Correlation between damage evolution and resistivity reaction of concrete in-filled with graphene nanoplatelets

https://doi.org/10.1016/j.conbuildmat.2019.03.036Get rights and content

Highlights

  • Within the elastic regime, the resistivity drops as the compression increasing.

  • The resistivity reaction can match well with the damage developing process.

  • The damage calculated with resistivity can arrive 0.8 at last.

Abstract

Pilot researches prove that graphene nanoplatelets (GNPs) are promising nano-sized additives to improve the smartness of cementitious materials. This work aims to reveal the explicit correlation between the damage development and the resistivity reaction of cementitious composites infilled with GNPs. A weight content of 4.5% (GNPs/cement) is used to cast two groups of concrete samples, named as C20 and C30 (according to their designed compressive strength), whose volume fractions of GNPs are 0.43% and 0.61%, respectively. Investigations shows different failure patterns during compression loading and their piezoresistive characteristics are probed systematically. Additionally, damages determined by strain-stress curves and ultrasonic pulse velocity penetrations in the middle section are also studied for comparing. The damage evolution process illustrated by resistivity reactions contains a slight decrease of resistivity within the elastic regime, a moderate damage developing stage before the peak force, an expeditive damage section just after the peak force and a relaxed damage expanding when the stress drops to less than 50% of the strength. At last, the damages obtained with resistivities increase to 0.8. This indicates that the piezoresistivity of smart concrete containing GNPs can be a promising tool to detect damages detailedly.

Introduction

Concrete is the most used material in infrastructures for its shapeability, high compressive strength and decent durability. Although concrete is called manmade stone, its durability is not as good as stone, not even close to it. Concrete has thousands of micro pores and cracks, which are sources of damage developed by loading, corrosion, leaching and so on. Therefore, structural health monitoring (SHM), especially in some critical parts of the structures, is becoming increasingly necessary. Traditional sensors, such as resistance strain gauges, piezoresistive ceramics and optical fiber sensors, have been widely used in SHM [1], [2]. In the last two decades, intrinsic self-sensing concrete (ISSC) has garnered increasing interests due to the fact that ISSC has similar durability with concrete and can work harmonically with it [3], [4].

The self-sensing characteristic of concrete also named as piezoresistance was firstly investigated by incorporating carbon fiber in concrete [5], [6]. Some other functional fillers, such as carbon black [7], carbon nanotube (CNT) [8] and nickel powder [9] were also carefully chosen to improve the piezoresistance of concrete. The conductive network inside cement-based composites was changed under loading. As a result, the strain and damage can therefore be detected by measuring the electrical signals of the cement-based materials. Normally, within the elastic stage, in smart concrete the resistance can drop linearly with increasing strain [7], [9]. If the stress employed on a concrete specimen was greater than its elastic capacity, the resistivity would have a nonlinear raise resulting from the appearance and growth of micro cracks and damages [10]. Downey et al. [11] proposed a resistor mesh model, which was based on an equivalent mesh of three different types of resistors, to detect, localize and quantify damage in conductive cement composites containing CNT.

The recent discovery of graphene nano platelets (GNPs) provides new candidates for conductive fillers that can improve the smartness of cementitious materials. GNPs exhibit a 2D sheet-like structure with a thickness of a few nanometers, which allows them to inherit extraordinary mechanical and electrical properties. It was reported that the graphene is the strongest material ever discovered, with an ultimate tensile strength of 130 GPa, compared to 0.4 GPa for normal structural steel, and the resistivity of graphene sheets is 10−6 Ω·cm, which is less than the resistivity of silver [12], [13]. Thus, using them to produce smart concrete attracts increasing research attention. Sedaghat et al. [14] showed the effect of graphene content on the electrical resistivity of hydrated graphene-cement samples. Their resistivity dramatically dropped with the increasing GNPs content from 1%, 5% to 10% (w/w). Liu et al. [15] also found that 6.4% GNPs content (w/w) may be the threshold value to produce smart concrete owning a high sensitivity. Saafi et al. [16] used graphene oxides in geopolymeric composites and found that the resistivity increases linearly with tensile strain and decreases with compressive strain. According to Liu et al.’s work, the resistivity amplitudes of smart concrete detectors embedded in a four-point bending beam can be transferred to strains by applying the gauge factor gained from free detectors. The calculated strains can conclude well with those obtained by strain gauges [17]. Le et al. [18] investigated the use of GNPs in cement composite to quantify the material damage extent. The results show that the fractional change in electric potential arising from damage is equivalent to the fractional change in elastic compliance.

Based on recent studies, valuable achievements in self-sensing concrete in-filled with various kinds of conductive fillers is used in detecting strain and damage. However, the complete damage evolution process measuring is still hard to obtain. The new candidate of GNPs is promising in improving the smartness of cementitious materials due to its outstanding mechanical and electrical properties. It is also because of this, the cementitious composites containing GNPs possess better sensitivity and stable piezoresistivity, which is possibly the solution to gain the complete damage evolution.

In this study, ISSCs in-filled with GNPs were investigated to determine piezoresistive responses during the compressive loading until failure. In addition to this, the ultrasonic detection was adopted to measure the damage by recording the ultrasonic pulse velocity penetration. The full strain-stress curves of concrete under compressive load can also illustrate the damage evolution process. By studying the complete damage evolution process of ISSC, suggestions for detecting the degree of damage in concrete can be provided.

Section snippets

Materials preparation

The cement used in this study was standard Type-42.5 (following Chinese specifications [19]) from Hailuo (Shanghai, China). The sand was normal river sand, which was washed to remove silt content and sieved to remove aggregates larger than 4.75 mm. Coarse natural aggregates (4.75–9.5 mm) used were washed and dried before use. This was done in order to remove the dust attached on coarse and fine aggregates, because the dust particles may pose influence on the hydration products. Graphene

Strain-stress curves and failure modes

The strain-stress curves of C20 and C30 samples are shown in Fig. 4, Fig. 5, respectively, along with images of the broken specimens. Taking C20 as an example, there are three samples and they are named as C20-1, C20-2 and C20-3 respectively. For indicating the direction and the location of the cracks clearly, the patterned failure sketches of the broken specimens are also plotted in Fig. 4, Fig. 5. In the failure pattern sketches, taking Fig. 4(c) as an example, four mesh probes and two

Conclusion

In this investigation, based upon the test results, the following conclusions may be drawn:

  • 1)

    During applying a compression on the smart concrete specimens of C20 and C30 until their failure, the resistivity variation includes a slight fall within elastic section and an increasing phase after that. The falling amplitude is only about less than 1% as to the initial resistivity. The increasing ratio can be from twice to five times, except those that do not break at the resistivity measuring position.

Conflict of interest

No conflict of interest.

Acknowledgements

This work is financially supported by the Shanghai Rising-Star Program (14QB1403800), China Postdoctoral Science Foundation (2018M642079), Joint Research Project between NSFC and PSF of China (No. 51661145023) and Jiangsu Province Higher Education Institutions Undergraduate Training Programs for Innovation and Entrepreneurship (201710299058Y).

References (26)

  • J. Chaboche

    Continuum damage mechanics: a tool to describe phenomena before crack initiation

    Nucl. Eng. Des.

    (1981)
  • J.K. Chen et al.

    Damage evolution in cement mortar due to erosion of sulphate

    J. Corros. Sci.

    (2008)
  • D.D.L. Chung

    Electrical conduction behavior of cement-matrix composites

    J. Mater. Eng. Perform.

    (2002)
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