Water Absorption into Construction Materials: Comparison of Neutron Radiography Data with Network Absorption Models

Abstract

Two different porous building materials have been previously measured and analysed (El-Abd and Milczarek, 2004, IEEE Trans. Nuclear Sci.; El-Abd et al., 2004, J. Phys. D) using neutron radiography to measure the water front position over time. The results from this experimental approach show a similar behaviour to the predictions from idealised model structures, in that there is a cross over point where the fastest rate of absorption at first favours the finer structure material and at later times favours the coarser pore structure material. The computer model, Pore-Cor** is used to generate the idealised structures and the absorption of fluid into porous structures follows a Bosanquet wetting algorithm for fluids undergoing both inertial and viscous dynamical flow (Ridgway and Gane, 2002, Colloids Surfaces A: Physicochem. Eng. Aspects 206, 217–239.). The model structures comprise cubic pores connected by cylindrical throats on a three-dimensional 10× 10× 10 position matrix simulating the void structure of porous media by fitting as closely as possible the modelled mercury intrusion curve to that of the experimentally determined mercury intrusion curve of the actual sample. They show the transition that occurs in the absorption behaviour from the linear t-dependent short timescale inertial regime to the familiar √t Lucas-Washburn viscous regime. The simulated absorption algorithm applied to these model structures also shows a fluid position behaviour that replicates qualitatively, given the limitation of representative sample volume, the cross over seen experimentally. Furthermore, the existence of a preferred wetting path is demonstrated in the experimental as well as the model wetting front behaviour. In the case of the structure containing the broader range of pore sizes, the wetting front is considered to proceed by a network of optimal size combinations (inertial wetting versus viscous drag) and connectivity, leaving some pores behind the wetting front unfilled or only partially filled.