Efficiency of RC square columns repaired with polymer-modified cementitious mortars Francesca da Porto ⇑ , Elena Stievanin, Carlo Pellegrino Department of Structural and Transportation Engineering, University of Padova, Via Marzolo 9, 35131 Padova, Italy article info Article history: Received 23 October 2010 Received in revised form 27 November 2011 Accepted 28 November 2011 Available online 20 December 2011 Keywords: Reinforced concrete Repair mortar Elastic modulus Compressive strength Columns abstract This paper regards the axial behavior of reinforced concrete columns repaired by polymer-modified cemen- titious mortars. Tests were performed on eight columns with square cross-section: six were repaired with three types of polymer-modified cementitious mortars on all faces, two were in non-damaged and non- repaired condition (control elements). Tests were repeated varying mechanical properties (elastic modulus and compressive strength) of repair materials, maintaining the same repair thickness, including the rein- forcement bars. Comparisons between repaired and control elements showed that polymer-modified cementitious mortars cannot restore the original load-bearing capacity of columns. In spite of this, selection of mortar mechanical properties plays a significant role. Among the three types of repair mortar tested in this experimental study, using the material with the most similar elastic modulus and higher compressive strength than that of the concrete substrate is recommended. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Reinforced concrete often shows its vulnerability to time depen- dent phenomena, including weathering, well before reaching the intended service life of the structure. The phenomenon is so wide- spread that systematic replacement of existing structures is not a possible measure. Thus, interest in rehabilitation and strengthening of reinforced concrete structural elements has been rapidly increas- ing around the world in the past two decades. Various research pro- grams were aimed at developing materials and methods for improving the safety and reliability of existing concrete structures. In this framework, externally bonded fiber reinforced polymers (FRPs) sheets/plates have several attractive properties, such as low weight-to-strength ratios, non-corrosiveness, and ease of application. A number of experimental and analytical studies have already been carried out at the University of Padova on flexural [1], shear [2] and bond behavior [3] of FRP strengthened elements. Add- ing or applying mortar, or spraying concrete or mortar with the aim of rehabilitating and/or strengthening of existing reinforced con- crete structures are also possible ways of intervening with a more traditional and common material. Emberson and Mays [4] discussed the mechanical and physical properties of mortar repair systems and created two- and three- dimensional linear elastic finite element models to reproduce axial load transfer through simple patch repairs in reinforced concrete members. They also worked on reinforced concrete beams in flexure and studied the effect of repairs in both compression and tension zones [5]. Pellegrino et al. [6] investigated the efficiency of rehabilitation interventions on reinforced concrete columns with polymer-modified cementitious mortar. Axially loaded ele- ments were tested by varying repair thickness, which included or did not include reinforcement bars. The mortar was applied on one face only of square columns. The authors found that the repair could not restore the same load-bearing capacity as non-damaged control columns. However, if repairs include longitudinal rein- forcement bars, the repaired element shows stable behavior, shar- ing of loads and plasticization of the material before failure. The same authors also studied the effect of repairs in both compression and tension zones, and including or not reinforcement bars, on reinforced concrete beams in flexure [7]. Mangat and O’Flaherty [8] studied the influence of elastic modulus on stress redistribution and cracking in repair patches for axially loaded elements. Results showed that repairs applied with relatively stiff materials display efficient structural interac- tion with the structure. High stiffness repairs are effective in redistributing shrinkage strain to the substrate and attracting external loads in the long term. Low stiffness repair materials are much more likely to undergo tensile cracking due to re- strained shrinkage, and are ineffective in redistributing strain. Sharif et al. [9] conducted an experimental investigation to assess the effectiveness of patch repairs in axially loaded columns. The load distribution between patch repair, concrete core and steel reinforcement depended on the modulus of elasticity and areas of these components in the composite repaired section. In order for patch repair to be structurally effective, the loads before 0958-9465/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.cemconcomp.2011.11.020 ⇑ Corresponding author. Tel./fax: +39 049 8275631. E-mail address: daporto@dic.unipd.it (F. da Porto). Cement & Concrete Composites 34 (2012) 545–555 Contents lists available at SciVerse ScienceDirect Cement & Concrete Composites journal homepage: www.elsevier.com/locate/cemconcomp