Smart Structures andMaterials in civil engineering

Smart materials are materials that have the intrinsic and extrinsic capabilities , firstly to respond to stimuli and environmental changes and secondly to activate their functions according to these changes.

Smart Materials

Scope of smart materials

Structural designs constructed using smart materials which adopt performance based design aims in solving following problems

• They act as actuators which can adapt to their environment by changing characteristics such as shape and stiffness.

• They perform as sensors providing actuators with information about structural and environmental changes.

CONTROLData

Transmission

Data

Transmission

ACTUATORS SENSOR

Bacterial concrete – Self healing Concrete 

• The "Bacterial Concrete" is a concrete which can be made by adding bacteria in the concrete that are able to constantly precipitate calcite, this phenomenon is called microbiologically induced calcite precipitation.

• It is process by which living organisms form an inorganic solids.

• It is same process as we people are producing teeth and bones.

• “Bacillus Pasteruii ” is a common soil bacterium, which can continuously precipitate a new impermeable calcite layer over the surface of concrete.

Self Curing Concrete • Curing is the maintenance of a satisfactory moisture content and

temperature in concrete for a period of time immediately following placing and finishing so that the desired properties may develop.

• Curing has a strong influence on the properties of hardened concrete ; proper curing will increase, durability, strength, water tightness, abrasion resistance, volume stability, and resistance to freezing and thawing etc.

(as per IS:456-2000 ) “ curing is the process of preventing the loss of moisture from the concrete.”

Curing does not only means application of water ,it means also creation of condition for promotion of Uninterrupted and Progressive hydration.

Concrete in which the mixing water is restricted by means of some chemical compounds, to go out from the concrete body is known as “self curing concrete.”

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The compound molecules is primarily hydrophobic in nature with hydrophilic terminal group.

Hydrophilic terminal group attaches it self to the film of bleeding water.

While the long Hydrophobic chain maintains a vertical orientation away from the bleeding water.

Water molecules do not possess sufficient energy to escape through the hydrophobic layer.

Which results into quick reduction in the evaporation loss.

H H H | | | H-C-H H-C-H H-C-H | | | H-C-H H-C-H H-C-H | | | H-C-H H-C-H H-C-H | | | H-C-H H-C-H H-C-H | | | O O O | | | H H H

MECHANISM:

TYPES OF COMPOUNDS:

a) Synthetic resin

b) Wax

c) Acrylic

d) chlorinated rubber

Shape Memory Alloys ( SMA)

The term shape memory refers to the ability of certain alloys (Ni – Ti, Cu – Al – Zn etc.) to undergo large strains, while recovering their initial configuration at the end of the deformation process spontaneously or by heating without any residual deformation .

An smart structure is a system that incorporates, smart materials which help in performing particular functions like sensing, transmitting and recording of data.

Smart Structures

• DATA TRANSMISSION

• DATA ACQUISITION

• ACTION DEVICE

• DATA INSTRUCTIONS

• COMMAND AND CONTROL PROCESS

Main factors affecting

structural healthDifferential settlementEarthquakes and vibrationsStructural DistressCorrosion of reinforcementTemperature stress

Differential settlementStructures constructed on clayey soil prone to differential settlement mainly for two reasons :1. Consolidation in clay is very slow2. Clay has high swell-shrink nature

The conventional methods adopted to overcome this problem are :3. Under reamed pile foundation4. Providing water proof apron5. Replacing a layer of clay with CNS

These photographs show the restoration process using Atlas Resistance Continuous Lift Piers. The recovery is approx. 50%.

The smart way of preventing settlement• The volume of clay remain unchanged if optimal moisture

content is maintained.• This can be achieved by adopting the principle of electro-

osmosis as shown above.

Earthquake and vibration• The seismic waves or other shock waves can be disastrous for a

structure if it is at resonant frequency.• It is characterized by suddenness of onset and violence of attack • The conventional design method of earthquake resistant structures

have not proved very effective so far.

Smart way of resisting earthquake

• Magneto-rheological fluid is a smart material which changes from liquid to solid when exposed to magnetic field.

• When this fluid is filled is a cylinder and exposed to alternate magnetic it can act as a damper for shock

• An ultrasonic device is used to detect the seismic waves. It is converted into AC current and passed to dampers.

• The solid-liquid transformation takes place at a frequency corresponding to that of seismic wave.

• The seismic wave is destructively interfered and the building is prevented from shock.

• It is estimated that a damper of 200Kg can resist a force of 20000 N of force.

• Many such dampers are fitted to the building as shown

Structural distressThe structural distress is caused mainly due to :1. Improper analysis and design2. Unexpected loading conditions

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

Distress in Deck Slab & Girder

Shear crack in girder

Dislocation of Bearing

Dynamic solution for Structural Distress• A piezoelectric sheet of polyvinylidene fluoride (PVDF) polymer is

placed the structure.• When a load causes deflection in beam it the PVDF develops electrical

charges.• These charges are amplified and converted into heat energy.• This heat energy is supplied to SMA at the sides of the structure.• The downward deflection caused by load is counteracted by the

lateral force exerted by the SMA.• 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.

Corrosion of reinforcementThe reinforcement bars undergo electrochemical reaction mainly due to • Use of salty water in preparation of mortar.• Due to seepage of water into the structure.

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

Most of the present corrosion sensing techniques that use eddy current monitoring, coatings etc.

Smart Way to Check Corrosion • A thin metal foil of non-corrodible material is provided surrounding

the reinforcement bar.• The metal sheet is given with positive potential and the rod is

given negative potential.• When the reinforcement increases in diameter it comes in contact

with the foil.• Now electroplating takes place in reverse direction. 

Advantages of smart structures

 • This structure cut downs a lot of material cost incurred in using

under reamed pile and factor of safety.

• India has 25% of area prone to earth quake. This smart technology will help in saving a lot of men and material.

• The health monitoring of structures will help in forecasting failure and will provide time for re-habitation.

• 35% of Deccan plateau has black cotton soil, the use of this technology can ensure safe and economical construction over there.

• As the structure is constantly maintained the service life increases and the need for repair decreases.