Freezing–thawing phenomena in fired clay materials and consequences on their durability

Up to now there were four freezing tests methods for tiles in the European Union. These methods derive from respectively four national methods: Benelux Method (A), German Method (B), French Method (C), and British Method (D). A new procedure, called method E, which consist in (i) covering the back face of the tile under test with a wet cloth, (ii) imposing a new defining saturating process and (iii) defining a minimum cycles number, was integrated as the fifth frost resistance test in the European Union. This procedure, implemented by the Tiles and Bricks Technical Centre (CTTB), leads to laboratory results which are in very good agreement with the behaviour on different European sites of products. Nevertheless despite these good results, the E-method presents the disadvantage, for the industrials point of view, to be time consuming, considering the great number of cycles which are expected. The motivation of this research is to better understand the physical phenomena involved during the freezing and thawing cycles in order to be able to predict what are the more relevant parameters where the control of which, during manufacturing of materials, could allow to reduce the time necessary for the qualification of the materials. We started in this work from the materials tested by European countries in the frame of the E-method, following it procedures and searching to understand why are the materials frost resistant or not. In this perspective the strains in two types of tiles were observed during freezing–thawing cycles without and with cloth. From the experimental strains, the pressure building up in the pores is calculated and the pressure of crystallization is thus identified. This step allows the pressure of the liquid phase to be deduced. For saturated products it as been stated that the water is subjected to an overpressure during the freezing test and a wet cloth placed in contact with the tiles increased its magnitude.