Pullout behavior of polypropylene macro-synthetic fibers treated with nano-silica

P Di Maida,E Radi,C Sciancalepore,F Bondioli

doi:10.1016/j.conbuildmat.2015.02.047

P Di Maida, E Radi + Show 2 more

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https://doi.org/10.1016/j.conbuildmat.2015.02.047

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Abstract

A study of the effects of nano-silica treatment on the bonding properties of macro synthetic polypropylene fibers embedded in a cement matrix is provided in the present paper as a step to improve interfacial properties of the fiber reinforced cementitious composites (FRCC). Polypropylene fibers were treated by sol–gel technique, allowing to obtain a nano-silica coating. Scanning electron microscopy was used to observe the morphological features of PP fibers surfaces before and after the pullout test. The effects of the treatment were investigated by comparative pullout tests on treated and untreated fibers. An increase in maximum load and energy necessary for the complete extraction of the fiber was observed, as a consequence of the improvement of the interface properties due to the nano-silica hydration activity. These two parameters control the crack-resistance and ductility properties of FRCC and are deeply influenced by bonding and friction phenomena. The hydration products act as chemical and physical anchors, thus producing a densification of the interface transition zone (ITZ). The abrasion phenomena occurring on the fiber surface during the pullout test are responsible of hardening behavior, consisting in the increase in the frictional shear stress with the fiber slip and thus in the energy required for fiber extraction.

Highlights

Nowadays, fiber reinforced concrete is widely used in the many civil engineering applications
The nanoparticle distribution on the treated macro synthetic fibers is not uniform, since the nanoparticles tend to agglomerate and to form large islands that seem to consist of a single layer of silica nanoparticle
The present work aims at improving the bond characteristics of PP macro synthetic fibers which, despite a poor interfacial bond strength, have seen an increase of their commercial attractiveness in recent years

Summary

Introduction

Fiber reinforced concrete is widely used in the many civil engineering applications (e.g. industrial pavements, tunnel linings, marine structures, earthquake‐resistant structures, etc). Due to the addition of fibers, plain concrete can be transformed from brittle into a ductile material, improving the resistance to crack formation and propagation. The use of polypropylene‐based fiber reinforced concrete (PFRC) has been encouraged for the design of road pavement in order to prevent micro‐ and macro‐cracking due to drying shrinkage and fatigue phenomena [2]. Experimental tests perfomed by Lanzoni et al [3] show that the addition of polypropylene‐based draw‐wired fibres significantly improves the crack resistance of the concrete mixture, enhancing toughness and durability of FRC structural components. At the same time, such improvement is attained without significantly affecting the workability of the mixture

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