PSI - Issue 64

M. Komary et al. / Procedia Structural Integrity 64 (2024) 1311–1317 Mahyad Komary/ Structural Integrity Procedia 00 (2019) 000 – 000

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deployed: one sealed within the concrete specimen to measure internal conditions, and another positioned externally close to the specimen for ambient environmental readings. This setup not only captures the temperature and humidity variations within and around the concrete but also allows for a comparative analysis of the micro-environmental impact on curing. Data was collected in real time, with readings every 20 min, and transmitted to the ThingSpeak platform. This approach enabled continuous monitoring of key environmental conditions affecting the concrete's curing process and early-stage properties. Prior to this, in order to validate the accuracy of the DHT22 sensor which was demonstrated in section 3.2 (to be ±0.5°C), a primary validation test was conducted using a high-precision thermocouple (EL-USB-2-LASCAR). The results showed a maximum deviation of ±0.3°C, confirming the accuracy and reliability of the DHT22 sensors used in this study 4. Results and Discussion The laboratory tests employing a low-cost IoT-based sensor system for early-stage concrete monitoring yielded substantial insights. Data from the DHT22 sensors, both embedded and external to the concrete specimens, provided detailed temperature and humidity profiles during curing. The initial ambient lab conditions (Figure 2) and controlled climate chamber conditions (Figure 3) constituted the two experimental phases. It is important to mention that the data acquisition rate was consistently set to 1 sample per 20 minutes. The perceived inconsistencies in Figures 2 and 3 are due to visualization purposes to highlight overall trends.

Fig. 2. Temperature and Humidity changes over 24 hours after the initiation of the casting (print screen from the UI).

The data from the initial phase demonstrated a diurnal pattern, with the internal sensor recording a significant temperature peak, indicative of the exothermic curing reaction. These findings are critical, as thermal cycles can impact the development of internal stresses and potential cracking, with implications for corrosion prevention in reinforced concrete. However, the observed peak in internal humidity, alongside the sustained 100% reading following the concrete's placement, indicates that moisture may have penetrated the sensor, suggesting an unsuccessful seal. Typically, the relative humidity trend in concrete is characterized by an initial rapid decrease post-placement, due to the high moisture diffusivity and non-equilibrium conditions. This is followed by an increase during the bleeding stage, where the moisture diffusivity starts to decline yet remains sufficiently high to sustain notable evaporation rates. Subsequently, in the post-bleeding stage, the relative humidity is expected to gradually equilibrate with the ambient atmosphere as moisture diffusivity reduces further. The absence of this expected trend in our observations implies that