Advanced monitoring methods are required to identify stop criteria in proof-load tests. In this study, the combined methodology of two-dimensional digital image correlation and acoustic emission is investigated for its applicability for future implementation in field tests. The two monitoring systems are deemed to provide valuable insight with external measurements from digital image correlation and internal measurements from acoustic emission. Two overturned T-section reinforced concrete slabs (0.37 × 1.7 × 8.4 m) tested under laboratory conditions are used for the assessment. The first slab test served as a preliminary test to enable sensor placement and creation of a relevant loading protocol. The main scientific results lead to a proposal for a test procedure using the combined methodology based on results, observations, and experiences from an individual stop criteria assessment for the two methods. The results include full-field plots, an investigation of the time of crack detection and monitoring of crack widths with digital image correlation, and a qualitative assessment of activity vs. load followed by a quantitative evaluation of calm ratios using acoustic emission. The individual results show that both digital image correlation and acoustic emission can identify damage occurrence earlier than other secondary methods. At crack detection (415 kN), crack widths were measured at widths between 0.078 mm to 0.125 mm and can be monitored until reaching the stop criterion at 463 kN (Eurocode SLS threshold of wmax = 0.2 mm). The acoustic emission results were limited by the pre-defined loading protocol and thus, only indicated that damage occurred sometime between 300 kN and 500 kN (pre-defined load levels). Therefore, the proposal for test procedure involves a methodology, where the loading protocol may be updated during testing based on monitoring results and thus provide even more valuable data.

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Advanced crack monitoring is crucial for high precision response- and threshold evaluation when performing proof- and diagnostic load tests on existing concrete structures. Mostly, crack monitoring techniques involve one monitoring method, which provide thresholds with regard to stop criteria and characterization information. In the ongoing Danish bridge testing research program, it is hypothesized that several independent monitoring techniques are needed to reduce uncertainties related to crack detection and categorization. A number of novel monitoring methods are used in the research project. A special focus is however dedicated to two-dimensional digital image correlation (2D-DIC) and acoustic emission (AE). This paper presents initial research concerning evaluations related to digital image correlation based on sub-component beam tests performed in the DTU CasMat laboratory facility. The tested beams were prefabricated as TT-elements with a length of 6.4 m and cut into two T-beam elements. The test matrix consisted of ten beams strengthened with carbon fiber reinforced polymer (CFRP) in different configurations with and without post-tensioning of the CFRP, thus resulting in different crack initiation behavior. The investigations in this paper include: (1) time of crack detection compared to visual detection, (2) time of crack detection compared to time of crack width threshold values, and (3) crack width evaluation using 2D-DIC strain correction for out-of-plane deflection. The results show that cracks can be detected prior to both visual detection and significant stiffness change. After detection, crack development can be monitored for crack width stop criteria. Crack widths can also be successfully monitored for surfaces subjected to out-of-plane movement using a geometric correction method. The methodology is hypothesized to be of significant importance in future testing of full-scale concrete slab bridges in the Danish bridge testing project.@en