Water absorption coefficient
The water absorption coefficient ( w-value for short ) indicates how much water a substance absorbs within a certain time.
A fabric with the base area A is immersed in water. The substance is weighed at certain time intervals and one obtains the mass of the absorbed water m as a function of the time t . This gives the water absorption coefficient
If you enter the mass m in a coordinate system , specifying the root time in the x-axis , a straight line results from the slope of which the water absorption coefficient w can be determined.
Use in building materials technology
The water absorption coefficient is often used in building materials technology because water damage is one of the most costly renovations, caused for example by moisture penetration, frost damage or mold and algae infestation.
The following classification of the water absorption coefficient is common:
- absorbent: w > 2 kg / (m 2 h 0.5 )
- water-resistant: w ≤ 2 kg / (m 2 h 0.5 )
- water-repellent: w ≤ 0.5 kg / (m 2 h 0.5 )
- impermeable to water: w ≤ 0.001 kg / (m 2 h 0.5 )
Examples of some building materials
- Solid brick: w = 20 to 30 kg / (m 2 h 0.5 )
- Light brick: w = 5 to 8 kg / (m 2 · h 0.5 )
- Expanded clay: w = 0.2 to 0.24 kg / (m 2 · h 0.5 )
- Cement plaster : w = 2 to 3 kg / (m 2 h 0.5 )
- Plastic dispersion: w = 0.05 to 0.2 kg / (m 2 h 0.5 )
- Spruce wood (axial): w = 2.0-3.0 kg / (m 2 · h 0.5 )
Web links
- Building physics interactive University of Duisburg-Essen