Confinement of reinforced concrete columns by means of carbon-FRCM jackets

The rehabilitation of existing reinforced concrete (RC) elements through jacketing technique has become widely-diffused practice, that allows members to attain both strength gain and, in most cases, ductility improvement, if compared to the original element. Such positive structural behavior is permitted by concrete confinement, that can be obtained for instance by both fiber reinforced polymer (FRP) or fiber reinforced cementitious matrix (FRCM) composites use. Here, the results of an experimental campaign aimed at studying the axial behavior of reinforced concrete columns confined with FRCM are shown. A carbon-based composite was used, that includes a balanced bidirectional carbon sheets embedded in a single-component fiber-reinforced cementitious matrix. Carbon sheets were used in 1 or 2 layers. The study involves the realization of twelve 1m-height columns, having two cross-section geometries, i.e. circle and square, this latter with rounded corner radius. Among the test specimens, eight were confined with carbon-FRCM (CFRCM) and four were left as control, without any external jacket. Additionally, two stirrups spacings were adopted, as a further investigation variable. Results were lastly analyzed in terms of stress vs. axial strain response, stirrup steel reinforcement and fiber hoop strains development.