Bond after fire

Published Date
1 February 2017, Vol.132:210–218, doi:10.1016/j.conbuildmat.2016.11.131

Author 

• Éva Lublóy-Viktor Hlavička 

• Department of Construction Materials and Technologies, Budapest, Hungary

Received 13 September 2016. Revised 24 November 2016. Accepted 28 November 2016. Available online 8 December 2016. 

Highlights

• Bond strength after tempereture loading.
• •
  Concrete structures.
• •
  Fire load.
• •
  Statistical and nummerical modelling.

Abstract

Bond between concrete and reinforcement is investigated in this project after a thermal cycle at high temperature to measure bond residual properties. Six mixes were prepared with either quartzitic gravel or expanded-clay aggregates, and two types of fibers were adopted as well. Cubes were cast to measure the residual compressive strength of the various mixes and specimens reinforced with a single bar were prepared, to study the residual bond properties.

The results show that the higher the maximum temperature attained during the thermal cycle, the greater the decrease of both the compressive and bond strength. The latter, however, is more affected by the temperature than the former.

A relationship was also found between the decreasing bond strength and the decreasing compressive strength in residual conditions. This relationship was instrumental in modelling bond behavior in order to describe its response in terms of applied pull-out load versus bar slip (at the unloaded end of the bonded bar), and to make comparisons with the experimental results.

Keywords

Concrete

Reinforcement

Steel

Bond

Elevated temperature

Fire

Modelling

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Paths Forged by Man and Beast

On Trails: An Exploration

By Robert Moor

Simon & Schuster, 2016, 352 pages
“Without trails, we would be lost.” The simplicity of this statement in the prologue of Robert Moor’s first book, On Trails: An Exploration, opens the door to an in-depth study of trails, their purpose, and their meaning.

Exploring paths forged by creatures ranging from ants to elephants to modern humans, Moor attempts to define the scientific and practical elements which combine to form trails. He goes on a quest to understand pathways across natural systems, exploring everything from deer trails in Alabama to the extensive International Appalachian Trail, sections of which cross North America and Europe.

Moor himself is no stranger to trails. In 2009, he completed a hike on the 2,000-mile Appalachian National Scenic Trail (AT), the southern link to the International Appalachian Trail. It was this trip that sparked his deep interest in trails, and the best moments in the book come during his deep dives into what it took to hike the AT and the fascinating history of this route. 

Conceptualized in 1921 by forester and conservationist Benton MacKaye, the AT was to be “not merely a footpath through the wilderness but a footpath of the wilderness,” a trail to connect dispersed farms and wilderness camps in the northeastern US. The AT evolved into a long-distance trail for hiking and adventure, and now stands as one of the most famous trails in the world. Asked to clarify the AT’s purpose in his later years, 92 and nearly blind, MacKaye said it was “To walk, to see, and to see what you see!”

This statement gets at the heart of On Trails, which looks past simple definitions of trails to their real purpose, not only as pragmatic shortcuts from Point A to Point B, but as portals to fulfill what is desired by those who travel them. “It is impossible to fully appreciate the value of a trail until you have been forced to walk through the wilderness without one,” Moor states. 

This becomes a good starting point to define the meaning of a “hike” as well. As the book hits its stride 200 pages in, the author outlines the criteria for a truehike: “The land must meet certain conditions: it must be both remote and reachable; it must be devoid of enemies or bandits, but also free of too many tourists or technology; and, most importantly, it must be deemed worth exploring.”

Moor delves into the drama and intrigue of difficulties faced by hikers on the trail. In one inspired section, he details an adventure by accomplished naturalist and author Henry Thoreau as he attempts to climb Mount Katahdin at the northern terminus of the Appalachian Trail. Thoreau and his two companions turned back after experiencing heavy weather and difficult conditions, and Thoreau later wrote that it was among “the most treacherous and porous country” he ever traveled.

Overall, Moor’s examination of how and why humans and animals make trails includes some great revelations, but the author ultimately gets distracted on side paths. For example, we lose sight of the book’s main theme during a detailed look at the history of livestock. Moor also spends too much time bogged down in the minutiae of scientific studies, and his argument that the movements of ancient marine organisms represent the earliest example of trails is not convincing. It’s a stretch to say that small creatures were developing “trails” while they were simply moving about.

It would also have been useful for Moor to document more formally established trail systems throughout the world. One example is the National Trails System in the United States – 30 long distance trails that cover the entire country. Only two of these routes receive mention in the book, the AT and the Trail of Tears. A study of other profoundly important trails in the system, like the Nez Perce National Historic Trail, would have been more compelling than the author’s preoccupation with scientific studies. Routes like the Nez Perce Historic Trail preserve culture and history, as do many other trails around the world, several of which have been important to the survival of entire peoples.

For readers who want to explore the endlessly fascinating world of trails, On Trails is a reasonable place to start, but it’s just a beginning. 

—BILL BUCK

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Conflicting Maps Complicate Fight Against Fires, Deforestation in Indonesia

BY NITHIN COCA – DECEMBER 7, 2016

Divergent land ownership claims make it difficult to hold accountable those responsible for igniting blazes, say advocates 

Indonesia's annual fires are only getting worse, as last year’s massive event made clear. The fires alone made the country one of the world's biggest emitters of greenhouse gases in 2015, resulting in an estimated 1.6 billion tons of carbon equivalent emissions. Researchers estimate that more than 100,000 people in Indonesia and neighboring countries may have died due to the resulting particulate pollution. Since the largely preventable fires, which were caused by farmers burning forests to clear land and exacerbated by El Niño-related dryness, subsided in October 2015, there have been myriad efforts to try to prevent similar scenarios in future years. Key to the success of all of these efforts, and to the future of Indonesia's forests, may be the One Map initiative.

Photo by Rainforest Action NetworkFires in Indonesia, which are often set to clear land for palm oil and timber development, are a major contributor to global emissions. Advocates believe conflicting land ownership maps are contributing to the problem by hampering enforcement efforts.

One Map aims to address what many activists, experts, and private companies see as a central barrier to stopping illegal deforestation and burning in Indonesia: the existence of numerous, conflicting land ownership maps among different levels of government, as well as private sector actors. Conflicting views of ownership make it nearly impossible to hold accountable those igniting blazes across the country. Not to mention that reluctance among some actors to even share their maps with the public leads to gaps in information.

The One Map initiative aims to rectify these divergent views and fill information gaps in order to provide a foundation for anti-deforestation enforcement efforts across the country. The United States Agency for International Development, the US Forest Service International Programs, and several environmental organizations are contributing to the challenging effort.

“The Indonesian people have a right to know what is happening on the ground,” said Longgena Ginting, strategy and analysis director with the environmental nonprofit Greenpeace Indonesia, which has been contributing to the One Map initiative, said in a statement. “The government should release the maps it has and name and shame companies that refuse to publish their own maps.”

However, the task of creating a single, accurate map is much easier said than done. Indonesia suffered through decades of poor land management practices due to rampant corruption and a national development policy that focused on resource-driven economic growth. This led to horrific deforestation, even in so-called protected areas, and countless illegal land grabs from indigenous groups. The national government has yet to implement a 2013 Supreme Court decision blocking government actors from selling indigenous-held land and reaffirming the rights of indigenous peoples to manage the lands on which they live. 

Environmentalists know the One Map initiative is a complicated one — they have been working on the effort for years. They came close to success in 2010 when then-President Susilo Bambang Yudhoyono's cabinet announced that it would work on releasing One Map. Though the cabinet began the project, six years later there is still no One Map. In the meantime, Indonesia has overtaken Brazil — a country with four times as much forested land — as the world leader in deforestation by total area.

Ideally, One Map would put an end to these overlapping concessions issues and make it clear on whose land fires are being set. It would empower law enforcement, activists, and land-owners themselves to participate in land management activities by making accessible basic information about land rights and responsibilities.

“As we don't know who owns the land, we never get anyone held responsible,” Annisa Rahmawati, forests campaigner with Greenpeace Indonesia, said.

The severity of last year's fires made it clear to many that it was time to stop waiting for the Government to act on the One Map initiative. Earlier this year, Greenpeace Indonesia released its own version of One Map, called Kepo Hutan, which loosely translates to “Curious about Forests.” It is an online, open-source tool that collects forest concession data from various sources — including the Roundtable on Sustainable Palm Oil and companies like Asia Pulp & Paper that have released concession information — and integrates it with satellite data about fires, making it easier to understand where, and on whose land, fires are burning. While it can't be as comprehensive as One Map without access to conflicting Government maps, it is a model that shows the path forward.

“[We wanted to] set an example for the kind of transparency we expect from the government and companies,” Rahmawati said, adding that the tool is already being used by journalists, local activists, and even businesses to monitor what is happening on the ground throughout Indonesia.

The nonprofit World Resources Institute (WRI) is taking a different approach, working at the local level and focusing on the Indonesian province at the center of the deforestation fight: Riau. Located on the island of Sumatra, more than 50 percent of Riau’s forest cover has been lost during the last 30 years, mostly due to the rapid growth of oil palm and paper pulp plantations.

WRI is working to figure out the origins of complex land claim conflicts in the province, and hopes that a bottom-up approach and improved clarity around local land rights will encourage buy-in from all involved parties when it comes to developing solutions. The nonprofit estimates it will take five years to complete the process and release a comprehensive One Map for Riau.

“The thing is, everyone knows that to synchronize maps, you need to go down to the field,” said Nirarta ‘Koni’ Samadhi, the country director for WRI Indonesia. “You cannot do it by sitting at the national level.”

“After five years, what we aspire to achieve is not simply the One Map, per se, but a new system of Government delivery that is [participatory],” Samadhi added.

The many challenges of completing the One Map project are compounded by the urgency of the situation. The map must be accurate in order to be useful, but it must also be done quickly enough to save Indonesia’s precious tropical forests and reduce the country’s emissions. The One Map initiative is ambitious, as it must be, and many agree the sooner it can be done, the better for Indonesians, its haze-breathing neighbors, and the planet.

Nithin Coca
Nithin Coca is a freelance journalist who focuses on environment and economic issues in developing countries, and has specific expertise in Southeast Asia. Nithin's feature and news pieces have appeared in global media outlets including Al Jazeera, Quartz, Atlantic Cities, SciDev.Net, Southeast Asia Globe, The Diplomat, and numerous regional publications in Asia and the United States

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Reframing the Climate Narrative

BY KARINA GONZALEZ

After 11 days of sleeping no more than three hours a night during the Paris Climate negotiations last December, I was more exhausted than I’d ever been, mentally, physically, and emotionally. While running between meetings and events and press conferences, I accidentally walked into an event hosted by a tech company. The speaker claimed to have the solution to climate change. This process he explained, “involves using filters, chemical reactions, and other special materials to collect greenhouse gases like carbon dioxide” from the atmosphere.

The speaker followed the same template the United Nations often uses, viewing greenhouse gases as the only problem. This mindset isolates the direct causes of climate change and does not address the broader systemic problems that allow climate change to exist in the first place. It uses CO₂ emissions as the agreed upon value, the number to minimize, and the metric upon which to base policy. It makes decisions by the numbers.

Doing this creates three problems: The unmeasurable and the qualitative are devalued; the metric applied perpetuates existing biases and power relationships; and it promotes the illusion of predictability and control that obscures the likelihood of unintended consequences.

This approach sits comfortably in our culture, which tries to solve problems by isolating the direct causes of issues rather than addressing the broader systemic problems that allow these problems to exist in the first place. As the war on crime, the war on drugs, and the war on terror demonstrate, causation is seldom linear. Crime, drugs, and terrorism are symptoms of deeper, systemic disharmony and addressing their direct causes in isolation cannot and will not be successful.

Climate change is like this too.

On December 12, 2015, the final day of the Paris Climate talks, I decided not to head to the Le Bourget Conference Center, where the negotiations were taking place, but rather, to attend the D12 climate march in Paris. Thousands of people from all over the world flooded the city streets to demonstrate that no matter what heads of state decided, we would continue organizing for climate justice. At that moment, I felt as if we were finally a big, beautiful, unified movement. 

I was filled with enormous hope as the much-awaited final agreement draft was released. Surrounded by cameras, police, and chanting marchers, I read through the draft on my smartphone. My feelings of hope quickly turned to despair as I read more and more of the text. Though it mentioned the importance of keeping global warming under 1.5 degrees Celsius, the limited commitments from countries still added up to well over 3 degrees of warming. 

I spent most of my time in Paris like this: oscillating between excessive hope and deep despair, feeling simultaneously more disempowered and empowered than I’d ever felt in my entire life. 

The way we’ve dealt with climate change in these international negotiating spaces emphasizes the global over the local, the distant over the immediate, the measurable over the qualitative. This oversight is part of the same mentality that is at the root of the climate crisis to begin with. It is the mentality that sacrifices what is precious, sacred, and immediate for a distant end. It is the mentality of instrumentalism that values other beings and the Earth itself in terms of their utility. It is the hubris of believing we can predict and control the consequences of our actions. 

Climate change is multifactorial; it cannot be addressed by linear strategies for reducing CO₂emissions. I am not arguing that we shouldn’t work to reduce direct emissions, but rather that technological approaches on their own cannot solve the problem. The problem lies in our relationship with each other and the Earth. Climate change is simply a symptom of this relationship.

This is why I focus my activism on fossil fuel divestment. Never in the 22 years of international climate negotiations has there been a single proposal to limit fossil fuel production. This is a testament to the current narrative around climate change, which sees climate as an issue of regulating and trading greenhouse gases. Divestment aims to reframe the climate narrative as a moral problem. In normal politics, efforts like these – that sacrifice what is sacred for a distant end – are a sad but necessary price of doing business. In a moral crisis, they’re intolerable. 

Karina Gonzalez is a student leader of Fossil Free North Arizona University, and a 2016 Brower Youth Award Winner.

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Crop Responses to Nitrogen

Published Date
pp 2661-2681

• Author 

• Gilles Lemaire 

Definition

A prerequisite for the analysis of crop responses to nitrogen (N) is the determination of the plant nitrogen content and repartition. How much N is incorporated within plants and crops? Within which plant tissue? For which physiological function? Thus, according to the answers to these questions, it is possible to determine a critical plant nitrogen status as the minimum plant N concentration that allows the maximum plant (or crop) growth rate. It has been demonstrated that this critical plant N concentration decreases as plant grows as the result of an ontogenetic plant architecture development leading to a dilution of N compounds within increasing proportion of free-N compounds as plant gets bigger. This N dilution process can be formulated through a negative power relationship between plant N concentration and crop mass. This critical N dilution curve allows the discrimination of situations of N deficiency (below the curve) and situa ...

This is an excerpt from the content

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