# Modern approach to surface layer modifications of hydrated cement paste for improving permeability estimates of virtual concrete

Piet Stroeven ^{1}, Kai Li ^{2}

^{1} Delft University of Technology, Faculty of Civil Engineering and Geosciences, the Netherlands

^{2} Hunan University, College of Civil Engineering, Changsha, China

*i.e.*, a 0.1 to 0.5 µm increased thickness. Therefore, in the normal 3D set up, the smooth vector-based hydration layer is given a stepwise thickness increase in this range, whereupon the consequences for pore geometry and topology, as well as for permeability can be investigated. The outcomes of this study are laid down in a separate publication. When further

*structural*information on nano level will become available in the near future, the simulations can be appropriately adapted. This paper specifically proposes as a practical methodology to slightly step-wise enlarge at the packing simulation stage the

*fresh cement grains*in proportion to their respective sizes. The herein introduced standard methodology for porosimetry and permeability estimation can readily be employed for simulating these cases. This is demonstrated for cement paste with

*w/c*= 0.5, whereby packing density is increased by about 1% per step. This can be associated with a fictitious reduction in

*w/c*from 0.49 to 0.45. It could be demonstrated this way that a permeability decline of one order of magnitude can be realized,

*i.e.*, at least enough to bridge the modest gap with corrected experimental permeability data. So, the final solution can be expected in this range.

**Key words**: Cement, hydration, surface modification, nano-packing, permeability, simulation