Archive for June, 2015

The self-healing concrete that can fix its own cracks

June 29th, 2015

Powered by Guardian.co.ukThis article titled “The self-healing concrete that can fix its own cracks” was written by Rosie Spinks, for theguardian.com on Monday 29th June 2015 06.00 UTC

Of all the carbon emitters that surround us every day it’s easy to overlook one of the most ubiquitous: concrete.

The material that builds our buildings, paves our roads and spans our bridges is the most widely produced and consumed material on earth apart from water, according to a WBCSD report. By 2030, urban growth in China and India will place global cement output at 5bn metric tons per year, with current output already responsible for 8% of the global emissions total, according to a WWF report.

Although its environmental impact is far from benign, concrete – defined as the mixture of aggregates, water and the hydraulic powder material known as cement – is incredibly useful and widely applicable. Thanks to its durability, easily-sourced raw materials and thermal resistance, it is unlikely that an alternative building material will replace it on a large scale any time soon.

Hendrik Jonkers, a microbiologist at Delft University and a finalist at the recent 10th annual European Inventor Awards, has a plan to increase the lifespan of concrete. His innovation, which embeds self-activating limestone-producing bacteria into building material, is designed to decrease the amount of new concrete produced and lower maintenance and repair costs for city officials, building owners and homeowners.

Jonkers’ self-healing concrete marries two fields: civil engineering and marine biology.

“One of my colleagues, a civil engineer with no knowledge of microbiology, read about applying limestone-producing bacteria to monuments [to preserve them],” Jonkers said. “He asked me: ‘Is it possible for buildings?’ Then my task was to find the right bacteria that could not only survive being mixed into concrete, but also actively start a self healing process.”

When it comes to Jonkers’ concrete, water is both the problem and the catalyst that activates the solution. Bacteria (Bacillus pseudofirmus or Sporosarcina pasteurii) are mixed and distributed evenly throughout the concrete, but can lie dormant for up to 200 years as long as there is food in the form of particles. It is only with the arrival of concrete’s nemesis itself – rainwater or atmospheric moisture seeping into cracks – that the bacteria starts to produce the limestone that eventually repairs the cracks. It’s a similar process to that carried out by osteoplast cells in our body which make bones.

Healing these cracks the old-fashioned way is no small expense. According to HealCON, the project working on the self-healing concrete, annual maintenance cost for bridges, tunnels and other essential infrastructure in the EU reaches €6bn (£4.2bn) a year.

The invention comes in three forms: a spray that can be applied to existing construction for small cracks that need repairing, a repair mortar for structural repair of large damage and self-healing concrete itself, which can be mixed in quantities as needed. While the spray is commercially available, the latter two are currently in field tests. One application that Jonkers predicts will be widely useful for urban planners is highway infrastructure, where the use of de-icing salts is notoriously detrimental to concrete-paved roads.

Encouraging as it sounds, Jonkers’ self-healing concrete can’t cure very wide cracks or potholes on roads just yet; the technology is currently able to mend cracks up to 0.8mm wide. And while making better concrete is a more feasible approach to sustainable building than shifting to an entirely new building material, that doesn’t mean the innovation is a sure bet. The current cost would be prohibitive for many. A standard-priced cubic meter of concrete is €70, according to Jonkers, while the self-healing variety would cost €100.

John Alker, director of policy at the UK Green Building Council, says the success of any new green infrastructure technology relies on innovators like Jonkers being able to demonstrate the particular benefit of a product, whether that’s around cost or enabling a client to meet environmental targets.

“We’ve seen a lot of innovation around concrete as it is a highly impactful product in terms of the energy that goes into producing it and it’s simultaneously a very important construction product globally,” Alker said. But persuading the construction industry to change its behaviour will be tough, he says. “It comes down to innovative clients and developers being willing to experiment with their building and try and test these materials and prove a track record before others will follow.”

Though Jonkers is aware of the challenges of reaching wide adoption of the material, he points out that in particularly vulnerable environments – such as coastal communities or tropical regions that are increasingly experiencing extreme rainfall – some are already seeing the cost-benefit analysis of using this technology from the outset.

“We did a project in Ecuador where we made a concrete canal and irrigation system with self-healing concrete,” Jonkers said. “We are doing tests all over the world in developing countries where they realise that though this is more expensive than current tech, they see the profit because they will have to avoid repair down the line.”

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The streets were paved with algae: a greener material?

June 11th, 2015

Powered by Guardian.co.ukThis article titled “The streets were paved with algae: a greener material?” was written by Rich McEachran, for theguardian.com on Monday 8th June 2015 12.38 UTC

The process of surfacing a road isn’t complicated. Layers of asphalt, which is composed mostly of bitumen (a byproduct of crude oil distillation), are poured over an aggregate of crushed stone and sand; the asphalt acts as a glue, binding the mixture together to form asphalt concrete.

Maintaining the roads, however, is a costly job. According to the Asphalt Industry Alliance it would cost more than £12bn to restore all road networks in England alone to a reasonable condition.

Simon Hesp, a professor and chemical engineer at Queen’s University in Ontario, believes standard industry asphalt is not sustainable. “The problem with the composition is that it’s poorly controlled … it uses materials with poor performances,” he says. Hesp says the presence of certain oil residues lowers the quality of the concrete and is a key reason why roads are failing and many potholes need to be filled and cracks fixed.

But there’s not just a maintenance cost. Asphalt, dependent as it is on the oil industry, is resource- and energy-intensive, which is why the race is on to develop a greener alternative.

In Sydney an experiment is under way using printer toner waste blended with recycled oil to produce an environmentally friendly asphalt. And in the past few years there have been studies into the development of non-petroleum bioasphalts.

At Washington State University researchers developed asphalt from cooking oil, and last year academics at Wageningen University in the Netherlands found that lignin – a natural substance found in plants and trees – is another suitable replacement for crude oil bitumen. Other investigations have looked into the use of soybean and canola oil (rapeseed oil) and coffee grounds.

The WSU research, led by Haifang Wen and published at the end of 2013, concluded that the introduction of cooking oil can increase bioasphalt’s resistance to cracking . Wenn also claims it’s possible that, if commercialised, such bioasphalts could cost much less per tonne. The price of standard asphalt can fluctuate wildly as it’s dependent on the price of oil.

Hesp isn’t convinced that cooking oil is the way forward. He says, like petroleum, over time it will cause roads to fail because of weak bonds.

Bruno Bujoli, director of research at CNRS (Centre National de la Recherche Scientifique), agrees that the use of cooking oil “chemically modified to reach appropriate mechanical properties” could significantly affect quality. He also sounds a note of caution about food security, saying that asphalt based on vegetable oils could, if scaled up, affect food stocks

Bujoli recently played a key role in developing a bioasphalt from microalgae. It uses a process known as hydrothermal liquefaction, which is used to convert waste biomass, including wood and sewage, into biocrude oil. The chemical composition of the microalgae bioasphalt differs from petroleum-derived asphalt, but initial tests have concluded that it also bears similar viscous properties and can bind aggregates together efficiently, as well as being able to cope with loads such as vehicles.

How it will perform over time is yet to be determined. The findings were published in April.

Green roads

Bujoli suggests that microalgae – also known for its use in the production of cosmetic and textile dyes – is a greener and more appropriate solution than agricultural oils. The latter, he says, should be kept for food production.

“The benefits of microalgae over other sources include low competition for arable land, high per hectare biomass yields and large harvesting turnovers. There is also the opportunity to recycle wastewater and carbon dioxide as a way of contributing to sustainable development,” he adds.

It’s a neat idea, with an admirable green mission behind it, but how much of an impact can it really have? Technology such as this is still in its infancy, suggests Heather Dylla, director of sustainable engineering at the National Asphalt Pavement Association, a US trade organisation for the paving industry.

“A lot of interesting work is being done in this area, looking at everything from algae, to swine waste, to byproducts from paper making. It’s worth exploring these alternatives, but we need to be sure they provide equivalent or improved engineering properties. We need to understand how they affect the recyclability of asphalt pavement mixtures,” she says.

She points to the “unique” advantage of asphalt when it comes to recycling. “Not only are the aggregates, which make up about 95% of [asphalt concrete], put back to use, but the bitumen can also be reactivated and used again as the glue that holds a pavement together.”

Microalgae could yet put the paving industry on the road to a greener future. For now though, there are plenty of challenges – from price to scalability – for Bujoli and his team to address if the bioasphalt is to be commercialised.

“This is our research focus for the near future. Our current laboratory equipment works in a batch mode,” explains Bujoli. “Scaling up the process will require the design of a large-volume reactor that can operate under continuous flow conditions.”

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