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    R E S E A R C H P A P E R

    Thermal conductivity measurements of road constructionmaterials in frozen and unfrozen state

    Norbert I. Komle Hui Bing Wen Jie Feng Roman Wawrzaszek Erika S. Hu tter Ping He Wojciech Marczewski Borys Dabrowski Kathrin Schroer Tilman Spohn

    Received: 5 January 2007 / Accepted: 16 May 2007 / Published online: 11 July 2007

    Springer-Verlag 2007

    Abstract A series of thermal conductivity measurements

    for various materials was performed in a large climatechamber. The size of the chamber allowed the preparation

    of relatively large samples in a controlled thermal envi-

    ronment. Three types of thermal sensors were used: (1) two

    needle probes; (2) a grid of temperature sensors, evenly

    distributed inside the sample; (3) two additional thermal

    probes, which were simplified versions of an instrument

    originally developed for measuring thermal properties of

    the ice/dust mixture expected to exist at the surface of a

    comet nucleus. They consist of a series of individual

    temperature sensors integrated into a glass fibre rod. Each

    of these sensors can be operated in an active (heated) or

    passive (only temperature sensing) mode. The following

    sample materials were used: fine-grained reddish sand,

    coarse-grained moist sand, gravels with various grain size

    distributions from < 1 cm up to about 6 cm, and for

    comparison and calibration pure water (with convection

    suppressed by adding agar-agar), compact ice, and compactgranite. Of particular interest are the measurements with

    composite samples, like stones embedded in an agar-agar

    matrix. We describe the evaluation methods and present

    the results of the thermal conductivity measurements.

    Keywords Gravel Permafrost Sand Thermalconductivity

    1 Introduction

    The experiments reported in this paper served a twofold

    purpose. First, in many physical and engineering problems

    the thermal conductivity of the materials is a key parameter

    controlling to a high extent the thermo-physical behaviour

    of the system. For example, in the construction of road and

    railway routes the distribution of artificially or naturally

    generated heat in the underground determines the stability

    of the bed and thus the safety of pathways. This is partic-

    ularly important on seasonally or permanently frozen

    ground, like the areas transected by the Qinghai-Tibet

    Railway [14, 15].

    The second aspect of our paper deals with the devel-

    opment of suitable sensors for thermal conductivity mea-

    surements itself. For our measurements we have used,

    among else, so-called needle probes. They belong to the

    category of transient or non steady state measurement

    techniques. In general, when using a transient measurement

    procedure, an unsteady temperature gradient is induced

    inside the sample by a constant heat source. The heating

    occurs over an adequate time period. The thermal con-

    ductivity and/or diffusivity can be derived from the mea-

    sured temperature response due to heating. Common

    Presented at the 1st Asian Conference on Permafrost (ACOP),

    Lanzhou, Gansu, China, 79 August 2006

    N. I. Komle (&) E. S. HutterSpace Research Institute, Austrian Academy of Sciences,

    Schmiedlstrasse 6, 8042 Graz, Austria

    e-mail: norbert.koemle@oeaw.ac.at

    H. Bing W. J. Feng P. HeCold and Arid Regions Environmental and Engineering

    Research Institute (CAREERI), Chinese Academy of Sciences,

    Lanzhou, China

    R. Wawrzaszek W. Marczewski B. DabrowskiSpace Research Centre (SRC), Polish Academy of Sciences,

    Warsaw, Poland

    K. Schroer T. SpohnInstitut fur Planetologie (IFP), Universitat Munster,

    Munster, Germany

    123

    Acta Geotechnica (2007) 2:127138

    DOI 10.1007/s11440-007-0032-1

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    commercialized techniques using this principle are needle

    probes, hot wire methods, and the hot strip method. A

    comprehensive summary of available transient as well as

    steady state methods can be found, e.g. on the evitherm

    website [5]. The advantages of transient measurement

    techniques as compared to steady state techniques (like the

    hot plate method) are (1) shorter measurement periods, (2)

    suitability for a wide range of materials (solid and granular)and (3) a lower technical complexity. The latter property

    makes them more suitable for field applications or even

    application in space missions. On the other hand, the

    measurement accuracy of transient methods is usually

    lower than that of steady state methods. Therefore, steady

    state methods may be more useful for calibration purposes.

    Interpretation of needle probe measurements in terms of

    thermal conductivity is most simple if the sample to be

    measured has a homogeneous structure, is originally iso-

    thermal, and is large enough that boundary effects can be

    excluded. However, under more complex conditions,

    which frequently occur in the natural environment, evalu-ation of thermal conductivity from measured temperature

    data needs great care. We will consider an appropriate

    reduction method for the raw data in order to derive reli-

    able conductivity values from measured raw data.

    Another way to evaluate thermal conductivity of a

    medium indirectly is to use a grid of temperature sensors,

    e.g. RTDs1 distributed across the sample and to introduce a

    vertical temperature gradient. One way to achieve this is to

    bring the bottom side of the sample in thermal contact with

    a cooling plate. In our tests, such a method was used to

    compliment and cross-check the needle probe measure-

    ments.

    In many applications the variation of thermal properties

    with depth is of interest. This cannot be easily achieved by

    standard needle probes like the Hukseflux TP02 [7]. They

    can only provide average values over the length of the

    probe. However, a thermal probe developed in the recent

    years in the frame of ESAs2 comet mission Rosetta has

    some ability to measure the variation of thermal properties

    with depth in a soil. This instrument (MUPUS3), being a

    part of the payload of the Rosetta Lander Philae, is cur-

    rently on the way to its target comet Churyumov-Gera-

    simenko. After landing on the comet nucleus surface, the

    thermal properties of the cometary near-surface ice will be

    derived [1, 8]. The probe consists of several segments

    which can be separately heated in order to measure the

    thermal properties of different layers subsequently. The

    concept of MUPUS may also be useful for applications in

    terrestrial environments. Therefore several probes of a

    simplified variant named EXTASE4 have been built in the

    frame of another project [10, 13]. First tests showed that

    the interpretation of temperature data recorded by the

    EXTASE probe in terms of thermal conductivity is by no

    means an easy task. It demands a rather detailed thermal

    model of the sensor itself and calibration measurements in

    various well-known materials. In order to support this goaland to provide a broader basis for the interpretation of the

    expected MUPUS measurements at the comet surface, we

    have done some parallel tests with the EXTASE probes and

    the needle probes in a well-known medium and compared

    the results in terms of the obtained thermal conductivity

    values.

    2 Experimental equipment and setup

    2.1 Climate chamber and sample container

    The tests were performed in a thermally controlled envi-

    ronment, namely a climate chamber of the CAREERI

    (Lanzhou, China). This climate chamber allowed to

    establish a homogeneous temperature environment in the

    range of 40C to + 70C. The interior size of the chamber

    is approximately a cube of 90 cm side length. A system of

    fans permits fast relaxation of temperature inside the

    chamber to a prescribed value. Furthermore, air humidity

    inside the chamber can be controlled externally and set to a

    prescribed value. During operation, the power devices of

    the chamber are cooled by a cold water circuit.

    The second major device used in our experiments is the

    sample container. It is of rectangular shape (70 cm

    70 cm 35 cm) and its sides are thermally insulated. The

    bottom is connected to a cooling system working with

    alcohol as cooling agent. This setup allows us to establish a

    constant temperature at the bottom of the sample container,

    which may differ from the set chamber temperature. Thus,

    it can be used to establish a vertical temperature gradient

    inside a test sample.

    2.2 Thermal conductivity sensors

    Three different methods for determining thermal conduc-

    tivity were applied: (1) A commercial needle probe (Hu-

    kseflux TP02); (2) a grid of individual temperature sensors

    (platinum RTDs) which measures the temperature varia-

    tions inside the sample during cooling periods; (3) a cus-

    tom-built sequentially working probe (EXTASE) for1 Resistance Temperature Device, see http://www.temperature-

    world.com/rtd.htm2 European Space Agency3 MUlti-PUrpose Sensors for surface and sub-surface science

    4 EXperimental Thermal probe for Applications in Snow research and

    Earth sciences

    128 Acta Geotechnica (2007) 2:127138

    123

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