Preventing Plastic-Shrinkage Cracks in GFRP-Bar Reinforced Concrete Using Fibers

Large horizontal concrete elements are susceptible to premature cracking due to environmental effects. The ASTM C1579 bottom-restraining technique cannot reliably induce controlled cracking. In this study, glass fiber-reinforced polymer (GFRP) bars were incorporated to enhance restraint and induce plastic-shrinkage cracking. Given the increasing use of GFRP bars in structures, this study investigates their influence on cracking. ASTM C1579 molds were reinforced with 13 mm and 16 mm GFRP bars, while short cellulose and polypropylene fibers were incorporated. Results indicated that samples reinforced with 16 mm GFRP bars induced more extensive cracking than those with GFRP 13 mm bars. Fibers at 0.2%, 0.25%, and 0.3% reduced cracking and enhanced mechanical strength. At 0.4%, crack mitigation was superior, though slight reductions in compressive and flexural strength were observed. Regression analysis indicated a nonlinear relationship between fiber dosage and crack reduction. Analysis of variance results revealed statistical significance (p < 0.05) for both fiber percentage and fiber type. Polypropylene outperformed cellulose fibers, although both effectively mitigated plastic-shrinkage cracking.