Analytical and experimental study on thermal conductivity of hardened cement pastes
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ORIGINAL ARTICLE
Analytical and experimental study on thermal conductivity of hardened cement pastes Mohammad Hajmohammadian Baghban Per Jostein Hovde • Stefan Jacobsen
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Received: 29 July 2012 / Accepted: 30 November 2012 / Published online: 11 December 2012 Ó RILEM 2012
Abstract Thermal conductivity of hardened cement pastes (hcps) in a wide range of water–cement ratio (w/c) is quantitatively investigated using a transient plane source measurement technique. Alkyl alkoxysilane and rapeseed oil were also added to determine the effect of internal hydrophobation on thermal conductivity of solid structure of hcps. The measurements were performed after drying at 50 and 105 °C as well as water submersion. A nonlinear relation was observed between thermal conductivity and w/c which is in alignment with Powers’ model. Samples dried at 50 °C still contained some moisture which increased thermal conductivity up to 11 % compared to samples dried at 105 °C. Furthermore, hydrophobic agents reduced thermal conductivity of dried samples up to 9 % which indicates the reduction in thermal conductivity of solid structure and is in line with observations by scanning electron microscope. A three phase model which can predict thermal conductivity of plain and hydrophobed hcps at different moisture states is
M. Hajmohammadian Baghban (&) P. J. Hovde Department of Civil and Transport Engineering, Norwegian University of Science and Technology, Trondheim, Norway e-mail: [email protected] S. Jacobsen Department of Structural Engineering, Norwegian University of Science and Technology, Trondheim, Norway
presented by exploiting composite models and Hashin–Shtrikman bounds. Keywords Cement paste Thermal conductivity Model Moisture Hydrophobic agent
1 Introduction Thermal conductivity is one of the key material properties that should be determined for the energy design process of the buildings. Since cement-based materials are considerably used in constructions, determination of thermal conductivity of these materials is of great importance. While cementitious composites with low thermal conductivity may be desirable for using as a part of heat insulation or for thermal bridge calculations, higher thermal conductivity can be of interest for the efficiency of embedded floor heating systems or when cement-based materials are exposed to the indoor environment to store heat and to mitigate temperature variations. Furthermore, thermal properties of cementitious composites are relevant to the other aspects such as structural behavior in which a low thermal conductivity may be desirable [1, 2]. Meanwhile, the given design values for thermal conductivity of cement-based materials are usually rudimentary in the building codes.
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Materials and Structures (2013) 46:1537–1546
Since cement paste, which controls most strength, transport and durability properties of cement-based materials, usually is also the most porous part of such materials, studying the properties of the paste can help understanding the behavior of the co
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