Measuring water sorption isotherm of mortar containing chloride

The water sorption isotherm of materials is of great importance to predict their durability. Many different methods are used in the literature to measure this water sorption isotherm. Chloride present in concrete elements/structures e.g. in marine exposure, can change the water sorption of the material. In this paper, the water sorption isotherm of a standard mortar with and without chloride is measured with a hygroscopic method. The chloride penetration into the sample is obtained by the vacuum saturation method. Subsequently the sample is placed in a glass vessel and dried. By injecting a known amount of water into the vessel, the water evaporates and is partly adsorbed by the sample until an equilibrium state is reached. With the known amount of the injected water into the vessel, the humidity inside the vessel and the volume of the vessel, one point of the adsorption isotherm is determined. For measuring the next point, more water is injected into the vessel. More points are measured in the same manner until the sample is saturated and with this the adsorption isotherm is completed. Afterwards, the measurement of the desorption isotherm starts with blowing dry air with a known flow, humidity and duration into the vessel. After reaching equilibrium, the first point of the desorption curve is measured. The next point is measured by blowing more dry air into the vessel. This continues until the sample is completely dry and with it the desorption isotherm is also completed.