Smart Structures and Materials

SMART STRUCTURES AND MATERIALS

By

Abhishek Singh

(09010403)

DEPARTMENT OF CIVIL ENGINEERING

INDIAN INSTITUTE OF TECHNOLOGY GUWAHATI

March, 2012

CERTIFICATE

It is certified that the work contained in the seminar report entitled “Smart Structure and Materials”, by Abhishek Singh(09010403)has been carried out according to the guidelines provided and that this work has not been submitted elsewhere.

Date: 23.03.2012

Dr. Sreeja P.

Assistant Professor

Department of Civil Engineering

Indian Institute of Technology Guwahat

Dr. Bimlesh Kumar

Assistant Professor

Department of Civil Engineering

Indian Institute of Technology Guwahati

Acknowledgement

It gives me great privilege and immense happiness to express my sincere thanks and feelings of gratitude to my supervisor Dr. Sreeja P. and Dr Bimlesh Kumarforproviding the opportunity to study and present a seminar on one of the most interesting topic in civil engineering.

I heartily thank all my friends for their kind cooperation in discussions during the project without which this endeavour could not have been possible.

Abhishek Singh

Abstract

Smart materials have one or more properties that can be dramatically altered. These are materials that respond to changes in external stimuli such as humidity, pH, temperature and pressure. Varieties of smart materials already exist, and are being researched extensively. Some everyday items are already incorporating smart materials (coffeepots, cars, the International Space Station, eyeglasses) and the number of applications for them is growing steadily.

Advanced man-made composites such as glass and carbon fibre reinforced plastics can be tailored to suit the requirements of their end application, but only to a single combination of properties. Whereas, the materials and structures involved in natural systems have the capability to sense their environment, process this data, and respond. They are truly ‘smart’ or intelligent, integrating information technology into structural engineering and actuation or locomotion.

Applications of Smart Materials

There are many possibilities for such materials and structures in the manmade world. Engineering assemblies could operate at the very limit of their performance envelopes and to their structural limits without fear of exceeding either. Smart materials and structures will solve engineering problems with hitherto unachievable efficiency, and provide an opportunity for new wealth creating products.

TABLE OF CONTENTS

Page no.

Certificate…………………………………………………………………………………...

Acknowledgement………………………………………………………………………….

Abstract……………………………………………………………………………………..

List of Figures……………………………………………………………………………

CHAPTER 1: INTRODUCTION…………………………………………………………..

1.1 General

1.2 Sensing or actuation

CHAPTER 2: SMARTSTRUCTURES……………………………………………………2

2.1 Definition...... 2

2.2 Main factors affecting structual health...... 2

2.2.1 Differential Settlement...... 3

2.2.1.1The smart way of preventing settlement...... 3

2.2.1.2Electro osmotic consolidation ...... 3

2.2.2 Earthquakes and vibrations...... 4

2.2.2.1Smart way of resisting earthquake...... 4

2.2.3Structural distress...... 5

2.2.3.1Dynamic solution for structural distress...... 5

2.2.4Corrosion of reinforcement...... 6

2.2.4.1Smart way to check corrosion...... 6

2.3Smart Building...... 7

CHAPTER 3: SMART MATERIALS……………………………………………………..8

3.1 Smart nano-materials in construction industry...... 8

3.1.1Nano-technology...... 8

3.1.2Graphene...... 9

3.1.3Nano composites...... 10

3.1.4Nano-cement particles...... 10

3.1.5Benefits...... 10

3.2Self healing materials...... 11

3.2.1 Bacterial concrete...... 12

3.2.1.1Introduction...... 12

3.2.1.2Different healing mechanisms...... 12

3.2.1.3Bacterial concrete...... 13

3.2.2Cracking in bacterium remediate...... 13

3.2.3Conclusion...... 15

ADVANTAGES OF THE SMART STRUCTURES………………………………………...16

REFERENCES……………………………………...………………………………………...17

LIST OF FIGURES

Figure
No. / Title / Page
No.

2.1 Monitoring bridge2

2.2 Electro-osmotic Consolidation

2.3 Magneto-rheological fluid

2.4 Dampers

2.5 Structural Distresses under piezoelectric monitoring5

2.6 Health monitoring of bridges5

2.7 Corrosion of reinforcement6

3.1 Characteristics of construction materials8

3.2 Atomic sizes of particles9

3.3 Graphene layer, Carbon Nano Tubes, and Carbon Nano Fibers9

3.4 New Jubilee Church (Rome, Italy) made of nano photocatylatic concrete10

3.5 Different healing mechanism12

3.6 Observed crack healing in concrete

3.7 Image showing effect of healing

1

CHAPTER 1

Introduction

1.1General

Each of us reacts to the world around and within us by sensing and actuating. When our hand is in contact with a hot object, we sense the heat, our brain sends a command, and our arm muscles actuate our hand away from the object. Similarly, because of internal sensing, we will tend to favour the burned hand until it has healed. As technology progresses, it becomes reasonable to ask, “Can we design analogous mechanisms that can intelligently interact with their environment, and structures that assess their own health?” Such smart structures could have a tremendous impact in advancing many fields including infrastructure, medicine, and robotics, among others.

1.2Sensing or Actuation

Often, simple devices made from a single sensing or actuating material are used in certain applications. However, systems that involve both sensing and actuating materials can be used to build more sophisticated applications. Such systems are referred to as smart structures, which incorporate sensors and actuators with processing/control units connecting them. To get an idea of how smart structures can be implemented, it is necessary to understand the fundamental components of these structures: sensor and actuator materials. Sensors are materials that respond to a physical stimulus, such as a changein temperature, pressure, or illumination, and transmit a resulting signalfor monitoring or operating a control. Actuators are materials that respondto a stimulus in the form of a mechanical property change such as a dimensional or a viscosity change.

CHAPTER 2

Smart Structures

Figure 2.1 Monitoring bridge

2.1 Definition

Research on smart or intelligent structure systems has been going on for over a decade. But it has been mainly in the field of mechanical engineering or focused on space structures. Recently the study of smart materials to apply to civil engineering has become a hot issue. To list some of these studies, health monitoring of members, self-repairing, actuating structural members are of interest. These aim to make the structures more highly characterized by using new technology and to make structural performance higher by using smart materials. So at a glance we can say that:

• A structure which can adapt to the changing environmental conditions is called SMART.
• This smartness can be achieved by using smart materials like Shape-memory alloys (SMA), piezoelectric crystal, magneto-rheological fluids etc.
• Smart structures can take care of their own health and resist natural calamities.

2.2 Main factors affecting structural health:

1. Differential settlement
2. Earth quakes and vibrations
3. Structural distress
4. Corrosion of reinforcement
5. Temperature stresses

2.2.1Differential settlement

Structures constructed on clayey soil prone to differential settlement mainly for two reasons:

1. Consolidation in clay is very slow
2. Clay has high swell-shrink nature.

The conventional methods adopted to overcome this problem are:

1. Under reamed pile foundation
2. Providing water proof apron
3. Replacing a layer of clay with CNS.

2.2.1.1 The smart way of preventing settlement

1. The volume of clay remains unchanged if optimal moisture content is maintained.
2. This can be achieved by adopting the principle of electro-osmosis as shown below.

2.2.1.2 Electro osmotic consolidation

Electro osmotic consolidation means the consolidation of soft clays by theapplication of electric current. It is inherent that fine grained clay particles with large interfacial surface willconsolidate and generate significant settlement when loaded. The settlement creates problem in the foundation engineering. Electro osmosis was originally developed as a means of dewatering fine grained soilsfor the consolidation and strengthening of soft saturated clayey soils.It is the process where in positively charged ions move from anode to cathode.ie. Water moves from anode to cathode where it can be collectedand pumpedout of soil.
2H2O -> O2 (g) + 4H+ +4e- oxidation (anode)
4H2O + 4e- -> 2H2 (g) + 4OH- reduction (cathode)
When electrodes are placed across a saturated clay mass and direct current is applied
,water in the clay pore space is transported towards cathode by electro osmosis.
In addition frictional drag is created by the motion of ions as they move through the
clay pores helping to transport additional water.The flow generated by the electric gradient is called electro osmotic flow.

2.2.2Earth quakes and vibrations

1. The seismic waves or other shock waves can be disastrous for a structure if it is at resonant frequency.
2. It is characterized by suddenness of onset and violence of attack.
3. The conventional design methods of earth quake resistant structures have not proved very effective so far.

2.2.2.1 Smart Way of Resisting Earth Quake

1. Magneto-rheological fluid is a smart material which changes from liquid to solid when exposed to magnetic field.
2. When this fluid is filled in a cylinder and exposed to alternate magnetic it can act as a damper for shock waves.

1. An ultrasonic device is used to detect the seismic waves. It is converted into AC current and passed to dampers.
2. The solid-liquid transformation takes place at a frequency corresponding to that of seismic wave.
3. The seismic wave is destructively interfered and the building is prevented from shock.
4. It is estimated that a damper of 200kg can resist a force of 20000N of force.
5. Many such dampers are fitted to the building as shown in fig.

2.2.3 Structural distress

The structural distress is caused mainly due to:

1. Improper analysis and design
2. unexpected loading conditions

Serious distress can even cause structural collapse. The conventional way overcoming this problem is by providing a factor of safety.

2.2.3.1 Dynamic Solution for Structural Distress

1. A piezoelectric sheet of polyvinylidene fluoride (PVDF) polymer is placed under the structure.
2. When a load causes deflection in beam it the PVDF develops electrical charges.
3. These charges are amplified and converted into heat energy.
4. This heat energy is supplied to a SMA at the sides of the structure.

1. The down ward deflection caused by load is counteracted by the lateral force exerted by the SMA.
2. This arrangement can be used to monitor the extent of deflection of the material and thus determine the point of distress before the actual failure.

2.2.4 Corrosion of reinforcement

The reinforcement bars undergo electrochemical reaction mainly due to

1. Use of salty water in preparation of mortar.
2. Due to seepage of water into the structure.

In both the cases localized electroplating occurs causing stress on concrete member.

The conventional solution for this problem is not economical.Many of the current corrosion sensors are limited by working only in direct application. Most of the present corrosion sensing techniques that use eddy current monitoring, coatings, neutron activation or chain dragging are not suitable for hostile environments.

Corrosion detection of metallic structural members (panels, rods, bars, tubes, etc) typically involves an electrochemical measurement to evaluate the change in the electrical properties due to the corrosion . Such resistivity, stray current, or potential–current measurements have had limited success in actual in-service corrosion detection and notification

2.2.4.1 Smart Way to Check Corrosion

1. A thin metal foil of non-corrodible material is provided surrounding the reinforcement bar.
2. The metal sheet is given with positive potential and the rod is given negative potential.
3. When the reinforcement increases in diameter it comes in contact with the foil.
4. Now electroplating takes place in reverse direction.

2.3 Smart buildings

By 2020 we can expect to:

1. Have new buildings completely “wired” (in sense of ubiquitous pervasive communications, both wired and wireless) and controlled as a single living entity.
2. Have old buildings in the process of “retrofitting” to become “smart buildings”. This is likely to take place under the pressure to decrease energy consumption and to use locally produced energy.
3. Have products that start to make use of the smart ambient provided by the smart buildings and integrating their functionality in the ones provided by the building (e.g. make use of sound and displays provided by the walls, use power through induction, hook up on the local area network, relay on authentication provided by the building, accept guidelines and directive from the ambient…).

Smart buildings will be network (and often very complex networks) in themselves requiring specific networking expertise, operation and management, and interaction with a variety of users, humans as well as objects (and sensors). They will be communications providers to a variety of terminals, some being a stable part of the building, many being “in transit”.

They will support mirroring functions, authentication, visibility segmentation, data storage, conditional access and so on. To all effect they will be a communications network formed by many communications networks.

Their complexity may vary, going from a private villa to a skyscraper, but they will have in common many issues, like the management of different constituencies having different interfaces and functionalities.

CHAPTER 3

Smart Materials

3.1 Smart nano-materials in construction industry

Concrete, steel, glass, and timbers are the most common materials, being used in the field of modern construction. In the following table, some important characteristics of the above-mentioned materials are tabulated.

Material / Young’s Modulus (GPa) / Tensile Strength (GPa) / Density (g.cm-3)
Concrete / 30 / 0.007 / 2.3
Steel / 208 / 1.0 / 7.8
Glass / 50-90 / Negligible / 2-8
Timber / 16 / 0.008 / 0.6

Figure 3.1 Characteristics of construction materials

If we compare these properties with those of a carbon nanotube, the results are astonishing. A carbon nanotube has a Young’s modulus of 1054 GPa, a tensile strength of 150 GPa and a density of 1.4 g-cm-3. Thus a carbon nanotube has strength of 150 times that of steel and at the same time approximately six times more lighter.

Based on the above statistics, it was thought (in UK Delphi Survey 1990), that the Construction industry would benefit the most from Nanotechnology. However, Construction industry lags behind other industrial sectors in terms of appealing investment from large corporate sectors.

3.1.1 Nano-technology

Nano-technology is a technology that enables to develop materials with improved or totally new properties. It is an extension of the sciences and technologies already developed for many years to examine the nature of our world at an ever smaller scale. A nanometer is one billionth of a meter. Nano particles is defined as a particle that has at least one dimension less than 100nm. The size of the particle is very important because at the length scale of the nanometer, i.e. 10-9 m, the properties of the material actually become affected.

3.1.2 Graphene

Carbon nanotubes and nanofibers present an important classification of nano-materials. They are made from Graphene. Graphene is defined a monolayer of carbon atoms packed into a honeycomb lattice. It can also be defined as an atomic-scale chicken wire made of carbon atoms and their bonds. If graphene layers are arranged as stacked cones, cups or plates, it is known as Carbon nanofibers (CNF) and if the grapheme layers are wrapped into perfectcylinders, they are termed as Carbon nano tubes (CNT).

3.1.3Nano composites

Nano composites are produced by adding nano-particles to a bulk material in order to improve the bulk material properties. Materials reduced to nano-scale can suddenly show very different properties compared to what they exhibit on a macroscale, enabling unique applications. For instance, opaque copper substances become transparent and inert platinium materials attain catalytic properties.

Nano-technology is a dynamic research field that covers a large number of disciplines including construction industry. Concrete is a material most widely used in construction industry. Concrete is a cement composite material made up of Portland cement, sand, crush, water and sometimes admixtures. Interest in nano-technology concept for Portland-cement composites is steadily growing.

The materials such nano-Titania (TiO2), Carbon nanotubes, nano-silica (SiO2) and nano-alumina (Al2O3) are being combined with Portland cement. There are also a limited number of investigations dealing with the manufacture of nano-cement. The use of finer particles (higher surface area) has advantages in terms of filling the cement matrix, densifying the structure, resulting in higher strength and faster chemical reactions (e.g. hydration reactions).

3.1.4 Nano-cement particles

Nano-cement particles can accelerate cement hydration due to their high activity. Similarly, the incorporation of nano-particles can fill pores more effectively to enhance the overall strength and durability. Thus nano-particles can lead to the production of a new generation of cement composites with enhanced strength, and durability.

3.1.5 Benefits

According to researchers, following is a list of areas, where the construction industry could benefit from the nano-technology.

1. Replacement of steel cables by much stronger carbon nanotubes in suspension bridges and cable-stayed bridges
2. Use of nano-silica, to produce dense cement composite materials
3. Incorporation of resistive carbon nanofibers in concrete roads in snowy areas
4. Incorporation of nano-titania, to produce photocatalytic concrete
5. Use of nano-calcite particles in sealants to protect the structures from aggressive elements of the surrounding environment
6. Use of nano-clays in concrete to enhance its plasticity and flowability.
7. Urban air quality could be improved by if the civil structures are treated with nano TiO2

3.2 Self healing materials

Self-Healing Materials are a type of smart materials that have the built in capability to repair the early stage damage that would finally lead to material failure. This research is inspired by nature as living organisms already possess the capability of self-healing (repair of damage like wound healing, recovery of broken limbs).

The areas that can be selected for the research in Self-Healing Materials are:

1. Asphaltic materials
2. Bio-inspired technical materials
3. Cementitious materials
4. Composites and hybrids
5. Metals
6. Paints and other coatings
7. Structural polymers
8. Biological systems

Usually, cracks are repaired by hand, which is difficult because cracks are often hard to detect. A material (polymers, ceramics, etc.) that can repair damage caused by normal usage could lower production costs of a number of different industrial processes through longer part lifetime, reduction of inefficiency over time caused by degradation, as well as prevent costs incurred by material failure. For a material to be defined as self-healing, it is necessary that the healing process occurs without human intervention.

3.2.1 Bacterial concrete

3.2.1.1 Introduction:

1. Concrete is a material which is the most widely used building material in the world.
2. Natural processes such as weathering, faults, land subsidence, earthquakes, and human activities create cracks in concrete structures.
3. Concrete expands and shrinks withchanges in moisture and temperature and this tendency to shrink and expands causes cracks in concrete.
4. We do not like cracks in concrete because cracks form an open pathway to the reinforcement and can lead to durability problems like corrosion of the steel bars.
5. These cracks should be repaired because they can reduce the service life of structure.
6. In case of historical monuments cracks spoils the appearance of structure.
7. Remediation of already existing cracks has been subject of research for many years.
8. The various product such as structural epoxy, resins, epoxy mortar, and other synthetic mixtures are used as filling material but they are not environmentally friendly not even safe for human health.

3.2.1.2 Different healing mechanisms

Here are some four possible mechanisms given for self-healingof concrete which are as under

a)Formation of material like calcite

b)Blocking of the path by sedimentation of Particles

c)Continued hydration of cement particles

d)Swelling of the surrounding cement matrix.