Anomalous water diffusion in concrete based on neutron backscattering measurements

Abstract EN

This work presents a new method based on neutron backscatter measurements to study isothermal water flow and distribution in concretes.

Ordinary concrete samples with different percentages of silica fume are used to study the water profiles (0-x) which describe the water infiltration in the samples along the flow directions, x.

for different absorbing times.

The macroscopic theory of water infiltration in porous media was used to model the infiltration process.

The obtained results show that the diffusion process is anomalous; Le., the water front position, ip does not follow the square root behavior of the absorption time, -ft and the water profiles [o x/J~t) do not collapse to the universal one master curves for all samples.

It is shown that the diffusion process is a super, the power law.

xp = yp t 53successfully describes the advance of water front with time and the water profiles collapse to universal one master curves (9-y )• The water diffusivities were derived in an analytical form for the investigated samples.

They have the hyper- diffusion behavior; i.e.

diffusivities decrease as the water content increase.

It is shown that the diffusivity for all water contents deceases with increasing the silica fume percentage np to 15 However, for concrete with silica fame - 20 % the observed phenomenon is reversed due to the deterioration of concrete physical and mechanical properties.