Optical fiber sensor system for real-time concrete compressive strength monitoring

The development of mechanical strength in concrete during curing is a crucial factor in evaluating the structural integrity and quality control of concrete. This study proposes the application of an optical fiber-based Mach–Zehnder interferometric (MZI) system for non-destructive monitoring of the compressive strength development of unreinforced concrete beams. Low- and high-strength concrete beams and cubes were cast, with a single-mode fiber (SMF) embedded at the center of each beam. The samples were cured in a temperature-controlled water tank, and compressive strength was continuously monitored in each mixture for 28 days. The logarithmic slopes derived from the low-strength mixture MZI-calibrated compressive strength development showed sensitivities of 5.508 MPa/ln(days) and 13.194 MPa/ln(days) for the MZI-derived strength of the high-strength mixture, in comparison to the corresponding cube-derived strength sensitivities of 4.782 and 14.311 MPa/ln(days), respectively. The findings indicate that the embedded MZI system can replicate the logarithmic strength–time curve with sensitivities that are equivalent to, and in some instances marginally surpass, those derived from conventional cube testing, especially for low-strength concrete. The close agreement between the slopes produced from MZI and cube measurements, without the need for further calibration, reinforces the appropriateness of the proposed MZI method for non-invasive, in situ assessment of high-strength concrete compressive strength progression.