High-compatibility thick-film smart aggregates for strain monitoring of concrete

Thick-film resistors (TFRs) have shown considerable promise for civil engineering applications due to their high durability, strain sensitivity, and suitability for mass production, thereby fulfilling the long-term monitoring requirements of concrete structures. However, the significant disparity in elastic modulus between conventional alumina ceramic substrates and cementitious materials leads to strain mismatch, compromising the fidelity of the strain response of embedded sensors. This study proposes the use of fluorophlogopite glass-ceramic (FGC) to address this interfacial compatibility challenge. The performance of these smart aggregates under compressive loads was evaluated both before and after embedding in the mortar specimens. The matching performance of smart aggregates based on FGC substrates and alumina substrates within the mortar matrix was studied and compared. Results indicate that TFRs on FGC substrates exhibit good sensitivity, excellent linearity and repeatability, and minimal hysteresis. Within the frequency range of 0.1 Hz to 5 Hz, the sensor maintains a robust dynamic response. Crucially, FGC substrates demonstrate enhanced mechanical compatibility with mortar, as evidenced by a 74.5% reduction in modulus mismatch error (from 0.734 for alumina to 0.187 for FGC) and a 403% improvement in strain transfer efficiency (output ratio increasing from 0.0837 for alumina to 0.421 for FGC). These experimental findings align with theoretical predictions regarding stress-strain continuity at heterogeneous material interfaces. When embedded in mortar, TFRs on FGC substrates exhibit superior repeatability under repeated compressive loading compared to those on alumina ceramic substrates.