Green and net-zero

Infrastructure heal thyself

At a time of tight budgets, the development of smart infrastructure and assets requiring greatly reduced maintenance includes some very clever solutions designed to tackle minor damage before it causes major problems, as Jon Herbert discovers.

( Text content written by Jon Herbert for Croner-i Environment Inform )

Winter road damage that almost magically repairs itself long before becoming a pothole hazard for vehicles has obvious appeal in the UK.

However, self-sealing leaks in hard-to-reach damaged pipelines, plus many other utility services that simply run better with little direct human intervention, could be equally important for asset managers.

These dreams are becoming realities. Technologies that may sound fantastic today but could be routine in the foreseeable future are under serious development.

Technologies and innovations that can squeeze extra life and capacity out of expensive-to-build assets, while also providing superior consumer services, have obvious appeal. Making taxpayers’ money go further and faster more cheaply could help to overcome the serious problem of ageing public infrastructure.

The next revolution

The UK still largely depends on structures created by forward-thinking Victorian and Edwardian builders and engineers whose ideas were revolutionary more than a century ago.

Their 21st century counterpart is the growing use of new smart technology to ensure that new infrastructure ages gracefully and continues to do its job more effectively for far longer. The ease with which small, low-cost, internet-enabled sensors with extended battery life can now be installed and interrogated continuously makes it possible to understand what is happening to structures in real-time detail.

As part of the fourth industrial revolution, “digital twinning” computer models loaded with real-time data are revealing exactly how much design lifetime has already been used up and what remains. The historic tendency to over-engineer safety factors is being turned into a bonus today.

Smart and very clever

Increasingly widespread use of IT sensor technology, real-time information and big data allows the detection of minute stresses, temperature and humidity changes, relative movements, tilt, rust, corrosion and other potential failure conditions early enough for less disruptive remedial action to be taken.

A topical case is the Forth Road Bridge where a fractured truss end link spotted by an engineer escorting a group of visitors led to partial road closure in December 2015. The component was previously visually inspected every six months. The bridge, now with one of the world’s most advanced asset monitoring systems, was reopened to public traffic on 31 January 2018. The nearby new Queensferry Crossing will have nearly 2000 sensors installed.

At the far technological end of the scale, what might seem to be a science fiction vision of swarms of municipal repair robots working autonomously in the urban environment is being taken very seriously in a least one English city (see Self-repairing cities, below). Meanwhile, other breakthroughs, which if not strictly smart are certainly very clever, are also being made in materials technology.

Repairing the cracks in crumbling concrete

Part of the solution is a better understanding of the processes of breakdown and decay. This is especially important in complex structures that once built are buried, embedded, and for lack of access, forgotten.

In January 2018, the State University of New York at Binghamton (Binghamton University) explained how it is making advances in a new concept of self-healing fungi that it says could provide a permanently low-cost, pollution-free, sustainable solution to repair cracks in crumbling concrete.

The basic problem, according to Binghamton, is tiny cracks that without proper early treatment widen to allow in water, oxygen, CO2 and chlorides that corrode steel reinforcement and promote internal structural failure.

The university’s mechanical engineering facility was originally inspired by the human body’s ability to heal cuts, bruises and even broken bones, says assistant professor Congrui Jin. She explains how “the host will take in nutrition that can produce new substitutes to heal the damaged parts”.

The researchers’ current solution is to incorporate in concrete a fungus called Trichoderma reesei which can secrete large amounts of cellulolytic enzymes, some of which have industrial applications in the conversion of cellulose into glucose. Curiously, the fungus was originally isolated from the Solomon Islands in World War II where it degraded US Army canvas and garments. All strains currently in use are said to come from this one isolated source.

As a concrete damage remedy, the aim is to mix fungal spores, plus nutrient, into the concrete matrix where they will lie dormant until the first cracks appear. The eventual entry of water and will cause the spores to germinate, grow and deposit calcium carbonate that will heal the fissures.

Conveniently, when no more water and oxygen can make their way in, spores will again form and wait until later cracks appear. Then the process will be repeated. Several issues are still outstanding, including the long-term survival of the fungus in the harsh concrete environment. Alternative fungi and yeasts will be considered.

Dutch solution for roads

Research at Delft University of Technology in the Netherlands is following a parallel but non-biological route for road surface asphalt repair where small cracks are precursors of potholes. Applying asphalt, or the semi-solid and highly viscous form of petroleum known as bitumen, involves warming, mixing and laying the material which then hardens on cooling. However, the presence of pores that absorb noise (compared to concrete roads) allows water which then causes deterioration.

Erik Schlangen, Civil Engineering professor at Delft University and Chair of Experimental Micromechanics, recently presented his ideas as a Technology, Entertainment, Design (TED) talk. TED’s slogan is “ideas worth spreading”; previous speakers have included presidents and prime ministers.

His solution at Delft is to include small steel fibres which make asphalt conductive. When heated by a large induction machine, small cracks close themselves up. Sunshine has a similar but more limited effect.

Self-healing asphalt has been tested on 12 roads in the Netherlands, including the A58 near Vilssingen. Although they are reported to be functioning well, ordinary asphalt roads are good for some 7 to 10 years. It is in these later years where the test results could be most important. Materials will be an estimated 25% more expensive but double road life, potentially saving the Netherlands €90 million annually.

One other development area is metal coatings with self-healing properties based on micro-capsules that can repair damaged or corroded pipelines on primary steel structures. Extensive research is underway in the harsh offshore environment where thermally sprayed aluminium (TSA) coatings have the potential to replace the use of expensive aluminium sacrificial anodes on vulnerable assets such as wind turbine foundations. In the aviation sector, polymers could be used to repair hairline cracks in aircraft wings.

Self-repairing cities

In a leap of faith and ingenuity that could herald the future, Leeds in Yorkshire hopes to become Britain’s first self-repairing city by 2035 if a £4.2 million infrastructure R&D programme is successful at the School of Civil Engineering of the University of Leeds. The project is being developed in collaboration with Leeds City Council and the UK Collaboration for Research in Infrastructures and Cities.

The concept is to create a fleet of sustainable repair robots that “live” permanently within the urban environment where they will routinely detect and mend early damage to streets, buildings, utilities and pipelines.

The five-year project launched in 2016 aims to produce robots and technologies in three main areas. The first is drones perched on high structures from where they can move out to repair damaged amenities such as street lighting. The second should be able to autonomously spot and patch up fledgling potholes. The third are intended to live within pipelines where they can inspect, repair and report back to humans on any issues they find.

The fundamental concept is that rather than interfere with the city’s daily human life, packs of intelligent machines will be able to communicate and co-ordinate themselves to get the job done quietly without road closures and heavy machinery. The aim will be zero disruption.

As well as making precision repairs, the project is also being designed to track social, environmental, political and economic impacts for emerging technologies on city life.

With people described as high-tech gardeners to an urban ecosystem, the eventual goal is to produce robots that look after buried water mains, electricity cables and hunt down and attack blockages in sewerage systems. Others will have diagnostic missions. While introducing urban resilience is regarded as positive, the programme is also mindful of cyber-security challenges and ensuring that the robots cannot be hacked and reprogrammed against human interests.