The number of hybrid concrete structures is increasing due to the need for repairing/strengthening existing structures and the development of new hybrid concrete systems. The structural response of these hybrid structures might be governed by the strength of the interface between the two concretes, making it essential to characterize the mechanical response of the interface. In this research, a notch beam tests is proposed to investigate the structural behavior of the interface. Hybrid beams consisting of Strain Hardening Cementitious Composites (SHCC) and conventional concrete are designed with a notch at mid-span and are tested under a four-point bending configuration. The effect of interface treatment (i.e. surface roughness) and the curing condition is tested using two sets of hybrid beams. The first set has three beams which are cured in sealed conditions until the day of testing and the interface is varied between smooth, profiled and roughened. The second set has two beams with smooth interface where one beam is seal cured and the other one is exposed to drying in the laboratory. The opening of the interface is visualized using Digital Image Correlation (DIC) and quantified using Linear Variable Differential Transformers (LVTDs) during testing of the hybrid beams. It is observed that increasing the roughness of the interface leads to higher load-bearing capacity and controlled opening of the interface. The beam exposed to drying showed somewhat reduced capacity, possibly due to the pre-damage caused by differential shrinkage of the two concretes.@en

The focus of this study is to characterize delamination using static and dynamic tests and to assess the interface failure mechanism of an innovative hybrid concrete beam, made out of conventional concrete and a special class of fibre reinforced material, known as Strain Hardening Cementitious Composite (SHCC). Three SHCC beams were subject to four-point bending tests, differing in the interface surface preparation and curing method. Damage and delamination were gradually induced due to increasing loads in steps of 2.5 kN, and their propagation was tracked by the use of linear variable differential transformers and Digital Image Correlation technique. Dynamic hammer tests were also carried out to identify the natural frequency variation due to progressive damage. The outcome of this comparison allowed us to assess the capability of using a frequency-based monitoring technique for possible early-stage delamination detection of hybrid civil structures. To understand the influence of delamination on the dynamic response, a simplified finite element modelling approach of delamination was adopted. The induced damage was modelled in a simplified manner by reducing the stiffness of the elements in the damaged area. This model can be potentially integrable into large-scale numerical models for Structural Health Monitoring purposes.@en