ABSTRACT
The reasons for the different damping maximums of hardened cement paste (hep) in a temperature range between +20°C and -160°C have been analysed. The bending vibration of a hep beam has been induced and the eigenfrequency and damping have been measured. Five temperature regions are apparent which correspond to the different damping mechanisms of pore water. Region II from -5°C to -50 °C contains a damping maximum due to the internal friction between the crystals of ice and salt in capillary pores of hep. In region III between -30°C and -70°C the damping peak characterizes phase transition of gel pore water. The sharp peak at -90°C in region IV between -60°C and -120°C is mainly due to a mechanical relaxation process of a defect monolayer of water molecules. It can be attributed to the interaction between the pore water and the internal solid surface of hep. Keywords: Cement paste, Low temperature, Dynamic elastic modulus, Damping maximum, Internal friction, Pore solutions, Activation energy, Dispersion, Mechanical relaxation
1. Introduction
The freezing of water in porous systems is determined by the solid-water interaction at the internal surface of hep which can exceed 100 m2/g. The freezing point is increasingly depressed with decreasing pore size and increasing salt concentration. Several physical and mechanical tests on the interaction between pore ice, the adsorbed water films and the internal surface of the solid have been published [1-10].
