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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maintained at 20°C (±2°C) and 100% relative humidity for 28 days to ensure proper curing. The average compressive strength was recorded at 45.25 MPa, with a residual flexural strength of PPFRC (fR1) measured at 1.59 MPa.

Table 3. Mix design and specimen breakdown.

Composition

PPFRC

H-PPFRC

Cement [kg/m3] Water [kg/m3]

500 230 879 360 150 300 3.50 8.65 6.00

500 230 879 360 150 300 3.50 8.65 7.00

Sand (0/4 mm) [kg/m3] Sand (0/2 mm) [kg/m3]

Coarse aggregate (4/10 mm) [kg/m3] Coarse aggregate (10/20 mm) [kg/m3]

Plasticizer [kg/m3]

Superplasticizer [kg/m3] Polypropylene fibres [kg/m3]

Steel bar reinforcement Concrete cover [mm] Number of beams [-]

- -

1 bar Ø 6mm

25 12

9

3.2. Sensor and Microcontroller specifications The DHT22 sensor produced by Kuongshun Electronic company (China) which costs approximately $10, is characterized by its polymer capacitor sensing element which operates within a humidity range of 0 – 100%RH and a temperature range of – 40 to 80°C. It features a working voltage of 3.3 – 6V DC, with notable accuracy (±2%RH for humidity and ±0.5°C for temperature) and a sensing period averaging 2 s. The NodeMCU microcontroller produced by Espressif Systems (China) which costs around $5, is powered by the ESP8266 chipset which facilitates data processing and wireless communication, thanks to its built-in WiFi capability and TCP/IP protocol suite. Figure 1 shows the schematics of DHT22 sensor and NodeMCU microcontroller.

a

b

Fig. 1. (a) DHT22 sensor; (b) NodeMCU microcontroller.

3.3. System Integration and Data Collection The integration of the DHT22 sensor with the NodeMCU microcontroller forms the core of the monitoring system. Programming of the microcontroller was conducted using the Arduino Integrated Development Environment (IDE), which allowed for the implementation of a codebase to control sensor readings and data transmission. The code includes functions for initializing the DHT22 sensors, reading temperature and humidity values at predefined intervals, and transmitting the data to the ThingSpeak cloud platform via HTTP requests allowing for immediate data visualization and analysis. Exception handling mechanisms were incorporated to ensure system resilience against potential sensor reading errors. This system's design aims to provide an efficient, low-cost solution for early-stage concrete monitoring, leveraging the IoT capabilities to facilitate remote monitoring and data management. 3.4. Laboratory Setup In our laboratory setup, concrete specimens were cast in standard molds and underwent controlled curing to simulate early-stage conditions. To comprehensively monitor the curing environment, two DHT22 sensors were