Permeability refers to how readily liquids or gases can move through concrete. This characteristic is relevant for ensuring the impermeability of structures that retain liquid and resist chemical degradation.
Concrete permeability is assessed with a basic lab test, wherein all sides except the top of a concrete sample are sealed. Pressurized water is then applied to the top surface.
Upon reaching a steady state, which may take around ten days, the volume of water that has permeated through a set thickness of the concrete over a specific duration is recorded.
For concrete, which consists of standard normal-weight aggregates, permeability is determined by the porosity of the cement paste.
The permeability of hydrated cement paste is not only determined by the small pore size within the gel but is influenced by the presence of larger capillary pores.
As hydration progresses, the permeability of the cement paste declines because some of the spaces originally filled with water are closed off.
At lower water-to-cement ratios, typically below 0.6, permeability decreases because the capillaries become segmented or broken up, impeding fluid flow.
