Deterioration of concrete or reinforcing through contaminant penetration is often the result of repeated wetting and drying of exposed structures. Uptake of water (and therefore ions) by unsaturated, hardened concrete may be characterised by the Sorptivity. This is a simple parameter to determine and is increasingly being used as a measure of concrete resistance to exposure in aggressive environments. The complete absorption process is described by a nonlinear diffusion equation, with the hydraulic diffusivity a strongly nonlinear function of the degree of saturation of the concrete. A simple formula for the wetting profile is derived from this equation for an exponential dependence of diffusivity on the moisture content. Furthermore, the required diffusivity parameters are shown to be easily obtained from suitable sorptivity measurements. The accuracy of the absorption formula as well as the diffusivity derived from the Sorptivity Test are tested and confirmed by comparison with data obtained by NMR imaging of water absorption in a large concrete sample.

  • INTRODUCTION

  • THEORY

  • APPLICATION

  • CONCLUSIONS

  • ACKNOWLEDGEMENTS

  • REFERENCES

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