Empirical Estimation of the Hydraulic Diffusivity and Sorptivity of Unsaturated Concrete Subjected to Sustained Compressive Loading

The hydraulic diffusivity and sorptivity of cement-based materials are commonly regarded as two important properties to characterize the durability potential of building structures, especially when they are subjected to sustained loading. This paper presents an empirical analytical approach developed to theoretically estimate the hydraulic diffusivity of concrete from easily measured sorptivity under compressive loading. On the basis of unsaturated-flow theory (UFT), a general empirical estimation model for hydraulic diffusivity D(theta) of unsaturated concrete under sustained compressive loading is developed with the water-retention curve (WRC) and saturated permeability. By introducing the Boltzmann variable,. phi = xt(-1/2), the extended analytical method is applied to establish the relationship between hydraulic diffusivity and sorptivity under various compressive stress levels. An improved test apparatus was designed for real-time measuring the amount of water absorbed by hollow cylindrical concrete specimens under sustained axial loading. Compared with the traditional gravimetric method, this new apparatus can realize the combination of water movement and uniaxial loading action. By fitting the experimental results of cumulative water content versus square root of time (i - t(1/2)), the quantitative relationship between sorptivity and compressive stress level was obtained, which was then used to validate the proposed theoretical estimation model. Finally, it indicates that the empirical estimation approach could be used for refined modeling and simulating of the coupling issues between loading and environment. (C) 2017 American Society of Civil Engineers.