Isotopic methods for tracing moisture and sampling

The isotopic composition of water can reveal its origin and provide information about the physical processes that water has undergone. The knowledge of the effects of the transport mechanisms and reactions on the isotopes can be used to identify the sources of moisture in buildings as shown in previous research by Gudmundsson (2001). In short water in the environment consists of various isotopes of oxygen and hydrogen including the most common of 1H and 16O as well as their sister isotopes: deuterium D and oxygen-18. These isotopes are stable and can therefore serve as a distinct signature to every water sample. Previous studies have been based on the comparison of various samples of free water and their isotopic content. In order to develop the method further some methods for retrieving water from porous material and air have now been investigated. Three different methods of retrieving water from the porous material have been tested. Two of them, squeezing and distillation, are direct methods. The squeezing method was carried out on a saturated sample of concrete by the means of a hydraulic press. In the distillation process hygroscopic moisture was collected from a sample of light aggregate concrete. 30% and 50% of the pore water was retrieved by squeezing and evaporation respectively. In both direct methods samples were initially crushed. The third method is a dilution method, in which we take advantage of diffusion of isotopes from pores water into surrounding water. Because we do not test directly the water from the porous material but its solution, it is called indirect method. Furthermore some methods of retrieving water from water vapor were investigated. Firstly by using a pipe containing liquid nitrogen (boiling point -195,8 oC) that induces condensation and freezing of water vapor on the surface of the pipe, where water was collected for isotope analysis. This method makes it possible to measure the isotopic composition of water vapor from both sides of a building envelope. Secondly we have used LiCl salt to gather water from the surrounding air from a source with known isotopic content.