Concrete beams stiffened by polymer-based mortar layers: experimental investigation and modelling

In the present work, the main results provided by an experimental investigation, assessing the mechanical performances of concrete elements stiffened by a single or more layers of different kinds of polymer- modified cementitious repair mortar, are presented. The study is aimed in order to investigate the failure mechanism occurring in the samples under bending loading. In particular, the experimental investigation allows checking if the collapse mechanism is driven by delamination occurring along the interface among the overlays or by cracks propagating from the tensile region to the compressive zone, as it occurs in a typical failure mechanism driven by flexure. Thirty-eight precast and pre-stressed concrete samples were realized and cured to simulate load-bearing concrete ceiling beams widely employed as floor systems for residential buildings. After curing, the samples were subjected to three-point loading bending tests in order to evaluate the mechanical response of the specimens in terms of load vs. mid-span transverse dis- placement. Through the experimental tests, the crack initiation and propagation during the bending load- ing have been also investigated. Simplified finite element (FE) models were performed to properly reproduce the actual response of ceiling beams under non-symmetric loading bending. It is shown that the proposed FE model can be straightforwardly used to predict the behavior of concrete beams stiffened by polymer-based repair mortar layers.