An Experimental Study On The Water Permeability Of Cement Paste And Concrete

Water permeability of concrete plays an important role in various performance deteriorations and is of great practical significance for the durability assessment and design of concrete structures. The water permeability of cement paste and concrete is studied in this paper through the steady flow method. The mercury intrusion test for the structure of cement paste is combined to qualitatively analyze the relationship between the microscopic pore structure and the macroscopic water permeability. Based on the relevant theories, the fractal characteristics of the microscopic pore structure and the computation of the interfacial transition zone(ITZ) volume fraction in concrete are discussed.The experimental results show that the porosity of cement paste increases with the water/cement ratio, while the parameters of the pore structure distribution first increase and then decrease with an increase in water/cement ratio and increase rapidly at the water/cement ratio of 0.5. The water permeability coefficients of cement paste and concrete decrease with increasing the curing age or decreasing the water/cement ratio. For a given water/cement ratio, the water permeability coefficient of concrete is larger than that of cement paste. The water permeability coefficient of concrete first decreases and then increases as the aggregate volume content increases and reaches the minimum value at the aggregate volume content of 55 %. Compared with concrete made with the Fuller gradation, concrete made with the equal volume fraction gradation has a lower water permeability coefficient.Theoretical analysis shows that the water permeability coefficient of cement paste decreases with the increase of the thickness for a given cross-sectional area of the structure and increases with increasing the cross-sectional area for a given thickness of the structure. The water permeability coefficient increases with the increase of the area fractal dimension for a given tortuosity fractal dimension or with the decrease of the tortuosity fractal dimension for a given area fractal dimension. The ITZ thickness and the maximum aggregate size are the most and lest important factors that affect the ITZ volume fraction. The ITZ volume fraction in concrete made with the equal volume fraction gradation is approximately twice that with Fuller gradation.