Usually the ’ water is lost due to the competition of two different phenomena, l’imbibition and capillarity, the first is physical-chemical nature and the second is purely physical nature.
In both cases, holding capacity is due to electrostatic forces that you establish between molecules d ’ water and solid support matrix (be it soil or bricks). It is necessary to exert pressure to subtract the water retained by the ’ solid matrix is called the matrix and voltage is usually negative values.capillary moisture
The capillary restraint is due to the result of forces acting on each molecule d ’ water that occupies pores of the material; These forces are always caused by four distinct and well-known forces:
– gravitational forces which act on molecules;
– internal cohesion forces between molecules of water ’;
– attractive forces between the ’ atmosphere of support and d ’ water molecules;
– adhesion forces between molecules of water and ’ the surface of the solid matrix.
About molecules arranged in a short distance from the solid particles of support, the result is concorde adhesion forces, While the relatively distant molecules, It exerts a gravitational force resulting concorde. In other words, where the water is ’ away from solid particles, This is subject to downward percolation because attracted by gravity, while where the particle is closer and closer to the solid particles is liable to be withheld because attracted by adhesion forces. capillary moisture
Even more simply: in a system consisting of two solid particles arranged mutual distance and space between them including, the ’ water that occupies this space is subject to percolation if the distance exceeds a certain value, While it is subjected to capillary restraint if the same distance is less. The reference value of this distance is 8 µm: the pores with diameters less than 8 µm (these pores) hold the capillary water ’ winning the force of gravity, While those with a diameter of more (known as Macropores) Unable to hold back the water ’ subjected to gravity.
Under optimal conditions of moisture and aeration then the micropores and the macropores are occupied by water from the air. capillary moisture
The presence of ’ water in Macropores can be:
– of a temporary nature since it is free of water and is intended to move vertically or along the profile of the support and in any case down. capillary moisture
– semi permanent nature since it is imprisoned in salty water tends to accumulate hygroscopic which do not allow the descent. capillary moisture
By Convention call:
– capillary water those detained in the pores and you have statically forming concave meniscus at the ’ interface of air/water separation.
– gravitational water that subject to movement through Macropores or who remains imprisoned in them as a result of water retention due to hygroscopic salt or components.
The imbibition restraint is due to the properties of particles with electrical charges to attract the ’ surface water due to electrostatic forces due to the ion-dipole type. L ’ electrostatic attraction is exercised both ions incorporated into the crystal lattice of minerals, by dissociated functional groups of organic compounds, both the ions adsorbed on the surface of the colloids. capillary moisture
By virtue of these forces, l ’ water tends to form a thin layer whose thickness depends on the electrostatic field strength ’ generated by solid particles. The ’ interaction between water and solid particle is superficial and therefore depends on electrical particle density. Like all d ’ surface interface phenomena, the ’ intensity of this interaction increases all ’ the surface to volume ratio and, then, It decreases with increasing particle size. capillary moisture
In practice, the forces of attraction are:
– very intense in the case of Atomic-sized particles (ions)
– relatively intense in the case of colloidal particle size (less than 0,1 µm)
– very weak in the case of macroscopic size particles (clay of over 0,1 µm, limo, sand and skeleton).
The different intensity of d ’ attraction forces results in the development of d ’ hydration layers of different thickness: the ions are surrounded by a thick layer of d ’ water molecules determines the dispersion in solution; small colloidal particles generate intense enough fields to tie exchangeable ions and, through their hydration, a layer of water molecules d ’ quite often. The thickness of this layer does not allows the dispersion, therefore flocculano support colloids remaining gel State.
Only in the case of large amounts of soda will ’ adsorbed moisture to disperse colloids. The larger particles, Finally, generate an electric field of low intensity and the amount of water that can bind ’ is modest.
Based on the foregoing, the ability of a support to hold the water ’ (in the absence of hygroscopic or salt content) depends essentially on two factors: total porosity and pores/Macropores and only they will depend on the ability of the wire support l ’ water by capillarity.
These two properties are derived from the texture and structure:
– a rich support of coarse particles will have a modest surface development, therefore a low porosity largely represented by Macropores
– a rich support of fine particles will have a highly developed area ’ therefore a high porosity (even more than 50%) and a relationship between micro and Macropores sharply in favor of the first.
As a result of all the above, It is shown as a masonry, Although potentially capillary porous and ideally, would not that be traced back the water ’ (and then the ’ moisture) In addition very circumscribed limits and never in addition to theoretical levels of a few centimetres from the ground.
And’ therefore generally wrong to define the phenomenon of rising damp in masonry as capillary moisture.
IgroDry Research Centre