Behavior of hybrid reinforced concrete columns

Abstract

This paper involves an experimental investigation to study the behavior of short rectangular columns cast with hybrid concrete, to compare the strength, stiffness and toughness provided by the hybrid structural system and the results collected may be used as basic data for future development of design models for this combination of materials.Seven columns were cast and tested under concentric loading; the variables studied included the diameter of steel bars for both longitudinal and lateral reinforcement. The dimensions of rectangular columns were: 100 mm x 200 mm x 740 mm high. Two columns were cast as full conventional concrete and full reactive powder concrete columns acted as control specimens. The remaining five were cast as hybrid columns having the conventional concrete at the core and surrounded by a 40 mm thickness of reactive powder concrete, with 1% micro steel fiber.The combination of these two types of concrete into the hybrid concrete columns was very useful because it enhanced the ultimate capacity of the columns with respect to the conventional concrete in about 179% compared to the enhancement produced due to using the reactive powder concrete alone which was 203%, therefore, it was concluded that using this hybrid concrete combination in concrete industry would be more economical than the use of reactive powder concrete; moreover, based on the mode of failure observed, it would be safer to use the hybrid structural system because of the destructive type of failure for columns cast with conventional concrete. Increasing the diameter of the main reinforcement gave an average increase in the percentage of the failure load with respect to the conventional concrete column of about 179% compared to the increase in the diameter of the ties which gave an average increase of 185%; which leads to the conclusion that the effect of lateral reinforcement was more pronounced than the effect of the longitudinal reinforcement in hybrid columns, due to the increase in confinement produced by both the reactive powder concrete cover in the hybrid concrete columns and the ties represented by the lateral reinforcement.