We can no longer leave the issue of sustainability to the next generation. As the global population increases, it is concentrated in cities. Consumption of energy, higher costs, climate change, emissions, and noise pollution are some of the main challenges that cities of the future will face. Urban areas are being pushed to the brink. 

In 2018, the United Nations stated that 55% of the global population lived in cities, which could rise to 68% by 2050. The dense population in cities increases levels of traffic, air pollution, noise emissions, as well as other environmental concerns. The energy consumption of cities causes 60-70% of greenhouse gases. 

Smart cities are the way forward, with benefits that go beyond creating a healthier environment.  If urban infrastructure is put to better use in a smart city, people living there will see a drastic improvement in quality of life. For example 125 hours a year could be saved by reduced congestion on the roads. 

As smart cities grow and develop, new technologies are emerging and smart materials can be used to create them. Smart materials are materials that are manipulated to respond in a controllable and reversible way. Their properties are modified as a result of external stimuli such as temperature, sound, pressure, magnetic field, light, and other variables. Smart materials can change in colour, opacity, shape, viscosity, or size. Because of their reactive nature, smart materials are also known as responsive or intelligent materials.

Examples of Smart Materials

Piezoelectric

Piezoelectricity is the electricity resulting from pressure and latent heat; crystals gain a charge when they are compressed or misshaped. There are two characteristics. First, deformed piezoelectric materials emit a small amount of electrical charge. On the other hand, when electrical current passes this material, it grows exponentially. 

Shape Memory Materials

As the name implies, shape-memory materials (SMMs) are able to revert back to their original shape when a particular stimulus is exerted. When this occurs, it is known as the shape memory effect or SME. Specific examples would be super-elasticity in alloys or viscoelasticity in polymers. 

Chromoactive Materials

This is a rather large group of smart materials with one unique feature— external stimuli will cause the materials to change colour. Chromoactive materials include:

• Thermochromic – they will change colour when exceeding a certain temperature. Due to the vast range of colours and temperature settings, they have broad potential in industrial applications.

• Photochromic – colour changes are caused by particular types of light, for example, ultraviolet (UV) wavelengths. 

• Hydrochromic – we have seen hydrochromic materials in smart textiles and ink. Water reacts to the materials, and colours change.

Magnetorheological Materials

Magnetorheological materials are magneto-sensitive. External magnetic fields can control materials. They are popular because the process is fast, reversible, and on-going. The extent of MR materials is vast, but AI and automotive industries can benefit. Today, they are used in construction. MR materials are used as shock absorbers in bridges and skyscrapers in areas of high seismic activity.

Using Smart Materials in Construction to Build Smart Cities

As we see a greater need for advanced materials to support technology progress these responsive materials have moved up the technological value chain, becoming a cheaper and more powerful alternative to traditional materials.

The global smart city market was valued at $410.8 billion in 2020. With an annual growth rate of 14.8%, the market could reach $820.7 billion by 2025. Smart materials will be essential in the construction of smart cities with cutting-edge innovations needed in transport, construction, and materials. Emerging responsive materials already improving our cities include:

Smart Concrete

A composite of concrete and carbon fibers, smart concrete has the ability to detect minute issues as well as being stronger. Smart concrete can be used as a sensor, as loading and unloading cause it to lose and regain conductivity. It can be used as part of a traffic-sensing recording system and to melt snow on highways or airfields. 

Self-healing concrete is a smart concrete that will repair itself. Bacteria that sit in cracks will react to water (stimuli) and produce limestone, which will fill the crack. 

Smart Bridges

Though not limited to bridges, smart materials can control vibrations and noise in structures, improving safety. With smart bridges, cable-stayed bridges allow for a wider span without increasing vulnerability to vibrations from wind, rain, traffic, etc. Such bridges don't need as much maintenance and can be monitored more easily.

Shape Shifting Metal 

Similar to smart bridges, shape shifting metals are ideal for areas that are prone to earthquakes and hurricanes. These metals can change shape when under pressure and return to their original shape after. 

Smart Glass

The light-changing properties in smart glass will make a massive difference in numerous products such as windows, doors, sunroofs, and skylights. Switchable glazing or dynamic glazing can help to control the amount of light that passes through the window depending on external stimuli.

In Conclusion

From sustainability to energy and everything in between, it’s clear that technology and smart materials have a vital role to play in building the society of the future. Our first priority should be to maximise the benefits of smart materials in the creation of smart cities to help reduce pollution and contribute to a healthier planet. That's not to say that more commercial applications won't take advantage of smart materials. The European Space Agency is just one example of an organisation looking to use smart materials to resolve pressing issues. 

The next five years will show further developments and more exciting possibilities in smart materials and smart cities. We look forward to being a part of it.