'Green' liquid asphalt cement
-by Korky Koroluk
Researchers looking for alternatives to products made from fossil fuels have been interested in algae for some time. Some of the tiny plants contain a lot of natural oil. That's why science has made significant progress in using them to manufacture "biodiesel" as a sustainable alternative to conventional diesel.
A group of researchers in France have come up with a way to use algae in the manufacture of "green" asphalt, since it's made without using petroleum.
Microalgae is useful for making more than biodiesel. French researchers have recently demonstrated the viability of what they're calling bioasphalt. They've published the results of their work in the April issue of the journal ACS Sustainable Chemistry & Engineering.
Microalgae are single-celled plants that range in size from a few micrometres to a few hundreds micrometres, depending on their species. They have no roots, stems or leaves, but they are capable of performing photosynthesis and are thus important for life on earth.
Scientists tell us there are somewhere between 200,000 and 800,000 species, only about 35,000 of which have been scientifically described. Researchers in France have used them to make compounds of use to the cosmetics industry, and it is the residue from that process that they use to create a black, viscous material that closely resembles the asphalt derived from oil petroleum.
The chemical composition of bioasphalt is completely different from its oil-based counterpart. But it can be used to coat mineral aggregates, instead of coating them with what road builders call liquid asphalt cement, or bitumen.
Researchers have already found that aggregates treated with bioasphalt are capable of supporting mechanical loads. Now they're testing its behaviour over time, as well as studying costs in an attempt to evaluate its potential for large-scale production. But algae-based asphalts are not the only bioasphalts being studied.
In the Netherlands, research is being done in the use of lignin, a natural adhesive material, in another form of synthetic asphalt. Lignin gives structure to all kinds of plants and trees. It is, for example, an important part of straw.
People have long guessed that both algae and straw could be important as we make the transformation to a low-carbon economy, and several governments and companies have shown interest in these two scientific projects.
Dutch researchers are busy testing their lignin-based bioasphalt, and expect to be able to improve functional properties of their asphalt, including its rolling resistance, and making road running surfaces quieter.
As part of that, they hope to have a section of road and/or a parking area paved with their lignin bioasphalt this year, so they can enlarge their testing program.
Liquid AC has been an excellent product, used by road builders and in the production of roofing felt, and for sealing flat or low-slope roofs. But it is obtained from the distillation of crude oil, a process that releases a lot of carbon dioxide, a greenhouse gas. If we're to make the transition to a low-carbon economy, we'll need to have access to not only biofuels, but bioasphalts as well. The work of these teams in France and Holland will be closely watched.
To Read more: http://journalofcommerce.com/Technology/News
The Louvre Museum, Abu Dhabi
Ultra-High Performance Fibre Reinforced Concrete
From its start to its completion this year, The National has been given unprecedented access to the building of Louvre Abu Dhabi, the first of the crown jewels of the new Saadiyat Island Cultural District.
Simplicity can be deceptive, as the white concrete cladding of the Louvre Abu Dhabi will reveal. The museum's panels are as intricate in design as the canopy which will cover them, with both structures complementing one another.
Such is the case with the cladding that now envelops the galleries that are nearing completion beneath the giant saucer-shaped roof of Louvre Abu Dhabi on Saadiyat Island.
At first sight, there could not be a greater contrast between the 180 metre-wide canopy and the "museum city" that shelters beneath it.
The complexity of the museum's mighty canopy is visible for all to see. It is dense, multi-layered and interconnected, like a giant woven constellation or some enormous upturned nest.
The galleries that now sit beneath, however, could not appear more different. Dressed in what look like enormous blocks of smooth, finely-cut white stone, the buildings are the very model of simplicity; the stark contrast is intended, of course.
In one important respect, however, the museum's buildings and canopy are more similar than they seem. Both rely on a complex system of cladding to achieve the effects desired by their architect, Ateliers Jean Nouvel (AJN).
In the case of the canopy, that cladding consists of 5,000 tonnes of supersized structural steel and 7,850 aluminium "stars", while in the case of the buildings it involves 4,680 panels of a substance called ultra-high performance fibre reinforced concrete.
AJN has designed Louvre Abu Dhabi's buildings to echo the architecture of a traditional Arabian community or souq, but it also hopes it will communicate a sense of serenity, strength and gravity of the kind that results from age-old processes and construction techniques.
"It needs to make sense overall. To create an illusion, you have to make every effort to create the sense that is intended," says Damien Faraut, the site project leader with AJN from his team's permanent office at the museum's construction site.
"We want the appearance of dry, Cyclopean stone assembly," the architect explains, referring to the kind of massive masonry that is more usually found in ancient Greek citadels such as Tiryns and Mycenae.
To achieve what Mr Faraut describes as an "archaic effect" on the museum's immaculately smooth walls however, Louvre Abu Dhabi's designers have had to employ a material that could not be more state-of-the-art.
Ultra-high performance fibre reinforced concrete is normally used on large-scale infrastructure projects such as tunnels and bridges. Unlike traditional reinforced concrete, which uses steel for its reinforcement, the museum's specialist concrete relies on a matrix of glass fibres to increase its compressive and tensile strength.
It also benefits from minimal shrinkage and impermeability, an important quality for a material that will regularly come into contact with the seawater that will eventually flow between the museum's precincts, turning the whole complex into a miniature Venice on the Arabian Gulf.
"The cladding is going to be very exposed," Mr Faraut explains. "Some panels will be permanently submerged in seawater, so the material needs to be extremely strong and non-porous, and this material is the technical answer to that."
Louvre Abu Dhabi's concrete cladding is manufactured by Fibrex, an Abu Dhabi-based construction company that has used similar materials on the facades of the Sheikh Zayed Grand Mosque, the Emirates Palace hotel and the Foster + Partners-designed Abu Dhabi World Trade Centre and Central Market.
At Louvre Abu Dhabi, the result is a cladding system that operates like a giant three-dimensional jigsaw composed of more than 4,680 pieces, 3,821 of which are unique.
"Every one is unique because there is absolutely no repetition in the size or the height of the buildings," says the architect, describing subtle differences in scale and composition that are intended to communicate an almost impalpable sense of a settlement that has been hand-crafted over time.
"The position of the doors or the openings and the proportions are always slightly different, so that is why all of the panels are different."
As Stuart Keane, the senior owner's representative with the museum's developer, Abu Dhabi's Tourism & Development Investment Company, explains, the bespoke nature of the cladding panels means they have much more in common with the museum's dome above than appearances might suggest.
"Similar to the stars [in the canopy], each panel has its own unique location. Panel one, for example, cannot connect to panel five and each piece has to be installed in a certain sequence if all the cladding is to fit," he says.
"This means that there's a lot of coordination required to have the panels fabricated and ready for installation, and the construction sequence of the buildings dictates the fabrication process.
"Each building's structural concrete has to be completed, the waterproofing has to be done, as does the insulation, before each panel can be installed."
The largest panels, which are uniform in size, are being used to clad the museum's "wearing wall", which will be partially submerged once the Louvre Abu Dhabi site is flooded and seawater surrounds the museum. They measure up to 30 metres square and weigh in at almost 12 tonnes.
"Because they will be exposed to continuous wave action and because, theoretically, a boat might hit them, the panels on the wearing wall have stainless steel reinforcement on the inside," says Mr Keane.
A subtle exercise in architectural composition, all of the panels have a chalky, stone-like appearance that flips between brilliant and off-white, flat matte and gloss depending upon the light, the weather conditions and the perspective of the viewer.
"It's not a flat matte finish. It looks that way from certain angles, but when you look at it from an oblique angle you start to see some reflection," says Mr Faraut.
"We were able to adjust the colour and the glossiness to a very precise level so the final selection was an extra-white semi-gloss."
The ability to ensure a consistent finish was another reason why the material was selected for the museum's cladding.
"From panel one to panel 3,000, it will always have the same colour," explains Mr Keane.
"It's also very easy to repair. In any construction, panels might get chipped as it is being installed but with this, if pieces are scratched or chipped, they can be sanded out and patched, and that blends right in, whereas if it was a regular concrete panel, you'd always see the patch."
The finish of the museum's external walls may seem like a minor detail, but as Mr Faraut explains, the way they respond to light is crucial to the success of a building whose design is predicated on the control and manipulation of what promises to be the museum's piece de resistance, Jean Nouvel's much-illustrated but little understood Rain of Light. Created by nothing more than the movement of the Sun and its passage through Louvre Abu Dhabi's canopy, the Rain of Light will bathe the museum's precincts in a constantly shifting display of kaleidoscopic, reflected light.
"Everybody knows the effect of light as it passes through [the canopy of] a tree. You can see that it creates round spots, not because of the shape of the openings [in the canopy] but because of the shape of the Sun itself," says Mr Faraut.
"What is happening under the dome is similar, but it is also a little bit more than that. If you had just one layer with holes in it, you would see the shape of the opening being traced on the ground with some rounding around the edges because of the shape of the Sun. It's not a triangle, for example, it's a triangle with round edges because the Sun is round," the architect explains.
"If you have one layer, the spot moves as the Sun moves, but if you have two layers, the combination between the openings in the two layers changes as the angle of the Sun changes.
"So, we have four layers [of cladding] above the dome and four layers below so the spots will not only move but appear and disappear because of the changing relationship between those openings and the angle of the Sun."
The cladding of the museum's precisely finished and pristine walls may be less starry than the cladding employed in its canopy, but both play a crucial role in the building's sense of spectacle and drama, as Mr Faraut explains. "The surfaces of the building envelope are going to receive this light and the simplicity of their shapes. Their very flat and consistent character is the white page on which all of this can be accurately read. We will be able to read and contemplate this fantastic cinematography on these very simple white planes."
Source: http://www.thenational.ae/uae
Acceptance of Tilt-Up Concrete Continues to Rise
Over the past 10-plus years, much has been published regarding the capacity of tilt-up to deliver multistory, irregularly shaped, complex projects. The Tilt-Up Concrete Association's Annual Tilt-Up Achievement Awards Program has evidenced the ever increasing variety of project types, forms and sizes that have since become commonplace. The reputation of tilt-up as solely a way to construct plain big boxes has begun to fade and tilt-up is now regularly considered for almost every project type, depending on the region. "From warehouses and functional origins, tilt wall has begun to transverse building types at an amazing rate," writes Jeffrey Brown of Powers Brown Architecture. "While there is still much work to do regarding the seriousness with which architects and academia take the method as an innovative way of form making, tilt-up has come a long way."
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Still, among all of these efforts and the success tilt-up has had expanding into new markets, it is important to acknowledge and discuss the relevance and dominance tilt-up enjoys when it comes to the construction of the building type known within the industry as the rigid wall, flexible diaphragm, large box structure. "There is simply no way to beat tilt-up when constructing a building of this nature," says Mike Wolstenholme, National Tilt-Up Sales Manager for Meadow Burke. "It remains the most cost-effective, time-sensitive and efficient way to construct a warehouse box and, therefore, it remains the bread and butter of our industry." Although "simple" is often used to describe these structures, many times the projects are far from simple either in structure, configuration or site adaptation. The moniker "simple", however, is used to refer to the relationship of the perimeter wall envelope supporting an expansive roof with few juxtapositions or features that present challenges to engineering.
Perfecting the box
"Are we getting better at the simple buildings? Yes," says Laurence Smith, P.Eng., Vice President of Engineering with Lindsay Construction in Dartmouth, Nova Scotia, Canada, "and the improvements exist across the entire process. From the time before the building is designed to the setting of the last panel, the process continues to get better."
One factor contributing to increased efficiencies in some markets, according to Smith, is their maturation. Eight to ten years ago, Smith had to sell the concept of tilt-up to clients. Now they come wanting it from the beginning. Even so, as early as five years ago Smith says clients would come with a building designed in another system that required conversion to tilt-up in order to deliver the advantages they desired. "The process of converting these projects, while worth it, took so much energy and time," said Smith. "In mature markets, much of this is gone."
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Smith explained that new markets can present challenges in the field as well. "With the oil industry boom in Canada, companies were bringing in these large cranes to regions that before had no access to the machinery needed to lift large panels efficiently," says Smith. Because of this, Lindsay Construction was able to expand and bring tilt-up to markets unfamiliar with the building system. Smith explained that at home there were one or two cranes and one or two crane operators and for them lifting panels was second nature. As Smith visited jobsites in this new region and asked those who had never seen anything like this to raise their hand, he was only slightly surprised to find that he was one of the only ones with his hand down. "It's exciting and extremely gratifying to introduce something completely new," said Smith, "but it obviously comes with some complexity. I tell them, take the first one slow. They listen. Then I say, let's do another."
This penetration of tilt-up into new markets continues to improve efficiencies as more clients and contractors become familiar with the method. Contractors in Florida, Texas, and California haven't encountered these issues for years. However, in these markets, advancements in lifting and bracing technology have fueled greater efficiency where according to Wolstenholme, "large, simple boxes are coming back in a huge way."
"Although we've done a large number of Class-A office buildings in tilt-up with fantastic results, the economy and speed that tilt-up brings to warehouse type construction is unmatched," says Chip Dehart, an Estimator for Suntec Concrete, Inc., one of the largest commercial concrete construction companies in the Southwest. "We can put up a 400,000 square-foot warehouse (footings, slabs, and panels erected) in six weeks or less."
Dan Dancer, Product Line Manager for Dayton Superior, an industry leader in the design, manufacturing and distribution of specialized concrete construction products, says, "By in large, the majority of our work for the tilt-up industry comes from single-story tilt-up projects." For that reason, they and other industry manufactures continue to develop simpler, faster and therefore more economical ways of forming, lifting and bracing tilt-up panels.
"Meadow Burke has an extremely fast, safe and strong lift system called Super Lift III," says Wolstenholme. "It allows for panels to be erected at a fast rate, especially in the repetitive process." Wolstenholme explained that engineers work to keep rigging changes to a minimum during lifting and bracing engineering, which facilitates faster erection times.
Methods of securing the braces to the slab also continue to improve. "We have developed strong, safe and fast brace-anchoring systems such as the Slam Anchor and the MB Brace Bolt," says Wolstenholme. "The system allows for quick attachment of the braces to the floor while meeting the strict brace loads required." Even the average height of the panels has changed in the simple big box as developers have required greater interior clear heights for their tenants. The taller the panel, the greater the force on the floor slab during the bracing period, and this can be a real challenge.
Additionally, bracing to the outside of the building is becoming a more and more common practice. Initially developed primarily for multistory projects and/or projects with a relatively small footprint, these larger "simple" projects can have issues related to the preservation of the slab (no holes) and the facilitation of quicker, more efficient steel erection. The experience in bracing to the outside from the newer markets has made this strategy a good option. Manufacturers continue to refine lifting and bracing systems, making them more efficient and versatile. Today, helical ground anchoring systems have become the primary method used to brace panels to the outside, significantly speeding up the process and applying greater safety around the perimeter where large blocks of concrete, called "deadmen", used to be found.
Keeping it simple and turning a profit
In addition to being the building type that brings out the very best of tilt-up's efficiencies, many contractors would agree that these projects are also the most profitable. Clay Fischer, CEO at Woodland Construction Company, Inc. once proclaimed, "If we won an award for the project, we probably didn't make much money on it." Many have shared this opinion as they jokingly describe the complexity and unforeseen challenges many times found in projects that the judges often react to most favorably. It also implicates that projects many consider mundane are the ones where contractors can produce the best results for their profitability.
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According to Smith, "It's not the size of the project that is necessarily the determining factor for efficiency or profitability. I can look at a basic project (without high-end finishes) under construction, and based on the simplicity of the bracing scheme, give you a ball-park square foot cost," Smith explains. "The two are directly related in my experience." No matter the size of the box, what Smith refers to is the relative simplicity to which the big box building type is known. Panels are routine or repetitive in their size, bracing schemes and lifting layouts are not altered significantly, and openings are repetitive. They account for as basic an approach to both cost estimating and construction as possible in any industry, but especially so for tilt-up.
When asked about the best size for tilt-up projects with this idea in mind, Smith, a past president of the Tilt-Up Concrete Association, explained that everything goes full circle. "With regards to the feasibility of a tilt-up project and its economies related to size, a 20,000 square-foot project was once considered the minimum," says Smith. "Then it went down to 15,000 square feet, then 10,000 square feet. We have done 5,000 square-foot projects very economically and the clients are happy." For Smith, it is all about the simplicity and efficiency of the design.
Projecting the future
While there is no science behind the prediction of what the future holds for the industry, one thing is clear: the economy has rolled around to the return of this big box. Companies like Amazon, Wal-Mart and many more are once again committing to massive projects with a basic perimeter envelope and acres of roof area. This has the tilt-up construction industry poised to display the effectiveness and the efficiency that became the calling card for many contractors during the 90's and early part of this millennium.
The past is still not the future, however, and today's new big box projects have implemented many design changes that are introducing new challenges to construction professionals. New requirements for energy performance and air barrier construction are ushering in a new era of insulated wall technology to a building category that had been largely exempt from the control of energy consumption.
"While we are always evolving," says Smith. "That one market will never go away. When that building comes along, and tilt-up is an option, it will always be the best solution." Tilt-up's position among other methods of constructing relatively large low-rise hard-walled structures is rarely challenged. While tilt-up is being employed as a project solution for an ever-increasing variety of building types, these projects continue to exploit some of the most valuable of the building system's advantages, and they are only getting better.
To Read More:http://www.forconstructionpros.com/article