Smart Construction Materials
Whenever you hear the term ‘civil engineering ‘, what is it that comes to your mind intuitively? Most probably, it is about the high raised skycrappers, dams that control large volume of water or maybe bridges that supports number of vehicles. In addition, giving it a thought, what might it take to build such massive structures? Preferably, it is knowledge and experience, nothing much complicated.
However, working upon such projects is too tiresome and difficult, sometimes dangerous too. Hence, for the help of civil engineers, some helpful materials make the work easier and less convoluted. They are called smart materials and called so because of their property to act smart and adoptive that suits the environment while construction. More often than not, smart materials are attributed to their properties of smart memory and super elasticity.
Smart materials are actually compositely designed materials having one or more properties significantly changeable in a controlled fashion by application of external stimuli or inputs. The inputs are mostly in the form of mechanical stress/ strain, change in temperature, pH, light or moisture, induction of electric or magnetic fields, light, or chemical compounds. Having such properties, they are rightly also called as intelligent or responsive materials. In this article, I will thoroughly discuss about the properties, types and applications of Smart Construction materials with examples.
Further dwelling into it, there are different types or categories of smart materials that can be cited as examples.
Shape memory alloys (SMAs)
Shape-memory alloys and shape-memory polymers are smart materials in which the change inducing inputs are temperature or stress changes (pseudo elasticity). Large deformation can be induced and recovered through pseudo elasticity. The applications of shape memory alloy, in civil engineering, are
- repeated absorption of strain energy without permanent deformation,
- for obtaining wide range of cyclic behaviour,
- to resist fatigue resistance under large strain cycles, due to their great durability and reliability in the long run. .
The shape memory effect results due to respectively martensitic phase change and induced elasticity at higher temperatures.
Magnetostrictive materials exhibit smart material characteristics as a change in shape under the induced stimuli of magnetic field and a change in their magnetization under the influence of mechanical stress/ strain. Magnetic shape memory alloys are materials that change their shape in response to a significant change in the magnetic field. These materials undergo mechanical deformation in proportion to the square of the electric field, which in turn refers to the material quality of changing size in response to either an electric or magnetic field, and also conversely, producing a voltage when stretched. These materials are also used in other fields of engineering along with civil engineering.
Piezoelectric materials are such smart materials that produce a voltage when stress is applied. Since this effect also applies in a reverse manner, a voltage across the sample will produce stress within sample. Suitably designed structures designed from these materials can, therefore, be constructed that bend, expand or contract when a voltage is applied making them adaptive to environmental situations. When integrated into a structural member, a piezoelectric material generates an electric field in response to mechanical forces.
These colloidal suspensions undergo changes in viscosity when subjected to an electric field. Such fluids are highly sensitive and respond instantaneously to any change in the applied electric field. Civil engineers mostly find their application in shock absorbers.
These materials alter their light transmission properties when voltage is applied which makes them adaptive enough to maintain chromatic panels and similar structures.
Application of Smart Materials
Different kinds of smart materials are used in different projects or field of study in civil engineering. Classification of these materials as according to their adaptability and super elasticity criterion can help in correct assessment of structural requirements. Some basic applications of these smart materials in the field of civil engineering has been noted down. This is to be noted that they are more properties that these materials are capable of .
Smart concrete (a composite of carbon fibres and concrete) used in smart structures is capable of sensing minute structural cracks / flaws. In high rise buildings, such detection can help in proper functioning of buildings and maintaining serviceability. Smart concrete under loading and unloading process will loose and regain its conductivity, thus serving as a structural material as well as a sensor. This also helps in longevity of the structures.
In smart building, it used to transform efficiency, comfort, and safety for people and assets under the serviceability requirements. Smart materials are used for vibration control, noise mitigation, safety and performance in construction of smart buildings, for environmental control and structural health monitoring. In addition, smart materials reduce the effects of earthquakes.
There has been an extensive use of Smart Construction materials for the maintenance purpose as well. In fact, they can be used to rehabilitate the cracking of concrete when super elasticity smart material is used as the reinforcement bar. They are used to monitor the civil engineering structures to evaluate their durability and load carrying capacity for longer duration.
In addition, the super elastic behaviour of smart materials has attracted the attention of civil engineers. Several experiments and incorporations have been done to test its adaptability. Its major field of application is retrofitting structures in an earthquake design. A project was executed to retrofit the earthquake resistant bell tower of the Church of San Giorgio, Italy.
The study of Tamarat.K shows that Fe-based SMA like Fe-Mn-Si-X, Fe-Ni-C and Fe-Ni-Co-Ti also referred to as shape memory steel or Ferrous SMA have the potential for use in civil structures. Graesser E.J successfully used Ni-Ti SMA for damping of seismic loads. A real scale application of a super elastic SMA device is the earthquake resistant retrofit of the Basilica San Francesco at Assisi, Italy Castellano, M.G., and Brite E. .
Diverse Civil Engineering Applications
The use of smart materials permits the construction of smart bridges especially cable-stayed bridge with a wider span to avoid the increased susceptibility to vibrations caused by ambient factors such as wind, rain or traffic. Furthermore, in marine and rail transport , smart materials find applications for strain monitoring using embedded fiber optic sensors.
Repeated absorption of large amounts of strain energy under loading without permanent deformation helps in large dams and tunnels such that under large pressure, they maintain sustainability.
Smart materials have excellent property of corrosion resistance (comparable to series 300 stainless steels) and are nonmagnetic in nature. In deep underground tunnels, such properties help in increasing their duration.
Connections of different structural components are more likely to get damaged on occurrence of earthquake. SMA connectors have been designed to provide damping and resist relatively large deformations.
Use of smart materials in civil engineering is definitely a new approach for sustainable and durable construction of important structures. With minimal chance of load exceedance and collapse of structures, the time life of such structures can be increased with the use of smart materials. Therefore, it is very important to develop a smart system for reinforced concrete structures, which can minimize internal and external disturbances for structural safety and extension of its service life.