and ecological systems. Climate and land use change are two important factors that affect water supply. Since the 1990s, China has implemented a series of land use policies, such as the grain-for-green program, which have significantly changed land use patterns. However, the effect of global climate change on water resources in China is growing, resulting in water shortages and deterioration of the aqueous environment. In this context, China's land use change, concurrent with the impacts of climate change on regional water resources, has become an issue worthy of discussion. This work analyzed the effect of land use and climate change on water yield in 1990 and 2010 using the Sancha River Basin as a case study. The variations in water yield in Sancha River Basin were simulated using the water-yield module in the InVEST (Integrated Valuation of Ecosystem Services and Tradeoffs) model for three scenarios. The first scenario incorporated land use and climate change into the model in accordance with actual conditions. The second scenario was a simulation without climate change, and the third was without land use change. Water yield in Sancha River Basin increased by 17% between the two time periods in the actual scenario. In the scenario without climate change, land use conversions led to a 0.46% reduction in water yield. In the scenario without land use change, climate change led to a 17.50% increase in regional water yield due to precipitation. The impact of rainfall change on the Sancha River Basin water yield was as high as 97.44% while that of land use change was only 2.56%. This study shows that the grain-for-green program has negatively impacted water yield. Furthermore, to improve the ecological environment of the river basin, a comprehensive scheme for controlling water and soil erosion should be implemented according to the actual variation in water yield. This would give full consideration to the utility of water resources.

      PubDate: 2017-06-07T07:00:24Z
      DOI: 10.1016/j.pce.2017.06.003
       
  • Reactive transport modelling of cement-groundwater-rock interaction at the
           Grimsel Test Site
    • Authors: M. Carme Chaparro; Maarten W. Saaltink; Josep M. Soler
      Abstract: Publication date: Available online 13 May 2017
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): M. Carme Chaparro, Maarten W. Saaltink, Josep M. Soler
      An in situ experiment at the Grimsel Test Site (Switzerland) to study water-cement-rock interaction in fractured granite was modelled. It consisted of a hardened cement source in a borehole intersecting a water conducting fracture. Grimsel groundwater was injected into this borehole. Two other boreholes at about 0.56 m and 1.12 m from the emplacement borehole were used to monitor the evolution of water composition for 5 years. The modelling approach was based on a 1D radial model for the emplacement borehole and a small volume of rock (fault gouge) around it, and a 2D model for the rest of the domain. The results of the 1D model were used as input for the 2D model. Both models showed dissolution of the fault gouge minerals. Results from the 1D model showed dissolution of portlandite in the cement with an increase in porosity. The 2D model showed a reduction in porosity in the fault gouge due to mineral precipitation. Near the emplacement borehole ettringite precipitated. At the centre of the plume there was precipitation of C-A-S-H and hydrotalcite. At the edge of the hyperalkaline plume calcite, hydrotalcite and illite precipitated.

      PubDate: 2017-05-18T05:40:43Z
      DOI: 10.1016/j.pce.2017.05.006
       
  • The urbanization efficiency in Chengdu City: An estimation based on a
           three-stage DEA model
    • Authors: Siqi Jia; Chengxin Wang; Yifan Li; Fan Zhang; Wei Liu
      Abstract: Publication date: Available online 12 May 2017
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Siqi Jia, Chengxin Wang, Yifan Li, Fan Zhang, Wei Liu
      With economic development and population growth occurring throughout China, there has been increasing conflicts between resources, environmental protection and economic development in many regions, especially in the developed regions. Therefore, it is important to correctly evaluate the pressure of human activities on the natural environment and the ecosystem carrying capacity at a regional scale. This paper evaluated the urbanization efficiency based on the three-stage Data Envelopment Analysis (DEA) model, which takes the impacts of exogenous factors on the urbanization rate into consideration. From the perspectives of governmental management and urban growth and scale, this paper indicated the current urbanization mode and features in Chengdu based on land use data, socioeconomic and natural data in each district and county. The results show that Jinjiang, Longquanyi, Qingbaijiang, Qingyang districts, Pujiang, Xinjin counties and Dujiangyan county-level city are always with the balanced urbanization efficiency; while the efficiency in Dayi, Pi counties, Chongzhou, Pengzhou, Qionglai county-level cities and Jinniu, Chenghua districts still needs to be improved; and Shuangliu and Jintang counties keep the lowest urbanization level. Overall, the average reduction rate in built-up area in highest at 29.57% among the three input indicators (land, capital and labor), which means that the superfluous area of built-up land hinders the balanced development of urbanization in Chengdu. It also suggests that three-stage DEA model is effective to reflect the realistic level of urbanization efficiency by eliminating environmental impact. Finally, this paper further provides improved directions and policy suggestions for the sustainable and well-rounded urban development.

      PubDate: 2017-05-13T05:19:01Z
      DOI: 10.1016/j.pce.2017.05.003
       
  • Set pair analysis method for coordination assessment in water resources
           utilizing conflict
    • Authors: Zhengwei Pan; Yanhua Wang; Juliang Jin; Xiaowei Liu
      Abstract: Publication date: Available online 12 May 2017
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Zhengwei Pan, Yanhua Wang, Juliang Jin, Xiaowei Liu
      In order to describe management problems of water resource system conflicts quantitatively, six elements were proposed in the management of water resources conflicts, which are coordination participator, coordination goal, coordination index, behavioral strategies, coordination situation and coordination rule. In the coordination management of conflicts in water resource systems a coordination index has a lower limiting value meeting the coordination participator interests, and has an upper limiting value for ensuring the interests of the overall system and other coordination participators. When the coordination index value exceeds the limiting range, the interests of the overall system and other coordination participators cannot be guaranteed. The coordination indexes of water resources conflict are interval numbers. According to the characteristics of interval pattern indexes, the bidirectional connection number was proposed to describe the coordination degree. Based on the bidirectional connection number, the coordination evaluation method was developed, and was used in the coordination evaluation of water resource conflicts in the Yellow River basin. The results showed that the coordination status of water resources utilization was generally acceptable. However, with increasing water consumption in some provinces in the Yellow River basin in recent years, the available water supply cannot meet the allocation plan for water resource supply. The coordination degree of water resources utilization has, therefore, been declining.

      PubDate: 2017-05-13T05:19:01Z
      DOI: 10.1016/j.pce.2017.05.009
       
  • Transport properties evolution of cement model system under degradation -
           Incorporation of a pore-scale approach into reactive transport modelling
    • Authors: N. Seigneur; E. L’Hôpital; A. Dauzères; J. Sammaljavi; M. Voutilainen; P.E. Labeau; A. Dubus; V. Detilleux
      Abstract: Publication date: Available online 6 May 2017
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): N. Seigneur, E. L’Hôpital, A. Dauzères, J. Sammaljavi, M. Voutilainen, P.E. Labeau, A. Dubus, V. Detilleux
      This paper describes a multi-scale approach for the modelling of the degradation of model cement pastes using reactive transport. It specifically aims at incorporating chemistry-transport feedback results from a pore-scale approach into a continuum description. Starting from a numerical representative elementary volume of the model cement paste, which was built according to extensive experimental dedicated chacarterizations, this paper provides three separate descriptions of two different degradations: leaching and carbonation. First, 2D pore-scale simulations are performed and predict degradation depths in very good agreement with experiments. Second, 3D pore scale descriptions of how the microstructre evolves provides accurate description of the evolution of transport properties through degradation. Finally, those latter results are incorporated as a feedback law between porosity and effective diffusion coefficient into a 1D continuum approach of reactive transport. This paper provides pore-scale explanations of why reactive transport modelling has encountered mitigated success when applied to cementitious materials, especially during carbonation or degradations consisting of precipitation reactions. In addition to that, different degradation modellings are in very good agreement with experimental observations.

      PubDate: 2017-05-08T04:45:44Z
      DOI: 10.1016/j.pce.2017.05.007
       
  • A sorption model for alkalis in cement-based material – Correlations
           with solubility and electrokinetic properties
    • Authors: Pierre Henocq
      Abstract: Publication date: Available online 5 May 2017
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Pierre Henocq
      In cement-based materials, radionuclide uptake is mainly controlled by calcium silicate hydrates (C-S-H). This work presents an approach for defining a unique set of parameters of a surface complexation model describing the sorption behavior of alkali ions on the C-S-H surface. Alkali sorption processes are modeled using the CD-MUSIC function integrated in the Phreeqc V.3.0.6 geochemical code. Parameterization of the model was performed based on (1) retention, (2) zeta potential, and (3) solubility experimental data from the literature. This paper shows an application of this model to sodium ions. It was shown that retention, i.e. surface interactions, and solubility are closely related, and a consistent sorption model for radionuclides in cement-based materials requires a coupled surface interaction/chemical equilibrium model. In case of C-S-H with low calcium-to-silicon ratios, sorption of sodium ions on the C-S-H surface strongly influences the chemical equilibrium of the C-S-H + NaCl system by significantly increasing the aqueous calcium concentration. The close relationship between sorption and chemical equilibrium was successfully illustrated by modelling the effect of the solid-to-liquid ratio on the calcium content in solution in the case of C-S-H + NaCl systems.

      PubDate: 2017-05-08T04:45:44Z
      DOI: 10.1016/j.pce.2017.05.004
       
  • Modelling of Chemical Degradation of Blended Cement-based Materials by
           Leaching Cycles with Callovo-Oxfordian Porewater
    • Authors: Javier Olmeda; Pierre Henocq; Eric Giffaut; Mireia Grivé
      Abstract: Publication date: Available online 4 May 2017
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Javier Olmeda, Pierre Henocq, Eric Giffaut, Mireia Grivé
      The present work describes a thermodynamic model based on pore water replacement cycles to simulate the chemical evolution of blended cement (BFS + FA) by interaction with external Callovo-Oxfordian (COx) pore water. In the framework of the radioactive waste management, the characterization of the radionuclide behaviour (solubility/speciation, adsorption) in cementitious materials needs to be done for several chemical degradation states (I to IV). In particular, in the context of the deep geological radioactive waste disposal project (Cigéo), cement-based materials will be chemically evolved with time in contact with the host-rock (COx formation). The objective of this study is to provide an equilibrium solution composition for each degradation state for a CEM-V cement-based material to support the adsorption and diffusion experiments reproducing any state of degradation. Calculations have been performed at 25 ºC using the geochemical code PhreeqC and an up-to-date thermodynamic database (ThermoChimie v.9.0.b) coupled to SIT approach for ionic strength correction. The model replicates experimental data with accuracy. The approach followed in this study eases the analysis of the chemical evolution in both aqueous and solid phase to obtain a fast assessment of the geochemical effects associated to an external water intrusion of variable composition on concrete structures.

      PubDate: 2017-05-08T04:45:44Z
      DOI: 10.1016/j.pce.2017.05.008
       
  • Adsorption of gluconate and uranyl on C-S-H phases: Combination of wet
           chemistry experiments and molecular dynamics simulations for the binary
           systems
    • Authors: Iuliia Androniuk; Catherine Landesman; Pierre Henocq; Andrey G. Kalinichev
      Abstract: Publication date: Available online 4 May 2017
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Iuliia Androniuk, Catherine Landesman, Pierre Henocq, Andrey G. Kalinichev
      As a first step in developing better molecular scale understanding of the effects of organic additives on the adsorption and mobility of radionuclides in cement under conditions of geological nuclear waste repositories, two complementary approaches, wet chemistry experiments and molecular dynamics (MD) computer simulations, were applied to study the sorption behaviour of two simple model systems: gluconate and uranyl on calcium silicate hydrate phases (C-S-H) – the principal mineral component of hardened cement paste (HCP). Experimental data on sorption and desorption kinetics and isotherms of adsorption for gluconate/C-S-H and U(VI)/C-S-H binary systems were collected and quantitatively analysed for C-S-H samples synthesized with various Ca/Si ratios (0.83, 1.0, 1.4) corresponding to various stages of HCP aging and degradation. Gluconate labelled with 14C isotope was used in order to improve the sensitivity of analytical detection technique (LSC) at particularly low concentrations (10−8–10−5 mol/L). There is a noticeable effect of Ca/Si ratio on the gluconate sorption on C-S-H, with stronger sorption at higher Ca/Si ratios. Sorption of organic anions on C-S-H is mediated by the presence of Ca2+ at the interface and strongly depends on the surface charge and Ca2+ concentration. In parallel, classical MD simulations of the same model systems were performed in order to identify specific surface sorption sites most actively involved in the sorption of gluconate and uranyl on C-S-H and to clarify molecular mechanisms of adsorption.

      PubDate: 2017-05-08T04:45:44Z
      DOI: 10.1016/j.pce.2017.05.005
       
  • Ecological security assessment based on ecological footprint approach in
           Beijing-Tianjin-Hebei region, China
    • Authors: Xi Chu; Xiangzheng Deng; Gui Jin; Zhan Wang; Zhaohua Li
      Abstract: Publication date: Available online 4 May 2017
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Xi Chu, Xiangzheng Deng, Gui Jin, Zhan Wang, Zhaohua Li
      Recently, researcher have been extensively using ecological footprint to quantitatively measure human pressure on ecosystems. This paper put forward ecological tension index (ETI), ecological occupancy index (EOI) and ecological economic coordination index (EECI) to evaluate ecological security of the Beijing-Tianjin-Hebei (BTH) region between 1995 and 2010. The results came as follows. (1) The ecological footprint of BTH region was increased, while the carrying capacity (biocapacity) of the terrestrial ecosystem was decreased. This led the region to a serious ecological deficit that was increased by 1.77 times. (2) ETI level of the region was found very risky. EOI level fluctuated from poor to moderately poor, indicating that rapid economic development has pressurized the ecosystem. EECI level indicated a very poor coordination between economic development and ecosystem conservation. (3) As to the indices results for sub-regions, ETI level in Tianjin was evaluated very risky, in Beijing it was changed from risky to very risky, while in Hebei it was changed from very risky to risky. EOI level in Beijing was changed from moderately poor to poor, keeping poor for long time. However, the EOI level in Tianjin and Hebei was found opposite to Beijing. It was changed from poor to moderately poor. While EECI level of Beijing, Tianjin and Hebei was found very poor, meaning economic development and ecosystem conservation are maintained imbalanced. This study finally concludes that whether the whole region or the sub-regions, their existing development patterns were unsustainable, and ecological security situation was serious.

      PubDate: 2017-05-08T04:45:44Z
      DOI: 10.1016/j.pce.2017.05.001
       
  • Factors influencing sustainability of communally-managed water facilities
           in rural areas of Zimbabwe
    • Authors: T. Kativhu; D. Mazvimavi; D. Tevera; I. Nhapi
      Abstract: Publication date: Available online 29 April 2017
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): T. Kativhu, D. Mazvimavi, D. Tevera, I. Nhapi
      Sustainability of point water facilities is a major development challenge in many rural settings of developing countries not sparing those in the Sub-Saharan Africa region. This study was done in Zimbabwe to investigate the factors influencing sustainability of rural water supply systems. A total of 399 water points were studied in Nyanga, Chivi and Gwanda districts. Data was collected using a questionnaire, observation checklist and key informant interview guide. Multi-Criteria analysis was used to assess the sustainability of water points and inferential statistical analysis such as Chi square tests and Analysis of Variance (ANOVA) were used to determine if there were significant differences on selected variables across districts and types of lifting devices used in the study area. The thematic approach was used to analyze qualitative data. Results show that most water points were not functional and only 17% across the districts were found to be sustainable. A fusion of social, technical, financial, environmental and institutional factors was found to be influencing sustainability. On technical factors the ANOVA results show that the type of lifting device fitted at a water point significantly influences sustainability (F=37.4, p< 0.01). Availability of spare parts at community level was found to be determining the downtime period of different lifting devices in the studied wards. Absence of user committees was found to be central in influencing sustainability as water points that did not have user committees were not sustainable and most of them were not functional during the time of the survey. Active participation by communities at the planning stage of water projects was also found to be critical for sustainability although field results showed passive participation by communities at this critical project stage. Financial factors of adequacy of financial contributions and establishment of operation and maintenance funds were also found to be of great importance in sustaining water supply systems. It is recommended that all factors should be considered when assessing sustainability since they are interrelated.

      PubDate: 2017-05-02T04:14:40Z
      DOI: 10.1016/j.pce.2017.04.009
       
  • Dispersion of inorganic contaminants in surface water in the vicinity of
           Potchefstroom
    • Authors: A. Manyatshe; E. Fosso-Kankeu; D. van der Berg; N. Lemmer; F. Waanders; H. Tutu
      Abstract: Publication date: Available online 27 April 2017
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): A. Manyatshe, E. Fosso-Kankeu, D. van der Berg, N. Lemmer, F. Waanders, H. Tutu
      Potchefstroom and the neighbouring cities rely mostly on the Mooi River and Vaal River for their water needs. These rivers flow through the gold mining areas and farms, and are therefore likely to be contaminated with substantial amounts of inorganic pollutants. Water was collected along the rivers network, streams, canals and dams in Potchefstroom and the vicinity. The samples were characterized for geochemical parameters, metals and anions concentrations. The results showed high concentrations of potentially toxic elements such as As (4.53 mg/L – 5.74 mg/L), Cd (0.25 mg/L – 0.7 mg/L), Pb (1.14 mg/L – 5.13 mg/L) and U (0.04 mg/L – 0.11 mg/L) which were predominantly found around the mining areas. Elevated concentrations of anions such SO4 2- and CN- were detected around mining areas while NO3 - was dominant near farms. The relatively high levels of anions and metals in the surface water made it unfit for domestic or agricultural use. The study showed that contaminants in mining and agricultural facilities were potentially mobilised, thus impacting the nearby water systems.

      PubDate: 2017-05-02T04:14:40Z
      DOI: 10.1016/j.pce.2017.04.008
       
  • Short-term effects of tidal flooding on soil nitrogen mineralization in a
           Chinese tidal salt marsh
    • Authors: Haifeng Gao; Junhong Bai; Xiaoya Deng; Qiongqiong Lu; Xiaofei Ye
      Abstract: Publication date: Available online 26 April 2017
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Haifeng Gao, Junhong Bai, Xiaoya Deng, Qiongqiong Lu, Xiaofei Ye
      Tidal flooding is an important control of nitrogen biogeochemistry in wetland ecosystems of Yellow River Delta, China. Variations in hydrology could change soil redox dynamics and conditions for microorganisms living. A tidal simulation experiment was designed to extract tidal flooding effect on nitrogen mineralization of salt marsh soil. Inorganic nitrogen and relevant enzyme were measured during the 20-day incubation period. Considering the variation of both inorganic N and enzymes, nitrogen mineralization process in tidal salt marsh could be divided into 2 phases of short term response and longtime adaption by around 12th incubation day as the inflection point. Soil ammonium nitrogen (NH4 +-N) and volatilized ammonia (NH3) occupied the mineralization process since nitrate nitrogen (NO3 --N) was not detected over whole incubation period. NH4 +-N varied fluctuant and increased significantly after 12 day’s incubation. Released NH3 reached to peak value of 14.24 mg m-2 d-1 at the inflection point and declined thereafter. Inorganic nitrogen released according to net nitrogen mineralization rate (RM) under the tidal flooding condition without plant uptake except first 2 days. However, during the transitional period of 6 to 12 days, RM decreased notably to almost 0 and increased again after inflection point with the value of 0.182 mg kg-1 d-1. It might be due to the change of microbial composition and function when soil shifted from oxic to anoxic, which were reflected by arylamidase, urease and fluorescein diacetate. Fluorescein diacetate hydrolysis and arylamidase had the similar variation of U style with decreasing activities before 12 days’ incubation. All the enzymes measured in this experiment increased after inflection point. Whereas, urease activity kept constant from 2 to 12 days. Alternant oxidation reduction condition would increase N loss through denitrification and ammonia volatilization during the transitional period, while more inorganic nitrogen would be available in reductive environment of long-term tidal flooding. Therefore, hydrological process regulation has great influence on nitrogen cycling and further influence on wetland productivity.

      PubDate: 2017-05-02T04:14:40Z
      DOI: 10.1016/j.pce.2017.04.002
       
  • Soil carbon, nitrogen, and phosphorus stoichiometry of three dominant
           plant communities distributed along a small-scale elevation gradient in
           the East Dongting Lake
    • Authors: Cong Hu; Feng Li; Yong-hong Xie; Zheng-miao Deng; Xin-sheng Chen
      Abstract: Publication date: Available online 4 April 2017
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Cong Hu, Feng Li, Yong-hong Xie, Zheng-miao Deng, Xin-sheng Chen
      Soil carbon (C), nitrogen (N), and phosphorus (P) stoichiometry greatly affects plant community succession and structure. However, few studies have examined the soil stoichiometric changes in different vegetation communities of freshwater wetland ecosystems along an elevation gradient distribution. In the present study, soil nutrient concentrations (C, N, and P), soil stoichiometry (C:N, C:P, and N:P ratios), and other soil physicochemical characteristics were measured and analyzed in 62 soil samples collected from three dominant plant communities (Carex brevicuspis, Artemisia selengensis, and Miscanthus sacchariflorus) in the East Dongting Lake wetlands. The concentration ranges of soil organic carbon (SOC), total soil nitrogen (TN), and total soil phosphorus (TP) were 9.42–45.97 g/kg, 1.09–5.50 g/kg, and 0.60–1.70 g/kg, respectively. SOC and TN concentrations were the highest in soil from the C. brevicuspis community (27.48 g/kg and 2.78 g/kg, respectively) and the lowest in soil from the A. selengensis community (17.97 g/kg and 1.71 g/kg, respectively). However, the highest and lowest TP concentrations were detected in soil from the A. selengensis (1.03 g/kg) and M. sacchariflorus (0.89 g/kg) communities, respectively, and the C:N ratios were the highest and lowest in soil from the M. sacchariflorus (12.72) and A. selengensis (12.01) communities, respectively. C:P and N:P ratios were the highest in soil from the C. brevicuspis community (72.77 and 6.46, respectively) and the lowest in soil from the A. selengensis community (45.52 and 3.76, respectively). Correlation analyses confirmed that SOC concentrations were positively correlated with TN and TP, and C:N and N:P ratios were positively correlated with C:P. These data indicated that soil C, N, and P stoichiometry differed significantly among different plant communities and that these differences might be accounted for by variations in the hydrological conditions of the three communities.

      PubDate: 2017-04-11T02:34:06Z
      DOI: 10.1016/j.pce.2017.04.001
       
  • Vertical distribution of mercury and MeHg in Nandagang and Beidagang
           wetlands: Influence of microtopography
    • Authors: Ruhai Liu; Yanyan Zhang; Yan Wang; Jin Zhao; Huayao Shan
      Abstract: Publication date: Available online 4 April 2017
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Ruhai Liu, Yanyan Zhang, Yan Wang, Jin Zhao, Huayao Shan
      Wetlands often show different small-scale topography, such as riffle, habitat island, deep water, shallow water zone and dry zone. Core soils in different micro topographical landforms of Nandagang and Beidagang wetlands in North China were sampled for THg and MeHg to analyze the influence of microtopography. Results showed that THg content in surface soil (<2 cm) was little higher than that at depth 2–4 cm of all stations. There were several peaks in the profile, which reflected mercury pollution in past. High THg content in undisturbed natural wetland soil implied accumulation of mercury. Harvest of plant, drained water decreased the accumulation of mercury in wetlands. Water level caused by microtopography affected the production of MeHg. Depth of the highest MeHg content decreased from N1, N2, N6, N3 to N4 following the increase of water level. Plant type and coverage also affected the vertical distribution of MeHg. More detailed profiles of MeHg, organic matter and total phosphorus in different sites show strong differences in soil chemistry, suggesting a complex interplay among hydrology, biogeochemistry and microtopography.

      PubDate: 2017-04-11T02:34:06Z
      DOI: 10.1016/j.pce.2017.04.003
       
  • Effects of soil abiotic factors on the plant morphology in an intertidal
           salt marsh, Yellow River Delta, China
    • Authors: Shanze Li; Baoshan Cui; Junhong Bai; Tian Xie; Jiaguo Yan; Qing Wang; Shuyan Zhang
      Abstract: Publication date: Available online 4 April 2017
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Shanze Li, Baoshan Cui, Junhong Bai, Tian Xie, Jiaguo Yan, Qing Wang, Shuyan Zhang
      Plant morphology plays important role in studying biogeography in many ecosystems. Suadea salsa, as a native plant community of northern China and an important habitat for diversity of waterbirds and macrobenthos, has often been overlooked. Nowadays, S. salsa community is facing great loss due to coastal reclamation activities and natural disturbances. To maintain and restore S. salsa community, it's important to address the plant morphology across marsh zones, as well as its relationships with local soil abiotic conditions. In our studied intertidal salt marsh, we found that less flood disturbance frequency, softer soil conditions, rich soil organic matter, total carbon and total nitrogen, lower water depth and water content, less species competition will benefit S. salsa plant in the morphology of high coverage, above-ground biomass, shoot height and leaf length. Lower soil porewater salinity will benefit the below-ground biomass of S. salsa. Thus, we recommend managers help alleviate soil abiotic stresses in the intertidal salt marshes, making the soil conditions more suitable for S. salsa growth and succession.

      PubDate: 2017-04-11T02:34:06Z
      DOI: 10.1016/j.pce.2017.04.004
       
  • Impacts of water scarcity on social economic development: A case study of
           Gaotai County, China
    • Authors: Qing Zhou; Xiangzheng Deng; Feng Wu
      Abstract: Publication date: Available online 3 April 2017
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Qing Zhou, Xiangzheng Deng, Feng Wu
      Provisioning services for socio-economic development is an important hydrological ecosystem services human obtains from freshwater. The dilemma between water scarcity and economic development in arid regions influence water utilization among different sectors. A water resource embedded Social Accounting Matrix (WSAM) helps to analyze the interrelation between water resource utilization and social economic development. In this paper, by establishing the WSAM and applying SAM multiplier and decomposition analysis in Gaotai County northwestern China to explore the economic structure and the feedback mechanism and water flows among different sectors, we found that though agriculture is less productive than the second industry due to its low development stage and lack of deep processing chain, as the dominated sector, it still plays the most important part in the whole national economy in the study area. Considering the strategic location of Gaotai county, which is an important hub in the One Belt and One Road economic zone, different economic development scenarios were modeled. Analysis shows that expanding agricultural exports can promote rural employment and improve rural household welfare, but will also lead to water resources outflow and aggravate the water conflicts among different water users. In order to simulate the water price reform effects, the price multiplier was calculated to measure the social economic effects of the irrigation water price reform on the whole economic system. Results indicate that the price of agriculture products, industrial products, and price of labour will increase by 0.03, 0.018 and 0.005 units respectively when water price increase by one unit. And the Consumer Price Index (CPI) will increase by 0.005 units.

      PubDate: 2017-04-11T02:34:06Z
      DOI: 10.1016/j.pce.2017.03.009
       
  • Soft X-ray absorption near-edge investigations of Mg-containing mineral
           phases relevant for cementitious materials
    • Authors: M. Vespa; R. Dähn; T. Huthwelker; E. Wieland
      Abstract: Publication date: Available online 18 March 2017
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): M. Vespa, R. Dähn, T. Huthwelker, E. Wieland


      PubDate: 2017-04-11T02:34:06Z
      DOI: 10.1016/j.pce.2017.03.006
       
  • Interaction processes at the concrete-bentonite interface after 13 years
           of FEBEX-Plug operation. Part I: Concrete alteration
    • Authors: María Cruz Alonso; José Luis García Calvo; Jaime Cuevas; María Jesús Turrero; Raúl Fernández; Elena Torres; Ana I. Ruiz
      Abstract: Publication date: Available online 14 March 2017
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): María Cruz Alonso, José Luis García Calvo, Jaime Cuevas, María Jesús Turrero, Raúl Fernández, Elena Torres, Ana I. Ruiz
      This paper evaluates the modifications created in the concrete of the FEBEX shotcreted concrete plug after 13 years in the Grimsel Test Site conditions. During this time the concrete interacted with granite groundwater and also with bentonite porewater at the concrete/bentonite contact. Three long cores and 6 small cores from different parts of the concrete plug were evaluated. Mechanical performance was not modified during this time but hydraulic conductivity increased. The main transport mechanisms involved in the alteration of the concrete were groundwater flow from the host rock to the concrete and diffusion at the concrete/bentonite interface. Leaching occurred in the concrete parts near the host rock due to the action of granite water with further portlandite dissolution. The joint action of granite groundwater and bentonite porewater has caused many changes to the concrete matrix which was located at a depth lower than 5 cm from the bentonite-concrete interface. In the first centimetre C-S-H was significantly altered, incorporating elements like Al, S and Mg which change the initial microstructure by loss of compactness. The ettringite content was very high along the length of the concrete plug due to the shotcreting technique which made use of accelerator additives that caused the formation of ettringite. An increase in the ettringite content is also shown near the bentonite barrier. Therefore, sulphate diffused from the bentonite into the concrete, causing the massive formation of new ettringite. Chloride also diffused from the bentonite barrier deeper into the concrete by up to 4–5 cm from where the formation of Friedel's salt was detected.

      PubDate: 2017-04-11T02:34:06Z
      DOI: 10.1016/j.pce.2017.03.008
       
  • Effects of calcium leaching on diffusion properties of hardened and
           altered cement pastes
    • Authors: Kiyofumi Kurumisawa; Kazuko Haga; Daisuke Hayashi; Hitoshi Owada
      Abstract: Publication date: Available online 14 March 2017
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Kiyofumi Kurumisawa, Kazuko Haga, Daisuke Hayashi, Hitoshi Owada
      It is very important to predict alterations in the concrete used for fabricating disposal containers for radioactive waste. Therefore, it is necessary to understand the alteration of cementitious materials caused by calcium leaching when they are in contact with ground water in the long term. To evaluate the long-term transport characteristics of cementitious materials, the microstructural behavior of these materials should be considered. However, many predictive models of transport characteristics focus on the pore structure, while only few such models consider both, the spatial distribution of calcium silicate hydrate (C-S-H), portlandite, and the pore spaces. This study focused on the spatial distribution of these cement phases. The auto-correlation function of each phase of cementitious materials was calculated from two-dimensional backscattered electron imaging, and the three-dimensional spatial image of the cementitious material was produced using these auto-correlation functions. An attempt was made to estimate the diffusion coefficient of chloride from the three-dimensional spatial image. The estimated diffusion coefficient of the altered sample from the three-dimensional spatial image was found to be comparable to the measured value. This demonstrated that it is possible to predict the diffusion coefficient of the altered cement paste by using the proposed model.

      PubDate: 2017-04-11T02:34:06Z
      DOI: 10.1016/j.pce.2017.03.007
       
  • Zeolite formation in the presence of cement hydrates and albite
    • Authors: Barbara Lothenbach; Ellina Bernard; Urs Mäder
      Abstract: Publication date: Available online 21 February 2017
      Source:Physics and Chemistry of the Earth, Parts A/B/C
      Author(s): Barbara Lothenbach, Ellina Bernard, Urs Mäder
      Zeolite formation caused by interactions between cement hydrates and rock forming minerals was investigated by two sets of batch experiments and supported by thermodynamic modelling. The first set of batch experiments investigated the interaction between calcium silicate hydrates (C-S-H) (Ca0.8SiO2.8·32H2O) and ettringite (Ca6Al2(SO4)3(OH)12(H2O)26) as cement hydrate minerals and albite (NaAlSi3O8) as a rock forming mineral at 20, 50 and 80°C. The dissolution of C-S-H, ettringite and albite led to relatively high calcium and low silicon and sodium concentrations and to the formation of zeolite P(Ca) (Ca2Al2Si2O8·4.5H2O) and natrolite (Na2Al2Si3O10·2H2O). The second set of experiments used ettringite and silica fume as cement phases and NaAlO2 to represent a rock forming mineral. High initial sodium, hydroxide and aluminium concentrations were observed leading to the precipitation of zeolite X (Na2Al2Si2.5O9·6.2H2O) and C-S-H gel at 20 and 50°C where only 40 to 60% of the silica had reacted after 3 years. At 80°C where more silica fume had reacted, the formation of SiO2-rich zeolite Y (Na2Al2Si4O12·8H2O) and chabazite (CaAl2Si4O12·6H2O) was observed. Solubility products for the zeolite P(Ca), natrolite, chabazite, zeolite X and zeolite Y were obtained from the measured concentrations. Comparison with values published in the literature shows a high variability due to the flexibility of the Si to Al ratio in zeolite structures and underlines the need for systematic experimental determination of the solubility of different zeolites.

      PubDate: 2017-02-22T20:52:05Z
      DOI: 10.1016/j.pce.2017.02.006
       
 
 
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