Influence of Microstructure on the Tritiated Water Diffusivity of Mortars

Four different series of mortars were cast to study the influence of the microstructure on the transport coefficient of tritiated water. Test parameters included type of binder, water/binder ratio (0.25 and 0.45), and sand volume fraction (0% and 50%). Mercury intrusion porosimetry was used to characterize the pore structure of all mixtures. The effective tritiated water diffusion coefficients were determined using a simple diffusion test. The test results show that the reduction of the water/binder ratio and the use of silica fume significantly contribute to reduce the transport properties. The test results also indicate that aggregates modify both the microstructure and the transport properties of mortars. The diffusion coefficient of tritiated water was found to decrease with an increase of the sand volume fraction. The increased tortuosity of the matrix induced by the presence of aggregates thus appears to be more important than the influence of the interfacial transition zone. Results also clearly underline the influence of the preparation technique prior to a mercury intrusion experiment.