Page 80 - Build 165

So, salt deposition is unlikely to be the key factor contributing to material degradation in this environment with weak marine in uences.
Remarkably lower corrosion when less time of wetness
Material degradation relies on the presence of a moisture layer on its surface. This layer provides a medium critical for the occurrence of degradation reactions and dissolution of gaseous and/or solid pollutants. Therefore, environmental time of wetness was monitored following the ISO 9223:2012 Corrosion of metals and alloys – Corrosivity of atmospheres – Classi cation, determination and estimation de nition. This is the period during which the temperature is higher than 0°C while the humidity is higher than 80%.
This study found that the time of wetness values of the sheltered areas on the north and south walls were approximately 1,400 hours less than those of other areas (approximately 4,200–4,700 hours) during the 1-year monitoring period. The signi cant decrease in the time of wetness in the sheltered areas could lead to a remarkable reduction of material degradation despite more salt deposits being collected.
Hence, time of wetness rather than salt deposition is likely to be a factor that dominates material degradation within the di erent micro-environments on this building.
Implications of this eld monitoring
This study indicates that a simple rule for position-dependent material performance may not exist, and that the factor dominating material degradation processes may di er in di erent environments. Micro-environments on building envelopes are a complicated function of:
● local meteorological conditions
● concentration and type of atmospheric pollutants
● geometry and orientation of buildings.
These factors should be analysed further to establish an environ- mental pro le of building envelopes and improve understanding of positional material degradation.
More information coming to help speci ers
Monitoring is also being carried out on buildings subject to strong marine or geothermal influences for a more complete picture of di erent building micro-environments and their in uence on positional material degradation.
This will aid industry in making informed decisions when specifying the right materials and maintenance schemes to improve overall building performance.
78 — April/May 2018 — Build 165