FRP tube encased rubberized concrete cylinders

In this study, FRP tube encased waste tire rubber modified concrete cylinders were investigated. Four batches of confined and unconfined concrete cylinders with a diameter of 101.6 mm and a height of 304.8 mm were prepared. Each batch contained three confined cylinders and three unconfined cylinders. The total number of effective cylinders prepared was 24. Batches 1-3 were made of rubberized concrete. In Batch 1, 15% by volume of coarse aggregate was replaced by waste tire fibers or stripes; in Batches 2 and 3, 15% by volume of sand and 30% by volume of sand were replaced by crumb rubbers, respectively. Batch 4 was a control batch with conventional plain concrete. Uniaxial compression tests were conducted on all the cylinders per ASTM C39. Strain gages were installed on the encased rubberized concrete cylinders to obtain local strain distributions. The compressive strength and strain at the peak load were compared with the predictions by available design-oriented confinement models. It is found that the FRP tube encased rubberized concrete cylinders have higher confinement effectiveness, ductility, and elastic regions than FRP tube encased conventional concrete cylinders. Waste tire fiber modified concrete performs better than crumb rubber modified concrete with a lower cost. Instead of volume contraction, FRP encased rubberized concrete cylinders experience volumetric expansion. The current design-oriented confinement models cannot consistently predict the compressive strength and strain of the encased cylinders. An 1-D coupon test cannot uniquely determine the hoop tensile strength of the FRP tubes which are subjected to a 2-D stress condition.