827 Computational Modelling of Concrete Structures – Bic ´ anic ´ et al. (Eds) © 2014 Taylor & Francis Group, London, ISBN 978-1-138-00145-9 Numerical study of a strain hardening cementitious composite overlay system for durable concrete repair M. Luković, E. Schlangen, B. Šavija, G. Ye & K. van Breugel Microlab, Faculty of Civil Engineering and Geosciences, Delft University of Technology, Delft, The Netherlands ABSTRACT: Innovative cement-based repair materials may require different procedures for application in comparison to standard repair requirements. Before their field application, a proper protocol should be established. Apart from laboratory experiments, numerical simulation can be of great use. Herein, a lattice type model is used to simulate fracture performance of fiber reinforced repair material—Strain Hardening Cementations Composite (SHCC) and its performance in the repair system. Repair material was first tailored through numerical testing in a single fiber pullout test and a direct tension test. Further on, structural behavior of the repair system and impact of initial defects in the mortar substrate (reflec- tive cracking) was examined. The influence of fiber addition, different simulated substrate roughness and interface properties between two materials on the performance of the repair system is investigated. The numerical study gives insight into the benefits of distributed microcracking and high ductility of the fiber reinforced system over localized cracking and inherent brittleness of a non-reinforced repair system. It is envisioned that this approach can be used to tailor the properties of the repair system for specific applica- tions, resulting in more reliable and durable concrete repairs in the future. old and new material in concrete repair applica- tions. Although very promising, a procedure for practical application of this material is not yet established. Apart from laboratory experiments, numeri- cal simulation can be of great use in investigating performance of different repair materials in a com- posite system. Here, a lattice type model (Schlan- gen 1993) is used to simulate fracture performance of fiber reinforced repair material. The presented model is based on the principle of embedding dis- crete fibers in a random lattice mesh representing the material matrix (Schlangen & Qian 2009). The influence of addition of polyvinyl alcohol-PVA fibers (2% by volume)is examined and compared to non-reinforced material. SHCC was first designed through numerical testing in a single fiber pullout test and a direct tension test. Once local material properties for the simulated repair material are determined, structural behavior and debonding tendency of the repair system is investigated. Cracking and/or debonding of the overlay reduces the load-carrying capacity of the overlay system and allows water and other hazardous substances to penetrate into concrete. Predicting and quantifying behavior of overlay will, therefore, enable more reliable esti- mation about performance and service life of the repair system. 1 INTRODUCTION Durability of concrete repairs, including all types of repairs and application of different materi- als, often shows problems (Tilly & Jacobs 2007). Most of the past efforts focused either on reduc- ing free shrinkage of repair material, increasing its compressive/tensile strength, or increasing bond strength between a repair material and a concrete (or mortar) substrate. However, all these attempts resulted in only marginal improvements as they did not address inherent behavior of concrete as a brittle material (Li 2009). What is more, brittle- ness is even more pronounced in high performance concrete, as it is more prone to cracking. In order to address brittleness as an intrinsic issue of repair systems, Li and Horii (Li, Horii, Kabele, Kanda, & Lim 2000) developed an ultra-ductile fiber rein- forced composite called Strain Hardening Cemen- titious Composite (SHCC). SHCC is characterized by formation of nar- row microcracks and strain hardening behav- ior. Multiple cracks are beneficial for relief of stresses induced by deformational incompatibil- ity between the new and old material. Moreover, high ductility of this material, achieved through dense microcracking, showed to have great potential in effectively suppressing crack locali- zation and interface delamination between the