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. 2024 Dec 14;24(24):7998.
doi: 10.3390/s24247998.

Smart Concrete Using Optical Sensors Based on Bragg Gratings Embedded in a Cementitious Mixture: Cure Monitoring and Beam Test

Edson Souza  1 , Pâmela Pinheiro  2 , Felipe Coutinho  2 , João Dias  2 , Ronaldo Pilar  2 , Maria José Pontes  1 , Arnaldo Leal-Junior  1
Affiliations

Smart Concrete Using Optical Sensors Based on Bragg Gratings Embedded in a Cementitious Mixture: Cure Monitoring and Beam Test

Edson Souza et al. Sensors (Basel). .

Abstract

Smart concrete is a structural element that can combine both sensing and structural capabilities. In addition, smart concrete can monitor the curing of concrete, positively impacting design and construction approaches. In concrete, if the curing process is not well developed, the structural element may develop cracks in this early stage due to shrinkage, decreasing structural mechanical strength. In this paper, a system of measurement using fiber Bragg grating (FBG) sensors for monitoring the curing of concrete was developed to evaluate autogenous shrinkage strain, temperature, and relative humidity (RH) in a single system. Furthermore, K-type thermocouples were used as reference temperature sensors. The results presented maximum autogenous shrinkage strains of 213.64 με, 125.44 με, and 173.33 με for FBG4, FBG5, and FBG6, respectively. Regarding humidity, the measured maximum relative humidity was 98.20 %RH, which was reached before 10 h. In this case, the recorded maximum temperature was 63.65 °C and 61.85 °C by FBG2 and the thermocouple, respectively. Subsequently, the concrete specimen with the FBG strain sensor embedded underwent a bend test simulating beam behavior. The measurement system can transform a simple structure like a beam into a smart concrete structure, in which the FBG sensors' signal was maintained by the entire applied load cycles and compared with FBG strain sensors superficially positioned. In this test, the maximum strain measurements were 85.65 με, 123.71 με, and 56.38 με on FBG7, FBG8, and FBG3, respectively, with FBG3 also monitoring autogenous shrinkage strain. Therefore, the results confirm that the proposed system of measurement can monitor the cited parameters throughout the entire process of curing concrete.

Keywords: curing concrete; fiber Bragg grating; shrinkage strain; smart concrete.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
FBG Hygrometer Sensor. The zoomed-in view shows details of the FBGs.
Figure 2
Figure 2
The curing concrete setup photo is presented in (A). The experimental components are identified in the schematic drawing (B).
Figure 3
Figure 3
The photo (A) presents the shrinkage bench, where the autogenous shrinkage strain was measured. The distribution of the FBG strain sensors is identified in the schematic drawing (B).
Figure 4
Figure 4
The bend test using three-point bending. (A) presents a photo of the positioning of smart concrete and (B) presents a schematic representation using two supports and one loading point, highlighted in red.
Figure 5
Figure 5
Temperature sensitivity calibration for FBG2 for relative humidities of 60 %RH, 70 %RH, 80 %RH, 90 %RH, and 95 %RH.
Figure 6
Figure 6
Temperature sensitivity calibration for FBG1 for relative humidities of 60 %RH, 70 %RH, 80 %RH, 90 %RH, and 95 %RH.
Figure 7
Figure 7
Relative humidity sensitivity calibration for FBG1 for temperatures of 30 °C, 40 °C, and 45 °C.
Figure 8
Figure 8
Comparison between the temperature curves obtained by the thermocouple and FBG2.
Figure 9
Figure 9
Relative humidity variation versus the test time, monitored by FBG1.
Figure 10
Figure 10
Monitored temperature by thermocouple versus time in the concrete specimen of shrinkage bench.
Figure 11
Figure 11
Monitored strain by the FBG4, FBG5, and FBG6 strain sensors versus time. For FBG3, the Bragg wavelength shift during the test is presented.
Figure 12
Figure 12
Monitored autogenous shrinkage strain by FBG4, FBG5, and FBG6 versus test time.
Figure 13
Figure 13
FBG7, FBG8, and FBG3 strain responses to applied bend load cycles.
See this image and copyright information in PMC

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