研究者データベース

エラクネス ヨガラジャ(エラクネス ヨガラジヤ)
工学研究院 環境循環システム部門 資源循環工学分野
准教授

基本情報

所属

  • 工学研究院 環境循環システム部門 資源循環工学分野

職名

  • 准教授

学位

  • 学士(モラトゥワ大学、スリランカ)
  • 修士(北海道大学)
  • 博士(北海道大学)

ホームページURL

J-Global ID

研究キーワード

  • Surface chemistry   multi species transport   EOR   durability   Cement chemistry   

研究分野

  • 環境・農学 / 環境負荷低減技術、保全修復技術
  • 社会基盤(土木・建築・防災) / 土木環境システム

担当教育組織

研究活動情報

論文

  • Siventhirarajah Krishnya, Kirushnapillai Kopitha, Yuya Yoda, Ryoma Kitagaki, Yogarajah Elakneswaran
    Cement and Concrete Composites 146 2024年02月 
    This study established a new transport model by using the COMSOL-IPHREEQC interface to simulate the changes in the morphology of hydrated cement paste due to the diffusion of carbon dioxide and chloride ion. A series of constitutive models such as the cement hydration model (to compute the dissolution rate of each clinker mineral), thermodynamic model (to perform the hydration reaction, reaction due to transport of ions, chemical and physical adsorption of chloride ion during the chloride ion ingression and dissolution rate of calcium-silica-hydrate (C–S–H) simultaneously with portlandite for the carbonation), porosity determination, and COMSOL Multiphysics (for the calculation of transport problems) were integrated using MATLAB language to determine the pore solution chemistry, hydrates assemblage, and porosity of the cement paste exposed to aggressive environments. During the diffusion of carbon dioxide gas, the decalcification of C–S–H was realistically considered by assuming that the Ca/Si ratio of C–S–H decreased from 1.67 (Jennite type C–S–H) to 0.67 (Tobermorite C–S–H), and then from 0.67 to 0 (silica gel). The proposed integrated platform was well verified with different sets of reported and raw experimental results and existing models, indicating a realistic predictability for chloride ion ingression and carbonation. The developed model discloses the effect of coupling the progression of hydration with reaction due to the transport of ions by using the free chloride ion profile and phase assemblages during the chloride ion ingression.
  • Xiaobo Niu, Yogarajah Elakneswaran, Raudhatul Islam Chaerun, Chuwei Fang, Naoki Hiroyoshi, John L. Provis, Tsutomu Sato
    Separation and Purification Technology 324 124530 - 124530 2023年11月
  • Kirushnapillai Kopitha, Yogarajah Elakneswaran, Ryoma Kitagaki, Ryosuke Saito, Masato Tsujino, Akira Nishida, Hisanori Senboku, Naoki Hiroyoshi
    Chemical Engineering Journal 475 146067 - 146067 2023年11月
  • Yongqiang Chen, Javad Shokri, Vahid Niasar, Mohamed Mehana, Colin D. Wood, Yogarajah Elakneswaran, Juju Zhao
    Journal of Molecular Liquids 390 123142 - 123142 2023年11月
  • Xingjuan Hao, Yogarajah Elakneswaran, Sadia Afrin, Mai Shimokawara, Yoshitake Kato, Ryuta Kitamura, Naoki Hiroyoshi
    Geoenergy Science and Engineering 227 211905 - 211905 2023年08月
  • Takunda Joseph Mhandu, Ilhwan Park, Sanghee Jeon, Sohta Hamatsu, Yogarajah Elakneswaran, Mayumi Ito, Naoki Hiroyoshi
    Metals 13 8 1357 - 1357 2023年07月28日 
    The use of thiosulfate to extract gold from refractory ores is promising because of its non-toxicity and high selectivity. Sulfide minerals (i.e., pyrite, arsenopyrite, chalcopyrite), major gold carriers in refractory gold ores, however, hinder gold extraction due to the high consumption of a lixiviant. In this study, a new method to improve gold extraction from sulfide bearing gold ores is proposed based on the model experiments using a mixture of gold powder and arsenopyrite-bearing sulfide (HAsBS) ore. The effects of HAsBS ore on gold leaching in ammonium thiosulfate solutions were investigated, and it was found that gold extraction in the presence of HAsBS ore was suppressed because of the unwanted decomposition of thiosulfate on the surface of sulfide minerals. To improve gold extraction in the presence of the sulfide minerals, this study investigated the effects of the pretreatment of HAsBS ore using ammonium solutions containing cupric ions and confirmed that HAsBS ore was oxidized in the pretreatment and its surface was covered by the oxidation products. As a result, thiosulfate consumption was minimized in the subsequent gold leaching step using ammonium thiosulfate, resulting in an improvement in gold extraction from 10% to 79%.
  • Joshua Zoleta, Sanghee Jeon, Akuru Kuze, Nako Okada, Ilhwan Park, Mayumi Ito, Yogarajah Elakneswaran, Naoki Hiroyoshi
    Metals 13 7 1289 - 1289 2023年07月18日 
    Ammonium thiosulfate leaching is a promising alternative to the conventional cyanide method for extracting gold from ores. However, strategies for recovering gold from the leachate are less commercially used due to its low affinity to gold. The present study investigated the recovery of gold from the leachate using iron oxides (hematite, Fe2O3 or magnetite, Fe3O4). Cementation experiments were conducted by mixing 0.15 g of aluminum powder as an electron donor and 0.15 g of an electron mediator (activated carbon, hematite, or magnetite) in 10 mL of ammonium thiosulfate leachate containing 100 mg/L gold ions and 10 mM cupric ions for 24 h at 25 °C. The results of the solution analysis showed that when activated carbon (AC) was used, the gold was recovered together with copper (recoveries were 99.99% for gold and copper). However, selective gold recovery was observed when iron oxides were used, where the gold and copper recoveries were 89.7% and 21% for hematite and 85.9% and 15.4% for magnetite, respectively. An electrochemical experiment was also conducted to determine the galvanic interaction between the electron donor and electron mediator in a conventional electrochemical setup (hematite/magnetite–Al as the working electrode, Pt as the counter electrode, Ag/AgCl as the reference electrode) in a gold–thiosulfate medium. Cyclic voltammetry showed a gold reduction “shoulder-like” peak at −1.0 V using hematite/Al and magnetite/Al electrodes. Chronoamperometry was conducted and operated at a constant voltage (−1.0 V) determined during cyclic voltammetry and further analyzed using SEM-EDX. The results of the SEM-EDX analysis for the cementation products and electrochemical experiments confirmed that the gold was selectively deposited on the iron oxide surface as an electron mediator.
  • Madhan Nur Agista, Mahmoud Khalifeh, Arild Saasen, Elakneswaran Yogarajah
    SPE Journal 1 - 13 2023年07月01日 
    Summary Shallow-depth cementing presents unique challenges due to its low temperature and low pore pressure characteristic. The curing process of the cementitious material is typically prolonged at low temperatures resulting in a delayed curing process. The use of a low-density slurry to mitigate low pore pressure introduces another challenge, as it leads to a reduction in the final compressive strength. On the other hand, the operation requires the material to develop enough strength swiftly to be able to efficiently continue the next drilling operation. In addition, the presence of flow zones such as shallow gas and shallow water flow increases the complexity of the cementing process. There have been many developments in cementitious materials for shallow-depth cementing such as rapid-hardening cement and gas tight cement. However, there is little research focusing on the performance evaluation of each material at low-temperature conditions. This paper aims to present a thorough material evaluation for low-temperature shallow-depth cementing. The incorporated materials are American Petroleum Institute (API) Class G cement, rapid-hardening cement, gas tight cement, and geopolymer. Geopolymer is included to evaluate its potential as the green alternative to Portland-based cement. The sets of characterization were conducted during the liquid, gel, and solid phases. The samples were prepared under wide-ranging low temperatures and typical bottomhole pressures for shallow sections. The result shows different performances of each material and its behavior under low temperatures such as prolonged strength development and low reactivity, which necessitates further development of these materials.
  • Mylvaganam Nithurshan, Yogarajah Elakneswaran
    Case Studies in Construction Materials 18 e01830 - e01830 2023年07月
  • Takato Ishida, Ryoma Kitagaki, Yogarajah Elakneswaran, Junji Mizukado, Hideyuki Shinzawa, Hiroaki Sato, Hideaki Hagihara, Ryota Watanabe
    Macromolecules 56 3 883 - 891 2023年01月18日 
    To study the degradation of thermosetting polymers, we apply a novel method to simultaneously study the chemical structural changes and network topology: evolved gas analysis-mass spectrometry combined with principal component analysis (EGA-MS-PCA). This technique was applied to thermo-oxidative aging of an epoxy/amine network. The signals of various pyrolyzates remain overlapped in the complicated EGA-MS profiles. The key fragments of thermally evolved gases derived from the components of the network are effectively selected by PCA from the complicated EGA-MS profiles. EGA-MS-PCA provides information on the network structure: (i) the oxidized fraction of cross-links (i.e., chemically damaged cross-links), (ii) the relative quantification of unbonded chains, and (iii) the formation of dangling chains. The proposed technique can simultaneously characterize chemical degradation and network structural properties. This characterization technique can be utilized as a generally applicable tool for determining the structural durability of thermosetting polymers.
  • Siventhirarajah Krishnya, Yogarajah Elakneswaran, Yuya Yoda, Ryoma Kitagaki
    RILEM Bookseries 43 686 - 696 2023年 
    The prediction of chloride ingression in cement-based material has gained a great deal of interest among researchers as it causes long-term structural damage in buildings by chloride-induced reinforcement corrosion. The Cl− diffusion in mortar is influenced by internal factors including pore-structure and hydrates which are determined by clinker properties, mixture recipe, and curing conditions and exposure conditions. The Cl− penetration in mortar leads to the modification of the microstructure and pore-solution due to the disequilibrium of the hydrates-pore solution system. Considering the complexity of the process by incorporating all aforementioned factors and interaction of Cl− with hydrates, a new model is herein proposed for predicting the microstructure of the mortar during the Cl− diffusion. In this work, the microstructure of mortar is considered as a three-phase material: aggregates, interfacial transition zone (ITZ) and bulk paste, and ITZ is realistically considered as high W/C paste compared to the initial W/C. The developed COMSOL-IPHREEQC model involves hydration model for calculating the dissolution of clinker in bulk paste and ITZ, thermodynamic model including the surface complexation model to predict the hydrates and the Cl− adsorption by hydrates, homogenization approach to compute the average hydrates, porosity, pore solution composition and diffusion parameters of the mortar and COMSOL Multiphysics to perform the transportation calculation. The predicted results are validated with experimental results available in the literatures to verify the reliability of the proposed model. The effect of ITZ on the penetration of Cl− is also assessed in this work.
  • Chuang Li, Siventhirarajah Krishnya, Masataka Ogino, Eiji Owaki, Yogarajah Elakneswaran
    Construction and Building Materials 361 129629 - 129629 2022年12月
  • Angelo Kennedy Lino Limaluka, Yogarajah Elakneswaran
    Day 4 Thu, November 03, 2022 2022年10月31日 
    Abstract Chemical enhanced oil recovery (CEOR) techniques are some of the most effective and economical tertiary oil extraction processes. As a key tool for the recovery performance evaluation, reservoir simulation plays an instrumental role in the expansion of the field application of CEOR. However, their framework models essentially the physical aspect of the recovery process. The significant influence of geochemical interactions on the recovery performance remains largely unintegrated. In this study, MATLAB Reservoir Simulation Toolbox (MRST) was coupled with PHREEQC for improved modeling and simulation of polymer flooding and low salinity water flooding (LSWF). The MRST’s polymer model was extended for multi-phase chemical transport by the addition of chemical species in wells boundary conditions, and phase relative permeabilities were modified to account for the wettability alteration effect of the flooding process. In validation, the coupled model showed a good match against PHREEQC in a simulation of a single-phase carbonate core low salinity water flooding (LSWF). It also validated well in the case of matching high salinity experimental results. A demonstrative application of the coupled model in the simulation of LSWF showed 27% maximum incremental oil recovery with a 3.3 mean water-oil ratio (WOR). Furthermore, combining LSWF with polymer flooding achieved the same recovery potential but with much lower water production (0.2 WOR) and doubled production period. These results preliminarily indicate that polymer flooding and LSWF could be combined for at least 27% additional original oil in place (OOIP) recovery with no more than 1 WOR in carbonate reservoirs. However, as this recovery performance evaluation was done in 1D, further work on the coupled model includes improving it for multi-dimensional application.
  • Raudhatul Islam Chaerun, Natatsawas Soonthornwiphat, Kanako Toda, Kazuma Kuroda, Xiaobo Niu, Ryosuke Kikuchi, Tsubasa Otake, Yogarajah Elakneswaran, John L. Provis, Tsutomu Sato
    Journal of Hazardous Materials 440 129732 - 129732 2022年10月
  • Takato Ishida, Ryota Watanabe, Hideyuki Shinzawa, Junji Mizukado, Hideaki Hagihara, Ryoma Kitagaki, Yogarajah Elakneswaran
    Polymer Testing 112 107587 - 107587 2022年08月 
    A novel technique, in-situ infrared (IR) cure monitoring coupled with two-trace two-dimensional (2T2D) correlation analysis, is developed to probe the property-enhancement mechanism of a newly developed thermosetting nanocomposite comprising an acrylic-urethane network (AUN) and silica nanospheres (SNS). The IR spectra were collected in real-time during the curing process at 100 degrees C. We employ the 2T2D correlation analysis to identify the spectral variations of the interfacial interaction. The curing reaction initially proceeds throughout the sample solution. After the network percolation, the unreacted sites react near the SNS surface and yield additional hydrogen-bonded C = O groups that interact with the surface silanol groups. The matrix-filler interactions play a key role in enhancing the hardness and thermal stability of the AUN/SNS nanocomposites by restricting the mobility of the polymer molecules. The proposed technique provides sequential mechanisms in the curing process and a picture of the interfacial interaction for the thermosetting nanocomposite system.
  • Xiaobo Niu, Yogarajah Elakneswaran, Chaerun Raudhatul Islam, John L. Provis, Tsutomu Sato
    Journal of Hazardous Materials 429 128373 - 128373 2022年05月
  • Xingjuan Hao, Moataz Abu-Al-Saud, Subhash Ayirala, Yogarajah Elakneswaran
    Day 3 Wed, April 27, 2022 2022年04月18日 
    Abstract Wettability alteration considered as the principal mechanism has attracted more attention for low salinity waterflooding effect. It was significantly affected by electrokinetic interactions, which occurred at the interfaces of rock/brine and crude oil/brine. The mineral impurities of natural carbonate releasing ions have an important impact on the electrokinetics, which could lead to wettability shift subsequently. In this study, the effect of dolomite and anhydrite as the main impurities in natural carbonate, which caused wettability alteration, was evaluated using triple-layer surface complexation and thermodynamic equilibrium models coupled with extended Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The electrokinetics of crude oil and carbonate in brines were predicted by the triple-layer surface complexation model (TLM) based on zeta potential, while thermodynamic equilibrium model was mainly used for analyzing the carbonate impurities on wettability alteration. The equilibrium constants of reactions were determined by successfully fitting the calculated zeta potentials with measured ones for crude oil and carbonate in different solutions, which were validated for zeta potential prediction in smartwater. The disjoining pressure results show that there is a repulsion between crude oil and carbonate in Na2SO4 brine (Brine3) or smartwater (Brine4) equilibrating with calcite when comparing to that in MgCl2 (Brine1) and CaCl2 (Brine2), indicating the water-wet condition caused by the presence of sulphate ions. Moreover, the equilibrium of carbonate impurities with smartwater increases the repulsion between oil and carbonate. When the sulphate ion concentration in the adjusted smartwater exceeds a certain value, the effect of carbonate impurities on wettability alteration is not significant. Finally, the influence of smartwater pH on the interaction between oil and carbonate was evaluated with or without considering the equilibrium of carbonate impurities.
  • Yogarajah Elakneswaran
    Day 2 Tue, April 26, 2022 2022年04月18日 
    Abstract The wettability alteration is the most prominent mechanism for a favorable effect of low salinity water flooding in enhanced oil recovery. It has been accepted that the surface charge at crude oil/brine and rock/brine interfaces significantly influences the interaction of the crude oil with rock surface and thus wettability changes. In this study, the interface characteristics were coupled with a solute transport model to simulate low salinity waterflooding in carbonate and sandstone reservoirs. The ionic transport and two- phase flow of oil and water equations were solved and coupled with IPhreeqc for geochemical calculations. The dissolution and precipitation of minerals were considered thorough thermodynamic equilibrium reactions in IPhreeqc. In addition, a triple layer surface complexation model was employed in IPhreeqc to predict electrokinetic properties of crude oil/brine and rock/brine interfaces. The wettability alteration was calculated based the adsorbed polar components of crude oil on minerals’ surface, which changes the relative permeability. The coupled model able to predict the spatiotemporal variation of ionic profiles, surface and zeta potentials, dissolution and precipitation of minerals, total disjoining pressure, and wettability index in addition to oil recovery for the injection of brines. The validity of the coupled model results was tested against PHREEQC in a single-phase flow without the presence of oil. Moreover, the modelling results were compared with the published experimental data for a single-phase flow in carbonate cores. A very good agreement between experimental data and modelling results was obtained. Furthermore, the coupled model was applied to predict ionic concentration, pH profile, and oil recovery in both carbonate and sandstone cores and verified with experimental data. The modelling results reproduce well the experimental data, suggesting that model captures the geochemical and interface reactions. Finally, the coupled model can be used to optimize brine composition for improved oil recovery in carbonate and sandstone reservoirs.
  • Yuka Morinaga, Yuya Akao, Daisuke Fukuda, Yogarajah Elakneswaran
    Materials 15 8 2727 - 2727 2022年04月07日 
    Superabsorbent polymers (SAPs) are used as internal curing agents in cementitious materials, which reduce autogenous shrinkage in concrete as they have a low water-to-cement ratios and improve the freeze–thaw resistance. However, the compressive strength of concrete may also be reduced due to additional voids in the hydrated cement matrix. In this study, we fabricated a delayed absorption type of SAP (I-SAP) composed of cross-linked modified acrylate and studied its absorption characteristics and effect on compressive strength after 28 days. Furthermore, the effect of curing conditions on the strength of concrete and hydrated cement paste with SAP were investigated. The absorption capacity of I-SAP in the synthetic pore solution and deionised water was examined and compared with that of a conventional SAP, and the former was absorbed more by I-SAP. The results revealed that the compressive strength of concrete increased with the addition of I-SAP, particularly with the curing condition of 60% RH. Although the compressive strength of hydrated cement paste with I-SAP reduced in water or sealed curing conditions, no loss of strength in the paste cured at 60% RH was seen. The cement matrix densification due to hydration of belite around the SAP surface is the main mechanism for strength development in concrete cured at sealed and 60% RH. However, the voids formed by SAP control the compressive strength of hydrated paste.
  • Takato Ishida, Emmanuel Richaud, Matthieu Gervais, Alain Gaudy, Ryoma Kitagaki, Hideaki Hagihara, Yogarajah Elakneswaran
    Progress in Organic Coatings 163 106654 - 106654 2022年02月 
    This study addresses the multiscale analysis of acrylic urethane networks (AUN). To establish the kinetic model for predicting AUN oxidation, this study considered the pure thermal oxidation of AUN at 160, 180, and 200 degrees C. Chemical changes were monitored using infrared spectroscopy. These indicated the presence of an imide, presumably generated from the oxidation of CH2 at the alpha-position of nitrogen. On the macromolecular and macroscopic scales, oxidation was shown to induce predominant crosslinking, leading to a drop in toughness (i. e., embrittlement). The novel kinetic model of AUN thermal aging was developed from a mechanistic scheme previously established for polyamide 11, by adding some extra paths of thermolytic alkyl radical formation, oxidative N-H bonds decomposition and coupling of aminyl radicals.
  • Siventhirarajah Krishnya, Charith Herath, Yogarajah Elakneswaran, Chamila Gunasekara, David W. Law, Sujeeva Setunge
    Construction and Building Materials 320 126228 - 126228 2022年02月
  • Siventhirarajah Krishnya, Yogarajah Elakneswaran, Yuya Yoda
    Materials Today Communications 29 102858 - 102858 2021年12月
  • Xingjuan Hao, Moataz Abu-Al-Saud, Subhash Ayirala, Yogarajah Elakneswaran
    JOURNAL OF MOLECULAR LIQUIDS 340 2021年10月 
    Low salinity water flooding (LSWF) has been considered as a promising technique for enhanced oil recovery (EOR). The wettability alteration towards a more water-wet state is recognised as the main mechanism for the positive LSWF effect. Electrokinetic interactions occurring at crude oil/brine and rock/brine interfaces affect the wettability alteration. Most of the studies reported in the existing knowledge considered synthetic calcite to understand the electrokinetics of natural carbonate with brines. The mineral impurities present in natural carbonate could influence the electrokinetics and subsequently wettability alteration. In this study, the surface complexation model, thermodynamic equilibrium model, and extended Derjaguin-Landau-Verwey-Overbeek (DLVO) theory were combined to evaluate the effect of impurities (dolomite and anhydrite) in natural carbonate on wettability alteration. The surface complexation modelling parameters were first estimated by fitting the calculated zeta potential to that of measured value in various brines and then validated in smartwater. The thermodynamic equilibrium of impurities is largely insensitive to crude oil/brine interface properties. However, the calculated carbonate/brine surface or zeta potential changed from positive to negative with anhydrite equilibrium in the brines containing Ca2+ or Mg2+ ions. The attractive or repulsive forces between crude oil and carbonate were estimated from disjoining pressure using extended DLVO theory and compared with measured adhesion forces. The computed disjoining pressure was used as an indicator to evaluate wettability alteration. It is found that brine with SO42- ions can result in highest water-wet condition, followed by smartwater (brine with Ca2+, Mg2+, and SO42-) and brine with either Ca2+ ions or Mg2+ ions. The de-ionic (DI) water is unfavourable for wettability alteration. The effect of impurities equilibrium and the crude oil surface site densities on the disjoining pressure were also discussed. (C) 2021 Elsevier B.V. All rights reserved.
  • Satoshi Yoshida, Yogarajah Elakneswaran, Toyoharu Nawa
    Cement and Concrete Composites 121 104109 - 104109 2021年08月 
    The adsorption capacity of cement hydrates considerably affects the ionic ingress into cementitious materials. In this study, the surface electrostatic properties of calcium silicate hydrate (C-S-H) and calcium aluminosilicate hydrate (C-A-S-H) were determined to understand the effects of the properties on calcium and chloride adsorption. The density of the surface functional groups was determined by analysing the structure of C-S-H and CASH through Al-27 and Si-29 MAS NMR. The surface sites of SiOH and AlOH are available in CASH whereas C-S-H has SiOH groups for ionic adsorption. We found that the incorporation of aluminium decreases the number of total adsorption sites in C-A-S-H. Furthermore, the site density increased with Ca/(Si + Al). To understand the C-A-S-H/solution interface, a triple-layer surface complexation model was developed and the associated equilibrium constants for depmtonation, calcium, and chloride adsorption were determined by fitting the experimental data of potentiometric titration and zeta potential measurement results. The estimated surface complexation modelling parameters were verified by predicting the experimental data of calcium and chloride adsorption on C-S-H and C-A-S-H.
  • Natsumi Noguchi, Krishnya Siventhirarajah, Takashi Chabayashi, Hiroyoshi Kato, Toyoharu Nawa, Yogarajah Elakneswaran
    CONSTRUCTION AND BUILDING MATERIALS 288 2021年06月 
    The hydration process in ferrite-rich cement (FC) and its pore structure have been investigated by experimental and thermodynamic modelling techniques. X-ray diffraction (XRD)/Rietveld analysis, thermogravimetry (TG), and mercury intrusion porosimetry (MIP) were performed to study the hydration process, pore volume-pore size distributions, and Fe uptake in calcium-silicate-hydrate (C-S-H). Similar phases were found in both FC and ordinary Portland cement (OPC). The hydration degree of FC was higher at the early stage compared with that of OPC; however, the hydration of OPC exceeded that of FC after 14 days because the high amount of C2S in OPC promoted the late hydration. The XRD-TG results revealed relatively similar Fe uptake by C-S-H in both FC and OPC. The thermodynamic model confirmed the formation of a high amount of Fe phases in FC. Moreover, the model predictions agreed well with the experimental results, demonstrating the accuracy of the proposed model for FC. (C) 2021 Elsevier Ltd. All rights reserved.
  • Takato Ishida, Ryoma Kitagaki, Hideaki Hagihara, Yogarajah Elakneswaran
    Polymer Testing 96 107123 - 107123 2021年04月 
    In this work, the role of moisture in photo-ageing was discussed for the case of an acrylic-urethane network. Ageing behaviours were characterised by Fourier transform infra-red spectroscopy, positron annihilation lifetime spectroscopy, sol-gel analysis, and differential scanning calorimetry. Two common features between dry and wet photo-ageing, namely, decrease in the mean free volume and increase in the glass transition temperature were observed as photo-oxidation progressed. The characteristics of the final internal structure of the wet photo-aged sample differed from those of the dry photo-aged sample. Although the dry photo-aged samples suggested network densification due to extensive crosslinking formation, wet photo-ageing led to an inhomogeneous structure wherein the average molar mass between crosslinks (at a scale of several nanometres) increased and some domains crosslinked at the sub-nanoscale. Considering the physical (plasticisation) and chemical (hydrolysis) effects induced by water, a possible mechanism for the evolution of the macromolecular architecture was proposed for photo-ageing in dry and wet environments.
  • Yogarajah Elakneswaran, Amir Ubaidah, Miku Takeya, Mai Shimokawara, Hirofumi Okano
    ACS OMEGA 6 5 3727 - 3735 2021年02月 
    Wettability alteration (from oil-wet to mixed- or water-wet condition) is the most prominent mechanism in low-salinity water flooding (LSWF) for enhanced oil recovery (EOR) in sandstone reservoirs. Although several factors influence the wettability alteration, many efforts have been made to find the main controlling factor. In this study, the influence of interface properties of sandstone/brine and thermodynamic equilibrium of sandstone minerals were evaluated to understand the wettability alteration during LSWF. A triple-layer surface complexation model built-in PHREEQC was applied to a quartz/brine interface, and the modeling results were verified with zeta potential experimental data. This model was combined with that of kaolinite/brine to predict sandstone/brine interface properties. The measured and predicted sandstone zeta potentials were between those obtained for quartz and kaolinite in the diluted seawater. The predicted surface potential of sandstone together with that of crude oil was used in extended Derjaguin-Landau-Verwey-Overbeek theory to estimate the attractive or repulsive force. Consideration of thermodynamic equilibrium between minerals and solution significantly increased the pH and hence resulted in an increase in negative surface potential in the surface complexation. This provided a strong repulsive force between crude oil and sandstone, thus resulting in a more water-wet condition.
  • Siventhirarajah Krishnya, Yuya Yoda, Yogarajah Elakneswaran
    CEMENT & CONCRETE COMPOSITES 115 2021年01月 
    The mechanical properties such as compressive strength, Young's modulus and Poisson's ratio are the most important parameters for design and structural analysis in the field of Civil Engineering. In hydrated cement paste, these properties are significantly determined by its microstructure. In this research work, a two-stage model is proposed to systematically predict the mechanical properties of the cement paste from the microstructure. In Stage-1, relative humidity, thermodynamic, cement hydration and model for volumetric prediction are integrated to accurately predict the volume fraction of hydration products. Subsequently the Stage-2 proposes a multi-scale model (in three hierarchical levels) initiating from C-S-H matrix considering the formation of two types of C-S-H (low- and high-density C-S-H) to cement paste for the computation of the intrinsic mechanical properties of cement paste. As the volume fraction of C-S-H and capillary porosity are the most significant components which determines the mechanical properties of cement paste, prime consideration herein is given to C-S-H space ratio. The proposed model is well verified at the predictions of relative humidity, chemical shrinkage and capillary porosity in Stage-1; compressive strength, Young's modulus and Poisson's ratio in Stage-2 with independent sets of experimental results.
  • Yogarajah Elakneswaran, Chuang Li, Tomohiro Kajio, Eiji Owaki, Masataka Ogino, Toyoharu Nawa
    MATERIALS AND STRUCTURES 53 6 2020年12月 
    Sulphate ions induce severe chemical deterioration in a cement matrix due to expansive product (e.g. ettringite and gypsum) formation or sodium sulphate crystallization. Considerably high sodium sulphate concentration can cause U-phase [(CaO)(4)(Al2O3)(0.9)(SO3)(1.1)(Na2O)(0.5):16H(2)O] formation, which leads to increased deterioration of the cement matrix after prolonged exposure to service aqueous environments. However, U-phase stability in cementitious materials is not well understood. This study evaluated U-phase formation in hydrated white Portland cement (WPC) and slag-blended WPC (42 and 70% slag ratio) and observed its degradation in water and sodium sulphate and magnesium sulphate solutions. The U-phase was found to coexist with ettringite in WPC and slag-blended WPC when hydrated with 13% Na2SO4 solution, wherein the hydration reaction and slag addition promoted U-phase formation. The U-phase-containing hydrated cement was immersed in Na2SO4 and MgSO4 solutions for 28 days to investigate phase changes. In addition, the hydrated samples were exposed to water, 1300 mmol/L Na2SO4, and 1300 mmol/L MgSO4 for 1 year to determine the changes in spatial mineralogical distribution. Ettringite formed due to the reactions between sulphate and cement hydrates as well as U-phase destabilisation. This ettringite formation was found to be the primary degradation mechanism in hydrated cement exposed to water and Na2SO4. However, MgSO4 degradation was attributed to gypsum formation. By replacing a proportion of the cement with slag in the slag-blended cement, the material exhibited a very high resistance to external Na2SO4 attack, but it was severely susceptible to damage in the MgSO4 environment.
  • Yongqiang Chen, Amir Ubaidah, Yogarajah Elakneswaran, Vahid J. Niasar, Quan Xie
    Journal of Molecular Liquids 317 114003 - 114003 2020年11月
  • T. Ishida, R. Kitagaki, H. Hagihara, Y. Elakneswaran
    XV International Conference on Durability of Building Materials and Components. eBook of Proceedings 2020年10月 [査読有り][通常論文]
  • Natatsawas Soonthornwiphat, Yutaro Kobayashi, Kanako Toda, Kazuma Kuroda, Chaerun Raudhatul Islam, Tsubasa Otake, Yogarajah Elakneswaran, John L. Provis, Tsutomu Sato
    JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY 57 10 1181 - 1188 2020年10月 
    Titanate adsorbents have been used to remove Sr radioisotopes from contaminated water at the Fukushima Daiichi Nuclear Power Station site. This process leads to the generation of spent adsorbents, which require stabilization for long term storage and disposal. Geopolymers are candidates for matrices to achieve this consolidation. However, more data are needed to assess the leaching behavior of Sr from the adsorbents embedded in a geopolymer matrix. In this study, leaching experiments and observations of the Sr distribution of spent titanate adsorbent embedded in geopolymers, loaded with Sr at realistic concentrations were conducted. The experimental results illustrate that only 0.75% of the Sr was leached out from a K-geopolymer loaded with 30% (by solid weight) of spent adsorbent after 360 days of immersion in deionized water. From the observations of Sr distributions by electron and isotope microscopy, Sr remained in the titanate adsorbent and did not diffuse into the geopolymer matrix. Leaching of Sr (loaded at a similar concentration) from the K-geopolymer without the adsorbent was also limited, only 0.05% after 360 days of leaching. In conclusion, both titanate adsorbent in K-geopolymer matrix, and the K-geopolymer itself, offer an attractive potential for Sr immobilization.
  • Takato Ishida, Ryoma Kitagaki, Ryota Watanabe, Hideaki Hagihara, Yogarajah Elakneswaran, Hideyuki Shinzawa
    POLYMER DEGRADATION AND STABILITY 179 109242 - 109242 2020年09月 
    The molecular architecture changes of crosslinked urethane during photo-oxidation was investigated by Fourier transform infrared spectroscopy (FTIR) in combination with two-dimensional (2D) correlation analysis. The 2D correlation FTIR spectroscopy provided insight into molecular architectural dynamics during photo-aging, where the sequential order of peak changes was determined upon perturbation with photo-aging. Photo-oxidation was monitored from the decrease in the peak intensity at 1537 cm(-1) (attributed to the urethane group) and the generation of the hydrogen bonded C=O groups at 1698 cm(-1) immediately after urethane decomposition. Several notable peaks appeared (1712,1650, and 1750 cm(-1)) in the later stages, which were attributed to the free photo-oxidative product. In summary, photo oxidation involved a cleavage of urethane crosslink and generation of end groups that formed hydrogen bonds with surrounding hydrogen bonding sites. Further degradation of the free photo products was observed likely because of the small number of accessible hydrogen bonding sites due to the increasing heterogeneity of the internal structure. (C) 2020 Elsevier Ltd. All rights reserved.
  • Mari Masanaga, Tsuyoshi Hirata, Hirokatsu Kawakami, Yuka Morinaga, Toyoharu Nawa, Yogarajah Elakneswaran
    MATERIALS 13 13 3018 - 3018 2020年07月 
    Shrinkage-reducing agents have been developed to mitigate shrinkage and to control cracks in concrete. This study aims to evaluate the impact of a newly developed shrinkage-reducing agent (N-SRA) on concrete properties and to compare its properties with a conventional shrinkage-reducing agent (C-SRA). The hydration rate, compressive strength, splitting tensile strength, shrinkage, occurrence of cracking, and freezing and thawing were investigated. N-SRA showed higher surface tension than C-SRA and reduced shrinkage to the same degree as C-SRA with half the dosage of C-SRA. The addition of N-SRA or C-SRA did not influence the early compressive strength but slightly reduced splitting tensile strength at seven days. Concrete with N-SRA showed higher compressive strength at 28 days than those of concrete with C-SRA or without SRA. Furthermore, concrete with N-SRA extended the period for the occurrence of shrinkage cracking under restrained conditions. It was found that N-SRA provided excellent freezing and thawing resistance because of the formation of good air voids, while C-SRA demonstrated inefficient behaviour in such an environment.
  • Miku Takeya, Amir Ubaidah, Mai Shimokawara, Hirofumi Okano, Toyoharu Nawa, Yogarajah Elakneswaran
    JOURNAL OF PETROLEUM SCIENCE AND ENGINEERING 188 106913 - 106913 2020年05月 
    The determination of the electrokinetic properties of crude oil/brine and rock/brine interfaces is necessary to understand and evaluate the low salinity waterflooding (LSWF) effect on wettability alteration and enhanced oil recovery (EOR). The interface properties and characteristics of oil and rock minerals significantly affect LSWF and must be elucidated in detail. Herein, the interaction of crude oil, brine, and rock was studied to elucidate the LSWF effect in carbonate and sandstone reservoirs. A triple-layer surface complexation model was proposed to describe the calcite/brine and kaolinite/brine interfaces and was verified with zeta potential experiments at various pH and calcium, magnesium, and sulphate concentrations. Furthermore, the surface complexation model prediction of zeta potential agreed well with the measured data for the suspension in seawater, formation water, and associated dilutions. The predicted surface potential of crude oil, calcite, and kaolinite was used in Derjaguin-Landau-Verwey-Overbeek (DLVO) theory to estimate the total disjoining pressure as attractive/repulsive forces. The interaction between crude oil and calcite/kaolinite on seawater dilution and in the presence of sulphate in the diluted solution for calcite was evaluated via disjoining pressure. Moreover, the importance of electrokinetic properties on attractive/repulsive forces and the mechanisms for wettability alteration in crude oil-brine-kaolinite due to LSWF as well as in oil-brine-calcite because of sulphate addition are discussed.
  • Takato Ishida, Ryoma Kitagaki, Hideaki Hagihara, Yogarajah Elakneswaran
    POLYMER 186 122035 - 122035 2020年01月 
    Structural changes induced by photo-aging have significant influence on material properties. The prediction of the period prior to the onset of significant morphological changes is useful in determining material service lifetime. We assume "degelation" to be the starting point of significant morphological change during photo-aging. Herein, we demonstrated the relationship between such time and the "degelation" phenomenon for an acrylic-urethane network polymer. We also derived a "degelation" theory considering network imperfections, e. g. dangling chains and looping chains. This provides a more accurate representation of reactive curing polymers widely used in industries. Lastly, we estimated the "imperfection degree" by comparing the number of elastically active chains obtained from a swelling experiment with the theoretically derived number. In this system, samples may originally possess approximately 10% network imperfection and it influences on the degelation period in aging process. Our study may potentially contribute to a more accurate prediction of the onset of significant structural change.
  • Miku Takeya, Mai Shimokawara, Yogarajah Elakneswaran, Hirofumi Okano, Toyoharu Nawa
    ENERGY & FUELS 33 5 4211 - 4218 2019年05月 [査読有り][通常論文]
     
    Understanding crude oil/brine interface chemistry is essential to elucidating the effect of low-salinity waterflooding (LSWF) on enhanced oil recovery (EOR). The acid and base functional groups in crude oil result in an electrostatic interaction with the rock's surface, thereby affecting wettability conditions. Moreover, the content of carboxyl acid components is a key factor influencing electrostatic interaction during LSWF. In this study, the number of carboxyl groups in four different crude oils with varying acid number (AN) was estimated using a combination of zeta potential experiments and a triple-layer surface complexation model. In addition, the surface complexation modeling parameters for the dissociation of carboxyl groups and the adsorption of calcium and magnesium ions were also determined. The experimentally determined parameters and carboxyl groups sufficiently predicted the crude oil/brine interface at high and low salinities of seawater and formation water. The density of carboxyl groups (expressed in sites/nm(2)) is logarithmically related to the AN of crude oil, and it is revealed that the effect of AN on the density is lower for high-AN crude oil. Further, for crude oils with high AN, divalent cations exhibit higher adsorption ability than those with low-AN crude oil. The percentage of resin components in crude oil has a linear relationship with the number of carboxyl sites, thus indicating the importance of resin components in crude oil/brine interface chemistry. The study discusses the influence of AN on potential distribution and possible wettability alteration by LSWF in sandstone and carbonate reservoirs.
  • Yogarajah Elakneswaran, Natsumi Noguchi, Kazuki Matumoto, Yuka Morinaga, Takashi Chabayashi, Hiroyoshi Kato, Toyoharu Nawa
    FRONTIERS IN MATERIALS 6 97  2019年05月 [査読有り][通常論文]
     
    The cement industry is an energy-intensive industry, and improving the energy efficiency of cement has become necessary to reduce its carbon footprint and to compete in the global market. Clinker production consumes more than 90% of the total energy used in the cement industry. Therefore, a reduction in the burning temperature of the cement clinker can reduce the energy consumption; however, it alters the mineralogy of the clinker composition. Ferrite-rich Portland cement can be produced by lowering the burning temperature by similar to 100 degrees C (i.e., at 1,350 degrees C), which can reduce the energy consumption by similar to 5% in comparison with ordinary Portland cement (OPC) clinker. In this study, the hydration reaction and properties of the ferrite-rich Portland cement were examined by experimental techniques and thermodynamic modeling approach, and the results were compared with that of OPC. The produced ferrite-rich cement has almost twice the amount of ferrite phase and half the amount of belite phase contents present in the OPC. The hydration reaction and the composition of hydrates were studied by the X-ray diffraction (XRD)/Rietveld analysis and thermogravimetry (TG) and differential thermal analysis (DTA). The different proportions of the ferrite and belite phases in ferrite-rich cement change their hydration reaction from that of the OPC, but not the total hydration of cement. The XRD results reveal similar phases in both the cements, and the analysis could not identify the new phases formed in the ferrite-rich cement. An equal degree of hydration and quantified hydrates at the early age results in almost identical initial and final setting times in both the cements. The ferrite-rich cement demonstrates a high early strength and relatively slower strength development; however, it can develop adequate strength at 28 days. The thermodynamic model predicts the hydration of ferrite-rich cement and shows comparatively high amount of Fe-containing phases, mainly Fe-ettringite and Fe-siliceous hydrogarnet. Model predictions of the hydrates compositions agreed with the experimental results, and a relationship between the predicted total porosity and the measured compressive strength was derived.
  • Mai Shimokawara, Elakneswaran Yogarajah, Toyoharu Nawa, Satoru Takahashi
    JOURNAL OF THE JAPAN PETROLEUM INSTITUTE 62 1 19 - 27 2019年 [査読有り][通常論文]
     
    Recently, the use of carbonated water injection has been considered for enhanced oil recovery (EOR), and it provides a great potential for reducing CO2 emissions. Both laboratory and field applications on EOR using carbonated water injection have been reported, and various mechanisms have been suggested for oil recovery. However, the interaction between the carbonated water and rock and its influence on EOR remains unclear. Therefore, the objective of this study was to evaluate the carbonated water-rock interactions through core flooding experiments and using an advective-reactive transport model. The experimental results pertaining to permeability of the core sample, and effluent pH value and calcium concentration were presented as a function of the amount of injectant. The effect of oil present in the core sample, ageing, and kind of injectant, on the interaction and oil recovery were analyzed. The results showed that calcite in the carbonate rock dissolved owing to its interaction with carbonated water; this increased the porosity, and thus, the permeability of the rock, and effluent pH value and calcium concentration also increased. The simulation results for effluent calcium concentration and pH agree well with experimental data, indicating the applicability of the model for further understanding the interactions in the carbonate reservoir.
  • Miku Takeya, Mai Shimokawara, Yogarajah Elakneswaran, Toyoharu Nawa, Satoru Takahashi
    FUEL 235 822 - 831 2019年01月 [査読有り][通常論文]
     
    The low-salinity waterflooding (LSWF) technique during enhanced oil recovery has received increasing attention over the last decade. Several studies have attempted to understand the effects of LSWF through both experiments and modelling, but their results are inconsistent due to a lack of understanding of the crude oil/brine and brine/rock interfaces. In this paper, the crude oil/brine interface was studied by developing a triple-layer surface complexation model. The carboxyl groups(-COOH) were attributed to the surface charge and electrical triple-layer development of the crude oil in LSWF. The zeta potentials of the emulsion at various pH levels and the calcium and magnesium concentrations were measured to examine the interface. These data were then directly fitted to the simulated zeta potentials to determine the surface site density of -COOH and the associated equilibrium constants for the dissociation and adsorption of calcium and magnesium. The -COOH site density was determined by fitting the pH-independent zeta potential, while the equilibrium constant values were estimated from the variations in the zeta potential with the changes in pH and the concentrations of calcium and magnesium. The determined surface complexation parameters were validated by comparing the experimental zeta potential data from different ionic solutions. The developed surface complexation model was used along with the estimated parameters to predict the interface of crude oil in seawater, formation water, and their dilutions. The simulated zeta potential results agreed well with the experimental data, demonstrating that the model is applicable to understand the crude oil/brine interface in LSWF. Finally, the importance of the prediction of the surface and zeta potentials in the evaluation of the interface and the estimation of electrostatic forces, and thus the wettability alteration, was discussed.
  • Yogarajah Elakneswaran, Eiji Owaki, Toyoharu Nawa
    APPLIED SCIENCES-BASEL 8 12 2597  2018年12月 [査読有り][通常論文]
     
    Cementitious materials are one of the essential components for low- and intermediate-level waste disposal sites. Low-level nuclear waste from power plants consists of highly concentrated (similar to 25 wt %) Na2SO4, and the wastes are solidified with cementitious materials. Degradation of cementitious materials that result from chemical and physical sulphate attack is a major concern in the safety of the waste disposal. In this study, hydration and reactive transport models, developed in previous works by the authors, were applied with Pitzer interactions coefficients to evaluate the long-term performance of Port-land cement (PC) solidified with high concentration of Na2SO4. Expansive sulphate-bearing products of ettringite and mirabilite were formed and filled the pores in the hydrating PC with 25% of Na2SO4 by weight, but they were destabilised as temperature increased. Influence of Na2SO4 concentration and temperature on mineralogical changes is discussed. The simulation results from the reactive-transport model showed that the degradation of solidified Na2SO4 waste by cementitious materials exposed to 10% Na2SO4 for 1000 years is due to dissolution of mirabilite and secondary formation of ettringite, but not Na2SO4 crystallisation. The phases and porosity became stable close to exposure surface after 10 years, although the deterioration progressed from the surface to core with exposure time.
  • エラクネス ヨガラジャ
    Journal of the American Ceramic Society 101 10 4549 - 4559 2018年10月 [査読有り][通常論文]
     
    The dissolution behavior of Pyrex glass in a model system consisting of 1-M NaOH with varying amounts of portlandite, representing the glass dissolution in alkaline environment and alkali-silica reaction (ASR) in cementitious materials, is studied. The Pyrex glass dissolution and the reaction products were characterized using X-ray diffraction (XRD), Si-29 nuclear magnetic resonance (Si-29-NMR), and scanning electron microscopy with energy dispersive X-ray (SEM/EDX), and the silica and calcium concentrations in the liquid phase were determined using inductively coupled plasma atomic emission spectroscopy (ICP-AES). The experimental results show that the dissolution of the Pyrex glass continued until it consumed the portlandite and then reached a constant rate, with a linear relationship with the amount of portlandite. The absence of calcium and reduction of silica concentration in the liquid phase with the increase in portlandite indicate the formation of high-reaction products with portlandite, confirmed by XRD and Si-29-NMR. The calcium sodium silicate hydrate (C-N-S-H) and sodium silicate hydrate (N-S-H) are the main ASR products; their composition and proportions strongly depend on the reaction time and the amount of portlandite added. A thermodynamic model, which couples geochemical code (PHREEQC) and the experimental silica dissolution rate, was used to predict ASR products and the remaining portlandite. The simulation results predicted the experimental data fairly well for different portlandite additions. The mechanism for Pyrex glass dissolution in the presence of varying portlandite additions is discussed with regard to experimental data and simulation results.
  • Elakneswaran Yogarajah, Toyoharu Nawa, Kiyofumi Kurumisawa
    JOURNAL OF MATERIALS IN CIVIL ENGINEERING 30 5 1  2018年05月 [査読有り][通常論文]
     
    In this study, the surface electrical properties of calcium silicate hydrate (C-S-H) and their influence on ionic adsorption have been investigated to be able to predict chloride binding in slag-containing cementitious materials. The experimental data showed that the electrokinetic potential of slag cement paste (SCP) is intermediate between hydrated cement paste (HCP) and C-S-H with Ca/Si of 1.0 (C-S-H:1.0) or slag calcium hydroxide paste (SCHP). Two types of C-S-H available in the hydrated SCP for ionic adsorption are considered: one is similar to the C-S-H of HCP and other is like C-S-H:1.0. The surface complexation modeling parameters for ionic adsorption on C-S-H:1.0 were estimated by fitting the experimental data to simulation results. The estimated parameters for C-S-H:1.0 together with surface complexation modeling parameters for HCP were used to predict the adsorption of chloride on SCP. The simulation results show good agreement with experimental data and follow a Freundlich isotherm. When portland cement is partially replaced by slag, it modifies the surface electrical properties of C-S-H in addition to mineralogy and pore structure and leads to change in the chloride adsorption behavior.
  • Akira Hatanaka, Yogarajah Elakneswaran, Kiyofumi Kurumisawa, Toyoharu Nawa
    JOURNAL OF ADVANCED CONCRETE TECHNOLOGY 15 8 426 - 439 2017年08月 [査読無し][通常論文]
     
    The purpose of this study is to determine the tortuosity of cementitious materials containing blast furnace slag (BFS). Furthermore, the influence of tortuosity on multi-species transport into these materials is studied. The porosity and diffusivity of calcium silicate hydrate (C-S-H) were predicted using a three-dimensional spatial distribution model, which were then fitted to Archie's law to determine tortuosity. The tortuosity increased with the slag replacement ratio, suggesting that the diffusion path for ions becomes complicated and lengthy due to slag addition. Thermoporometry was used to determine the pore size distribution of hydrated slag-blended cement. A partial replacement of ordinary Portland cement (OPC) with BFS modified the mineralogy (especially in the types of C-S-H), resulting in changes to the pore structure. The determined tortuosity and porosity were used in a reactive transport model to predict multi-species transport. Experimentally measured and simulated chloride profiles were in good agreement for hydrated OPC and slag-blended cements exposed to sodium chloride solutions. The causes for the low penetration rate of chloride in slag-blended cementitious materials are discussed considering their pore structure and surface electrical properties. The role of tortuosity on Cl-/OH- for the evaluation of chloride induced corrosion was also discussed.
  • Tomohiro KAJIO, Yuka MORINAGA, Yogarajah ELAKNESWARAN, Toyoharu NAWA
    Cement Science and Concrete Technology 71 1 40 - 47 2017年
  • Yogarajah Elakneswaran, Eiji Owaki, Shigeyoshi Miyahara, Masataka Ogino, Tsuyoshi Maruya, Toyoharu Nawa
    CONSTRUCTION AND BUILDING MATERIALS 124 615 - 625 2016年10月 [査読有り][通常論文]
     
    Thermodynamic calculations, using the geochemical code PHREEQC coupled with empirical equations for kinetics of cement hydration and slag reaction, were carried out to predict the compositions of the hydrate assemblage and pore solutions of hydrating Portland cement and cement blended with slag and the blended cement containing limestone. The predicted compositions of hydration products and element concentrations in pore solutions compared well with experimental data reported in literature. The calculation results showed the varying Ca/Si and Al/Si ratios of calcium aluminosilicate hydrate (C-A-S-H)(1) in the hydration products due to hydration and slag addition. Limitations on the equation for reaction of slag and the importance of a C-A-S-H solid solution model in prediction of hydration products are discussed. (C) 2016 Elsevier Ltd. All rights reserved.
  • Y. Elakneswaran, T. Ishida
    Life-Cycle of Structural Systems: Design, Assessment, Maintenance and Management - Proceedings of the 4th International Symposium on Life-Cycle Civil Engineering, IALCCE 2014 1655 - 1662 2015年 
    © 2015 Taylor & Francis Group, London. In this study, combined experimental and modeling works have been carried out to investigate the chemical degradation of cementitious materials in various sulfate environments. Three types of cement paste specimens were immersed in deionized water and sodium and magnesium sulfate solutions with 100 mmol/1 of SO42- concentration for 9 months. Visual observation of the exposed surface and spatial changes of solid phases, which were quantified by XRD/Rietveld analysis, were recorded at the end of exposure period, and the results are presented and discussed in here. The influence of the composition of cement paste on the resistance to calcium leaching in deionized water and external sulfate attack is discussed. A coupled physicochemical and geochemical model was used to predict experimentally determined phases changes in ordinary Portland cement paste exposed to deionized water and sodium and magnesium sulfate solutions. The miner- alogical distributions observed experimentally were compared with those from the model.
  • Yogarajah Elakneswaran, Tetsuya Ishida
    JOURNAL OF ADVANCED CONCRETE TECHNOLOGY 12 4 111 - 126 2014年04月 
    In this study, a multi-scale model called DuCOM (Durability COncrete Model), which is developed by the Concrete Laboratory at the University of Tokyo, is extended by coupling the geochemical code PHREEQC. The coupled numerical framework can address physicochemical and geochemical processes such as the hydration of cement particles, pore structure formation, multispecies transport, activity effect, thermodynamic reaction between aqueous solution and solids, etc. in cementitious materials, and therefore, it can potentially be used to assess the long-term durability of concrete structures. The model prediction for the composition of cement hydrates, pore solution chemistry, calcium profiles for the cement paste exposed in pure water, and calcium and sulphur profiles for the cement paste immersed in the sodium sulphate solution are qualitatively and quantitatively compared with experimental results obtained from literature. Finally, the importance of the strong coupling among various processes and mechanisms in the DuCOM-PHREEQC system is discussed.
  • Yogarajah Elakneswaran, Tetsuya Ishida
    Sustainable Construction Materials and Technologies 2013-August 2013年 
    © 2013 Sustainable Construction Materials and Technologies. All rights reserved. In this study, a coupled physiochemical and geochemical model is developed for the prediction of long-term performance of cementitious materials under combined effects of sulphate attack and leaching. DuCOM (Durability COncrete Model) and geochemical code PHREEQC were used for development of the numerical framework. The coupled model retains all the capabilities of these models, and it allows predicting the spatial and time variation of minerals compositions, pore water concentrations, and other hydration and pore structures properties simultaneously. The coupled model was applied to understand the underlying mechanisms on sulphate attack and leaching. Further, the influence of bicarbonate ions on the dissolution and formation of sulphate phases is examined. The main simulation results agree qualitatively and quantitatively well with published experimental data in terms of hydrated cement products, porosity, pore solution chemistry, sulphate bearing products. The detailed experimental works have been considered for further verification of the model.
  • 岩浅 瑛大, 合田 義, 名和 豊春, ELAKNESWARAN Yogarajah
    セメント・コンクリート論文集 65 1 54 - 60 Japan Cement Association 2011年 
    塩化物イオン拡散メカニズムの解明は構造物の耐久設計に重要である。塩化物イオンの拡散過程において、特にC-S-H表面への物理吸着の影響が支配的であるとされているが、C-S-H表面における電気的性質について明らかにされていない。そこで本研究では、C-S-H表面における反応基であるSiOH基の表面錯体反応を考え、SiOH基密度や表面錯体反応の平衡定数の算出を目的とした。算出においては表面錯体モデルを用い、SiOH基の電離やカルシウムの吸着をモデル化し、塩基滴定実験やカルシウム吸着実験の実験結果と照合することにより、Ca/Siの異なる合成C-S-Hの表面電荷密度および平衡定数の算出を行った。その結果、SiOH基密度と平衡定数がC-S-HのCa/Siに依存することが明らかとなった。
  • ELAKNESWARAN Y, IWASA A, NAWA T, SATO T, KURUMISAWA K
    Cement and Concrete Research 40 12 1756 - 1765 Elsevier 2010年 [査読無し][通常論文]
     
    The main objective of this investigation is to describe the interaction between cement hydrates and electrolyte solution to understand multi-ionic transport in cementitious materials. A surface complexation model in PHREEQC including an electrostatic term is used to simulate the ionic adsorption on the calcium silicate hydrate (C-S-H) surface. The equilibrium constants for the adsorption of ions on C-S-H surfaces are obtained by fitting experimental data to the model. The adsorption of both divalent and mono-valent cations, and also anions significantly changes the surface charges of hydrated paste. Chloride is being held in a chemical binding as Friedel's salt and bound mainly by the adsorptive action of C-S-H. An integrated modelling approach employing a phase-equilibrium model, a surface complexation model, and a multi-component diffusion model has been developed in PHREEQC to simulate the multi-ionic transport through hydrated cement paste. It was found that the physical adsorption of ions on C-S-H, the size of pores, and the surface site density of C-S-H govern the rate of penetration of ionic species. Finally, the proposed model has been validated against chloride profiles measured in this study as well as with data available in the literature for hydrated cement paste.
  • Y. Elakneswaran, T. Nawa, K. Kurumisawa
    CEMENT AND CONCRETE RESEARCH 39 4 340 - 344 2009年04月 [査読無し][通常論文]
     
    in this study, surface charge mechanism of cement hydrates and its relations to adsorption of chloride ions are investigated. Hydrated cement paste (HCP) shows net positive surface charge by dissociation and adsorption. In HCP, chlorides bind as Friedel's salt (chemical binding) as well as adsorb on the surface of hydrates (physical binding). A surface complexation model is used to predict the adsorption of chlorides on calcium silicate hydrates (C-S-H). A good agreement between experimental and predicted chloride adsorption isotherm clearly demonstrate that the chlorides adsorb on the surface of C-S-H and bringing additional negative surface charge (SiOHCl(-)). However, chloride ions neutralize the positively charged surfaces of portlandite and Friedel's salt by physical adsorption. From the results, it can be concluded that C-S-H is the dominant phase in terms of chloride adsorption in HCP. Crown Copyright (C) 2009 Published by Elsevier Ltd. All rights reserved.
  • Y. Elakneswaran, T. Nawa, K. Kurumisawa
    CEMENT & CONCRETE COMPOSITES 31 1 72 - 76 2009年01月 [査読無し][通常論文]
     
    Electrokinetic studies of interfaces between solid phase and aqueous solution have most often been undertaken to elucidate the mechanism of adsorption and transport of different species into cementitious materials. The zeta potential is used to understand the electrokinetic properties of interfaces. In the present paper, zeta potential studies of cements and paste, with and without addition of slag, in different electrolyte solutions are carried out to understand the effect of the adsorption of charged species. The amounts of adsorbed ions are also measured to verify the results obtained by zeta potential measurement. This study shows that the cements and paste particles are negatively charged in water, sodium chloride solution, and at low concentration of calcium. At high concentration of calcium a charge inversion is observed. Thus, both calcium and chloride are potential determining ions, whereas sodium behaves as an indifferent ion. Moreover, slag particles strongly influence the surface chemistry not just of the slag but of the whole paste. Crown Copyright (c) 2008 Published by Elsevier Ltd. All rights reserved.
  • ELAKNESWARAN Yogarajah, NAWA Toyoharu, KURUMISAWA Kiyofumi, HAYASHI Ami
    セメント・コンクリート論文集 61 108 - 114 2008年02月20日 [査読無し][通常論文]
  • Effect of GGBS on Membrane Potential of Pastes
    Y. Elakneswaran, T. Nawa, K. Kurumisawa, K. Fushimi
    RILEM Proceedings PRO 46, Concrete Durability and Service Life Planning (ConcreateLife’06) 405 - 414 2006年 [査読有り][通常論文]
  • Surface Charge of Hardened Cement Paste Determined by Membrane Potential
    Yogarajah Elakneswaran, Toyoharu Nawa, Kiyofumi Kurumisawa, Koji Fushimi
    Cement Science and Concrete Technology 60 111 - 117 2006年 [査読有り][通常論文]

その他活動・業績

  • 名和豊春, 胡桃澤清文, ELAKNESWARAN Y., 佐川孝広, 西祐宜 環境助成研究成果 概要集 第38回・2017年度分:11件 第39回・2018年度分:23件 令和2年度 2020年
  • 戸田賀奈子, SOONTHRONWIPHAT Natatsawas, TWO Hnin Wint Wint, 小林佑太朗, 黒田知眞, 森永祐加, 胡桃澤清文, YOGARAJAH Elakneswaran, 杉山隆文, KE Xinyuan, PROVIS John, 佐藤努 日本原子力研究開発機構JAEA-Review(Web) (2018-017) 2018年
  • Elakneswaran Yogarajah, Toyoharu Nawa, Toshifumi Igarashi THE THIRD INTERNATIONAL CONFERENCE ON SUSTAINABLE INFRASTRUCTURE AND BUILT ENVIRONMENT (SIBE 2017) 147 2018年 [査読有り][通常論文]
     
    A partial replacement of Portland cement (PC) by ground granulated blast furnace slag (GGBFS) is an effective method to improve the durability of concrete due to its lower diffusivity and higher chemical resistance compared to PC. Further, the microstructure of GGBFS blended cementitious materials controls the physicochemical properties and performance of the materials in concrete. Therefore, understanding of cement hydration and cementing behavior of GGBFS is essential to establish microstructure property relationship for predicting performance. In this study, hydration, microstructure development, and chloride ingress into GGBFS-blended cement have been investigated. Solid-phase assemblage and pore solution chemistry of hydrating PC and cement blended with GGBFS were predicted using thermodynamic model and compared with experimental data. A mathematical model integrating PC hydration, GGBFS reaction, thermodynamic equilibrium between hydration products and pore solution, ionic adsorption on C-S-H, multi-component diffusion, and microstructural changes was developed to predict chloride ingress into GGBFS blended cementitious materials. The simulation results on chloride profiles for hydrated slag cement paste, which was prepared with 50% of replacement of PC with GGBFS, were compared with experimental results. The model quantitively predicts the states of chloride such as free, adsorbed on C-S-H, and chemically bound as Friedel's salt.
  • エラクネスワラン ヨガラジャ, 名和 豊春, 佐藤 努, 胡桃澤 清文, Iwasa Akihito 日本原子力学会 年会・大会予稿集 2010 (0) 836 -836 2010年 [査読無し][通常論文]
     
    Cementitious materials are being used for encapsulation, back filling, and grouting purposes in deep geological repositories of long – lived radioactive waste. The long – term performance of cementitious materials has been investigating for safety disposal of radioactive waste. The durability performance of cementitious materials is mainly determined by resistance to transport of aggressive substances, however remain poorly understood. In this study, a thermodynamic integrated model has been developed to simulate multi-ionic transport in cementitious materials with considering ionic adsorption. The model has been validated against measured experimental data.
  • Y. Elakneswaran, T. Nawa, K. Kurumisawa MATERIALS AND STRUCTURES 42 (1) 83 -93 2009年01月 [査読無し][通常論文]
     
    The amount of free chloride content in concrete is one of major factors in initiating the corrosion process. The material and environmental factors play a key role in diffusing the chloride ion through the cover concrete to reinforcement. Thus, the electrochemical study is indispensable to understand the mechanism of chloride ingress into concrete. Determination of surface charge and its influence on diffusion of chloride ion into cement matrix of concrete are researched for Ordinary Portland Cement (OPC) paste and cement paste containing Ground Granulated Blastfurnace Slag (GGBS). Different kinds of experiments such as measurement of membrane potential, determination of porosity and pore size distribution, determination of pore solution concentration, and steady state diffusion coefficient of chloride and sodium ions are employed to understand the mechanism of chloride ingress. The obtained results show that the positive surface charge on the pore walls of hardened paste regardless of GGBS's presents. The surface charge of hardened paste mainly depends on pore solution concentration and cement composition. The physiochemical characteristics of the pores are affecting on transporting ions through it. Hardened paste has greater resistance to diffusing sodium ions than chloride ions. Moreover, there is a strong interaction between transport of chloride ion and surface charge in matured hardened paste.
  • Y. Elakneswaran, T. Nawa, K. Kurumisawa RILEM Workshop on Long-Term Performance of Cementitious Barriers and Reinforced Concrete in Nuclear Power Plants, NUCPERF 2009 135 -142 2009年01月01日 [査読無し][通常論文]
     
    The mechanisms of the transport of species into the cementitious material have lately received a great deal of attention in durability problems. Hydrated cement acquires an electrical charge when it contacts with polar medium and leads to formation of Electric Double Layer (EDL). In this study, the significant influence of EDL properties on ionic transport through cement - based materials was investigated. Hardened cement paste shows net positive surface charge due to ionization of surface sites and adsorption ions from pore solution. EDL properties such as surface charge significantly influence not just on ionic adsorption but also on ionic diffusion. An integrated modelling approach employing phase - equilibrium model, surface complexation model, and multicomponent diffusion model was developed using PHREEQC to simulate the ionic ingress through cement - based materials. A comparison of predicted and experimental chloride profile is presented for hydrated cement paste. The surface charge influence is much higher on ionic transport in gel pore as compared in other pores. Chloride is being held in chemical combination as Friedel's salt and also bound mainly by adsorptive action of cement hydrates. Finally, an influence of pozzolanic materials on chloride binding (chemical as well as physical) and diffusion is discussed.

共同研究・競争的資金等の研究課題

  • 日本学術振興会:科学研究費助成事業
    研究期間 : 2018年04月 -2021年03月 
    代表者 : Y Elakneswaran
     
    本研究では、Ca/(Si+Al)比の異なるC-(A)-S-Hを合成し、SiOH基及びAlOH基には反応性の異なる2つのサイトが存在すると仮定した。これらのサイトにおける表面錯体反応の平衡定数を算出し、吸着量予測を行うことで、合成系におけるモデルの構築を行った。C-S-HおよびC-A-S-Hへのカルシウムおよび塩化物の吸着の実験データを予測することによってモデルの検証を行った。
  • 日本学術振興会:科学研究費助成事業
    研究期間 : 2016年04月 -2018年03月 
    代表者 : Y Elakneswaran
     
    ポルトランドセメント(PC)やPCの一部が補助セメント混合材料(SCMs)に置換されたセメント系材料は、水和生成物の物理的化学的な特性による放射性廃棄物固化に向けて研究がなされている。この研究で異なる合成C-S-H及びC-A-S-Hの表面電荷(表面サイト密度と脱プロトン化の平衡定数)を特定することである。さらに、表面電荷がC-S-H及びC-A-S-H表面におけるイオン吸着に及ぼす影響を調査する。It is detailed in English.

教育活動情報

主要な担当授業

  • 大学院共通授業科目(一般科目):自然科学・応用科学
    開講年度 : 2021年
    課程区分 : 修士課程
    開講学部 : 大学院共通科目
    キーワード : Geochemistry, thermodynamics, minerals equilibrium, modelling
  • 資源生産システム
    開講年度 : 2021年
    課程区分 : 修士課程
    開講学部 : 工学院
    キーワード : Geochemistry, thermodynamics, minerals equilibrium, kinetics, surface complexation, modelling
  • 資源生産システム特論
    開講年度 : 2021年
    課程区分 : 修士課程
    開講学部 : 工学院
    キーワード : Geochemistry, thermodynamics, minerals equilibrium, kinetics, surface complexation, modelling
  • 資源生産システム特論
    開講年度 : 2021年
    課程区分 : 博士後期課程
    開講学部 : 工学院
    キーワード : Geochemistry, thermodynamics, minerals equilibrium, kinetics, surface complexation, modelling
  • 資源化学Ⅰ
    開講年度 : 2021年
    課程区分 : 学士課程
    開講学部 : 工学部
    キーワード : 無機固体化学、原子構造, 化学結合, 溶液化学, 界面化学
  • 資源化学Ⅱ
    開講年度 : 2021年
    課程区分 : 学士課程
    開講学部 : 工学部
    キーワード : 反応工学,物質収支,速度論,反応モデル
  • 資源循環システム実験Ⅰ
    開講年度 : 2021年
    課程区分 : 学士課程
    開講学部 : 工学部
    キーワード : 基本操作、物理計測、化学分析
  • 資源循環システム実験Ⅲ
    開講年度 : 2021年
    課程区分 : 学士課程
    開講学部 : 工学部
    キーワード : 構造解析,物性評価,鉱物の利用,流体の分析,選別技術


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