Evaluating the Self-Sensing Ability of Cement Mortars Manufactured with Graphene Nanoplatelets, Virgin or Recycled Carbon Fibers through Piezoresistivity Tests

Alberto Belli,Paulo Cachim,Tiziano Bellezze,Francesca Tittarelli,Alessandra Mobili

doi:10.3390/su10114013

Abstract

This paper presents the resistivity and piezoresistivity behavior of cement-based mortars manufactured with graphene nanoplatelet filler (GNP), virgin carbon fibers (VCF) and recycled carbon fibers (RCF). GNP was added at 4% of the cement weight, whereas two percentages of carbon fibers were chosen, namely 0.05% and 0.2% of the total volume. The combined effect of both filler and fibers was also investigated. Mortars were studied in terms of their mechanical properties (under flexure and compression) and electrical resistivity. Mortars with the lowest electrical resistivity values were also subjected to cyclic uniaxial compression to evaluate the variations in electrical resistivity as a function of strain. The results obtained show that mortars have piezoresistive behavior only if they are subjected to a prior drying process. In addition, dry specimens exhibit a high piezoresistivity only when loaded with 0.2 vol.% of VCF and 0.4 wt.% of GNP plus 0.2 vol.% RCF, with a quite reversible relation between their fractional change in resistivity (FCR) and compressive strain.

Highlights

Over the last few decades, the development of novel multifunctional materials for both structural and non-structural applications has been interesting
Liu and coworkers [26] explained that graphene nanoplatelet filler (GNP) should be preferred to graphene oxide nanoplatelets (GONP) for producing electrical conductive mortars; GNP added in a quantity of 6.4% by cement weight showed stable electrical resistance and immediate and accurate reaction to compressive stress, whereas higher (12.8%) or lower (3.2%) contents gave unstable piezoresistance; at 6.4% content, the workability decreases considerably, and the mortar required extra water and superplasticizer
The addition of commercial GNP at 4% by cement weight has not modified the flexural strength of the mortar, whose Rf value is similar to that of reference mixture (REF) and equal to 6.4 MPa

Summary

Introduction

Over the last few decades, the development of novel multifunctional materials for both structural and non-structural applications has been interesting. Self-sensing is the ability of a structural material to sense its own condition, including strain, stress, damage and temperature [12] This property is important for structural vibration control, load monitoring and structural health monitoring (SHM) for increasing the safety, durability and performance of the final material [13]. Liu and coworkers [26] explained that GNP should be preferred to graphene oxide nanoplatelets (GONP) for producing electrical conductive mortars; GNP added in a quantity of 6.4% by cement weight showed stable electrical resistance and immediate and accurate reaction to compressive stress, whereas higher (12.8%) or lower (3.2%) contents gave unstable piezoresistance; at 6.4% content, the workability decreases considerably, and the mortar required extra water and superplasticizer. (cVarCbFo)nafnibderresc(yVcCleFd)caanrdbornecfiybcelerds (cRaCrbFo)nalfoibneersan(RdCtoFg) eatlhoenrewaansdctoomgeptahreerdw, aansdcothmepirapreiedz, oarnedsisthtievier bpeiehzaovrieosriswtiavseibnevheastviigoartewdaus nindveersctoigmatperdesusniodne.r compression

Materials and Methods

Piezoresistivity Measurements

Mechanical Properties of Mortars

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