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 threedimensional 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.

Relating Liquid Location as a Function of Contact Time Within a Porous Coating Structure to Optical Reflectance

“…This results in a preferred pathway absorption through a network of pores defined by the inertial and plug-like flow within the fine scale connectivity. This has been demonstrated by the work of Schoelkopf et al and Gane and Ridgway using real and corresponding model network structures (Schoelkopf et al 2000a(Schoelkopf et al , 2004aGane 2004;Ridgway et al 2006a). The study reported here, sets out to define the saturation level as a function of distance approaching the wetting front so as to quantify the spatial definition of the preferred pathway mechanism as a function of reducing structural permeability (binder level and depth/time).…”

Neutron Radiography Studies of Water Self-Diffusion in Porous Medium

“…The studies were performed on a sample of fired clay brick of effective porosity ∼ 30% (36% as determined by destructive mercury intrusion), of the same kind as used previously as the medium in spontaneous imbibition studies [12][13][14]. The effective capillary radius of the sample as determined from the rate of water imbibition was ∼ 5.5 nm.…”

Visualization and quantification of water movement in porous cement-based materials by real time thermal neutron radiography: Theoretical analysis and experimental study

“…This method requires good experience and sophisticated analysis to fulfil its potential performance. 4) Radiation attenuation techniques: These include X-ray system [5], gamma ray system [6] and neutron radiography system [7][8][9][10][11][12][13][14][15]. Their attenuations can be related to water content within the materials.…”

“…For instance, Pleinert [7] studied the moisture distribution in mortar under drying condition by means of neutron radiography with high resolution; Hassanein [8,9] also presented the possibility and successfully studied the water imbibition into different building stones using neutron radiography; Masschaele [10] studied fluid motion into porous sand and limestone in three dimensions visibly; and Ridgway [11] established the network absorption model based on the experimental water absorption data of red clay brick and white siliceous brick by neutron radiography. Pugliesi [12] has utilized neutron radiography to observe cracks in concrete.…”