### What are the Difference Among Permeability, Diffusion and Sorption within Concrete?

Dear reader fluids travels through concrete not only by permeability but there have also other mechanisms. Here we will discuss about the process which facilitates easy movement of fluids into concrete. We have already had few ideas about affect of ingressed fluid and it becomes now very important to distinguish among processes of ingression of fluids.

The process involved is

a. Permeability

b. Diffusion

c. Sorption

We have discussed about permeability of concrete in our last post and previous posts. In our next post we will learn about mathematical expression for determining permeability.

In case of permeability, important parameter is pressure i.e. fluid flows due to difference in pressure between two regions with in concrete whereas diffusion depends on concentration. In diffusion process, fluid moves due to difference in concentration. The property that defines diffusion is called diffusivity of concrete. Diffusion may associated with gases; they can move through

-water filled space

-air filled space

But the rate of diffusion of gas differs greatly depending on the space through which it passes. Say diffusion through water filled space is slower than through air filled space by (104-105) times.

Now we will learn about another process sorption; this process allows fluid to move by capillary movement in pores of concrete exposed to ambient medium. It should keep in mind that sorption is valid when concrete is in partially dry or saturated states as capillary suction can only take under this condition. So we should not worry about a concrete suction of fully dry or saturated condition.