Relative humidity

Sandra Myrtue

« Back to list
corrosion relative humidity
A relative humidity above 40% can lead to corrosion.

Relative humidity plays a crucial role in the assessment of corrosion potential in structural health monitoring. Corrosion is a chemical process that occurs when metal surfaces are exposed to water and oxygen, resulting in the deterioration of the material properties. The minimum relative humidity required for the initiation of corrosion is typically around 40%. Therefore, if the relative humidity is below this threshold, it can be inferred that corrosion is not likely to occur, and no measures need to be taken to mitigate its effects. However, when relative humidity exceeds 40%, it is important to measure and monitor the progression of corrosion to determine if mitigation measures are necessary to prevent further deterioration of the structure.

In suspension bridges, dehumidification techniques are becoming increasingly common in the steel bridge girders and main cables to prevent corrosion in the deck and cables. The main cables of suspension bridges are typically composed of a large number of small steel wires, creating ample space for water to accumulate and increasing the surface area for corrosion to develop. By reducing the relative humidity within these structures, the risk of corrosion can be significantly reduced, preserving the integrity and longevity of the bridge.

Relative humidity sensors are frequently utilized as a component of weather stations or in conjunction with temperature sensors to evaluate the potential for corrosion in concrete structures and to monitor the curing process of concrete. The relative humidity level can provide valuable insight into the moisture content of the concrete and the surrounding environment, which is essential in assessing the risk of corrosion and ensuring proper curing of the concrete. Temperature and relative humidity are the two critical factors that determine the progress of the curing process. By monitoring these two factors, it is possible to establish the point at which the concrete elements are ready for construction use. With this information, construction teams can schedule the use of the concrete elements in a timely manner, ensuring that they are available for use as soon as they are ready, thus optimizing the construction process and minimizing delays.


Relative humidity is a measure of the amount of water vapor present in the air, relative to the maximum amount that the air could hold at a given temperature. It is typically expressed as a percentage. The formula for calculating relative humidity is:

Relative Humidity = (Actual Vapor Pressure / Saturation Vapor Pressure) x 100

where actual vapor pressure is the partial pressure of water vapor in the air, and saturation vapor pressure is the maximum partial pressure of water vapor that the air can hold at a given temperature.

« Back to list