Fresh and Hardened Properties of Self-CompactingConcrete Reinforced with Hybrid Recycled

Steel–Polypropylene FiberM. Mastali, Ph.D.1; and A. Dalvand2

Abstract: This paper presents the results of extensive experimental tests on the fresh and hardened properties of self-compacting concretereinforced with hybrid polypropylene (PP) fiber and recycled steel fiber (RSF) in different fiber volume fractions. In the present paper, RSFswere recovered from waste tires. The mix compositions were reinforced with different combinations of hybrid recycled-steel fiber (0.35, 0.7,and 1.05%) and PP fiber (0.35 and 0.7%). The fresh state of the mix compositions were assessed by using slump flow diameter, T500, and Tv.Moreover, the hardened properties of specimens were characterized by using compressive strength, flexural strength, and impact resistance.Regression analysis was executed on the relatively large amount of gathered experimental data to correlate properties of fresh and hardenedstates of self-compacting concrete reinforced with hybrid recycled steel–PP fibers. The results showed that adding hybrid recycled steel–PPfiber improves the impact resistance and mechanical properties. Adding recycled steel fiber led to higher improvement in the compressivestrength compared to PP fiber. Moreover, increasing the content of PP fiber reduces the effect of recycled steel fiber in improvement offlexural strength. DOI: 10.1061/(ASCE)MT.1943-5533.0001851. © 2017 American Society of Civil Engineers.

Author keywords: Hybrid fiber; Recycled steel fiber; Polypropylene fiber; Mechanical properties; Impact resistance.

Introduction

During the last 2 decades, various practical efforts have been madeto reduce the amount of waste materials that enter landfills. Due tolimited space for landfilling and its increasing cost, attentionhas been paid to new methods of recycling waste materials. Insustainable construction technology, using certain amounts of recy-clable waste materials such as steel, polymers, and plastic inconcrete mixes is favourable for researchers due to its economicand environmental advantages. One of the main problems of plainconcrete is its low ductility, as well as its low tensile and flexuralstrength and corresponding characteristics. Addition of fibers is aneffective method for enhancement of impact resistance andmechanical properties of plain concrete. This method has provedto enhance ductility and postcracking performance of reinforcedconcrete through fiber-bridging action and fiber/matrix interfacialbonds (Hamoush et al. 2010; Yap et al. 2013). This improvementmainly affects the mechanical properties (Hassanpour et al. 2012;Libre et al. 2011; Gao et al. 1997; Alhozaimy et al. 1996), tough-ness (Khaloo et al. 2005), ductility (Khaloo et al. 2005; Kim et al.2011), torsion strength (Slater et al. 2012; Okay et al. 2012), impactresistance (Mastali and Dalvand 2016a; Alavi Nia et al. 2012),and more. Using hybrid steel macrofibers–polypropylene microfib-ers introduces the benefits of hybridization in terms of postcrack

strength of the reinforced specimens under flexural tests (Sorelliet al. 2003).

Ahmed et al. (2007) worked on flexural response of hybridsteel–polyethylene (PE) fiber-reinforced cement compositescontaining high volumes of fly ash. The flexural assessment wascarried out by executing four-point bending tests. In order to main-tain a workable mix, the contents of fiber volume fractions werekept constant at 2.5%. Among mix compositions with different vol-ume ratios of steel and PE fibers, the reinforced specimen with1.0% steel and 1.5% PE showed the highest flexural strength,and the reinforced specimen with 0.5% steel and 2.0% PE exhibitedthe highest deflection and the highest flexural toughness (Ahmedet al. 2007). Khaloo et al. (2014) investigated properties of freshand hardened reinforced self-compacting concrete with steel fibers.Four different steel-fiber volume fractions (0.5, 1, 1.5, and 2%)were used to reinforce mix compositions in their tests. Therheological characteristics of mix compositions were measuredwith using a slump flow diameter, T500, V-funnel test, andL-box test. Additionally, properties of hardened specimens wereobtained through execution of a splitting tensile test, flexural test,and compressive test (Khaloo et al. 2014). They showed that ad-dition of steel fiber reduced the rheological characteristics of thereinforced mixtures. Moreover, it was revealed that addition of steelfiber improves splitting tensile strength, flexural strength, andflexural toughness, while reducing compressive strength (Khalooet al. 2014).

Martinelli et al. (2015) studied mechanical properties of fiber-reinforced concrete with both virgin and recycled steel fiber (RSF)recovered from waste end-of-life tires. Different proportions ofvirgin and RSF were used to reinforce plain concrete. All speci-mens were reinforced with an equal volume of fibers (0.5%).Compressive and flexural strengths were used to characterize thespecimens’ mechanical properties. The results showed that fibershave a negligible impact on the compressive strength, while higherdecay in the postcracking behavior was recorded in the reinforcedspecimens by increasing the content of RSF.

1Researcher, Institute for Sustainability and Innovation in StructuralEngineering, Dept. of Civil Engineering, Minho Univ., Campus de Azurem,4800-058 Guimaraes, Portugal (corresponding author). E-mail: m.mastali@civil.uminho.pt

2Assistant Professor, Dept. of Engineering, Lorestan Univ., 68151-44316Khorramabad, Iran.

Note. This manuscript was submitted on June 17, 2016; approved onOctober 10, 2016; published online on January 30, 2017. Discussion periodopen until June 30, 2017; separate discussions must be submitted for in-dividual papers. This paper is part of the Journal of Materials in CivilEngineering, © ASCE, ISSN 0899-1561.

© ASCE 04017012-1 J. Mater. Civ. Eng.

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