Development of a low-cost IoT-based sensor for early-stage concrete monitoring

ScienceDirect Available online at www.sciencedirect.com Procedia Structural Integrity 64 (2024) 1311–1317 2452-3216 © 2024 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of SMAR 2024 Organizers 10.1016/j.prostr.2024.09.202 10.1016/j.prostr.2024.09.202 2452-3216 Available online at www.sciencedirect.com ScienceDirect Structural Integrity Procedia 00 (2023) 000–000 www.elsevier.com/locate/procedia 2452-3216 © 2024 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of SMAR 2024 Organizers SMAR 2024 – 7th International Conference on Smart Monitoring, Assessment and Rehabilitation of Civil Structures Development of a Low-Cost IoT-based Sensor for Early-Stage Concrete Monitoring M. Komary*, P. Bajić, N. Tošić, A. De la Fuente, J. Turmo Universitat Politècnica de Catalunya, C/ Jordi Girona 31, Barcelona, 08034, Spain Abstract Concrete is an essential construction component that needs to be examined carefully for an early strength assessment in order to guarantee structural integrity and long-term durability. This paper delves into the viability of utilizing low-cost sensors, interfaced with an Arduino-based microcontroller, for real-time data acquisition in concrete structures. The study focuses on their application in the early stages to investigate the thermal cycles due to hydration reaction, particularly within macro-synthetic fibre reinforced concrete. DHT22 sensors are used to measure the concrete sample's temperature and humidity parameters. These sensors are linked to a NodeMCU microcontroller that has an integrated WiFi module to provide real-time data updates on the cloud. The programming code is created using the Arduino IDE platform and then loaded into the NodeMCU microcontroller to control sensor functions. The validation process consists of an early laboratory test and the placement of an additional DHT22 sensor outside the concrete sample to monitor the surrounding temperature and humidity to evaluate the system's operation and sensor´s accuracy. The collected data reveal promising insights, particularly in investigating corrosion within embedded reinforced rebar for future researches. © 2024 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of SMAR 2024 Organizers Keywords: Low-Cost Sensor; Concrete Monitoring; Early-Stage Assessment; Structural Health Monitoring. * Corresponding author: Mahyad Komary E-mail address: [email protected] Available online at www.sciencedirect.com ScienceDirect Structural Integrity Procedia 00 (2023) 000–000 www.elsevier.com/locate/procedia 2452-3216 © 2024 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of SMAR 2024 Organizers SMAR 2024 – 7th International Conference on Smart Monitoring, Assessment and Rehabilitation of Civil Structures Development of a Low-Cost IoT-based Sensor for Early-Stage Concrete Monitoring M. Komary*, P. Bajić, N. Tošić, A. De la Fuente, J. Turmo Universitat Politècnica de Catalunya, C/ Jordi Girona 31, Barcelona, 08034, Spain Abstract Concrete is an essential construction component that needs to be examined carefully for an early strength assessment in order to guarantee structural integrity and long-term durability. This paper delves into the viability of utilizing low-cost sensors, interfaced with an Arduino-based microcontroller, for real-time data acquisition in concrete structures. The study focuses on their application in the early stages to investigate the thermal cycles due to hydration reaction, particularly within macro-synthetic fibre reinforced concrete. DHT22 sensors are used to measure the concrete sample's temperature and humidity parameters. These sensors are linked to a NodeMCU microcontroller that has an integrated WiFi module to provide real-time data updates on the cloud. The programming code is created using the Arduino IDE platform and then loaded into the NodeMCU microcontroller to control sensor functions. The validation process consists of an early laboratory test and the placement of an additional DHT22 sensor outside the concrete sample to monitor the surrounding temperature and humidity to evaluate the system's operation and sensor´s accuracy. The collected data reveal promising insights, particularly in investigating corrosion within embedded reinforced rebar for future researches. © 2024 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of SMAR 2024 Organizers Keywords: Low-Cost Sensor; Concrete Monitoring; Early-Stage Assessment; Structural Health Monitoring. * Corresponding author: Mahyad Komary E-mail address: [email protected] © 2024 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license ( https://creativecommons.org/licenses/by-nc-nd/4.0 ) Peer-review under responsibility of SMAR 2024 Organizers 1312 M. Komary et al. / Procedia Structural Integrity 64 (2024) 1311–1317 2 Mahyad Komary/ Structural Integrity Procedia 00 (2019) 000–000 1. Introduction The monitoring of concrete structures in the early stages of curing and hardening is a critical component in ensuring their long-term structural integrity and durability. The early-stage monitoring of concrete can reveal essential information regarding its initial setting, strength development, and potential for early-age cracking, which are pivotal for predicting the lifespan and safety of civil structures [1]. Furthermore, the ability to detect and mitigate issues at this juncture can significantly reduce maintenance costs and extend the service life of infrastructure assets. Despite its importance, the widespread implementation of early-stage concrete monitoring faces substantial challenges, primarily due to the high costs and complexities associated with traditional monitoring technologies. Most existing solutions are either prohibitively expensive for widespread application or lack the precision and reliability needed for early detection of potential issues and above all of that they mainly require the presence of a technician for onsite measurements and lack the remote monitoring possibility. Table 1 summarizes the most common used technologies for early-stage monitoring of concrete and highlights that their high cost is the main reason for their limitations. This gap underscores a pressing need for innovative monitoring solutions that are both cost-effective and efficient in capturing critical early-stage data with the possibility of capturing data remotely and for long-term measurements applications. This research aims to explore the viability of a low-cost, Internet of Things (IoT)-based sensor for early-stage concrete monitoring. By leveraging the advancements in IoT technology and sensor development, this study proposes a novel approach to monitor the critical parameters of concrete in its early stages, such as temperature and humidity, which are indicative of its curing process and overall health. The objective is to demonstrate that a low-cost IoT-based sensor system can provide accurate, real-time data essential for ensuring the structural integrity and durability of concrete structures, thereby addressing the limitations of current methodologies and offering a practical solution for widespread monitoring needs. Table 1. Comparative Analysis of Sensor Technologies for Early-Stage Concrete Monitoring. Technology Type Application Measured Parameters Notable Outcomes Primary Limitation Cost range ($) Thermocouples Temperature monitoring to assess heat of hydration Temperature Enables understanding of thermal profiles and potential for thermal cracking Costs associated with wiring and data acquisition systems 50 - 200 Electrical Impedance Spectroscopy (EIS) Assessing setting time and early hydration processes Electrical Properties (Impedance) Can detect early-stage hydration characteristics and setting times High equipment cost and complexity of interpretation 5,000 – 10,000 Ultrasonic Pulse Velocity (UPV) Monitoring of concrete homogeneity and initial setting Pulse Velocity Effective in assessing initial setting and early strength development High cost of ultrasonic equipment and skilled operation required 2,000 – 10,000 Digital Image Correlation (DIC) Systems Surface monitoring for early crack detection Strain, Displacement Non-contact method to detect surface cracks and deformations High cost for setup, including cameras and software 10,000 – 20,000 2. Background Historically, concrete monitoring has been paramount in assessing the health and integrity of civil structures. Traditional methods, such as core sampling and ultrasonic pulse velocity tests, have provided valuable insights into the strength and condition of concrete. However, these methods are often invasive, labor-intensive, and not suitable for real-time monitoring. Recent advancements have seen the emergence of non-destructive techniques, including employing sensors as a part of Structural Health Monitoring (SHM) programs, which offer the potential for continuous monitoring without compromising the structure's integrity. Despite these advancements, challenges in cost, scalability, long-term durability and sensitivity especially for early-stage characterization of concrete remains. M. Komary et al. / Procedia Structural Integrity 64 (2024) 1311–1317 1313 Mahyad Komary/ Structural Integrity Procedia 00 (2019) 000–000 3 Recent trends in SHM programs have seen a growing interest among researchers in leveraging low-cost sensors and electronics to address traditional challenges in monitoring concrete structures. The utilization of low-cost sensors in SHM signifies a paradigm shift towards more economically feasible and scalable monitoring solutions with the possibility of increasing measuring points, thus resulting in the improvement of the resolution of the captured data. These sensors, coupled with innovative deployment strategies and enhanced through sophisticated programming codes [2], are beginning to match, and in some instances, surpass the performance of their more expensive counterparts. Table 2 highlights several instances where researchers have successfully employed low-cost sensors to monitor various parameters of concrete structures. One of the significant hurdles in adopting low-cost sensors has been concerns over their accuracy and reliability. However, recent studies demonstrate that through the application of powerful programming codes and algorithms, it is possible to calibrate these sensors and significantly improve their data fidelity [3]. This methodological advancement not only extends the utility of low-cost sensors but also opens up new avenues for their application in critical monitoring tasks. Table 2. Overview of Low-Cost Sensor Technologies in SHM applications. Sensor Type Application Measured Parameters Benefits Reference MEMS Accelerometers Vibration-based damage detection in buildings and bridges Acceleration, Displacement Compact, and easy to install; Suitable for dynamic analysis of structures [4][5] MEMS Inclinometers Monitoring tilts and deformations in structures Tilt, Angular Displacement High precision in detecting subtle shifts and structural deformations; [6][7][8] Environmental sensors Assessing environmental impact on structural health Temperature, Humidity, corrosion, Solar radiation Helps in understanding environmental contributions to structural degradation [9][10][11] The integration of IoT technology in the context of SHM represents a significant advancement, enabling real-time data collection and analysis. This capability is particularly beneficial for early-stage concrete monitoring, where realtime data on temperature and humidity can provide insights into the curing process, potentially influencing decisionmaking and intervention strategies. Despite the promising developments in the use of low-cost sensors and IoT technologies, there remains a gap in their application specifically tailored for early-stage concrete monitoring. This research aims to bridge this gap by developing a low-cost IoT-based system utilizing the DHT22 temperature and humidity sensor in conjunction with the NodeMCU microcontroller coupled with a built-in Wifi Module. The objective is to demonstrate the feasibility of employing such a system to provide accurate, real-time temperature and humidity readings, and to leverage the IoT capabilities of the ThingSpeak platform for data visualization and analysis. This approach underscores the potential of low-cost sensors and IoT technology in revolutionizing early-stage concrete monitoring, making it more accessible and actionable for stakeholders across the construction industry. 3. Methodology This study employs a concise and focused methodology to explore the viability of a low-cost IoT-based sensor system for early-stage concrete monitoring, incorporating the DHT22 sensor and the NodeMCU microcontroller. The methodology encompasses the production and preparation of concrete specimens, detailing the sensor and microcontroller specifications, system integration, and data collection process. 3.1. Concrete Specimens The research utilized 12 hybrid polypropylene fibre-reinforced concrete beams (H-PPFRC) with dimensions of 150 × 150 × 600 mm³ and 9 additional polypropylene fibre reinforced concrete (PPFRC) elements for material characterization. Table 3 shows mix proportions of concrete elements used in the experimental program which should satisfy structural requirements for typical applications in contemporary civil engineering practice. Specifically, the HPPFRC specimens are designed to enhance the mechanical properties and durability for structural applications, necessitating a higher fibre content. However, the PPFRC specimens serve as a control group for material characterization, which typically involves lower fibre content to establish baseline properties. These specimens were 1314 M. Komary et al. / Procedia Structural Integrity 64 (2024) 1311–1317 4 Mahyad Komary/ Structural Integrity Procedia 00 (2019) 000–000 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] 500 500 Water [kg/m3] 230 230 Sand (0/4 mm) [kg/m3] 879 879 Sand (0/2 mm) [kg/m3] 360 360 Coarse aggregate (4/10 mm) [kg/m3] 150 150 Coarse aggregate (10/20 mm) [kg/m3] 300 300 Plasticizer [kg/m3] 3.50 3.50 Superplasticizer [kg/m3] 8.65 8.65 Polypropylene fibres [kg/m3] 6.00 7.00 Steel bar reinforcement - 1 bar Ø 6mm Concrete cover [mm] - 25 Number of beams [-] 9 12 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. 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 a b M. Komary et al. / Procedia Structural Integrity 64 (2024) 1311–1317 1315 Mahyad Komary/ Structural Integrity Procedia 00 (2019) 000–000 5 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 1316 M. Komary et al. / Procedia Structural Integrity 64 (2024) 1311–1317 6 Mahyad Komary/ Structural Integrity Procedia 00 (2019) 000–000 future research should focus on improving the sealing technique to ensure the accurate capture of relative humidity values within the concrete. The significance of the findings lies in the successful demonstration of real-time monitoring capabilities using lowcost sensors, which can provide valuable data for early-stage concrete monitoring. The system's operation was effective, with the sensors showing good accuracy and repeatability in the readings. One challenge noted was the disparity in conditions between the internal and external environments of the concrete, which underscores the need for careful interpretation of sensor data when assessing concrete health. Upon transferring the specimens into the climate chamber after 24 hours from the casting with consistent conditions outlined in Section 3.1, the temperature and humidity values captured by the sensors stabilized (shown in figure 3), demonstrating the system's sensitivity to environmental control. However, challenges were noted with the sealed sensor's long-term stability and accuracy, highlighted by the high inside humidity reading post-curing, which indicated possible moisture ingress and sensor malfunction. This emphasizes the necessity for improved sensor encapsulation and reliability in data collection. Fig. 3. Temperature and Humidity changes over 24 hours period inside of the climate chamber 1 day after the casting (print screen from the UI). These results reinforce the potential of low-cost IoT systems in SHM, particularly for real-time monitoring of conditions that may lead to corrosion, and set the direction for future research to include corrosion detection and assess long-term sensor performance in adverse conditions. 5. Conclusion The study confirmed the efficacy of a low-cost IoT-based sensor system for monitoring the early stages of concrete curing. The DHT22 sensors effectively tracked temperature and humidity, capturing essential data on the exothermic reactions and moisture conditions during initial curing. The specimens' subsequent transition to a climate chamber showcased the system's versatility in adapting to and accurately measuring a controlled environment. The research emphasizes the substantial promise of low-cost IoT sensors in SHM, offering economical continuous monitoring of parameters critical to concrete's structural integrity. This capability enhances material quality assurance and paves the way for predictive maintenance strategies. The findings suggest expansive future SHM applications, with potential for sensor functionality to include parameters related to corrosion monitoring. This research affirms the practicality of implementing IoT technologies in civil engineering, heralding progress in the sustainability and longevity of concrete infrastructure. M. Komary et al. / Procedia Structural Integrity 64 (2024) 1311–1317 1317 Mahyad Komary/ Structural Integrity Procedia 00 (2019) 000–000 7 Acknowledgements This research has been supported by the Ministry of Science and the Investigation (Ministerio de Ciencia e Innovación), the State Research Agency (Agencia Estatal de Investigación) of the Kingdom of Spain, and the European Union “NextGenerationEU”/PRTR. Project references: PID2019-108978RB-C32, PID2021-126405OBC31 and PLEC2021-007982. References [1] H. Yoon, Y. Kim, H. S. Kim, J. W. Kang, and H. M. Koh, “Evaluation of Early-Age Concrete Compressive Strength with Ultrasonic Sensors,” Sensors 2017, Vol. 17, Page 1817, vol. 17, no. 8, p. 1817, Aug. 2017, doi: 10.3390/S17081817. [2] S. Komarizadehasl, M. Komary, J. Turmo Coderque, F. Lozano Galant, F. Lozano Galant, and J. A. Lozano Galant, “Using few accelerometer for improving the resolution and accuracy of low-cost accelerometers,” Bridge Safety, Maintenance, Management, LifeCycle, Resilience and Sustainability: Proceedings of the Eleventh International Conference on Bridge Maintenance, Safety and Management (IABMAS 2022), Barcelona, Spain, July 11-15, 2022, pp. 1575–1579, Jun. 2022, doi: 10.1201/9781003322641-193. [3] S. Komarizadehasl, F. Lozano Galant, M. Komary, J. A. Lozano Galant, and J. Turmo Coderque, “Resolution improvement of low-cost MEMS accelerometer by aligning simulations sensors,” IABSE Symposium Prague 2022 Report: Challenges for Existing and Oncoming Structures, pp. 1–6, 2022. [4] S. Komarizadehasl, F. Lozano Galant, M. Komary, J. A. Lozano Galant, and J. Turmo Coderque, “Development of an accurate lowcost device for structural vibration acquisition,” IABSE Symposium Prague 2022 Report: Challenges for Existing and Oncoming Structures, pp. 1–6, 2022. [5] S. Komarizadehasl, M. Komary, J. Turmo Coderque, V. Torralba Mendiola, F. Lozano Galant, and J. A. Lozano Galant, “Low-cost accurate acceleration acquisition sensor,” Bridge Safety, Maintenance, Management, Life-Cycle, Resilience and Sustainability: Proceedings of the Eleventh International Conference on Bridge Maintenance, Safety and Management (IABMAS 2022), Barcelona, Spain, July 11-15, 2022, pp. 803–810, Sep. 2022, doi: 10.1201/9781003322641-96. [6] S. Komarizadehasl, M. Komary, A. Alahmad, J. A. Lozano-Galant, G. Ramos, and J. Turmo, “A Novel Wireless Low-Cost Inclinometer Made from Combining the Measurements of Multiple MEMS Gyroscopes and Accelerometers,” Sensors 2022, Vol. 22, Page 5605, vol. 22, no. 15, p. 5605, Jul. 2022, doi: 10.3390/S22155605. [7] M. Komary, A. Alahmad, S. Komarizadehasl, J. Turmo, J. A. Lozano-Galant, and Y. Sun, “A novel low-cost inclinometer sensor based on fusion technology for structural health monitoring applications,” in Life-Cycle of Structures and Infrastructure Systems, CRC Press, 2023, pp. 1729–1736. doi: 10.1201/9781003323020-212. [8] M. Komary, S. Komarizadehasl, G. Ramos, and V. Torralba, “Developing and validation of an inclinometer sensor based on fusion of a magnetometer, an accelerometer and a gyroscope sensor for SHM applications,” in Bridge Safety, Maintenance, Management, LifeCycle, Resilience and Sustainability, 1st Editio., vol. 5, CRC Press, 2022, pp. 1607–1611. doi: 10.1201/9781003322641-198. [9] M. Komary, S. Komarizadehasl, N. Tošić, I. Segura, J. A. Lozano-Galant, and J. Turmo, “Low-Cost Technologies Used in Corrosion Monitoring,” Sensors, vol. 23, no. 3, p. 1309, Jan. 2023, doi: 10.3390/s23031309. [10] M. Komary, S. Komarizadehasl, J. Turmo, F. Lozano, J. A. Lozano-Galant, and X. Ye, “A review on low-cost sensors compatible with open-source platforms used for life-cycle monitoring of civil structures,” in Life-Cycle of Structures and Infrastructure Systems, CRC Press, 2023, pp. 1685–1692. doi: 10.1201/9781003323020-207. [11] M. Komary, S. Komarizadehasl, G. Ramos Schneider, N. Tošić, J. Turmo Coderque, and V. Torralba Mendiola, “Full review of lowcost electronics implemented in structural health monitoring applications for bridges,” Bridge Safety, Maintenance, Management, LifeCycle, Resilience and Sustainability: Proceedings of the Eleventh International Conference on Bridge Maintenance, Safety and Management (IABMAS 2022), Barcelona, Spain, July 11-15, 2022, pp. 980–985, 2022, doi: 10.1201/9781003322641-117.