Green cement a step closer to being a game-changer for construction emissions



If the cement industry were a country, it would be the third-largest emitter of CO₂ in the world.
Joe Mabel/Wikimedia, CC BY-SA

Yixia (Sarah) Zhang, Western Sydney University; Khin Soe, Western Sydney University, and Yingying Guo, UNSW

Concrete is the most widely used man-made material, commonly used in buildings, roads, bridges and industrial plants. But producing the Portland cement needed to make concrete accounts for 5-8% of all global greenhouse emissions. There is a more environmentally friendly cement known as MOC (magnesium oxychloride cement), but its poor water resistance has limited its use – until now. We have developed a water-resistant MOC, a “green” cement that could go a long way to cutting the construction industry’s emissions and making it more sustainable.

Producing a tonne of conventional cement in Australia emits about 0.82 tonnes of carbon dioxide (CO₂). Because most of the CO₂ is released as a result of the chemical reaction that produces cement, emissions aren’t easily reduced. In contrast, MOC is a different form of cement that is carbon-neutral.

Global CO₂ emissions from rising cement production over the past century (with 95% confidence interval).
Source: Global CO2 emissions from cement production, Andrew R. (2018), CC BY



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What exactly is MOC?

MOC is produced by mixing two main ingredients, magnesium oxide (MgO) powder and a concentrated solution of magnesium chloride (MgCl₂). These are byproducts from magnesium mining.

Magnesium oxide (MgO) powder (left) and a solution of magnesium chloride (MgCl₂) are mixed to produce magnesium oxychloride cement (MOC).
Author provided

Many countries, including China and Australia, have plenty of magnesite resources, as well as seawater, from which both MgO and MgCl₂ could be obtained.

Furthermore, MgO can absorb CO₂ from the atmosphere. This makes MOC a truly green, carbon-neutral cement.




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MOC also has many superior material properties compared to conventional cement.

Compressive strength (capacity to resist compression) is the most important material property for cementitious construction materials such as cement. MOC has a much higher compressive strength than conventional cement and this impressive strength can be achieved very fast. The fast setting of MOC and early strength gain are very advantageous for construction.

Although MOC has plenty of merits, it has until now had poor water resistance. Prolonged contact with water or moisture severely degrades its strength. This critical weakness has restricted its use to indoor applications such as floor tiles, decoration panels, sound and thermal insulation boards.

How was water-resistance developed?

A team of researchers, led by Yixia (Sarah) Zhang, has been working to develop a water-resistant MOC since 2017 (when she was at UNSW Canberra).

Adding industrial byproducts fly ash (above) and silica fume (below) improves the water resistance of MOC.
Author provided

To improve water resistance, the team added industrial byproducts such as fly ash and silica fume to the MOC, as well as chemical additives.

Fly ash is a byproduct from the coal industry – there’s plenty of it in Australia. Adding fly ash significantly improved the water resistance of MOC. Flexural strength (capacity to resist bending) was fully retained after soaking in water for 28 days.

To further retain the compressive strength under water attack, the team added silica fume. Silica fume is a byproduct from producing silicon metal or ferrosilicon alloys. When fly ash and silica fume were combined with MOC paste (15% of each additive), full compressive strength was retained in water for 28 days.

Both the fly ash and silica fume have a similar effect of filling the pore structure in MOC, making the cement denser. The reactions with the MOC matrix form a gel-like phase, which contributes to water repellence. The extremely fine particles, large surface area and high reactive silica (SiO₂) content of silica fume make it an effective binding substance known as a pozzolan. This helps give the concrete high strength and durability.

Scanning electron microscope images of MOC showing the needle-like phases of the binding mechanism.
Author provided



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Although the MOC developed so far had excellent resistance to water at room temperature, it weakened fast when soaked in warm water. The team worked to overcome this by using inorganic and organic chemical additives. Adding phosphoric acid and soluble phosphates greatly improved warm water resistance.

Examples of building products made using MOC.
Author provided

Over three years, the team has made a breakthrough in developing MOC as a green cement. The strength of concrete is rated using megapascals (MPa). The MOC achieved a compressive strength of 110 MPa and flexural strength of 17 MPa. These values are a few times greater than those of conventional cement.

The MOC can fully retain these strengths after being soaked in water for 28 days at room temperatures. Even in hot water (60˚C), the MOC can retain up to 90% of its compressive and flexural strength after 28 days. The values remain as high as 100 MPa and 15 MPa respectively – still much greater than for conventional cement.

Will MOC replace conventional cement?

So could MOC replace conventional cement some day? It seems very promising. More research is needed to demonstrate the practicability of uses of this green and high-performance cement in, for example, concrete.

When concrete is the main structural component, steel reinforcement has to be used. Corrosion of steel in MOC is a critical issue and a big hurdle to jump. The research team has already started to work on this issue.

If this problem can be solved, MOC can be a game-changer for the construction industry.




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The Conversation


Yixia (Sarah) Zhang, Associate Professor of Engineering, Western Sydney University; Khin Soe, Research Associate, School of Computing, Engineering and Mathematics, Western Sydney University, and Yingying Guo, PhD Candidate, School of Engineering and Information Technology, UNSW

This article is republished from The Conversation under a Creative Commons license. Read the original article.

We create 20m tons of construction industry waste each year. Here’s how to stop it going to landfill



Building construction and demolition create enormous amounts of waste and much of it goes into landfill.
Sytilin Pavel/Shutterstock

Salman Shooshtarian, RMIT University; Malik Khalfan, RMIT University; Peter S.P. Wong, RMIT University; Rebecca Yang, RMIT University, and Tayyab Maqsood, RMIT University

The Australian construction industry has grown significantly in the past two decades. Population growth has led to the need for extensive property development, better public transport and improved infrastructure. This means there has been a substantial increase in waste produced by construction and demolition.

In 2017, the industry generated 20.4 million tons (or megatonnes, MT) of waste from construction and demolition, such as for road and rail maintenance and land excavation. Typically, the waste from these activities include bricks, concrete, metal, timber, plasterboard, asphalt, rock and soil.

Between 2016 and 2017, more than 6.7MT of this waste went into landfills across Australia. The rest is either recycled, illegally dumped, reused, reprocessed or stockpiled.

But with high social, economic and environmental costs, sending waste to landfill is the worst strategy to manage this waste.




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What’s more, China introduced its “National Sword Policy” and restricted waste imports, banning certain foreign waste materials and setting stricter limits on contamination. So Australia’s need for solutions to landfill waste has become urgent.

China has long been the main end-market for recycling materials from Australia and other countries. In 2016 alone, China imported US$18 billion worth of recyclables.

Their new policy has mixed meanings for Australia’s waste and resource recovery industry. While it has closed China’s market to some of our waste, it encourages the development of an Australian domestic market for salvaged and recycled waste.

But there are several issues standing in the way of effective management of Australia’s construction and demolition waste.




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The producers should take more responsibility

In Australia, the main strategy to reduce the waste sent to landfill is the use of levies. But the effectiveness of levies has been questioned in recent years by experts who argue for smarter strategies to manage waste from construction and demolition. They say that imposing a landfill levy has not achieved the intended goals, such as a reduction in waste disposal or an increase in waste recovery activities.

One effective strategy Australia should expand is extended producer responsibility (EPR).

The idea originated in Germany in 1991 as a result of a landfill shortage. At the time, packaging made up 30% by weight and 50% by volume of Germany’s total municipal waste stream.

To slow down the filling of landfills, Germany introduced “the German Packaging Ordinance”. This law made manufacturers responsible for their own packaging waste. They either had to take back their packaging from consumers and distributors or pay the national packaging waste management organisation to collect it.

Australia has no specific EPR-driven legal instrument for the construction and demolition waste stream, nor any nationally adopted EPR regulations.

Waste piled at a demolition site at Little A’Beckett Street in Melbourne in April 2019.
Salman Shooshtarian, Author provided

But some largely voluntary approaches have had an impact. These include the national Product Stewardship Act 2011, New South Wales’ Extended Producer Responsibility Priority Statement 2010 and Western Australia’s 2008 Policy Statement on Extended Producer Responsibility.

These schemes have provided an impetus for industry engagement in national integrated management of some types of waste, such as e-waste, oil, batteries and fluorescent lights. Voluntary industry programs also cover materials such as PVC, gypsum, waffle pod and carpet.




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For instance, since 2002, the Vinyl Council of Australia has voluntarily agreed to apply EPR principles. Armstrong Australia, the world’s largest manufacturer of resilient PVC flooring products, collects the offcuts and end-of-life flooring materials for recycling and processing into a new product. These materials would otherwise have been sent to landfill.

In another example, CSR Gyprock uses a take-back scheme to collect offcuts and demolition materials. After installation, the fixing contractor arranges collection with CSR Gyprock’s recycling contractor who charges the builder a reasonable fee.

Connecting industries

But extending producer responsibility in a sustainable way comes with a few challenges.

Everyone in the supply chain should be included: those who produce and supply materials, those involved in construction and demolition, and those who recover, recycle and dispose of waste.

The goal of our work is to connect organisations and industries across the country so waste can be traded instead of sent to landfill.




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But the lack of an efficient supply chain system can discourage stakeholders from taking part in such schemes. An inefficient supply chain increases the costs associated with labour and admin staff at construction sites, transport, storage, separation of waste and insurance premiums.

All of these are not only seen as a financial burden but also add complexities to an already complicated system.

Australia needs a system with a balanced involvement of producers, consumers and delivery services to extend producer responsibility.

How can research and development help?

In our research, we’re seeking to develop a national economic approach to deal with the barriers preventing the effective management of construction and demolition waste in Australia, such as implementing an extended producer responsibility.

And a project aimed to find ways to integrate supply chain systems in the construction and demolition waste and resource recovery industry is supporting our efforts.

The goal is to ensure well-established connections between all parts in the construction supply chain. A more seamless system will boost markets for these materials, making waste recovery more economically viable. And that in turn will benefit society, economy and the environment.The Conversation

Salman Shooshtarian, Research Fellow, RMIT University; Malik Khalfan, Associate Professor, Property, Construction and Project Management, RMIT University; Peter S.P. Wong, Associate Professor and Associate Dean, School of Property, Construction and Project Management, RMIT University; Rebecca Yang, Senior Lecturer, Property, Construction and Project Management, RMIT University, and Tayyab Maqsood, Associate Professor in Project Management, RMIT University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Skyonic to soon start construction on large carbon capture plant in Texas


Gigaom

Startup Skyonic — which develops technology that turns carbon emissions from power plants and factories into substances like baking soda — plans to start construction on the largest commercial carbon capture plant in the U.S. next week. The plant will be built at a cement factory in San Antonio, Texas, and will capture carbon emissions, acid gases and heavy metals from the flue of the cement factory.

Skyonic’s technology is based around turning factory and plant emissions into usable products, like baking soda, hydrochloric acid and bleach. So the plant in Texas is expecting to pay off the investment — and turn a profit — by selling the products to buyers. The plant expects to convert 75,000 tons of CO2 into products, and offset another 225,000 tons per year.

The startup is announcing the start of construction during an event next week at the plant, where a local judge…

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Chile: Tierra del Fuego – Karukinka National Park


The link below is to an article reporting on the construction of a new walking trail within Karukinka National Park which will open in December 2012.

For more, visit:
http://news.mongabay.com/2012/0407-patagonia_wcs-pod.html

Asia: Dams to Cause Environmental Disaster – Mekong River


The link below is to an article reporting on the construction of some 78 dams along the Mekong River system in south-east Asia, raising major concerns for the health of the river system and its fish population.

For more visit:
http://www.scidev.net/en/agriculture-and-environment/news/dams-a-potential-catastrophe-for-mekong-fisheries.html