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In the last decades, the need for upgrading, strengthening and retrofitting of existing concrete structures is rapidly growing. Composite materials showed to be an optimal solution to face this problem, combining high efficacy with low invasiveness. The use of Fiber Reinforced Polymers (FRP) to wrap concrete columns has been widely investigated and became a very successful method to improve their structural performances. However, it has been recognized that FRPs, due to the presence of an organic resin, have a few drawbacks, such as poor mechanical behavior at high temperatures, lack of vapor permeability and impossibility to be installed on wet surfaces. This experimental work aims to propose a comparison between three different innovative methods as possible strengthening solutions for existing concrete columns. The structural behavior of 20 reduced scale concrete columns, realized by using a low performance concrete, in order to reproduce the poor mechanical properties of existing structures, was investigated. Two unreinforced column were tested in compression as reference. Six of them where reinforced by applying an external layer of FRP, with different types of fabric reinforcement (made of carbon or PBO fibers). Six columns were reinforced by using the same fabrics coupled with an inorganic matrix (FRCM) instead of epoxy. Six other columns were reinforced by using a layer of High Performance Fiber Reinforced Concrete (HPFRC) of 3 cm thick. Experimental results have been analyzed and performance of the three reinforcement systems have been compared.

This work is part of a wide study related to the structural behavior of concretes prepared by substituting natural aggregates with recycled aggregates from building demolition. In this work, recycled aggregates coming from an industrial crushing plant in which rubble are suitably treated were employed in substitution of ordinary aggregates. In order to evaluate the real-scale behavior of reinforced recycled-aggregate concrete, several beam-column joints were manufactured, then cured in open air at a temperature of approximately 20 [degrees]C in order to simulate the real conditions of the building site. Subsequently, they were submitted to low-cycle loading, characterized by a load history containing few cycles but having a large range of bond reversal stresses in order to simulate real structures subjected to earthquake or high winds. In this way, the ductility of joints, made of either ordinary or recycled-aggregate reinforced concrete, could be investigated and compared. The results gave experimental evidence of the suitability of recycled-aggregate concrete for structural use, although some measures in the structural design of the joint should be taken. DOI: 10.1061/(ASCE)0899-1561(2006)18:5(650) CE Database subject headings: Concrete; Joints; Sustainable development; Cyclic loads.