Production and Properties of Self-Compacting Lightweight Concrete Containing Waste Plastic Fibers

Abstract

The objective of this study in the first stage is to characterize fresh, hardened, and thermal properties of self-compacting concrete produced with natural lightweight coarse aggregates (Ponza aggregate). In this stage, total of five self- compacting lightweight concrete mixes (SCLC) including different volumetric replacement level of lightweight aggregate (0%, 40%, 60%, 80%, and 100%) were designed. The fresh properties were quantitatively evaluated by the slump flow diameter, slump flow time T500mm, L-box, and sieve segregation test. For the hardened properties, the investigation includes different tests as follows: dry bulk density, water absorption, porosity, compressive strength, flexural strength, splitting tensile strength, modulus of elasticity, and ultrasonic pulse velocity. Thermal properties were also evaluated by thermal conductivity test. All tests were performed at 28 days except compressive strength that has been evaluated at 7, 28, and 90 days. In the second stage of this study, the performance of self-compacting lightweight concrete reinforced with Polyethylene Terephthalate (PET) fibers were analyzed in terms of fresh, physical, mechanical, and thermal properties as well as its flexural toughness and impact behavior. Nine different mixes of fiber reinforced self-compacting lightweight concrete were designed using PET fibers at three different volume fraction (0.5%, 0.75%, and 1%) and three different aspect ratio (15, 30, and 45). After design process, similar properties in the first stage in addition to toughness and impact test were performed. Then, statistical evaluation of experiment results based on analysis of variance general linear model and multiple linear regression was performed. This is to show the statistical significance of parameters (volume fraction and aspect ratio of PET fiber) in a quantitative manner and to determine the effectiveness these parameters in controlling the SCLC properties. At last, desirability function approach is utilized for the optimization of these parameters. It was found that increasing replacement level of lightweight aggregate simultaneously enhanced the filling and passing ability by increasing slump flow diameter and L-box height ratio, respectively. Despite the increase in the segregation index induced from addition of lightweight aggregate, all of the mixes had good resistance to segregation according to EFNARC guide. The compressive strength at 28 days of SCLC was more than 42 MPa for all mixes except the mix with 100% lightweight aggregates. Test results also indicated that incorporating the lightweight IV aggregate decreased the flexural strength, splitting tensile strength, and modulus of elasticity. However, a considerable reduction in the dry bulk density was recorded that reduces the dead load of structural buildings. Finally, the results of thermal conductivity and ultrasonic pulse velocity revealed that proper addition of lightweight aggregate into self-compacting concrete can significantly enhance thermal and sound insulation performance. The enhancement of these properties increased with an increase in the replacement level of lightweight aggregate. Based on the results of second stage, it is verified that the use PET fibers in SCLC negatively effects on the flowability and passing ability, while improving the resistance to segregation. The compressive strength and modulus of elasticity fluctuated with PET fiber percentage but tensile strength are in positive relationship and the longer fiber gave best tensile characteristics. There is around 9%, 14%, 19% reduction in dry density, ultrasonic pulse velocity, and thermal conductivity respectively, with increase of PET fibers ratio from 0% to 1% at aspect ratio of 45. Further, the result of flexural toughness test showed that the use of PET fiber in SCLC leads to an interesting improvement in the post-cracking performance and enhanced ductility of concrete. Furthermore, there is a substantial improvement in impact resistance of all PET fiber reinforced SCLC mixes over control mix. Results clarified that PET fibers concrete mix of volume fraction 1% and aspect ratio 45 gave the best impact resistance, the improvement of its impact resistance at ultimate failure over control mix (without fibers) was 373.3%. Finally, the analysis of the derived statistical models demonstrate that this model can be used to derive desirable properties of SCLC. According to the desirability function approach, the optimum volume fraction and aspect ratio of PET fibers (needed to achieve the best properties of SCLC) were 0.65% and 35.6 respectively.