Self-Sensing Concrete in Smart Structures

Baoguo Han, Xun Yu, Jinping Ou

• Publisher: Butterworth-Heinemann
• Year: 2014
• Print ISBN: 9780128005170
• eBook ISBN: 9780128006580
• Topic: Technology & Engineering
• Subtopic: Civil Engineering
• Index: Technology & Engineering

Concrete is the second most used building material in the world after water. The problem is that over time the material becomes weaker. As a response, researchers and designers are developing self-sensing concrete which not only increases longevity but also the strength of the material. Self-Sensing Concrete in Smart Structures provides researchers and designers with a guide to the composition, sensing mechanism, measurement, and sensing properties of self-healing concrete along with their structural applications- Provides a systematic discussion of the structure of intrinsic self-sensing concrete- Compositions of intrinsic self-sensing concrete and processing of intrinsic self-sensing concrete- Explains the sensing mechanism, measurement, and sensing properties of intrinsic self-sensing concrete

Chapter 1

Structures of Self-Sensing Concrete

Abstract

Self-sensing concrete, which has a highly complex structure, is a multiphase and multiscale composite. At the macroscopic level, self-sensing concrete may be considered a two-phase material consisting of functional fillers dispersed in a concrete matrix. At the microscopic level, there is a third phase in self-sensing concrete: the interfaces between functional fillers and concrete matrix and those between functional fillers. The sensing properties of self-sensing concrete are closely related to its structure, especially the distribution of functional fillers in a concrete matrix, the interfaces between functional fillers and the cement matrix, and void and liquid phases in a concrete matrix.

Keywords

Filler phase; Interface phase; Matrix phase; Self-sensing concrete; Structure; Void and liquid phase

Chapter Outline

1.1 Introduction and Synopsis 1

1.2 Structures of Self-Sensing Concrete at the Macroscopic Level 2

1.3 Structures of Self-Sensing Concrete at the Microscopic Level 4

1.3.1 Distribution of Functional Fillers in Concrete Matrix 4

1.3.2 Interfaces between Functional Fillers and Concrete Matrix 4

1.3.3 Void and Liquid Phases 9

1.4 Summary and Conclusions 10

References 10

1.1. Introduction and Synopsis

Self-sensing concrete (also called self-monitoring concrete, intrinsically smart concrete, and piezoresistive or pressure-sensitive concrete) is fabricated by adding functional fillers (carbon fibers, steel fibers, carbon nanotubes, nickel powder, etc.) into conventional concrete to increase its ability to sense strain, stress, cracking, or damage in itself while maintaining or even improving mechanical properties. Conventional concrete includes concrete (containing coarse and fine aggregates), mortar (containing fine aggregates), and binder only (containing no aggregate, whether coarse or fine) in a generalized concept. It serves as a structural material with no or poor sensing ability. The presence of functional fillers enables the self-sensing property. The functional fillers need to be well-dispersed in a concrete matrix to form an extensive conductive network inside concrete. As the concrete material is deformed or stressed, the conductive network inside the material is changed, which affects the electrical parameters (e.g., electrical resistance, capacitance, and impedance) of the material. Strain (or deformation), stress (or external force), cracking, and damage under static and dynamic conditions can therefore be detected through measurement of the electrical parameters [1–5].

Structure–property relationships are at the heart of materials science. Self-sensing concrete, which has a highly complex structure, is a multiphase and multiscale composite. Its structure covers over 10 orders of magnitude in size, ranging from nanometers (e.g., hydration product and some functional fillers) to micrometers (e.g., binder and some functional fillers), and then from millimeters (e.g., mortar and concrete) to tens of meters (final structures) [6–8]. Chapter 1 will introduce the structures of self-sensing concrete at different scale levels and their effects on the sensing properties of the composite.

1.2. Structures of Self-Sensing Concrete at the Macroscopic Level

At the macroscopic level, self-sensing concrete may be considered a two-phase material consisting of functional fillers dispersed in a concrete matrix, as shown in Figure 1.1.

In general, the functional filler phase usually exists in one of the three forms: fiber, particle, or a hybrid of fiber and particle. These fillers distribute in the concrete matrix phase to form a conductive network. As shown in Figure 1.2, fillers can be a variety of materials such as carbon fiber, carbon nanotube, steel fiber, nickel powder, graphite, or a hybrid of them. The concrete matrix phase, composed of mineral aggregates glued together with a binder, supports the functional fillers and holds them in place. Here, the binder of concrete can be cement, asphalt, or even polymer [15,16].

Figure 1.1 Structure of self-sensing concrete.

Figure 1.2 Scanning electron microscopy (SEM) photos of typical self-sensing concrete, (a) Cement concrete with carbon fiber [9], (b) Cement concrete with nickel powder [10], (c) Cement concrete with carbon nanotube [11], (d) Cement concrete with hybrid carbon fiber and graphite powder [12], (e) Asphalt concrete with carbon black [13], (f) Asphalt concrete with graphite [13], (g) Asphalt concrete with hybrid carbon fiber and graphite [13], (h) Asphalt concrete with hybrid carbon fiber and carbon black [13], (i) SEM images of carbon fiber and carbon nanotube in a cementitious matrix: (left) carbon fiber in cement composite (100 × magnification), (right) carbon nanotube bridging hydration products (5000 × magnification) [14].

1.3. Structures of Self-Sensing Concrete at the Microscopic Level

1.3.1. Distribution of Functional Fillers in Concrete Matrix

At the microscopic level, the two phases of the structure of self-sensing concrete are not homogeneously distributed with respect to each other or to themselves. There are three levels of distribution in self-sensing concrete: distribution of functional fillers in binder, distribution of the binder with functional fillers among fine aggregates, and distribution of the fine aggregates ...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Dedication
• Preface
• Chapter 1. Structures of Self-Sensing Concrete
• Chapter 2. Compositions of Self-Sensing Concrete
• Chapter 3. Processing of Self-Sensing Concrete
• Chapter 4. Measurement of Sensing Signal of Self-Sensing Concrete
• Chapter 5. Sensing Properties of Self-Sensing Concrete
• Chapter 6. Sensing Mechanisms of Self-Sensing Concrete
• Chapter 7. Applications of Self-Sensing Concrete
• Chapter 8. Carbon-Fiber-Based Self-Sensing Concrete
• Chapter 9. Nickel-Powder-Based Self-Sensing Concrete
• Chapter 10. Carbon-Nanotube-Based Self-Sensing Concrete
• Chapter 11. Challenges of Self-Sensing Concrete
• Index