Construction Materials

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<img src="https://counter.theconversation.edu.au/content/57114/count.gif" alt="The Conversation" width="1" height="1">
GUEST OBSERVER
By itself, concrete is a very durable construction material. The magnificent Pantheon in Rome, the world’s largest unreinforced concrete dome, is in excellent condition after nearly 1,900 years. And yet many concrete structures from last century – bridges, highways and buildings – are crumbling. Many concrete structures built this century will be obsolete before its end.
Given the survival of ancient structures, this may seem curious. The critical difference is the modern use of steel reinforcement, known as rebar, concealed within the concrete. Steel is made mainly of iron, and one of iron’s unalterable properties is that it rusts. This ruins the durability of concrete structures in ways that are difficult to detect and costly to repair.
While repair may be justified to preserve the architectural legacy of iconic 20th-century buildings, such as those designed by reinforced concrete users like Frank Lloyd Wright, it is questionable whether this will be affordable or desirable for the vast majority of structures. The writer Robert Courland, in his book Concrete Planet, estimates that repair and rebuilding costs of concrete infrastructure, just in the United States, will be in the trillions of dollars – to be paid by future generations.
Steel reinforcement was a dramatic innovation of the 19th century. The steel bars add strength, allowing the creation of long, cantilevered structures and thinner, less-supported slabs. It speeds up construction times, because less concrete is required to pour such slabs.
These qualities, pushed by assertive and sometimes duplicitous promotion by the concrete industry in the early 20th century, led to its massive popularity.
Reinforced concrete competes against more durable building technologies, like steel frame or traditional bricks and mortar. Around the world, it has replaced environmentally sensitive, low-carbon options like mud brick and rammed earth – historical practices that may also be more durable.
Early 20th-century engineers thought reinforced concrete structures would last a very long time – perhaps 1,000 years. In reality, their life span is more like 50-100 years, and sometimes less. Building codes and policies generally require buildings to survive for several decades, but deterioration can begin in as little as 10 years.
Many engineers and architects point to the natural affinities between steel and concrete: they have similar thermal expansion characteristics, and concrete’s alkalinity can help to inhibit rust. But there is still a lack of knowledge about their composite qualities – for example, in regard to sun-exposure-related changes in temperature.
The many alternative materials for concrete reinforcement – such as stainless steel, aluminium bronze and fibre-polymer composites – are not yet widely used. The affordability of plain steel reinforcement is attractive to developers. But many planners and developers fail to consider the extended costs of maintenance, repair or replacement. 
There are technologies that can address the problem of steel corrosion, such as cathodic protection, in which the entire structure is connected to a rust-inhibiting electric current. There are also interesting new methods to monitor corrosion, by electrical or acoustic means.
Another option is to treat the concrete with a rust-inhibiting compound, although these can be toxic and inappropriate for buildings. There are several new non-toxic inhibitors, including compounds extracted from bamboo and bacterially derived “biomolecules”.
Fundamentally, however, none of these developments can resolve the inherent problem that putting steel inside concrete ruins its potentially great durability.
<h2>The environmental costs of rebuilding</h2>
This has serious repercussions for the planet. Concrete is the third-largest contributor to carbon dioxide emissions, after automobiles and coal-fuelled power plants. Cement manufacturing alone is responsible for roughly 5 percent of global CO₂ emissions. Concrete also makes up the largest proportion of construction and demolition waste, and represents about a third of all landfill waste.
Recycling concrete is difficult and expensive, reduces its strength and may catalyse chemical reactions that speed up decay. The world needs to reduce its concrete production, but this will not be possible without building longer-lasting structures.
In a recent paper, I suggest that the widespread acceptance of reinforced concrete may be the expression of a traditional, dominant and ultimately destructive view of matter as inert. But reinforced concrete is not really inert.
Concrete is commonly perceived as a stone-like, monolithic and homogeneous material. In fact, it is a complex mix of cooked limestone, clay-like materials and a wide variety of rock or sandy aggregates. Limestone itself is a sedimentary rock composed of shells and coral, whose formation is influenced by many biological, geological and climatological factors.
This means that concrete structures, for all their stone-like superficial qualities, are actually made of the skeletons of sea creatures ground up with rock. It takes millions upon millions of years for these sea creatures to live, die and form into limestone. This timescale contrasts starkly with the life spans of contemporary buildings.
Steel is often perceived to be inert and resilient too. Terms such as “Iron Age” suggest an ancient durability, although Iron Age artefacts are comparatively rare precisely because they rust. If construction steel is visible, it can be maintained – for instance, when the Sydney Harbour Bridge is repeatedly painted and repainted.
However, when embedded in concrete, steel is hidden but secretly active. Moisture entering through thousands of tiny cracks creates an electrochemical reaction. One end of the rebar becomes an anode and the other a cathode, forming a “battery” that powers the transformation of iron into rust. Rust can expand the rebar up to four times its size, enlarging cracks and forcing the concrete to fracture apart in a process called spalling, more widely known as “concrete cancer”. 
I suggest that we need to change our thinking, to recognise concrete and steel as vibrant and active materials. This is not a case of changing any facts, but rather of re-orientating how we understand and act on those facts. Avoiding waste, pollution and needless rebuilding will require thinking well beyond disciplinary conceptions of time, and this is especially true for the building and construction industries.
The collapsed civilisations of the past show us the consequences of short-term thinking. We should focus on building structures that stand the test of time – lest we end up with hulking, derelict artefacts that are no more fit for their original purpose than the statues of Easter Island.
Guy Ceulemans is associate lecturer, UNSW Australia and author for The Conversation. He can be contacted <a href="https://theconversation.com/profiles/guy-keulemans-182421" target="_blank">here</a>.
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jchancellor-FAypfDUnLy

The rust problem with reinforced concrete

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The use of cheap building materials imported from China could be compromising people's safety, according to construction materials company Boral Limited chief executive Mike Kane.
Concerns about cladding on buildings have been raised in the aftermath of the fire at London's  Grenfell Tower last week in which at least 79 people are feared killed.
The fire has led to speculation about the causal factors and raised questions about the <a href="https://www.urban.com.au/expert-insights/71811-london-apartment-tower-fire-and-possible-issues-in-australia" target="_blank">role of building products</a>. 
Kane, who saw several of his products boycotted by unions in Australia due to industrial action, said he was concerned about cheaper materials flooding into the country and being used for the apartment boom, The Australian Financial Review reported.
"The lure of cheap Chinese products that don't meet western standards is part of what has happened in England and Melbourne," Kane told the AFR.
"They do tend to be cheaper and that can be an incentive [for developers]."
The increased use of environment-efficient materials over safety standards could also pose a risk, added Kane.
"There are people who are so focused on climate change that they are forgetting safety. We have multiple obligations when building but the first is structural - the building shouldn't collapse and fire safety is fundamental of all."
Cladding on buildings may not comply with the Building Code of Australia either because of incorrect labelling - an issue industry bodies such as Ai Group have campaigned over - or because builders or subcontractors incorrectly use a product in a role other than that for which it is suited.
Melbourne's Lacrosse building, which caught fire in 2014, is a case in point. Aluminium composite panels of the sort used in Lacrosse are up to standard when used the right way internally but not when put on the outside of the building, as they are not strong enough to withstand fire. 
Last year, the Victorian Building Authority regulator referred building surveyor Anastasios Galanos for disciplinary action by the Building Practitioners Board, alleging he breached the Building Act and regulations when he certified the Lacrosse tower as compliant. 
Last July, imported roofing panels in Perth's newly built Children's Hospital were discovered to contain asbestos. A week later Australian Border Force suspended all imports by materials supplier Yuanda Australia. 
Private construction group Built chief executive Brett Mason also questioned some of the quality of Chinese products in the market.
"There was a flood of products that came in with the right stamps but some of the fittings and cladding were poorer quality and in some cases it looked as though it may not have been given genuine approval," Mason said.
"We now go and test everything ourselves even if it has a stamp of approval on it."
 
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jonathanchancellor-7SQnKwU6yx

Cheap Chinese building materials pose safety risk, says Boral's Mike Kane

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GUEST OBSERVATION
Would you live in a house made of fungus? It’s not just a rhetorical question: fungi are the key to a new low-carbon, fire-resistant and termite-deterring building material.
This type of material, known as a mycelium composite, uses the Trametes versicolor fungus to combine agricultural and industrial waste to create lightweight but strong bricks. It’s cheaper than synthetic plastics or engineered wood, and reduces the amount of waste that goes to landfill.
What a fun guy
<img src="https://images.theconversation.com/files/222698/original/file-20180612-182738-1ih1ie4.png?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip" alt="">
Fungal brick prototypes made from rice hulls and glass fines waste. Tien Huynh, Author provided
Working with our colleagues, we used fungus to bind rice hulls (the thin covering that protects rice grains) and glass fines (discarded, small or contaminated glass). We then baked the mixture to produce a new, natural building material.
Making these fungal bricks is a low-energy and zero-carbon process. Their structure means they can be moulded into many shapes. They are therefore suited to a variety of uses, particularly in the packaging and construction industries.
A staple crop for more than half the world’s population, rice has an annual global consumption of more than 480 million metric tonnes and 20% of this is comprised of rice hulls. In Australia alone, we generate about 600,000 tonnes of glass waste a year. Usually these rice hulls and glass fines are incinerated or sent to landfill. So our new material offers a cost-effective way to reduce waste.
<h2>Fire fighter</h2>
Fungal bricks make ideal fire-resistant insulation or panelling. The material is more thermally stable than synthetic construction materials such as polystyrene and particleboard, which are derived from petroleum or natural gas.
<img src="https://images.theconversation.com/files/222694/original/file-20180612-182738-2kd2vm.png?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip" alt="">
Rice hulls, glass fines and the mixture of rice, glass and fungus, before baking. Wikipedia/Tien Huynh, Author provided
This means that fungal bricks burn more slowly and with less heat, and release less smoke and carbon dioxide than their synthetic counterparts. Their widespread use in construction would therefore improve fire safety.
Thousands of fires occur every year and the main causes of fatalities are smoke inhalation and carbon monoxide poisoning. By reducing smoke release, fungal bricks could allow more time for escape or rescue in the event of a fire, thus potentially saving lives.
Bug battler
Termites are a big issue: more than half of Australia is highly susceptible to termite infestations. These cost homeowners more than A$1.5 billion a year.
Our construction material could provide a solution for combating infestations, as the silica content of rice and glass would make buildings less appetising to termites.
The use of these fire-and-termite-resistant materials could simultaneously revolutionise the building industry and improve waste recycling.
<img src="https://images.theconversation.com/files/222699/original/file-20180612-182733-qjotvb.png?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip" alt="">
 Figure 3. Termite infestation zones in Australia. termitesonline.com.au, Author provided
This is an exciting time to get creative about our waste. With China no longer buying Australia’s recycling – and new rules reducing plastic use in Australian supermarkets – we have the chance to move in line with communities in Japan, Sweden and Scotland that have near-zero waste.
Fungal bricks could be just one example of the creative thinking that will help us get there.
Tien Huynh, Senior Lecturer in the School of Sciences, RMIT University
Mitchell Jones, PhD Student, RMIT University
This article was originally published on <a href="http://theconversation.com" target="_blank">The Conversation</a>. Read the <a href="https://theconversation.com/scientists-create-new-building-material-out-of-fungus-rice-and-glass-98153" target="_blank">original article</a>.
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