Determination of the water retention curve from drying experiments using infrared thermography: A preliminary study

A method is proposed for experimental determination of the water retention curve from drying tests performed on capillary active materials. Non-destructive techniques (gravimetric analysis, infrared thermography) are employed for measuring water content, drying rate and surface temperature during time for a set of material samples. The surface relative humidity is calculated from the measured data through analytical procedure. Hence, assuming uniform water content distribution inside the samples, which applies if the mass transfer Biot number is small enough, the relation between relative humidity and water content is derived. This relation represents the water retention curve for the considered transient desorption behavior and, as shown in previous studies, it may deviate from the trend measured through steady state experiments. The proposed method differs substantially from other ones commonly employed to the same aim. It is useful for investigation of the so called dynamic effects, recently observed by other authors in the hygrothermal behavior of construction materials. For a first test, calcium silicate specimens are employed and the results are compared with those reported in the literature. An error propagation analysis is also included.