The Measurement of the Internal Relative Humidity of Concrete at Early Ages

Abstract

Abstract Measurement of the internal relative humidity (RH) in concrete can be used to describe the availability of water, which has implications on several properties including shrinkage and hydration rate. However, accurate measurement of the internal RH of concrete is challenging, especially at early ages. This article examines different methods of using capacitive sensors for measuring the internal RH of concrete. The capacitive RH sensors are typically placed inside a void that enables the RH of the air within the void to be measured. Condensation of water vapor (caused by variation in temperature of the sample) has been observed to result in unreliable measurements, calibration issues, sensor malfunction, and sensor damage. Sensors may be heated cyclically to evaporate the condensed water vapor; however, many of these sensors failed to operate properly. Continuously heated sensors maintain the sensor at a higher temperature than the ambient concrete to reduce the potential for the formation of condensation. The continuously heated sensor provided the best results and is a good candidate for future testing. Suggestions for the measurement of internal concrete RH and calibration of the sensors are provided.