Processed Coal Ash Waste Used to Cure Concrete

Rising from coal ash waste to cure concrete

---

A by-product of coal-fired power plants is the tens of millions of tons of coal ash that ends up in landfills each year. Now researchers from Drexel University, the National Institute of Standards  and Technology [UK] and the University of Antwerp have developed a way to turn this waste ash into a lightweight aggregate that can speed up the curing process for concrete and make it more durable and crack-free. Their discovery was recently reported in the journal Cement and Concrete Composites.

Concrete is made from a mixture of fine powder and coarse rock particles, called aggregates, bonded by a mineral glue called a ‘cementing matrix’ made of cement and water. The aggregates form the strong internal structure of the concrete as the cementing matrix hardens to bind the ingredients together in a process called curing. For concrete to reach its maximum durability, the cement must mix thoroughly with water during the curing process so it all dries — and cures — at the same time.

“This is a very important part of the process because if the concrete dries too quickly during its curing, due to added water shortage, it can form cracks and other flaws. These drying shrinkage cracks cause the surface to be susceptible to aggressive fluid ingress, creating concrete durability problems such as corrosion, salt damage or freeze-thaw damage,” said Yaghoob Farnam, PhD, an assistant professor in Drexel’s College of Engineering and principal investigator of the research.

To ensure even curing there are a number of things concrete contractors might have to do, including constantly spraying the concrete, covering it with a membrane to keep it moist, submerging it in water or creating pools of water on its surface. All of these strategies consume time and resources and are complex enough that flaws could creep into the process. To help prevent this, in the last decade researchers have developed an internal curing concept that uses porous lightweight aggregate to aid the curing process. The aggregate can maintain a consistent level of moisture inside the concrete to help it cure evenly from the inside out.

“The solution we came up with involved recycling this waste product, coal ash, into a porous, lightweight aggregate with excellent performance characteristics that could be produced at a lower cost than current natural and synthetic options,” Farnam said. “This material and process would not only benefit the concrete industry by improving the quality of their products, but it could also help keep coal ash out of landfills.”

The material the researchers came up with is called ‘spherical porous reactive aggregate’ — SPoRA for short. It is made by combining the ash with chemicals that facilitate aggregate sintering and bonding, forming them into tiny spheres and then baking them at 1160°C for a few minutes.

The end product is an aggregate pellet that can hold almost half its weight in water, which is better than traditional lightweight aggregates. And, as importantly, it can release that water at a regular rate from inside to the cementing matrix as it cures.

In the paper they report that two types of SPoRA perform better than some traditional lightweight aggregate materials — shale, clay and slate, and foamed glass — on measurements of shape, porousness, relative weight, and ability to absorb and release water. These are all key metrics related to its ability to integrate with the cement mixture and release its moisture at the right time and in the right part of the structure as it forms.

“As the concrete begins to cure on the outside, the aggregate pellets are also releasing their moisture to help it cure from the inside out as well,” said Mohammad Balapour, a doctoral researcher in Farnam’s lab and lead author of the paper. “This approach can help to maximise the durability of the concrete. And the SPoRA-making process is simple enough to produce aggregates of any size and water capacity, so we believe it could be used for a number of applications in the construction industry.”

Recycling a waste product like coal ash not only reduces the cost of making lightweight aggregate, it also ensures that concrete producers will have access to it.

Image credit: Drexel University.

If this really is a new concept that works it promises a lot, both in better materials and environmental benefits.  A lot of coal ash is produced each year!

Solar Panel Disposal - Emerging Problem?

So far there has been a relatively modest need for safe disposal of solar panels - most are going onto the roof and not off the roof!

Elsewhere in the world though some areas are now discussing how this disposal of the solar panels at "end of life" can be managed effectively.

The growth in solar energy use over the past 25 years has been exponential, at times being called a "sunrush". In addition to increasing global capacity from 100 MW to over 300 GW in that time, costs in 2017 were an impressive 86% less than in 2009!

A solar array in rural area

One emerging concern, however, results from the fact that the effective life cycle of a typical solar panel is about 25 years. The glass and metal material from retired photovoltaic (PV) panels will begin to add up to millions of metric tons in the near term, and current recycling infrastructure may not be sufficient for dealing with such a large quantity of these materials.

Perhaps unsurprisingly, the process of recycling solar panels is fairly complicated, involving heat systems that burn up the adhesives as well as other methods used to separate out the crystalline silicon and the precious metals in the panels. The wide variety of materials used—from glass, aluminum, and synthetic sealing materials to metals like lead, copper, and gallium—makes it difficult to efficiently process and recycle them. Mark Robards, director of special projects for ECS Refining in the USA, says, “Nearly 75% of the material that gets separated out is glass, which is easy to recycle into new products but also has a very low resale value” (quoted on the website Ensia.com). 

If they aren’t recycled, PV panels in many jurisdictions around the world cannot be sent to landfills since they are made with heavy metals and other toxic substances that can contaminate the surrounding soil, air, and water.  And not a lot to effectively solve the problem is occurring in Australia [maybe okay in South Australia].

Along with the current difficulties of recycling solar panels, the changing makeup of the panels themselves presents a challenge. As manufacturers continue to improve their technology, they search for more cost-effective ways to construct panels. These methods often involve using alternative components—like a material called perovskite—rather than more easily recyclable materials like silver and copper. While solar panel costs are dropping and enabling the technology to become more widespread, the need for better recycling infrastructure is growing every year as more and more panels reach the end of their life span.

Large commercial solar plant

The solar energy industry in the US may take inspiration from a recycling association in Europe called PV Cycle which has developed a process for PV module recycling that is both environmentally and economically conscious. In 2016, they achieved a 96% recycling rate, a new record for silicon-based solar panel recycling. The head of Treatment & Operations at PV Cycle, Olmina Della Monica, remarks that their success “is the result of both continuous improvement and intensive research and development along the value chain.” Here in Australia there has been so far, little recognition of the emerging and potential problem, and with solar energy development widespread across remote areas, safe disposal is looming as expensive and difficult.

In contrast to the US, Europe’s PV panel disposal management is regulated by the EU’s WEEE (Waste of Electrical and Electronic Equipment) directive. Manufacturers of solar cells must obey legal requirements and specific recycling standards, operating with the mindset that these panels will need to be recycled at the end of their life span. There is no similarly strict control in the US, but California has initiated legislation on solar panel disposal that supports the PV module industry in making end-of-life management of PV modules convenient for both consumers and the public. 

As the “sunrush” continues, legislation like this will hopefully become ubiquitous across some of the major adoptors including China, Australia and the USA.  If solutions are not explored and widely developed the disposal of these panels will be a serious and very significant waste problem.  Designing for easy separation of components and metals would be a sensible start to better disposal and recycling options.

[some material based on an article by Jessica Read in Forrester Daily News April 30 2018]

Law of Food Conservation

Sometimes you read an item that calls out for wider dissemination.

This link takes you to some commentary on food waste issues, and covers a few themes where there is potential for thoughtful change.

While based on US analysis I feel sure it can equally apply in many ways across other countries, with change for the better possible almost everywhere.

Read the article ............you might generate some thoughts and ideas for your community.

http://www.biocycle.net/2015/12/15/commentary-law-of-food-conservation/

Like most environment and conservation practices - it does start with you!

And I challenge you to rebuff the idea that you cannot implement some positive change to reduce food waste yourself. 

Plastics in the Oceans

The oceans continue to be a dumping ground for waste.

As well as the plastics discussed here, it was also revealed this week,that about 21000 tonnes of sewerage are dumped weekly by the world's cruise liners.  And that quantity is going up, not down!

Plastics are the big issue though.  Nearly 269,000 tons of plastic pollution may be floating in the world's oceans, according to a study published December 10, 2014 in the open-access journal PLOS ONE by Marcus Eriksen from Five Gyres Institute and colleagues.

Microplastic pollution is found in varying concentrations throughout the oceans, but estimates of the global abundance and weight of floating plastics, both micro and macroplastic, lack sufficient data to support them. 

To better estimate the total number of plastic particles and their weight floating in the world's oceans, scientists from six countries contributed data from 24 expeditions collected over a six-year period from 2007-2013 across all five sub-tropical gyres, coastal Australia, Bay of Bengal, and the Mediterranean Sea. 

The data included information about microplastics collected using nets and large plastic debris from visual surveys, which were then used to calibrate an ocean model of plastic distribution.  Most of the plastic weight comes from lost fishing buoys, though, not broken plastics.  Rubber and plastic thongs also contribute a significant amount of the total!

Based on the data and model, the authors of the study estimate a minimum of 5.25 trillion plastic particles weighing nearly 269,000 tons in the world's oceans. Large plastics appear to be abundant near coastlines, degrading into microplastics in the 5 subtropical gyres, and that the smallest microplastics were present in more remote regions, such as the subpolar gyres, which the authors did not expect. 

The distribution of the smallest microplastics in remote regions of the ocean may suggest that gyres act as 'shredders' of large plastic items into microplastics, after which they eject them across the ocean.  "Our findings show that the garbage patches in the middle of the five subtropical gyres are not the final resting places for the world's floating plastic trash. The endgame for micro-plastic is interactions with entire ocean ecosystems," says Marcus Eriksen, PhD, Director of Research for the 5 Gyres Institute.

Read the paper at PLOS ONE.  here.