Gas diffusivity test method development: Effect of cement paste saturation degree and concrete specimenthickness

The nature and structure of the concrete's pore system largely determine its durability. For example carbon dioxide gas transport through the pore system and its subsequent interaction with cement hydrates at the steel/concrete interface (SCI) is considered to be a big threat to reinforced-concrete structures. In a real environment, gas transport through cementitious materials is achieved by a diffusion process. Therefore, the determination of the gas diffusion coefficient of cementitious materials is necessary for the evaluation of their transport properties and the expectable service life. In the present study we describe a new technique for the determination of the gaseous oxygen diffusion coefficient of cement paste and concrete samples. For paste samples, we examine the influence of the degree of water saturation, hydration duration, and composition (samples with 10% silica fume and 50% slag are also tested) on the effective-diffusion coefficient of gaseous oxygen. As for concrete samples, we examine the relative influence of the specimen thickness on gas diffusivity. Oxygen-effective diffusion coefficient (De,O2) is found to be greatly influenced by the degree of water saturation of cement paste samples.