Verification of Concrete Slab Bridges using Smart Aggregates: Decoupling Temperature-Induced Effects and Addressing Data-Processing Challenges

Abstract

Over recent decades, advances in concrete design codes have left many existing bridges with outdated detailing and reduced nominal capacity, while traffic loads and intensities have continued to increase. Since many of these structures are now nearing the end of their service life, reducing uncertainty in their residual capacity has become critical. Structural Health Monitoring (SHM) offers a means to achieve this. This thesis investigates the applicability of Smart Aggregates (SA), a novel type of piezoelectric acoustoelastic sensor, for SHM of concrete slab bridges. A framework is proposed for SA data to decouple temperature related effects and an approach to signal data-processing challenges, in order to isolate stresses related to mechanical loading, enabling more reliable data interpretations of proof loadings and long-term monitoring. The approach is demonstrated on the Balladelaan Bridge in Amersfoort, a vintage structure with uncertain composite action between its original deck and a concrete topping layer. Signal processing was carried out using the stretching technique, which estimates relative velocity changes and cross-correlation between signals. A systematic window configuration strategy is proposed, based on wave interferometry of early-arrivals or fully diffused coda waves. A key data-processing challenge—sub-sample misalignment in the SA triggering mechanism—was identified and corrected using a confidence interval derived from reference data at the Zeeland Bridge. Temperature effects were decoupled by combining experiments and Finite Element Modeling (FEM). A negative linear relationship between temperature and wave velocity change in concrete is quantified, with velocity decreasing as temperature increases. The effect is found to be relatively more pronounced in the later coda waves compared to early-arrivals. Sub-zero temperatures indicated a non-linear temperature-velocity change relationship for freeze-thaw, important for passive monitoring applications. Simplified temperature-induced stresses, including mean temperature and linearized gradients, are evaluated using both (1) literature-based relations and (2) a parametric 2.5D finite element (FE) model, which should yield a similar result. For mean temperature changes, the literature-based approach overestimated temperature-induced stress effects compared to FE approach by an order of 10 when analyzing early-arrivals. This was caused mainly by unrepresentative assumed higher order constants relating wave velocity to stress change for the literature-based approach, and limitations of the finite element model to represent the stresses at the Balladelaan bridge. Linearized gradients showed unexpected behavior for sensor pairs at the interface between the original deck and the concrete topping layer, suggesting a complex stress state due to possible partial composite action. This is further reaffirmed by significant drops in correlation-coefficient for sensor pairs at the supports where the effect of sliding is expected. The proposed framework demonstrates how Smart Aggregates can support SHM of slab bridges, reducing uncertainty in safety assessments and extending service life through predictive maintenance and digital twin applications.