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  • 1.
    Badenes, Borja
    et al.
    Universitat Politècnica de València, Spain.
    Sanner, Burkhard
    UBeG GbR, Germany.
    Mateo Pla, Miguel
    Universitat Politècnica de València, Spain.
    Cuevas, Jose
    Universitat Politècnica de València, Spain.
    Bartoli, Flavia
    SPIN-PET, Italy.
    Ciardelli, Francesco
    SPIN-PET, Italy.
    González, Rosa
    AIMPLAS Plastics Technology Centre, Spain.
    Nejad Ghafar, Ali
    RISE Research Institutes of Sweden, Built Environment, Infrastructure and concrete technology.
    Fontana, Patrick
    RISE Research Institutes of Sweden, Built Environment, Infrastructure and concrete technology.
    Lemus Zuñiga, Lenin
    Universitat Politècnica de València, Spain.
    Urchueguía, Javier
    Universitat Politècnica de València, Spain.
    Development of advanced materials guided by numerical simulations to improve performance and cost-efficiency of borehole heat exchangers (BHEs)2020In: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 201, article id 117628Article in journal (Refereed)
    Abstract [en]

    One promising way to improve the efficiency of borehole heat exchangers (BHEs) in shallow geothermal applications is to enhance the thermal properties of the materials involved in its construction. Early attempts, such as using metal tubes in the 1980s or the utilization of thin–foil hoses, did not succeed in being adopted by the market for diverse reasons (cost, corrosion, fragility, etc…). In parallel, the optimization of pipe size, the use of double-U-tubes, thermally enhanced grout, etc. were able to bring the measure for the BHE efficiency, the borehole thermal resistance, from 0.20 to 0.15 K/(Wm) down to 0.08–0.06 K/(Wm) in the best solutions today. A further improvement cannot be expected without development of new, dedicated materials, combining the versatility of plastic like PE with an increased thermal conductivity that matches the respective properties of the rock and soil. This goal was included in the Strategic Research and Innovation Agenda of the European Technology Platform on Renewable Heating and Cooling in 2013. Within an EU supported project, both BHE pipes and grouting materials have been produced prototypically in small amounts, suitable for the first tests in the intended environment. The present work explains the research pathways envisaged and the resulting sensitivity analysis to highlight the influence of some of the most critical parameters that affect the overall performance of a GSHP system. The results have allowed guiding the real development of more efficient new advanced materials for different scenarios representative of different European regions. Finally the developed materials and their properties are discussed, including a comparative assessment about their compliance with reference material properties as currently seen in the BHE market. © 2020 The Author(s)

  • 2.
    Berktas, Ilayda
    et al.
    Sabanci University, Turkey.
    Nejad Ghafar, Ali
    RISE Research Institutes of Sweden, Built Environment, Infrastructure and concrete technology.
    Fontana, Patrick
    RISE Research Institutes of Sweden, Built Environment, Infrastructure and concrete technology.
    Caputcu, Ayten
    Cimsa Cimento Sanayi AS, Turkey.
    Menceloglu, Yusuf
    Sabanci University, Turkey.
    Okan, Burcu
    Sabanci University, Turkey.
    Facile synthesis of graphene from waste tire/silica hybrid additives and optimization study for the fabrication of thermally enhanced cement grouts2020In: Molecules, ISSN 1431-5157, E-ISSN 1420-3049, Vol. 25, no 4, article id 886Article in journal (Refereed)
    Abstract [en]

    This work evaluates the effects of newly designed graphene/silica hybrid additives on the properties of cementitious grout. In the hybrid structure, graphene nanoplatelet (GNP) obtained from waste tire was used to improve the thermal conductivity and reduce the cost and environmental impacts by using recyclable sources. Additionally, functionalized silica nanoparticles were utilized to enhance the dispersion and solubility of carbon material and thus the hydrolyzable groups of silane coupling agent were attached to the silica surface. Then, the hybridization of GNP and functionalized silica was conducted to make proper bridges and develop hybrid structures by tailoring carbon/silica ratios. Afterwards, special grout formulations were studied by incorporating these hybrid additives at different loadings. As the amount of hybrid additive incorporated into grout suspension increased from 3 to 5 wt%, water uptake increased from 660 to 725 g resulting in the reduction of thermal conductivity by 20.6%. On the other hand, as the concentration of GNP in hybrid structure increased, water demand was reduced, and thus the enhancement in thermal conductivity was improved by approximately 29% at the same loading ratios of hybrids in the prepared grout mixes. Therefore, these developed hybrid additives showed noticeable potential as a thermal enhancement material in cement-based grouts. © 2020 by the authors.

  • 3.
    Nejad Ghafar, Ali
    et al.
    RISE - Research Institutes of Sweden (2017-2019), Built Environment, CBI Swedish Cement and Concrete Research Institute.
    Draganovic, A.
    KTH Royal Institute of Technology, Sweden.
    Larsson, S.
    KTH Royal Institute of Technology, Sweden.
    A laboratory study on grouting in vibratory host rock2019In: ISRM 9th Nordic Grouting Symposium, NGS 2019, International Society for Rock Mechanics and Rock Engineering , 2019, p. 131-138Conference paper (Refereed)
    Abstract [en]

    To sufficiently seal an underground facility in fractured rock, it is necessary to obtain adequate grout spread into the surrounding fractures. The grout spread itself depends on parameters, the most significant of which are the grout filtration tendency and rheological properties. These properties can be affected by the applied pressure. Use of high-frequency oscillating pressure is a method that has been shown to improve grout spread by virtue of reducing the grout apparent viscosity. However, this method has not yet been industrialized due to limited efficiency and rapid attenuation of the oscillation along a fracture. To address these issues, we present a pilot investigation to show the potential of high-frequency oscillation applied to the host rock to improve grout spread in fractures. The proposed method is examined using an artificial fracture, the so-called Varying Aperture Long Slot (VALS) that has been recently developed. The results are compared between the two cases with and without vibration. The study shows the potential of the method on improving the grout spread in rock fractures.

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