Crack control for repair and strengthening of reinforced concrete structures using the multi-cracking behaviour of Ultra-high Performance Fibre Reinforced Shotcrete (UHPFRSC)

Abstract

Ultra-High Performance Fibre Reinforced Concrete (UHPFRC) is an innovative material for the repair and/or strengthening of reinforced concrete structures. In the field of traffic infrastructure, the outstanding mechanical properties are used as a protective surface layer and to increase the load capacity of the structure. UHPFRC is characterised by a dense granular structure and correspondingly high resistance against chloride attack. The material is typically applied as cast in-situ concrete. To optimise implementation of the strengthening and repair method, the UHPFRC is applied as sprayed concrete, so-called Ultra-High Performance Fibre Reinforced Shotcrete (UHPFRSC). The research aims to increase the service life of damaged and/or overloaded structures. Crack widths in the UHPFRSC layer must be limited to avoid migration of chlorides. The thin UHPFRSC layer provides crack distribution and control of localised macro cracks in the existing reinforced concrete structure. The fibres in the Ultra-High Performance Shotcrete (UHPSC) allows for limiting the crack width to 50 µm. When the UHPFRSC is applied on cracked reinforced concrete, it can be assumed that multi-cracking in the UHPFRSC surface layer will provide a chloride-dense layer equivalent to a coating. Under load, the two layers - UHPFRC and RC - act as a composite. For structural analysis, a particular focus must be placed on the interaction between cementitious materials. In addition, the pre-damage and pre-loading of the existing structure will influence the structural behaviour and crack formation. The paper presents the results of bending tests of UHPFRC - RC composite elements. The investigation shows the outstanding crack control behaviour of UHPFRSC. Based on this investigation, an analytical model will be provided, and a calculation of the crack widths will be derived. The research presents a central aspect of a large interdisciplinary research project at Munich University of Applied Science, called i-SCUP.