Compressive Performance of Steel Fibre Reinforced Concrete-Filled Plastic Tubes

This study investigates the compressive strength behaviour of concrete specimens with varying diameters (75 mm, 100 mm, and 150 mm), steel fibre contents (0%, 0.75%, and 1.5%), and confinement conditions using PVC tubes. A total of 54 cylindrical specimens were prepared across four groups: plain concrete (C), fibre-reinforced concrete (FC), plain concrete with PVC confinement (TC), and fibre-reinforced concrete with PVC confinement (TFC). Results showed that compressive strength increased with specimen diameter due to a fourfold increase in cross-sectional area and reduced slenderness (h/d ratio), with strength gains ranging from 4.3 to 5.4 times for unconfined specimens and 3.5 to 4.1 times for confined ones. However, in PVC-confined specimens, a decreasing 2t/d ratio with increasing diameter limited the confinement effectiveness. Steel fibres showed inconsistent effects on strength, likely due to poor workability and uneven distribution. PVC confinement generally enhanced compressive strength, particularly at 1.5% fibre content, with increases of 64%, 58%, and 45% for specimens with diameters of 75 mm, 100 mm, and 150 mm, respectively. Observed failure modes included bulging, shear, and tube bursting. Bulging was associated with more effective confinement. These findings highlight the importance of jointly considering geometric scaling and material parameters in the design of confined fibre-reinforced concrete elements.