Various recycled steel fiber effect on mechanical properties of recycled aggregate concrete

PurposeThe current study mainly focuses on the effect of varying diameter recycled steel fibers (RSF) on mechanical properties of concrete prepared with 25 and 50% of recycled coarse aggregate (RCA) as well as 100% natural aggregate (NA). Two types of RSF with 0.84 mm and 1.24 mm diameter having 30 mm length were incorporated into normal and recycled aggregate concrete (RAC).Design/methodology/approachThe fresh behavior, compressive, splitting tensile, flexural strengths and modulus of elasticity of all the mixes were investigated to evaluate the mechanical properties of RACs. In addition, specimen crack and testing co-relation were analyzed to evaluate fiber response in the RAC.FindingsAccording to the experimental results, it was observed that mechanical properties decreased with the increment replacement of NA by RCA. However, the RSF greatly improves the mechanical properties of both normal concrete and RACs. Moreover, mixes containing 1.24 mm diameter RSF had a more significant positive impact on mechanical properties than mixes containing 0.84 mm diameter RSF. The 0.84 mm and 1.24 mm RSF addition improved the mixes' compressive, splitting tensile and flexural strength by 10%–19%, 19%–30% and 3%–11%, respectively when compared to the null fiber mix. Therefore, based on the mechanical properties, the 1.24 mm diameter of RSF with 25% replacement of RCA was obtained as an optimum solution in terms of performance improvement, environmental benefit and economic cost.Practical implicationsThe practice of RCA in construction is a long-term strategy for reducing natural resource extraction and the negative ecological impact of waste concrete.Originality/valueThis is the first study on the effects of varying size (0.84 mm and 1.24 mm diameter) RSF on the mechanical properties of RAC. Additionally, varying sizes of RSF and silica fume added a new dimension to the RAC.

Laboratory Tests of Concrete Beams Reinforced with Recycled Steel Fibres and Steel Bars

This paper explores the possibility of the partial replacement of the longitudinal reinforcement in reinforced concrete (RC) beams with recycled steel fibres (RSF). Testing was focused on the contribution of two volume ratios of the RSF—0.5%, 1.0%. Basic compression and flexural tensile tests were performed to evaluate the effectiveness of the fibres following current standards. Additionally, the full-scale beams with and without conventional reinforcement were subjected to four-point bending tests. The results indicate that RSF improved the load-bearing capacity of the RC beams. Cooperation of RSF with the steel bars in carrying loads was proved. Findings from the Digital Image Correlation (DIC) revealed no impact on the cracking pattern of the RC beams.

Residual Strength and Drying Behavior of Concrete Reinforced with Recycled Steel Fiber from Tires

Fiber reinforcement of concrete is an effective technique of providing ductility to concrete, increasing its flexural residual strength while reducing its potential for cracking due to drying shrinkage. There are currently a wide variety of industrial fibers on the market. Recycled steel fibers (RSF) from tires could offer a viable substitute of industrialized fibers in a more sustainable and eco-friendly way. However, mistrust exists among users, based on fear that the recycling process will reduce the performance, coupled with the difficulty of characterization of the geometry of the RSF, as a consequence of the size variability introduced by the recycling process. This work compares the behavior of RSF from tires compared with industrialized steel or polypropylene fibers, evaluating the fresh state, compressive strength, flexural residual strength, and drying behavior. The concept of Equivalent Fiber Length (EFL) is also defined to help the statistical geometrical characterization of the RSF. A microstructural analysis was carried out to evaluate the integration of the fiber in the matrix, as well as the possible presence of contaminants. The conclusion is reached that the addition of RSF has a similar effect to that of industrialized fibers on concrete’s properties when added at the same percentage.

Impact of Length and Percent Dosage of Recycled Steel Fibers on the Mechanical Properties of Concrete

The global rapid increase in waste tyres accumulation, as well as the looming social and environmental concerns, have become major threats in recent times. The use of Recycled Steel Fiber (RSF) extracted from waste tyres in fiber reinforced concrete can be of great profitable engineering applications however the choice of suitable length and volume fractions of RSF is presently the key challenge that requires research exploration. The present experimental work aims at investigating the influence of varying lengths (7.62 and 10.16 cm) and dosages (1, 1.5, 2, 2.5, 3, 3.5, and 4%) of RSF on the various mechanical properties and durability of concrete. Test results revealed that the varying lengths and dosages of RSF significantly affect the mechanical properties of concrete. The improvements in the compressive strength, splitting tensile strength, and Modulus of Rupture (MOR) of RSF reinforced concrete observed were about 26, 70, and 63%, respectively. Moreover, the RSF reinforced concrete showed an increase of about 20 and 15% in the yield load and ultimate load-carrying capacity, respectively. The durability test results showed a greater loss in compressive strength and modulus of elasticity and a smaller loss in concrete mass of SFRC. Based on the experimental findings of this study, the optimum dosages of RSF as 2.5 and 2% for the lengths 7.62 and 10.16 cm lengths, respectively are recommended for production of structural concrete. Doi: 10.28991/cej-2021-03091750 Full Text: PDF

Circular Steel: How Information and Actor Incentives Impact the Recyclability of Scrap

Recycling plays a vital role in preserving resources like steel and consequently in a circular economy. Scrap dealers and steel mills, the main business units in this system, often encounter opposing financial and sustainability incentives in using scrap as feedstock because regular sorting and scrap-preparation infrastructure cannot deal with the increasing complexity of steel scrap. Mismatches between the inputs and the target composition of the recycled steel result in trade-offs that favor the economics at the expense of resource efficiency. By examining literature and interviewing several actors, different scrap characteristics were identified as dimensions of scrap quality. Quality is typically associated with chemical composition, which is important, but this study aims to elaborate the concept of quality further and to connect it to the realities of scrapyard operations. Industry actors have different definitions for desired content, physical condition, shape and size, and homogeneity, based on their needs. Very few studies examine these details. Additionally, the relationship of quality and the level of information about the characteristics of the material was established. Having more definitive information on scrap increases opportunities for resource-efficient actions. This work offers an alternative perspective on how to address issues pertinent to recycling. Graphical Abstract