سلوك البلاطات الخرسانية ثنائية الاتجاه ذاتية الرص والمسلحة بألياف بلاستيكية معاد تدويرها

Behavior of Self-Compacted Concrete Two-Way Slabs Reinforced with Waste Plastic Fiber

Abstract

The increasing environmental concern regarding the accumulation of non-biodegradable plastic trash has prompted researchers to investigate sustainable methods for its repurposing in construction. The present research investigates the structural and mechanical behavior of self-compacted concrete (SCC) two-way slabs reinforced with recycled waste plastic fiber (WPF). This study utilised polyethylene terephthalate (PET) waste plastic fibres, which were integrated into the concrete mixture as short fibres. Four mixes were prepared; one reference mix without fibres and three mixes incorporating PET fibres at dosages of 0.5%, 1%, and 1.5%. Several tests were conducted to assess the fresh properties of SCC using slump-flow, L-box, V-funnel, and U-box tests; and on the hardened performance of SCC using cubes, cylinders and prisms to test density, compressive strength, splitting tensile strength, and flexural strength at 28 days. Furthermore, the flexural behavior of self-compacted concrete (SCC) flat slabs incorporating PET fibers was also investigated. Eight SCC slabs have been designed to fail in flexure with dimensions of 1000 mm x 1000 mm x 70 mm. The slabs were split into two groups based on flexural reinforcement ratio (ρ); Group A (ρ1=0.43%) includes three specimens with various PET fibers and one without fibers considered as a reference specimen, while Group B (ρ2=0.65%) follows the same form. All the SCC slabs were tested at age 28 days under monotonic load and were simply supported. The fresh property test results indicated that an increase in PET fiber volume adversely impacted the workability of SCC mixes, due to decreasing flowability and passing ability. Incorporating PET fibers caused a slight decrease in density of up to 2.2% at a 1.5% fiber dosage, because plastic fibers have a low specific gravity, which leads to a lighter concrete composition. The mechanical performance enhanced with significant fiber incorporation; at 1% PET concentration, compressive and flexural strengths increased by 8.4% and 11.2%, respectively. The splitting tensile strength also improved, showing a 10.9% increase at 1% PET and reaching the greatest enhancement of 15.1% at 1.5% PET, demonstrating enhanced post-cracking performance.. Structural testing of SCC slabs indicated that the inclusion of fibers at 0.5% and 1% consistently enhanced all parameters, while 1.5% PET led to a decline in performance due to fiber agglomeration. The first cracking load was enhanced by 33.3% in Group A and 28.6% in Group B at 1% PET fiber content, while the ultimate load at 0.5% PET increased by 8.5% in Group A and 9.2% in Group B. The maximum deflection increased by 20% in Group A and by 15.4% in Group B at 0.5% PET fiber content, signifying improved deformability. At 0.5% PET fiber content, the ductility index, stiffness, and toughness showed notable improvements compared with the reference specimen, increasing by 35.9%, 23.2%, and 35.8% in Group A and by 36%, 28.5%, and 34.6% in Group B, respectively. An analytical investigation was performed using multiple linear regression models in SPSS to predict both fresh and hardened properties of concrete based on PET fiber content. The generated models revealed good correlations, which were further validated by comparison with previous studies. These relationships provide reliable predictions for SCC mix design within defined fiber content ranges, supporting early-stage estimation of workability and mechanical performance. In conclusion, the using of 0.5–1% PET into SCC slabs markedly improves mechanical and structural performance while promoting sustainability objectives through the repurposing of plastic waste. Excessive fiber content (>1%) may hinder performance due to inadequate dispersion.