May the Piezoresistivity of GNP-Modified Cement Mortar Be Related to Its Fractal Structure?

Nanxi Dang,Qiang Zeng,Weijian Zhao,Jin Tao

doi:10.3390/fractalfract5040148

Abstract

High piezoresistivity of cement-based composites tuned by conductible fillers provides a feasible way to develop self-sensing smart structures and buildings. However, the microstructural mechanisms remain to be properly understood. In the present work, the piezoresistivity of cement mortar with different dosages of graphene nanoplatelets (GNPs) was investigated, and the microstructure was assessed by electron scanning microscopy (SEM) and mercury intrusion porosimetry (MIP). Two surface fractal models were introduced to interpret the MIP data to explore the multi-scale fractal structure of the GNP-modified cement mortars. Results show that the incorporation of GNPs into cement mortar can roughen the fracture surfaces due to the GNPs’ agglomeration. Gauge factor (GF) rises and falls as GNP content increases from 0% to 1% with the optimal piezoresistivity observed at GNP = 0.1% and 0.05%. The GF values of the optimum mortar are over 50 times higher than those of the reference mortar. Fractal dimensions in macro and micro fractal regions change with GNP content. Analysis shows that the fractal dimensions in micro region decrease first and then increase with the increase of GF values. GNPs not only impact the fractal structure of cement mortar, but also alter the tunneling and contact effects that govern the piezoresistivity of composite materials.

Highlights

Piezoresistive cement-based materials (CBMs) are urgently needed for the development of self-sensing smart structures and buildings
graphene nanoplatelets (GNPs) impact the fractal structure of cement mortar, and alter the tunneling and contact effects that govern the piezoresistivity of composite materials
Compared with Graphene oxide (GO), that is widely used to enhance the mechanical properties of CBMs due to its stronger surface actions [12,13,14], GNPs that are composed of several layers of graphene with the diameter of several microns and thickness of less than 100 nanometers shows benefits to enhance the electrical properties of CBMs owing to its high electrical conductivity [15]

Summary

Introduction

Piezoresistive cement-based materials (CBMs) are urgently needed for the development of self-sensing smart structures and buildings. The improvement in the mechanical properties of CBMs by GBNFs is generally attributed to the enhanced cement hydration, tightly packed, and uniformly distributed hydration crystals, and decreased or eliminated cracks and flaws of the material matrix [16]. These effects may be counterbalanced by the raised flaws of the agglomerations of GBNFs, so strength may decrease at high GBNF dosages [17,18].

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