Determination of Optimum Proportions of Different Treated Plastic Fibers in Sustainable Self-Compacting Concrete

Abstract

The main aim of this research is to optimize various characteristics of Polyethylene terephthalate PET fibers in a sustainable self-compacting concrete in terms of volume fraction Vf, aspect ratio Ar and method of surface treatment and modification. In the first stage, the performance of PET fiber-reinforced self-compacting concrete was analyzed in terms of main fresh and hardened properties. Nine different mixtures were designed using three different ratios of Vf and Ar. The fresh tests were evaluated by the slump flow and T500 mm while the hardened tests include the compressive and splitting tensile strength. Therefore, analysis of variance was performed based on the general linear model (GLM-ANOVA) deepened on the statistical program (Minitab19). To describe the significance in a quantitative manner and to demonstrate the main effectiveness of the volumetric ratios and length of plastic fibers in SCC. The desirability function concepts were unitized to show the improvement of target functionality and to caught the optimal mixture ratio that improves SCC performance using PET fibers. It is clear from the results obtained in the first stage that the incorporation of PET as reinforced materials with different Vf and Ar has negatively affected the flow performance, but within the limits European Federation of National Associations Representing producers and applicators of specialist building products for Concrete (EFNERC). The compressive strength fluctuated with the percentage of plastic fibers, especially the short fibers, which gave better results than the long fibers. While the addition of fibers led to an increase in the tensile strength, the which increased with the increase in the aspect ratio of the plastic based on the Vf of the fibers, and the longer fibers showed better tensile strength. According to the Analysis of variance (ANOVA) method, the results showed that the length mainly controlled the slump flow, compressive and splitting tensile strength while the Vf mainly controlled the T500 mm. The multi-objective optimization results for the first stage indicated that the optimum Vf and Ar for PET fibers, to achieve the optimum performance in terms ofthe selected properties and the partitioning of sustainability aspects (CO2 emission and cost reduction), were 0.7% and 24.4, respectively. In the second stage, the optimal mixture is selected from the first stage to be a control mixture in addition to four other mixtures content treatment PET fibers. They chemically treated (NaOH) PET fibers, mechanically treated (surface roughness) and physically treated (gamma rays) in addition to the geometrically shaped fibers. In this stage, fresh properties include slump flow, T500mm, L-box, and sieve segregation while hardened properties include mechanical (compressive, splitting tensile, flexural strength, flexural toughness, modulus of elasticity and impact strength) and physical and durability hardening properties include (dry density, ultrasonic pulse velocity, porosity and water absorption. The treatment and modification used for the PET fibers slightly reduced the fresh properties but were within the limits of the SCC specification. However, the mechanical were significantly increased compared to the mixt of optimal (MOP). As for the increase of the ultrasonic pulse velocity, it can be concluded that fiber surface treatment can enhance the acoustic insulation performance. On the other hand, there was a reduction in the dry density, porosity and water absorption as a result of treating the surface of the fibers before mixing, which is an indication of the improvement of the hardened properties. It can be concluded from analyzing results that treating PET fibers by increasing the surface roughness with optimum properties of PET fibers in the first stage, in terms of Vf and Ar, can give the best performance for sustainable PET fiber reinforced SCC.