Published on the Journal of Materials in Civil Engineering, 16 [1] (2004) 8-14 © by American Society of Civil Engineers Thermal Conductivity of Clay Bricks Michele Dondi 1 , Francesca Mazzanti 1 , Paolo Principi 2 , Mariarosa Raimondo 1 , Giorgio Zanarini 3 1 CNR- Institute of Science and Technology for Ceramics, Faenza (Italy); 2 Department of Energetics, University of Ancona, Ancona (Italy) 3 Consorzio Alveolater, Bologna (Italy) Abstract: In the present work the thermal conductivity of twenty-nine samples of clay bricks was measured and the correlations of the thermal performance with the compositional, physical and microstructural features of products were investigated. The results obtained directed our attention toward a better understanding of the role played by some parameters (i.e. mineralogical components and pore size distribution), other than bulk density, in improving or depressing the insulating properties of bricks. Among them, the unfavourable role of quartz, Ca-rich silicates and amorphous phase came out, while the role of pore size and specific surface should be more accurately evaluated in the structural design of materials. Key Words: bricks, thermal insulation, bulk density, mineralogy, microstructure. 1. Introduction Due to the ever increasing requirements for energy saving and a pressing competition with alternative building materials, the thermal insulating properties of clay bricks have recently become more and more important (Krahl 1989). Many studies have been devoted to better understand the way of improving the thermal performance of clay bricks, acting on both the physical properties of terracotta (porosity, etc.) and the geometrical design of products (Hauck et al. 1998, Rimpel and Schmedders 1996, Jungk et al. 1997, Schmidt-Reinholtz 1990, Jungk and Krcmar 1996, Anton 1993, Krahl 1989). These studies point out that the thermal conductivity of bricks is mainly related to their bulk density, so that increasing the thermal insulating properties implies the production of materials with a higher porosity (Jungk et al. 1997, Schmidt-Reinholtz 1990, Jungk and Krcmar 1996). However, the correlation between thermal conductivity and bulk density is not statistically significant since data exhibit on the whole a considerable scattering (Fig. 1). As a matter of fact, bulk density alone is not able to describe and accurately reflect the thermal behaviour of clay bricks. The different analytical methods used to measure the thermal conductivity (Anton 1993, DIN 4108, UNI 1994, Albenque 1992) probably account for some discrepancies but, in most cases, the compositional and microstructural features of bricks play a very important role (Jungk and Krcmar 1996, Dondi et al. 2000, Schulle and Kutzendorfer 1988, Schlegek et al. 1999, Rimpel and El Ghazzali 1998). This work is aimed at outlining the thermal conductivity of clay bricks trying to single out the compositional, physical or microstructural parameters which affect their thermal behaviour most significantly. Moreover, a statistical treatment of data was performed in order to quantify the influence of the above mentioned characteristics on thermal conductivity. 1