Freezing–thawing curves of earthen bricks with dielectric measurement: Insight into the influence of pore structure and initial moisture content

Abstract

Under cold climate, poral water of building materials can be exposed to freezing–thawing (F–T) cycles that induce severe frost damage and jeopardize their durability. The F–T curve (variation in ice or unfrozen liquid content with negative temperatures) is a key property to examine and predict the behavior of porous materials under freezing temperatures. However, there is a lack of adapted procedures to evaluate the F–T curves of unsaturated earthen bricks. To fill this gap, this study proposes an experimental protocol, based on time domain reflectometry (TDR), to quantify the remaining liquid water in unsaturated earthen building materials at different temperatures from ＋10 °C to −20 °C. The validity of the device developed to determine F–T curves was verified with low temperature calorimetry (LTC). The dielectric measurement with TDR provides consistent quantification of remaining liquid water content with freezing temperatures. In this study, the influence of initial moisture conditions was investigated through both normal and pathological humid situations of earthen buildings. The normal service situation in winter season was studied with samples conditioned at relative humidity (RH) of RH75% and RH95% which lead to initial liquid saturation SL0 lower than 35% in the tested materials. The moisture pathological case was investigated with initial liquid saturation degrees of 75%, 85% and 95%. The necessary condition of water freezing in earthen materials, in function of their initial saturation ratio or conditioning relative humidity, was examined through a microstructural analysis. This approach also brought understanding about the dependency of the remaining unfrozen water with the freezing temperature.