Kinetics of confined water freezing – An application to the frost-resistance of porous materials

Abstract

In the manuscript one presents a regular study aiming to determine the relation describing the freezing kinetics as a function of temperature employing the following cooling rates: 2.5 °C/min, 5 °C/min, 7.5 °C/min and 10 °C/min. The increase in ice mass is determined using differential scanning calorimeter by integrating the net heat flow for two building materials: red clay brick and cement paste (w/c = 0.5). The isoconversional method, which states that the transition rate (the rate of ice mass) at constant extent of conversion (ice mass) depends only on temperature, is applied to determine a transition model. We select the most appropriate model and determine the kinetic triplet using the method proposed by Málek and recommended by International Committee for Thermal Analysis and Calorimetry (ICTAC). The activation energy is estimated using the differential Friedman's method. Both analysed materials evinced different microstructures, but the kinetic parameters determined for both of them are relatively similar. Hence, one might conclude that the kinetic of inpore water freezing is not very sensitive to size of voids. The results of experimental analysis enabled one to formulate the general kinetic equations for both analysed materials. The comparison of theoretical and experimental results evinces good agreement. Therefore, the formulas derived in the manuscript might be used for further analysis of the porous building materials durability, which experience significant temperature fluctuations. Furthermore, they can be used to design the most efficient testing procedure for the determination of frost resistance of concrete. The proposed procedure might be used for other problems related with the phase transition of water in porous materials, i.e., food freezing geotechnics, etc.Concluding, the results calculated using the proposed models for both materials are in good agreement with the experimental data. Therefore, the formulas derived in the manuscript might be used for further analysis of the porous building materials durability, which experience significant temperature fluctuations. Furthermore, they can be used to design the most efficient testing procedure for the determination of frost resistance of concrete. The proposed procedure might be used for other problems related with the phase transition of water in porous materials, i.e. food freezing geotechnics, etc.