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

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. BAPS.org/Wikimedia 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.

Previously, 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 is affiliated with the University of Melbourne, International Union of Laboratories and Experts in Construction Materials, Systems and Structures, the Australian French Association of Science and Technology, She receives funding from Australian Research Council.

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Airedale, West Yorkshire Under one board are two young lizards, one buff, one a dramatic charcoal-grey; under another a dark-green frog

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Here and there, in the riverside woodland, the warden has laid down boards of planking for young adventurers to peer beneath. Typically there’ll be worms and snails, sage-green slugs and hectic centipedes, perhaps a wood mouse’s midden of neatly nibbled cherry pits.

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It might feel like the depths of winter, but Australian fire services are preparing for an early start to the bushfire season. Sydney has been covered with smoke from hazard reduction burns, and the New South Wales Rural Fire Service has forecast a “horrific” season.

Predicting the severity of a bushfire season isn’t easy, and – much like the near-annual announcements of the “worst flu season on record” – repeated warnings can diminish their urgency.

However, new modelling that combines Bureau of Meteorology data with NASA satellite imaging has found that record-setting July warmth and low rainfall have created conditions very similar to 2013, when highly destructive bushfires burned across NSW and Victoria.

Crucially, this research has found we’re approaching a crucial dryness threshold, past which fires are historically far more dangerous.

Read more: Climate change to blame for Australia’s July heat

How to measure bushfire fuel

On September 10, 2013 several bushfires in Sydney’s West caused havoc well before the official start of the bushfire season. These were a precursor to fires that destroyed more than 200 properties a month later. Warm, dry winter weather had dried out the fuels in Sydney’s forests and bush reserves beyond “normal” levels for the time of year.

The timing and severity of those preseason fires were a reminder that the region’s forests are flammable all year round; they can burn whenever the fuel they contain dries out past a certain threshold.

In most forests, there is an abundance of fuel in the form of leaf litter, dead twigs, branches and logs, lower vegetation such as shrubs and grasses, as well as higher foliage and branches.

The flammability of all these different kinds of fuel depends largely on their moisture content. Leaf litter and fine dead branches on the soil surface can dry out in a matter of days, whereas logs may take weeks or months to lose their moisture. The moisture content of shrubs and tree canopies varies depending on the amount of water in the soil, so they reflect the overall rainfall and temperatures across a whole season.

The flammability of an entire forest is therefore a complex calculation of all these different kinds of fuel (both alive and dead) and their different moisture levels.

Mapping Sydney’s forests

In a recent collaborative study, we combined data from a Bureau of Meteorology project that maps water availability levels across Australia with satellite imagery to develop new tools for mapping and monitoring moisture levels of different fuels in forests and woodlands.

We checked these tools by modelling fuel moisture levels during fires in NSW, Victoria and the ACT between 2000 and 2014, and comparing our predictions to historical bushfires.

Our research has identified critical dryness thresholds associated with significant increases in fire area. Rather than a gradual increase in flammability as forests dry out, when dead fuel moisture drops below 15% subsequent bushfires are larger. Another jump occurs when dead fuel moisture levels fall below 10%. We found similar thresholds in growing plants, although their moisture content is measured differently.

These dryness thresholds are pivotal, because they may represent the breakdown of moist natural barriers in landscapes that prevent fires from spreading. Understanding these mechanisms makes it possible to predict fire risk much more accurately.

As part of this project we compared the fuel moisture in Sydney Basin’s forested areas in 2013 and 2017. As shown in the chart below, currently the live fuel moisture level is tracking well below the 2013 values, and is approaching a crucial threshold (indicated by the dotted line).

The moisture content of dead fuel has been more variable, but it has also dipped below the 2013 curve and, if warm dry weather continues, could reach critical levels before the end of August.

The median predicted dead fuel moisture content and live fuel moisture content in forest areas of the Sydney Basin Bioregion in 2013 and 2017. Black dashed horizontal lines indicate fuel moisture threshold values. The start dates of major fires in 2013 are indicated by orange vertical lines. Author provided, Author provided

In another worrying sign, mapping shows critically dry live fuel is much more abundant in 2017 than it was in 2013.

Remotely sensed live fuel moisture content in forest areas of the Sydney Basin Bioregion in July 2013 (left) and July 2017 (right). Click to enlarge. Author provided

It’s clear that much of the Sydney Basin is dangerously primed for major bushfires, at least until it receives major rainfall. Forecasts for windy but largely dry weather in coming weeks may exacerbate this problem.

These new insights into landscape-scale fuel dryness provide a powerful indicator of what might be expected. They also build our capacity for week by week monitoring of fire potential.

Preparation by both fire management authorities and exposed homeowners is now an immediate priority, to cope with the strong likelihood of an early and severe fire season.

Matthias Boer receives funding from The Australian Research Council and The Bushfire & Natural Hazards Cooperative Research Centre

Rachael Helene Nolan has received funding from the Australian Research Council.

Ross Bradstock receives funding from the ARC, the Bushfire and Natural Hazards CRC, the NSW and Victorian Governments

Fire threatening a house in Pelican Bay in 2006. If you need to shelter from a fire in your house, know where your exits are and be aware of surrounding vegetation. thinboyfatter/Flickr, CC BY-SA

When you live in a bushfire-prone area you can’t ignore the danger. Most individuals and families address this necessity by preparing a bushfire survival plan. The best way to survive a bushfire is not to be there when it arrives.

For most Australian fire agencies the “leave early” policy has largely replaced the previous “stay and defend or leave early” one. This reflects an emphasis on preserving human life during a bushfire event – an emphasis that has strengthened since the 2009 Black Saturday bushfires.

Read more: How to prepare your home for a bushfire – and when to leave

Even when planning to leave early, unexpected events can occur. Not being able to find a child or family pet may delay departure until it’s no longer safe to travel. Taking refuge in your home then becomes a last resort, a worst-case scenario. But this contingency is worth considering as part of your bushfire survival plan.

If you do need to take refuge inside your home during a bushfire, which parts are likely to be the safest? As part of my PhD research, I asked 252 residents living in bushfire-prone areas which parts of their houses they would shelter in during a bushfire, which parts they would avoid, and why. I then analysed the features of these locations against the known places where people died in their home during bushfires in Australia from 1901 to 2011.

Determining the safer places to shelter is further complicated as all houses are not the same. There are many different types, with large variations in design, construction materials, location and surrounding vegetation. It is therefore not possible to give absolute answers on where people should take shelter in their homes during a bushfire, but some general guidelines can be given.

Where are the safer spaces to shelter?

Upstairs is generally a more dangerous space to seek shelter during a bushfire. Upstairs levels are more difficult to escape from. Often they have large windows and sliding glass doors which are designed to capture views, but due to radiant heat and strong winds can crack and implode. Upper levels are often constructed of lightweight materials that are more flammable and vulnerable to direct flame contact from burning trees.

The ground floor is generally a safer space to shelter. The ground level usually has more external doors from which the occupant can escape. On a sloping block, however, the easiest level from which to exit may be the first floor. The ground level often has smaller windows (except those leading to entertainment areas). From the ground floor it is easier to get to the driveway and closer to an external water source such as a water tank.

People often suggest the bathroom as a good place to shelter during a bushfire. However, the bathroom can also be dangerous. During a bushfire, mains water is often cut or the pressure is reduced to a trickle. Despite having tiled walls, non-combustible fittings and a water supply, bathrooms like other rooms are vulnerable to the collapse of a burning ceiling when embers have ignited in the roof cavity.

Most bathrooms do not have an external door that residents can use to exit the house. In a bathroom it can be difficult to see the progress of a fire. And as bathrooms are small enclosed spaces they may be more vulnerable to carbon monoxide poisoning.

Read more: Low flammability plants could help our homes survive bushfires

My advice is to look at all the external ground floor doors (while remembering that glass doors can be dangerous because of their vulnerability to radiant heat), and determine which of them provide access to adjoining outside paved, gravel, concrete or other non-combustible areas. You should also see if there is a small window from which you can observe the progress of the bushfire, and if there is a sink close by to store water. Where possible consider installing a fire alarm that has a carbon monoxide sensor with audible and visual alerts.

When you have identified the most suitable place in the house to actively shelter during a bushfire, follow the bushfire preparation activities provided by fire authorities. Some of these will include looking out of a window to follow the progress of the fire and being aware of current bushfire updates on the radio and via mobile phone. There is no such thing as passive sheltering.

Being inside your home as the fire passes offers more protection than being outside. But it should be seen as a last resort, with leaving early the preferred action. Fire agencies work hard to inform residents of days when bushfires are likely, and to provide updates on fires that do break out. Residents in bushfire-prone areas should take these warnings and updates seriously and leave their properties when advised to do so, especially when catastrophic fires are expected.

The advice given in this article is general and may not suit every circumstance.

Douglas Brown is the Principal of Bushfire Architecture a research consultancy which provides design advice to building professionals with clients in bushfire-prone areas. He also works as a casual academic at Western Sydney University. He was the recipient of a PhD scholarship from Bushfire CRC.