Evaluating the short- and long-term moisture transport phenomena in lightweight aggregate concretes

摘要

The primary descriptor of moisture transport in concretes is sorptivity, which represents the moisture intake through the capillary pores at early times. Although the effectiveness of this parameter in quantifying the near surface characteristics is well established, it is also necessary to consider the effect of long-term moisture transport through the smaller pores at later periods of time (diffusion) in order meaningfully to compare the durability of different mixtures and to arrive at more accurate indicators of service life. The present paper uses a combination of the exponential equation for sorption and a solution of Fick's second law for diffusion to estimate the moisture transport parameters in lightweight aggregate concretes. Lightweight aggregate concrete specimens are subjected to different pre-conditioning regimes before being subjected to moisture transport tests in order to understand the influence of moisture conditions on the transport parameters. A 'saturation index' is used to quantify the influence of saturation levels in moisture transport. The transport parameters at any saturation level could be linked to the saturation indices and the corresponding parameters at near-perfect saturation. It is shown in this paper that the total mass of water absorbed by a specimen cannot be viewed as a direct indicator of its moisture transport parameters. The relative contributions of sorption and diffusion to the total moisture intake are also explored. While the contribution of diffusion to the total moisture intake never exceeds that of sorption in normal-weight aggregate concretes, it is seen that in lightweight concretes, as the saturation levels are lowered, the contribution of diffusion does exceed that of sorption.