Analysis and modeling of the interfacial transition zone between integrated fiber optic strain sensors and mortar and concrete matrices

• Applicant: Professor Dr.-Ing. Klaus Holschemacher
• Subject Area: Construction Material Sciences, Chemistry, Building Physics ; Architecture, Building and Construction History, Construction Research, Sustainable Building Technology ; Measurement Systems
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 518861712

The advancements in fiber optic sensing (FOS) technology has led to a wide range of applications in civil engineering over recent years. These include measurement tasks within building construction, special civil engineering or geotechnics. Distributed fiber optic sensing (DFOS) shows great potential for strain and crack measurement within the concrete matrix, especially with regard to resource-saving, long-term use of structures through comprehensive structural health monitoring (SHM). The used sensors consist of optical glass fibers, which are protected by a coating or cable structure. Since the strain is only measured in the fiber core, strain transmission losses can occur due to shear distortion or slip between the surrounding substrate and fiber core, depending on the thickness of the coating material or cable structure. Existing strain transfer models (STM) consider the losses within the sensor structure already. However, strain transfer losses along the interfacial transition zone (ITZ) between matrix and FOS could not be quantified or integrated into the STMs so far. Yet, this information is mandatory to adequately assess the strain signals of the FOS. The investigations include two primary methods: The recording of shrinkage strains via VFOS and CT scans (M1) and SEM investigations of the ITZ on cut interfaces (M2) of specimens from cement mortar with embedded FOS. In addition, a free (S1) and an interfered shrinkage deformation (S2) characterize two loading scenarios. The measurements are carried out after 24 hours (reference) as well as three and seven days. The objective of the project is a detailed examination of the ITZs properties between the FOS and the surrounding cement-based matrix, and the experimental determination of their influences using the approved research instrumentation (SEM, CT). Depending on the fiber coating material, sensor design as well as the properties and composition of the matrix (additives, admixtures), an analytical STM will be formulated and recommendations for the use of FOS for strain measurement within the SHM will be derived.

• DFG Programme: Research Grants