Hydration of Concrete
Concrete is made from cement, sand and water. The building material is particularly interesting because, as free-flowing fresh concrete, it can take on all conceivable forms and then be extremely resilient after a curing phase. Fresh concrete needs 24 hours to reach the first hardening stage and to completely change its consistency. This phase is also called the setting period.
During this time, hydration takes place. Overall, concrete curing is a lengthy process that can last anywhere from four weeks to several months. In the course of hydration, the concrete releases water and loses its moisture.
Installation of the Passive Sensor Tags in the Concrete
To ensure the stability of a building, the concrete must be perfectly cured before additional floors, piers, foundations or roadways can be added to the structure. Each stage of construction must be completed in a qualified manner. The hardness of concrete, foundation slabs or walls can be monitored using passive RAIN RFID moisture sensors.
The sensor tags are installed between 10 to 20 centimeters deep on metal grids in the concrete and are thus enclosed by the concrete. A reader can be used to read this tag regularly, so that the drying process of the concrete can be monitored seamlessly.
To generate sensor information from the passive tags and store it for long-term monitoring, the tags are queried cyclically by polling. In the process, energy and data streams are transmitted. Due to the alkaline concrete millieu, it is necessary to encapsulate the sensor tags.
"Leave and Forget"
Battery-less sensor tags in concrete can be used to monitor buildings for decades to come. Therefore, Asygn recommends that builders not only integrate a moisture sensor to monitor the drying process, but also a strain sensor. This sensor can measure the deformation of the concrete for decades and thus the changes in the stability of the building.
Long-term monitoring is particularly useful for monitoring bridges or very large building complexes and can indicate risks at an early stage. Monitoring concrete deformation can reveal that the building is no longer stable, especially in earthquake regions with steady low-level shaking.
Any homeowner could use a simple smartphone equipped with a RAIN reader to read the passive tags themselves and monitor their own home. Asygn calls this functionality "Leave and Forget" because years after installation, when the construction phase is already a thing of the past, the sensor tag is still functional.