Lena Mengel

Lena Mengel

Lena Mengel, M.Sc.

Mesoscale modeling of crack-induced permeability of reinforced concrete

Cracking due to tension in concrete is characteristic for reinforced concrete construction. In the case of macro cracks even small crack widths are able to impair the durability of struc- tures. In particular, the prediction of water transport focus great interest in practice. The influence of crack width on flow rates has been investigated in several researches.

Nowadays the fluid transport coul d be estimated considering crack opening and roughness of the crack surface. A flow law, which is often used because of its simplicity is the cubic law (q = (ξ∙g∙I∙b∙w³)/(12∙ν) [m³/s]).

The goal of the project is to improve the approach taking into account other important parameters of the material like concrete strength and concrete mixture. The degree of reinforce- ment and the element thickness are import ant factors as well.

Several experiments are planned. At first a permeation test of reinforced c oncrete samples with a specific crack width at the sample surface will be performed. Wedges will be pushed into the concrete sample in order to induce crack between 0,1 and 0,3 mm. In the first step the fluid will be water, in further steps also corrosive fluids will be investigated. Furthermore, several values like the used aggregates and w/c-values and concrete mixtures will be varied. To determine the effect of selfhealing of cracks the permeation test will be carried out as a short term and as a long term experiment. Micro-CT investigations will be carried out on cores drill ed from the permeation test samples. The crack will be filled with epoxy resin before x-rays measure ments to fix the crack pattern and get detailed information of the crack geometry. To estimate the roughness, the samples fractured surfaces will be analyzed with a digital microscope.

Approaches to develop the cubic law are:

  • Stochastic description of cr ack path and roughness of the crack surface,
  • Stochastic description of the crack width through the component thickness,
  • Description of the concrete permeability by taking into account the influence of macro cracks. A computational description model is plan ned b esides the mentioned experiments,
  • The experimental and computational results will be used to express a finer and more extensive description of the fluid transport for cracked porous structures for the practical applications.

Publications within the framework of the RTG:

Conference contribution with publication in conference proceedings:

L. Mengel, D. Köhnke and H. Budelmann. Radiation effects on concrete. Research on Radioactive Waste Management, Ethics - Society - Technology. Final ENTRIA Conference, Braunschweig, September 2017.