Hygrometric Assessment of Internal Relative Humidity in Concrete: Practical Application Issues

Abstract

The use of embedded relative humidity (RH) sensors for assessing the internal humidity in concrete is widely spread, dully backed by existing standards. Even though the approaches adopted in the literature seem to have several differences between each other, few or none research works were found to focus on the comparison of performance of sensors and methods for RH measurement. In view of this, several sets of experiments comparing the performances of different sensors and monitoring procedures will be presented in this paper, discussing the main findings and providing recommendations for the strategies to be adopted in what concerns the measurement technique. The main points addressed in this work are: (i) comparisons between readily available systems for RH measurement in concrete, as well as custom measurement strategies reported in the literature; (ii) issues related to calibration procedures and re-calibration necessity; (iii) relevance of the existence of an interface porous material between the embedded sensor and the measurement spot in concrete; (iv) importance of the size of the embedment body into which the RH sensor is inserted; (v) equivalence of results obtained when the probe is constantly inserted into the embedment body, or placed inside it at discrete instants.

Improving the Durability of High Early Strength (HES) Concrete Patching Materials for Concrete Pavements

“…These cells were sealed, and a heated capacitive type RH and temperature probe was inserted (Rotronic Sensor HC2-S[3]-HEATED [39]). The sensors had a reported accuracy of 6 1.3% RH from 0%-80%, although the accuracy was expected to decrease in the range of 80%-100% RH (40)(41)(42). The RH was measured until equilibrium was reached.…”

Moisture movement within concrete exposed to simulated hot arid/semi-arid conditions

“…Preformed cavities were chosen in preference to drilled holes due to potential damage caused by hammer-action drilling, particularly those cavities close to the test surface. The inside of each cavity was lined with a thin plastic sleeve (Granja et al, 2014;Holmes and West, 2013;Kim and Lee, 1999) with the end of the cavity exposed to ensure that the RH was representative of the concrete at that depth. A RH sensor was inserted within each cavity, which was then sealed with a tightly fitting rubber bung.…”

Embedded Wireless Sensor for In Situ Concrete Internal Relative Humidity Monitoring

“… Shrinkage control . Concrete shrinks as its internal moisture content decreases, either through exchange with the environment (evaporation) or through self-desiccation (hydration of cement particles), with its magnitude proportional to the amount of moisture lost [ 4 , 7 , 8 ]. The restraint of shrinkage-induced strains caused by moisture gradients is one of the most common causes of early cracking in concrete elements.…”

“…A review of sampling techniques can be found in [ 14 ]. Despite this being a straightforward method, the sample preparation is labor-intensive and the final measured values are often affected by variability related to the slicing process [ 7 , 15 ]. Moreover, this method cannot measure changes in the moisture condition produced by hydration of the cement or by changes in the capillary structure of the concrete [ 15 ].…”