Greening the concrete jungle: how to make environmentally friendly cement

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With some tweaks to the recipe, cement and concrete can be made kinder to the planet.
Postman Photos/

Rackel San Nicolas, University of Melbourne

Cement is the world’s most widely used material apart from water, largely because it is the key ingredient in concrete, the world’s favourite building material.

But with cement’s success comes a huge amount of greenhouse emissions. For every tonne of cement produced in Australia, 0.82 tonnes of CO₂ is released. That might not sound like much, especially when compared with the 1.8 tonnes emitted in making a tonne of steel. But with a global production of more than 4 billion tonnes a year, cement accounts for 5% of the world’s industrial and energy greenhouse emissions.

Read more: The problem with reinforced concrete.

The electricity and heat demands of cement production are responsible for around 50% the CO₂ emissions. But the other 50% comes from the process of “calcination” – a crucial step in cement manufacture in which limestone (calcium carbonate) is heated to transform it into quicklime (calcium oxide), giving off CO₂ in the process.

A report published by Beyond Zero Emissions (BZE) (on which I was a consultant) outlines several ways in which the sector can improve this situation, and perhaps even one day create a zero-carbon cement industry.

Better recipes

The cement industry has already begun to reduce its footprint by improving equipment and reducing energy use. But energy efficiency can only get us so far because the chemical process itself emits so much CO₂. Not many cement firms are prepared to cut their production to reduce emissions, so they will have to embrace less carbon-intensive recipes instead.

The BZE report calculates that 50% of the conventional concrete used in construction can be replaced with another kind, called geopolymer concrete. This contains cement made from other products rather than limestone, such as fly ash, slag or clay.

Making this transition would be relatively easy in Australia, which has more than 400 million tonnes of fly ash readily available as stockpiled waste from the coal industry, which represents already about 20 years of stocks.

Read more: Eco-cement, the cheapest carbon sequestration on the planet.

These types of concrete are readily available in Australia, although they are not widely used because they have not been included in supply chains, and large construction firms have not yet put their faith in them.

Another option more widely known by construction firm is to use the so-called “high blend” cements containing a mixture of slag, fly ash and other compounds blended with cement. These blends have been used in concrete structures all over the world, such as the BAPS Shri Swaminarayan Mandir Hindu temple in Chicago, the foundation slab of which contains 65% fly ash cement. These blends are available everywhere in Australia but their usage is not as high as it should due to the lack of trust from the industry.

Built on the fly (ash): a Hindu temple in Chicago. Commons, CC BY-SA

It is even theoretically possible to create “carbon-negative cement”, made with magnesium oxide in place of traditional quicklime. This compound can absorb CO₂ from the air when water is added to the cement powder, and its developer Novacem, a spinoff from Imperial College London, claimed a tonne of its cement had a “negative footprint” of 0.6 tonnes of CO₂. But almost a decade later, carbon-negative cement has not caught on.

Capturing carbon

The CO₂ released during cement fabrication could also potentially be recaptured in a process called mineral carbonation, which works on a similar principle as the carbon capture and storage often discussed in relation to coal-fired electricity generation.

This technique can theoretically prevent 90% of cement kiln emissions from escaping to the atmosphere. The necessary rocks (olivine or serpentine) are found in Australia, especially in the New England area of New South Wales, and the technique has been demonstrated in the laboratory, but has not yet been put in place at commercial scale, although several companies around the world are currently working on it.

Read more: The ‘clean coal’ row shouldn’t distract us from using carbon capture for other industries.

Yet another approach would be to adapt the design of our buildings, bridges and other structures so they use less concrete. Besides using the high-performance concretes, we could also replace some of the concrete with other, less emissions-intensive materials such as timber.

The ConversationPreviously, high greenhouse emissions were locked into the cement industry because of the way it is made. But the industry now has a range of tools in hand to start reducing its greenhouse footprint. With the world having agreed in Paris to try and limit global warming to no more than 2℃, every sector of industry needs to do its part.

Rackel San Nicolas, Academic specialist, Infrastructure Engineering, University of Melbourne

This article was originally published on The Conversation. Read the original article.

Concrete jungle? We’ll have to do more than plant trees to bring wildlife back to our cities

Peter Fisher, RMIT University

The federal environment and acting cities minister, Greg Hunt, on Tuesday pledged to increase the number of trees in Australian cities. In a bid to fight higher urban temperatures, the plan will set targets for tree cover.

This is part of a green revolution spreading through the world’s cities. From New York to Singapore, urban areas are undertaking bold “greenspace” initiatives – removing concrete and allowing trees and vegetation back in.

Some of the benefits include replacing the ugly infrastructural trappings of vehicles and motorways as well as cooling cities, absorbing air pollution and minimising runoff. These greenings further have mental health benefits, by bringing residents and visitors alike back into contact with the land.

But what about wildlife? Trees alone aren’t enough to bring back nature. In the rush to create greenspace, we have to make sure we build it in a way to help wildlife thrive. That will take careful thought and planning.

Nature paved over

Many of the world’s cities don’t have anything special to offer in terms of nature – either because they never had all that much in the first place, or they’ve long since been lost to urban development.

Melbourne is a case of the latter. James Boyce (in his book 1835) records:

By the time Anthony Trollope visited, then a city of 206,000 “souls” in the early 1870s, the city had already largely turned its back on the Yarra [River], drained the swamps, filled in the lakes and flattened the hills, so that Trollope knew “of no great town in the neighbourhood of which there is less to see in the way of landscape beauty”.

That sounds like many a world city.

Reconstruction of Williams Creek, Melbourne, which now lies under the city’s asphalt.

London, New York, Hamburg, Madrid, Detroit, Chicago, Seoul and Singapore are among cities that have undertaken bold greenspace initiatives. These cities have recognised the distinct benefits that flow from connecting people back to the natural world.

Detroit and Singapore have strong biodiversity themes and that’s needed too given the global decline in wildlife. Such initiatives help us to view cities from a non-human-centric perspective.

i-Tree world

Back in Australia “green infrastructure” has similarly taken hold with councils, property owners and private companies signing up to a national 202020 vision to create 20% more greenspace by 2020. The main underpinning of that “greenspace” is the “urban forest”.

While urban forest has a broad definition, cities usually take it to mean tree cover. This has been revolutionised and driven by satellite mapping (known as i-Tree) from the US Department of Agriculture.

This mapping has recently been used to shed light on the performance of Australia’s municipalities. Ranking them according to their percentage of tree cover, parts of Melbourne and Sydney scored badly, with many suburbs having less than 20% tree cover overall. Brisbane scored well, with most areas having more than 50% tree cover.

As cities attempt to increase canopies, it’s worth noting that these trees will have to deal with increasing extreme weather as the world warms.

Rewilding the city

However, trees on their own won’t bring wildlife back into our cities. In fact, canopies tend to create spaces for dominant native birds such as the Noisy Miner and Red Wattlebird, which by their behaviour exclude smaller birds.

Birdlife Australia suggests that a dense understory of shrubs up to two metres high is required for small ground birds like thornbills, robins, scrubwrens and fairy-wrens to roost in and make brief forays into grassed areas. Thickets also provide protection from eagles and hawks and other predators.

The late Victorian naturalist Alan Reid suggested:

a mixture of fine-leaf and broad-leaf plants with a high percentage of native species, especially at intermediate and ground levels, will provide the greatest opportunities for attracting and holding wildlife.

Private gardens have inadvertently edged towards this prescription, along the way forming “nuclei” for wildlife. To create these on public land, areas will need to be set aside in parklands and other community spaces where small birds and small animals can congregate, breed and flourish.

This may require fencing to counter fox and cat predation, and possibly incorporate bird hides, interpretative apps and surveillance to ensure personal security. We need to give attention to the subtle connections between species.

Wildlife corridors are another construct – in effect they’re flyways for larger birds. Some of these already take advantage of the routes provided by revegetated creek and river banks.

Reid suggests that “corridors as narrow as 5 metres will allow passage of lorikeets and wattlebirds even when gaps exceed 30 metres”.

But if the gaps in 20-metre-wide corridors grow to more than 30 metres they will block many upper-level feeders including butterflies, pygmy possums and marsupial mice.

As the take-up of greening in places like New York, Hamburg and Seoul shows, it’s becoming mainstream in city halls around the world. And we now know that it helps settle the brains of those otherwise enmeshed in asphalt, glass and concrete.

There are some encouraging signs that developers “get it”: witness Singapore building an entire forest in a high-rise apartment atrium. A connection-to-nature element also forms part of the revamped Green Building Council of Australia’s Innovation Challenge Program. Let’s hope it won’t be long before that awareness spills over into popular planning thought.

As the world continues to change under human pressure, we need to make sure our cities can be homes for wildlife too.

The Conversation

Peter Fisher, Adjunct Professor, Global, Urban and Social Studies, RMIT University

This article was originally published on The Conversation. Read the original article.