Experimental investigation of interface behaviour of RC beams strengthened with concrete layers

Flexural strengthening of concrete elements by adding new concrete layers is a common strengthening technique. In design, in order to simplify the calculations, the strengthened element is usually assumed monolithic but, in many cases, this assumption is not conservative as interface slip is a critical parameter that affects the level of damage to a strengthened element. In the present study, an experimental investigation of RC beams strengthened with concrete layers is presented. From bending tests, the interface slip value is evaluated. It is found that interface preparation and the type of strengthening (tensile or compressive) considerably influence effectiveness. Through a comparison between strengthened and respective monolithic and initial specimens, the efficiency of the strengthening technique is evaluated. In addition, a comparison with respective experimental results from the literature is presented.

► Strengthening at the compressive side leads to a monolithic behaviour of the element.
► When strengthening at the tensile side, an anchorage of the new layer is required.
► When strengthening at the tensile side, a very good interface roughening is required.
► Adding a layer at the tensile side is the most efficient technique.
► Slip measurements showed that interface adhesion depends on local conditions.