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A composite based on polyaniline (PANI) and low density polyethylene (LDPE) with electrical conductivity was developed. Polyaniline was polymerized by chemical oxidation and doped with dodecyl-benzene-sulfonic acid (DBSA). PANI-LDPE composites were prepared via melt blending and the films were obtained by compression molding. The influence of three variables of the blending (temperature, [PANI], rotor speed) on conductivity, microstructure and mechanical properties of the composites was studied by means of statistical tools and a 2 3 experimental design. The results show that the PANI concentration is the most influential variable, which mainly affects the conductivity and the elongation at break of the composites. These changes are related to the microstructure of the composites. Statistically, the other variables don't show significant influence on conductivity and mechanical properties in the studied range. POLYM. COMPOS.

Concrete dams located in northern regions are subjected to severe cyclic seasonal temperature variations, which may contribute significantly to the deterioration of the exposed faces and the long-term degradation of strength and stiffness properties. This paper presents a comparative study of thermal protection methods that might be used to improve the durability of concrete dams subjected to freeze–thaw cycles. First, the thermal, structural, and physical processes that affect the dam's resistance to freeze–thaw cycles are discussed. The thermal durability of existing northern concrete dams is then reviewed. Three thermal protection schemes are presented: (i) insulation membranes applied directly to the concrete facings, (ii) insulation membranes with air spaces for drainage or visual inspection, and (iii) insulation made of granular material. Two-dimensional thermomechanical finite element analyses of a typical gravity dam located in Quebec are then carried out to assess the performance of thermal protection systems using different configurations of insulating materials and exposure conditions, and to develop appropriate design criteria. Key words: concrete dams, thermal analysis, insulation, finite element method.

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