ABSTRACT
Our built environment during the last 100 years has expanded more than ever referring to material consumption of the construction industry. Especially for engineering structures, the most common building material is reinforced concrete due to its performance, cost-efficiency and availability. However, this material poses special challenges regarding non-destructive monitoring of both the condition and integrity of civil engineering structures, which is an increasingly important part within life cycle analysis. Ultrasound-based Coda Wave Interferometry (CWI) is one of the most promising monitoring techniques as it can detect and localize even weak changes in the microstructure of heterogeneous materials. Recent research has shown that this technique is also applicable for identifying precursors of deterioration processes.
One of the challenges for concrete monitoring using CWI is the separation of reversible changes due to temperature and moisture as well as mechanical stresses from irreversible changes such as damage in the structure. Previous studies investigated these impacts in the framework of ‘one-dimensional’ experiments at the specimen scale under laboratory conditions. From each experiment, we derived calibration curves for the relation between the individual external impact and the Coda Waves’ velocity variations, which are consistent for one concrete mix. In this contribution, we summarize these relations and propose equations, allowing us to distinguish between the causes of velocity variations of Coda Waves propagating in concrete. With this research, we aim at generating a model that will enable the separation of reversible and irreversible changes in concrete using Coda Wave Interferometry. Our results will contribute to establishing CWI as an early-warning-system for engineering structures made from reinforced concrete and therefore increasing the safety of large parts of our infrastructure.
