Non-destructive strength estimation of concrete elements for direct reuse

Katja Irene Møller Thygesen

A pressing issue in the construction industry is how to adapt to the increased demand for sustainable practices. Three of the main obstacles in this regard are the CO2 production, the consumption of limited raw materials, and the waste generation.
A way of remedy on all three obstacles is for the industry to start recognising the building mass of the many buildings being demolished every year as a useful resource. By strengthening the circular economy and reusing more, less new production of construction elements will be necessary and thereby, CO2 production, consumption of raw materials, and the waste generation, will be brought down.

With concrete being the most used material in writing time, it is natural to investigate what can be done in this regard. Studies point to the lack of labels and certifications as a hindrance for a transformation of the supply chain to include more reuse. This thesis had the goal of developing and testing a strength investigation procedure suitable for certification of concrete elements for direct reuse. This was achieved by creating an overview of the available research on the subject through a literature review, and subsequently piecing together an investigation procedure based on these findings. The main goals for the procedure were for it to be non-destructive, cheap, fast, reliable, and possible to perform on-site. The procedure was afterwards tested in a field study.
Through the literature review, it was found that a lot of relevant research has been done.

Although none of the found articles deals explicitly with reuse purposes, a lot of them share similar goals, and were found useful for this specific purpose. Some essential findings were; the many factors affecting the non-destructive data and thereby jeopardising the reliability of the assessment, emphasis on measuring technique to minimise errors, coring strategy, model parameter identification approach and error assessment.

In the field study, the columns of a to-be-demolished building were investigated. The strength was found to be 22.91 MPa, with a prediction error of 0.894 MPa. Through these findings, the columns were found useful for reuse, although with a lower strength than originally designed. The procedure was found to be suitable, however, not optimal.

Through the discussion, the newly developed bi-objective model parameter identification approach was performed on the non destructive data separately. It was found that this approach used with the ultrasonic pulse velocity data enabled a larger utilisation of strength with a lower prediction error and is therefore recommended to implement in the investigation procedure.
The concluding remarks of this thesis was that developing a strength investigation procedure suitable for direct reuse purposes was indeed possible with the available research, taking the industry one step closer to more circular economy of building mass.

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