Evaluation of concrete–steel interfaces in steel tubes filled with chipped rubber–concrete

Abstract

The objective of this study was to evaluate the bond behaviour of concrete-filled steel tubes (CFSTs) where waste chipped rubber, sourced from scrap tyres, partially replaces natural coarse aggregate. A series of push-out tests on 112 circular and square CFST specimens were investigated with the main parameters considered in the tests being: (a) cross-sectional type (circular and square); (b) cross-sectional dimensions; (c) concrete type (normal and rubberised concretes); (d) replacement ratio of recycled chipped rubber; and (e) concrete age (28–365 days). Four rubber chip replacement ratios (0, 10, 20 and 30%) by volume of coarse aggregate were used. The experimental results indicated that cross-sectional type and dimensions have a high impact on the interfacial bond strength. The bond strength in larger circular tubes was about 60% more than the bond strength in smaller circular tubes, and about 127% and 42% more than the bond strength in large and small square tubes, respectively. It was also found that CFSTs incorporating chipped rubber shared a generally similar interface bond behaviour between the concrete core and steel tubes with conventional CFSTs. Moreover, the bond strength decreased remarkably with the increase of concrete age.