Reuse of Structural Concrete Elements: Documentation of Properties by Non-Destructive Testing

The environmental impact of concrete production, particularly due to cement-related emissions, poses a significant challenge for sustainable development. As demand for new construction continues to increase, reusing structural concrete elements is emerging as a promising strategy to reduce embodied emissions, preserve raw materials, and support the transition to a circular economy. Despite the potential, the implementation of reuse remains limited due to barriers such as the lack of reliable and practical methods for documenting the technical properties of the structural concrete elements for reuse.

This PhD project addresses key knowledge gaps that act as barriers to the widespread reuse of structural concrete elements. The objective is to develop a reliable and practical methodology for documenting concrete properties using non-destructive testing (NDT) methods in the donor buildings. The methodology focuses on assessing essential parameters for reuse, including mechanical properties, internal defects, and reinforcement layout. The research specifically targets elements in passive environmental exposure classes (X0 and XC1), where durability-related deterioration risks are limited.

The study followed a structured methodology consisting of two main parts and six interlinked steps. The first part focused on developing in-situ documentation procedure and includes (1) a literature review to identify suitable NDT methods for reusability documentation, (2) a laboratory investigation to evaluate the performance of ultrasonic pulse velocity (UPV), rebound hammer (RH), and electrical resistivity (ER) under conditions relevant to reuse, and (3) an analysis of in-situ strength estimation when core sampling is constrained. The second part focused on the iterative development and refinement of an in-situ documentation procedure, followed by its field validation. It included (4) refining the procedure based on field insights, (5) applying it in nine field studies, including a full-scale case, and (6) developing a reusability assessment guideline under the auspices of Danish Standards.

The literature review concluded that available NDT methods, when appropriately combined, can provide reliable documentation of the required concrete properties for. The laboratory study revealed that material parameters such as saturation level and aggregate characteristics strongly influenced the relationship between target properties and NDT results. A case study involving assessments in eight buildings confirmed that calibration was critical when core samples were constrained. Calibrating NDT relationships from a comprehensive database improved estimation reliability and reduced the risk of extrapolation. The first part of the research concluded with the in-situ documentation procedure.

The procedure combines four NDT methods: ground-penetrating radar (GPR), ultrasonic pulse echo (UPE), UPV, and RH. The workflow includes visual inspection, subsurface assessment, reinforcement evaluation, and compressive strength estimation. The in-situ documentation procedure is refined through case studies. Nine field studies, including a full-scale study, confirmed that the documentation procedure can be applied in operational buildings with minimal disruption, supporting data-informed reuse planning.