CarbonNeutral Road
Posted by: ashmann in: ● September 8, 2009
Making our roads green matters, and it matters a lot. We may not realize it, but under that smooth, clean strip of asphalt we drive on — and the layers of rock and soil further down — lies an economic and environmental disaster that has been kept quiet for too long.
And yet, new technologies and new mindsets have begun evolving to help transform traditional blacktop. As the world turns its attention to addressing long overdue ecological and economic challenges, we have an unprecedented opportunity. Driving cleaner cars and commercial vehicles on dirty roads solves only a part of the problem — get ready for green roads.
The Status Quo
The global roads network is vast and growing at one of the fastest paces in history. In 97 percent of the continental U.S., you’re no more than three miles from a paved road of one kind or another, and the most recent CIA World Fact Book places the number of worldwide paved roads at 15.99 million kilometers.
By comparison, the moon is a mere 384,400 kilometers (almost 239,000 miles) away. China’s latest Five Year Plan calls for the building and renovation of 1.2 million kilometers (almost 746,000 miles), making good on its promise to build “a road to every village.” Brazil, Russia, India and even Africa are not far behind, each with plans to massively invest in long-needed road infrastructures.
The American Society of Civil Engineers says $186 billion is required to just improve the U.S. highways, and several thousand shovel ready projects are already benefiting from President Obama’s stimulus package.
A new road can reduce the travel time and distance for transporting people and products and other material from place to place. However, for each mile of these new but traditionally constructed roads, thousands of tons of materials such as aggregate rock, concrete, asphalt and steel are needed, let alone all of the diesel fuel required to power the construction equipment. One mile of two-lane asphalt road with aggregate base can require up to 25,000 tons of aggregate rock (aggregates are the most mined resource in the world and are almost entirely non-renewable).
In terms of greenhouse gas emissions, between the pavement and sub-base — all the mining, transporting, heating, earthwork and paving work — the average single lane-mile of freeway, will emit enough pollution to equal up to 1,200 tons of CO2. That’s about the same as the total annual emissions of 210 passenger cars. In 2007, the U.S. alone laid down close to 37,000 lane-miles of new road.
The environmental effects of a road do not stop when construction is complete. The new road affects local plant and animal life as well as the region’s water and soils. The road acts as a barrier that cuts through animal ranges and creates a crossing hazard, further diminishing wildlife habitats, especially if trees were cleared to make way for the road.
Increased travel through the area introduces invasive plant species to the existing vegetation. For as many as 1,000 meters from the road, water and soils must contend with increased heavy-metal and salt deposits from gasoline and de-icing, as well as changes to run-off patterns and underground flow rates that affect larger bodies of water further downstream. In addition, the heat island effect that is generated does not just threaten creatures such as birds and snakes. Cool rainwater that lands on hot roadbeds is heated and then runs off into nearby aquatic ecosystems, where the rapid temperature changes can put fatal stress on life in the water.
And in populated areas, the general rise in atmospheric temperatures in the vicinity of the new road creates greater human demand for cooling, increasing emissions of carbon dioxide, sulfur dioxide and mercury.
While it is highly encouraging to see new efforts to green the transportation infrastructure (cleaner cars, light rail, urban mass transit), most of the world still goes to work each day on a road designed and built with yesterday’s thinking.
Turning a Corner
So how can we reconcile the need for vastly improved and more extensive road infrastructure with the need to do so in a less damaging way?
A number of efforts are beginning to generate interest in and momentum for what can be called green roads. Combined efforts by the EPA and Federal Highway Administration through support for the Green Highways Partnership, a standards setting program called Greenroads, and the Recycled Materials Resource Center, as well as efforts by the road building industry itself, has led to the beginnings of a new framework for green roads. Though acceptance, while growing, is still its infancy.
The Green Highways Partnership was born in 2002 when the Federal Highway Administration, in consultation with the EPA, named environmental stewardship and streamlining to be one its vital few goals. The GHP operates through a network of private and public partnerships to study and implement best management practices for concepts such as: watershed management; reuse and recycling programs for products that include coal fly ash, slag cement and old asphalt; and conservation and ecosystem protection such as wildlife crossings.
Building a green road with ECOroads materials.
Separate from the GHP work, EPA efforts include the new Tier 4 standards for non-road diesel engines, which are to reduce exhaust emissions by more than 90 percent and eventually reduce diesel fuel sulfur content from 3,000 PPM to 15 PPM. When fully applied, the agency says, “these reductions in NOx and PM emissions from non-road diesel engines will provide enormous public health benefits. The EPA estimates that by 2030, controlling these emissions would annually prevent 12,000 premature deaths, 8,900 hospitalizations, and one million work days lost.” Both Cummins and Caterpillar have promised to meet these aggressive new standards.
Universities are also in on the effort.
The University of Washington, in a joint effort with the global civil engineering and construction firm CH2MHill, has created the Greenroads Sustainability Performance Metric for design and construction of new, reconstructed or rehabilitated roads. This system of credits is similar in nature to the LEED rating system designed for buildings. Through its seven categories of sustainable design features, credits are awarded based on dozens of initiatives, including storm water management, bicycle and pedestrian access, reduced fuel use and paving emissions, recycled content and pavement technology.
The University of New Hampshire-Durham, in cooperation with the University of Wisconsin-Madison and the Federal Highway Administration, has created the Recycled Materials Resource Center. For over a decade, their efforts have focused on developing guidelines for — and promoting the use of — recycled materials in transportation infrastructure construction and maintenance. Currently, about 94 percent [PowerPoint] of the 3.2 billion tons of aggregates used every year are virgin aggregate rock while 20 percent of all hot mix asphalt and Portland cement concrete end up clogging landfills.
Adding ECOroads to windrows and sub base.
The paving industry, too, is not blind to its environmental record. Both the cement and lime industries have spent years working on productivity and efficiency gains. In the United Kingdom, manufacturers exceeded their targets of improving specific energy consumption by 26.6 percent over 1990 levels ahead of schedule, recording a reduction level of 33.7 percent, the Mineral Products Association said in a recent article on AggregateResearch.com. Manufacturers in the lime sector achieved a specific energy consumption of 940kW h/tonne against a target of 955kW h/tonne, the article said.
In the U.S. and Canada, the cement industry reduced energy consumption by 37.5 percent from 1972 to 2006, according to the Portland Cement Association. In addition, the industry has formed the Cement Sustainability Initiative. The initiative, consisting of 18 of the world’s major cement producers, promotes research into more efficient cement and has a created a framework of performance indicators for companies to keep track of their progress. The asphalt industry has also taken commendable steps to reduce its carbon footprint through the development of warm mix asphalt. This new asphalt requires substantially less heat and therefore consumes less energy and emits fewer greenhouse gasses.
Finally, a number of innovative and eco-friendly products are also beginning to emerge. Among the most promising are soil stabilizers and asphalt binders that provide the equivalent strength of aggregate base rock at a fraction of the cost and environmental impact. Many of these show promise in the green building space as well, proving that green roads innovations can provide benefits across the sustainability value chain. This could eventually lead to greener office buildings, residential developments, schools and the rest of the built environment.
Final shaping of the green road.
These innovators will have to contend with agencies and individuals wedded to the old way of doing things. The task is no easy matter, as these agencies can be burdened with bureaucratic inertia and bias toward existing industries and technologies. That said, several state departments of transportation are starting to recognize that the industry — and overall approach to road building — is due for a change, especially given an economy that is forcing most states and local governments to do more with less.
New York State Department of Transportation Commissioner Astrid C. Glynn said recently, “By encouraging sustainable transportation project designs, we are taking significant steps to conserve our natural resources, enhancing the quality of our lives and reaffirming our commitment to future generations.”
While there is still a long way to go, when all these concepts are implemented, the complete product is a road that reduces toxic and greenhouse gas emissions, protects watersheds, reduces landfill use, protects ecosystems and preserves space for recreation. It is an engineering, economic and public policy achievement that proves that infrastructure construction and environmental preservation do not have to be a zero-sum game.
The Time is Now
There remains one other reason why green roads are so important and require a solution now, not tomorrow. In order to compete in the 21st Century, the developing world has to build out its own highway infrastructure, as we’ve discussed, to the tune of several million kilometers over the next 10 to 20 years. Builders and public works officials in Africa, India, China, Russia and all over Latin America have a choice: blacktop or green, dirty or clean.
Final compaction of the green road.
To use the same old construction methods would lead to unprecedented environmental impact and further contribution to global warming, all while incurring great economic costs to the budget. Now is the time for decision makers to embrace a new way to design, plan, build and maintain their road infrastructure, consistent with green road building practices, leveraging new technologies and know-how, and preparing their countries to take a leadership role in environmental stewardship and infrastructure development.
In the developing world, every single mile of road built is associated with a significant economic return, as reduction in travel times and costs improve all factors of life. Poverty can be reduced, as it was in Laos. Access to healthcare improves, lessening risks to pregnant woman and children, as occurred in India. School enrollment can increase as it did in Morocco. Income and employment opportunities rise as new businesses are created along the roads, and better access to financial services increases investment towards non-agricultural industry. Land values go up, further increasing access to capital and stimulating entrepreneurial investment. And, according to the Asian Development Bank, in China’s Shaanxi province “for every CNY10,000 invested in roads, 3.2 poor people are lifted out of poverty; and for every 1 percent increase in kilometers of road per capita, household consumption increases by 0.08 percent.”
Of course all of this development does not just happen in the rural countryside. From Sao Paulo to Lagos to Delhi, by 2050 the world’s cities will see their populations expand by 3.1 billion new residents. All that growth will bring with it a massive new demand for infrastructure. Green roads in conjunction with modern power grids, cleaner cars, large and dependable public transportation systems and sewage treatment facilities will help to greatly reduce the per capita carbon footprint of these thriving mega-urban regions.
As growth proceeds apace, it is also important to note that shifting a supply chain to another part of the globe merely moves the source of the smog to a new region. Instead of improving environmental impacts, the change can make things worse: A significant new part of the pollution over American soils now originates in China. That said, expanded infrastructure in the developing world will lead to significant improvements in supply-chain efficiencies of Western companies, leading to cost reductions and a smaller carbon footprint per unit of product — a tangible benefit for companies, employees, and customers in the developed world.
The End of the Road as We Know It…
The old ways are fading and new approaches to road construction are finally catching up with the times. A standard four-lane highway should not consume, over its lifetime, 2,600 barrels of oil worth of energy per kilometer. Just as the green building movement has finally reached the spotlight and gone mainstream, the green roads movement is not far behind.
By: Omri Dahan and Alex Goykhman
8 Comments to "CarbonNeutral Road"
1 | ashmann
15 de September de 2009 to ● 4:39 pm
The eyes of the world, it seems, are on a $1.4 million paving project in Shoreview.
Construction groups, civil engineers and public works officials are touring the job site. Just the other day, a group from Sacramento, Calif., flew in to take a look at the project. Media types from Miami to Bakersfield are asking questions. There’s even an eye-catching video on Youtube.
“We have been talking to people from New York to California about this thing,” said Mark Maloney, Shoreview’s public works director. “It is very unusual to be involved with an infrastructure project that has that much national attention.”
The fuss is about “pervious concrete,” a green technology that allows water to pass through instead of running off the surface, thus reducing the need for expensive storm water retention ponds and other infrastructure. Pervious concrete also provides a natural filter for polluted “run-off” – such as petroleum products – that would otherwise flow unimpeded into lakes, streams and rivers.
Pervious concrete isn’t new; it has been used in Minnesota for at least five to 10 years, mostly on walkways, parking lots and the like. However, Shoreview is using the technology on a three-quarter-mile residential roadway – the first time, in Minnesota at least, that this type of concrete has been applied to a project of this size.
The project, which began in July and is just wrapping up, features a seven-inch bed of pervious concrete on top of 18 inches of aggregate.
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The concrete doesn’t contain fine sands. Instead, it’s made up of a “concrete matrix” that’s specially designed to allow water to pass through, according to Mendota Heights-based Cemstone, which is supplying 1,800 cubic yards of concrete for the project.
“The water goes through the pervious concrete, gets in this layer of crushed aggregate, and naturally filters into the soil,” said John Lee, a sales manager with Cemstone. “For lack of a better analogy, it looks like a Rice Krispies bar.”
It’s not a cookie-cutter concept. In fact, the concept runs afoul of the traditional view of concrete used in cold climates.
In northern climates, the industry has typically designed concrete to keep water out, thereby preventing freeze-thaw damage. So it’s not surprising that there’s some skepticism about the future of pervious concrete on Minnesota.
The jury is still out on the Shoreview project; a lot more will be known about its durability after it gets past its first winter.
But Lee said the early indications are promising. In a recent demonstration that’s documented on Youtube, crews put the concept to test by dumping 2,000 gallons of water on a finished portion of the street.
The water “disappeared in about a minute,” according to Lee.
“When we go to the site, appearance-wise, the concrete looks remarkably well,” Lee added. “The contractor [Ramsey-based North Country] has done an absolutely fabulous job. The appearance looks very uniform. As far as driving on it, and walking on it, it feels like a regular pavement.”
The pavement isn’t cheap; its upfront cost is about 50 percent more than traditional concrete, Lee noted. But he hastened to add that it’s cost-effective considering that “you are getting a storm water management system” instead of just a driving surface.
Maloney concurs.
“When you net out what you don’t have to build – mainly ponds and piping and catch basins and manholes – when you consider the cost of those things, it is almost a break-even,” Maloney said. “We would not be doing the project if that weren’t the case.”
As more contractors become familiar with the product, and learn how to apply it with the proper tools and techniques, the price is likely to come down.
Maloney said the city’s construction bids specified that experience with pervious concrete, including the proper certification, is a must.
Ramsey-based North Country is a paving subcontractor for general contractor Veit Cos. on the project.
“It’s the largest project we as a company have completed as far as pervious goes,” North Country project manager Cliff Swenson said. “It’s a pretty big undertaking for us.”
From a construction standpoint, pervious concrete differs from standard concrete paving, Swenson noted. Tools and techniques are different. For example, crews must take care not to over-compact, a mistake that could prevent the all-important water infiltration.
The curing is “really, really important,” Swenson said.
“The process – it is pretty critical. You don’t have a lot of time. You need to get it down, rolled and cured as quickly as you can.”
Swenson credits Shoreview officials for “taking a risk with a fairly new material, even though we have been working with it for years. They have put a lot of faith in us and the supplier and general contractor, Veit, to give them a good product.
“And we feel we have. … We want to make sure it’s successful, not just for ourselves, but we feel we are working for the industry as a whole.”
Maloney said the project has “evolved into a partnership that is very, very different than the typical model that has delivered infrastructure. It has been a very positive experience, with all these different market sectors pulling in the same direction to advance something.
“For a city of our size, we don’t normally get involved in projects where that’s the case.”
2 | ashmann
15 de September de 2009 to ● 4:55 pm
Caterpillar Inc. was named to the Dow Jones Sustainability Indexes for the ninth consecutive year, the company announced.
Caterpillar also retained its Sustainable Asset Management Gold Class position in the Industrial Engineering sector, it said in a news release.
Launched in 1999, the annual DJSI process involves an analysis of economic, environmental and social performance, assessing issues such as corporate governance and citizenship, risk management, climate strategy, standards for suppliers, product stewardship and occupational health and safety.
“As Caterpillar continues on its sustainability journey, our ongoing inclusion on the DJSI exemplifies our progress in aligning our sustainability efforts with our business strategy,” said Doug Oberhelman, Caterpillar group president, in the news release.
Caterpillar the past year has focused on its 2020 goals for products, services and solutions, as well as operations. Caterpillar continues to look for opportunities to improve efficiencies in operations and products and services offerings, increase recycling and remanufacturing, as well as increasing life cycle value throughout its product line, the release said.
“Our employees, dealers and suppliers continue to work together to help our customers achieve improvements in material and energy efficiency, emissions reductions and job site safety,” said Oberhelman. “At the same time, energy efficiency continues to be a key focus in our facilities; and we continually challenge ourselves to find innovative ways that will increase efficiency while reducing emissions.”
Caterpillar’s annual Sustainability Report can be read on the company’s Web site at http://www.cat.com.
3 | ashmann
15 de September de 2009 to ● 5:16 pm
CEMEX UK, building materials provider, is currently trialling an innovative transport solution, Iso-veyors, to transport pulverised-fuel-ash from West Burton power station to Tilbury, for the production of blended cements.
The new grinding and blending facility at Tilbury will be officially opened this month.
Iso-veyors, a more sustainable bulk transport system, were previously used by the company to transport materials to T5 at Heathrow airport. The system provides a logistical and flexible alternative to traditional silos providing storage for 28 tonnes of material per unit which can be transported by any combination of road, rail or ship.
The cylinder- shaped containers are filled at source, West Burton power station in Lincolnshire, and transported by rail approx 170 miles to Tilbury in East London. It is anticipated that this transport solution will save 600,000 road miles and 720 tonnes CO2, the difference between road and rail transportation, per annum.
Once at Tilbury, the 30ft containers, which have been constructed within the frame dimensions of a standard commercial container, are handled as standard ISO containers, utilising skeletal trailers and conventional rolling stock. They are placed on trucks to go into a storage area until required where they can be stacked three units high and moved using conventional lifting gear.
This system provides flexible weatherproof storage, eliminates cross contamination and reduces environmental damage.
“From an operations perspective, the Iso-veyors enables us to move far larger loads over greater distances in less time, giving environmental benefits. It also ensures that we always have a constant supply of P-FA. We are continually looking for innovations that are also more sustainable, Iso-veyors and the recent successful introduction of the Epod,(electronic proof of delivery) fulfill these criteria “, comments Graham Russell, Vice President Commercial, Logistics and Building Products.
4 | ashmann
26 de September de 2009 to ● 12:46 am
Over a two-day period the lightweight concrete was poured to a depth of 650 millimetres and then topped up with granular material and asphalt. Within about two weeks the road was reopened compared to the several weeks it would have taken with traditional construction, says Barry Mulcahy, a project manager with Peel’s transportation division. “We’re always looking for innovative solutions,” says Mulcahy.
(Ontario, Canada) — Not only did it minimize the environmental impact on an adjacent wetland, what may be the first-ever application of a lightweight cellular concrete product on an Ontario road saved time and money and lessened inconvenience to adjacent residents, say Peel Region officials.
Some 950 cubic metres of the lightweight concrete was poured along a 120-metre-long stretch of Dixie Road in Caledon in late August by Calgary-based Cematrix Cellular Concrete Solutions, the proprietary developer.
Rather than pouring concrete from a waiting convoy of ready-mix trucks, the concrete was sprayed into place by assistant project manager Brad Garity operating a large hose attached to a mobile command mixing centre where water, a foaming agent, compressed air, and Portland cement—from an adjacent 30-ton silo — were mixed together.
Over a two-day period the lightweight concrete was poured to a depth of 650 millimetres and then topped up with granular material and asphalt. Within about two weeks the road was reopened compared to the several weeks it would have taken with traditional construction, says Barry Mulcahy, a project manager with Peel’s transportation division. “We’re always looking for innovative solutions,” says Mulcahy.
While not considered a hazard to the driving public, the peat moss conditions in the adjoining wetlands have been the source of settling problems for several years, he says.
Traditional construction would have required considerable dewatering, extensive peat removal, the erection of sheet piling and then replacing the peat with granular material, says Bob Bower, vice president of Delcan Corporation Engineers, the consulting engineer: “It (traditional construction) would have been very costly.”
While basically a test experiment for Peel Region and the first application in Ontario, the concrete has been successfully used in Western Canada.
“We’ve been at this for 10 years,” says Cematrix vice president Steve Bent. The lightweight concrete offers a cost-effective innovative solution to difficult and challenging road reconstruction in areas where there is weak soil, peat moss or where there is highly plastic clay, say Bent.
Other applications include lightweight back fill for retaining walls and bridge abutments.
In Alberta where the below ground frost level can range from 10 feet in Calgary to 14 feet in Fort McMurray, it has been used as an insulator for utility lines, says Bent.
Installation is rapid, with a capacity of from 20 to 150 cubic metres per hour in all conditions says Bent, noting the pouring hose can be extended a kilometre.
By: DAN O’REILLY
5 | ashmann
20 de October de 2009 to ● 5:30 pm
Where many coal-fired power plants see waste, researchers at Louisiana Tech University see an opportunity to curb greenhouse gas emissions, protect aquifers and change engineering forever.
The researchers, led by Erez Allouche, an assistant professor of civil engineering and associate director of the Trenchless Technology Center, and Sven Eklund, an assistant professor of chemistry, are working with a group of students to create a geopolymer concrete, or GPC, made from a waste byproduct produced by coal fired power plants called “fly ash.”
The power plants typically store the ash, one of the most abundant industrial byproducts on earth, in massive lagoons and storage facilities. That method of storage puts aquifers and surface bodies of fresh water in danger if storage goes awry, and takes up thousands of acres. But GPC can help eliminate the need for that storage.
“It is important research for the U.S. because it’s environmentally friendly,” said Ivan Diaz, a PhD candidate who has been working on the research team for several years.
“We’re keeping the fly ash out of the landfills and we’re creating a valuable material.”
The researchers use another byproduct from the paper pulp industry, sodium hydroxide, to start the reaction that turns fly ash into GPC.
The goal is to market GPC as a substitute for Portland cement, the most widely produced man-made material on earth and one scientists have pegged as a major contributor to global warming.
An estimated 5 percent to 8 percent of all human-generated atmospheric carbon dioxide (CO2) worldwide comes from the concrete industry. More than 2.6 billion tons of Portland cement are produced per year, and production is growing 5 percent annually.
Compared to Portland cement, GPC produces 90 percent less CO2 during production.
According to Allouche, GPC offers several additional advantages compared to Portland cement.
GPC features greater resistance to corrosion, more fire resistance, greater strength and less shrinkage.
Companies have tried a mixture that used 85 percent Portland cement and 15 percent GPC, but “why use 15 percent we can use 100 percent?” Allouche asked.
So far, the Tech research team has produced a 5,000 pound block of GPC and constructed a 100-square foot gazebo made entirely of GPC.
The researchers are working with about 30 power plants to provide fly ash for the research, including Louisiana companies like Cleco Power of Pineville and Entergy.
Allouche said he foresees GPC being used for road and bridge construction, as well as for other civil-engineering products like sewer piping.
The researchers could reach that goal sooner rather than later, as Allouche said they are currently on the verge of marketing a sprayable geopolymer product.
“We’re not out to replace concrete, but we’d like to offer a complementary product,” he said.
Diaz said GPC is unlikely to replace Portland cement, but not because GPC isn’t a superior product.
“It’s not because it can’t do it, but because it’s really hard to change the minds of the civil-engineering community,” he said.
GPC currently costs about 15 percent more than Portland cement, “but that does not take into account savings (produced) by not having to store fly ash or ‘green’ tax credits,” Allouche said.
Allouche and Eklund, the other lead researcher, said the success of GPC will ultimately be determined by companies’ willingness to try something new.
“It’s up to the industry to accept it,” Allouche said.
By: Stephen Largen
6 | ashmann
27 de October de 2009 to ● 9:46 am
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7 | ashmann
27 de February de 2010 to ● 7:44 pm
Apparently thicker is better — at least when it comes to paving roads — according to an MTO expert.
The critical thing is good design, Chris Raymond, acting head of the Ministry of Transportation Ontario bituminous section recently told an industry audience.
“If you can’t afford a good design, I tell agencies and municipalities, you can’t afford to waste your money on a poor design — you’ll just be throwing your money away,”
A strong advocate of the MTO’s Superpave standard, Raymond also said lift is important and urged opting for more thickness to ensure better roads and longevity.
“Unfortunately, costs drive agencies to go for minimum thickness,” he said, “Pavement wears from the top but falls apart from the bottom.”
With limited dollars and a growing number of kilometres to pave, owners cut back but will pay for it in the long run because those installations will fail long before they should and start to pothole and crack.
“A higher lift, say going from 40 mm to 50 mm, isn’t a 25 per cent increase in cost because while you are using more asphalt cement and materials your equipment and labour costs are the same,” Sandy Brown, technical director of the Ontario Hot Mix Producers Association told a seminar during an association convention.
Brown said the optimum lift depends on the type of traffic the road faces and accordingly which aggregate has been specified. Thinner lifts stretch the asphalt and budget further, but add to later maintenance and rehabilitation costs.
“Most of the problems we find in forensic engineering analysis is that something simple was done wrong in the beginning of the process,” said Dale Decker, president of Dale S Decker LLC, a U.S. expert consultant who outlined five steps to better pavement.
In the end, it comes down to best practices, said Decker, whose recommended steps start with a design that addresses quality and function required of the road, specifications that clearly define the work, inspection to ensure proper construction according to the design, construction combing technology, workmanship and maintenance.
He said road designers must for consistently look to state-of-the-art design standards — not just what’s always been used before.
“Perpetual pavements, for example, have been used around the world for years and we’re just getting to use them in the U.S.”
Making sure the job is being done correctly is also critical.
“Who are the inspectors? Are they certified? We’re they working as a Wal-Mart greeter yesterday and working as a road inspector today?”
There’s a continuing shift by owners to an “end result contract” in which the contractor is given free reign to determine the construction of the road as long as it meets specifications.
But contractors must shoulder more responsibility and partner with owners to realize value engineering rather than take the old adversarial stance, he added.
He said the last step is the one which fails more often.
“Maintenance and rehabilitation is my major pet peeve,” he says. “We built one of the top 10 transportation systems in the world, but now three-quarters of our bridges are structurally unsound and our highways are in the same situation because we didn’t maintain the system.”
Vince Aurilo, manager of pavement engineering services at DBA Engineering, who also spoke on the specification and inspection process at the seminar, said partnerships between owner and contractors will be increasingly important.
Reducing variations from specification in aggregate mix, careful inspection and sampling, using the right equipment in the right way with trained, skilled workers is the surest way to meet the standards and get smooth, long-lasting pavement, he said.
“Stopping and starting the paver or bumping the screed because you are not using a shuttle buggy, for example, leads to bumps and affects the thickness. We’re going for smooth because smooth lasts longer.”
8 | ashmann
13 de March de 2010 to ● 3:19 am
A case study of a pervious concrete quality assurance program
Mar, 12 2010
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Research and experience have shown that pervious concrete mixtures proportioned to have 15 to 25% air void contents should have sufficient infiltration rates to limit storm water surface runoff and adequate strength to avoid raveling.1 Until recently, however, there were no U.S. standards for the verification of air void content in fresh concrete or infiltration rates for in-place concrete. To help producers, contractors, and owners verify that their pavement projects will perform as needed, ASTM Committee C09.49, Pervious Concrete, has recently introduced Standard C1688, “Standard Test Method for Density and Void Content of Pervious Concrete”2 and Standard C1701, “Standard Test Method for Infiltration Rate of Pervious Concrete.”3 These standards were used as part of the quality assurance program for the construction of a parking lot at the Metropolitan Community College (MCC) in Omaha, NE. Using test placements to develop a compaction-density relationship, appropriate mixture properties could be defined without guesswork. Workability tests and unit weight tests per ASTM C1688 were used to screen loads to ensure that we placed only workable concrete that could be consolidated to achieve a target air void content.
UNIT WEIGHT AND AIR VOID CONTENT
Pervious concrete typically comprises a zero slump mixture with little to no fine aggregate and uniformly graded coarse aggregate. The workability of such mixtures can be highly sensitive to variations in moisture content and compaction effort, leading to large variations in the final void contents for a given pavement project. By mixing trial batches for the contractor to use in test placements of pavement, the producer can obtain unit weight data per ASTM C1688 and air void content Vair (in %) from cylindrical samples according to the procedure in Reference 4. Vair is given by
V^sub air^ = [1 - (W^sub D^ - W^sub S^)/(gamma^sub W^ . V^sub T^)] x 100 (1)
where WD is the weight of the oven-dried sample, WS is the submerged weight of the sample (after tapping to release trapped air), gW is the unit weight of water, and VT is the calculated volume of the sample using its measured diameter and length.
For the MCC project, six mixtures were prepared and samples were produced per ASTM C1688 during placement of the preliminary test panels (Fig. 1). Unit weight and air void content for each mixture were measured and plotted, and a linear regression analysis was used to determine the relationship between air void content and unit weight (Fig. 2). As one might expect, there is a linear relationship between void content and unit weight of pervious concrete mixtures, with a maximum unit weight (about 150 lb/ft3 [2400 kg/m3]) associated with zero air void content.
It must be noted that the ASTM C1688 procedure (filling a 0.25 ft3 [7 L] cylindrical container in two lifts, with each lift consolidated using 20 blows from a standard Proctor hammer) will not produce the same air void content as would be produced in pavement. Our preliminary field determination for cores removed from the test panels indicated that a mixture with an air void content of 12% and unit weight of 133.5 lb/ft3 (2140 kg/m3) when tested per ASTM C1688 would have an in-place air void content (found per Eq. (1) using core sample data) of 17.5%. This in-place value was specified for the project.
QUALITY ASSURANCE PROGRAM
The owner recognized pervious concrete as a new product and thus made it very clear that, regardless if the product was successful or not, “we need to know why.” The team was therefore expected to implement procedures within a set quality control program, including:
* Aggregate moisture tests conducted by the concrete producer before batching operations;
* Unit weight tests per ASTM C1688 conducted at the batch plant by the producer and at the job site on every load of concrete;
* Inverted slump cone tests (described in the following section) conducted at the job site by the owner’s testing agency;
* Estimated unit weight test (described in the following section) conducted on site by the owner’s testing agency;
* Unit weight tests (five total) using 4 in. (100 mm) diameter cores taken from the hardened pavement and tested using the procedure described in Reference 4 by the owner’s testing agency; and
* Permeability tests (six total) per ASTM C1701, taken at the core locations (prior to coring) by the owner’s testing agency (Fig. 3).
UNIQUE TEST PROCEDURES
Inverted slump cone test
The inverted slump cone test is qualitative, but it allows a rapid evaluation of workability. The procedure involves resting the small opening of a slump cone against a smooth, hard surface. The cone is then filled with fresh concrete in one lift, with no consolidation. Excess concrete is struck off, level with the large end of the cone, and the cone is then lifted. The fresh concrete is observed as it flows out of the cone. If the bulk of the concrete remains in the cone and can only be discharged by vigorous shaking of the cone, the mixture will be unworkable. Figure 4 shows two different mixtures after discharge. The concrete in Fig. 4(a) was discharged after tapping of the cone-the batch was remediated by increasing the water content. The concrete in Fig. 4(b) flowed freely from the cone and was approved for placement.
Estimated in-place unit weight
In this procedure, a 0.25 ft3 (7 L) cylindrical container is filled with fresh concrete in one lift, with no consolidation. Excess concrete is struck off, level with the top of the container. The net weight of the concrete is determined and the unit weight of the test sample is calculated. The resulting value is multiplied by a compaction factor, which is based on observations that typical consolidation methods lead to a 1 in. (25 mm) reduction in thickness relative to the initial placement depth. Thus, for the 6 in. (150 mm) thick pavement required on this project, the compaction factor was 7 in./6 in. = 1.17. Estimated unit weight values were correlated with specific regions of the in-place pavement.
APPLICATION
Placement
The pervious concrete pavement was placed by directly discharging the concrete from mixer trucks onto an aggregate base. Concrete was raked into place and consolidated and finished using a hydraulic roller-screed operating directly on top of side forms. As per ACI 522.1-08, the concrete was covered with a polyethylene sheet immediately after finishing.5
The 5650 ft2 (525 m2) paved area required 110 yd3 (84 m3) of concrete, which was delivered in 14 truckloads. Most of the placement was completed in 2 days, during which the average ambient temperature was 65[degrees]F (18.5[degrees]C) and the relative humidity was 70%.
Inverted slump testing showed that the first truck was not workable and additional water was added until the concrete had about 12% air void content as measured per ASTM C1688. The second truck had too much water added at the concrete plant and was held until the concrete had about 12% air void content per ASTM C1688. The water content for the third truck was acceptable, so concrete from this truck was placed while the second load was being held. Tests of subsequent loads indicated they also had acceptable water contents.
Pavement sections were installed with no reports of consolidation or finishing problems. Workers with previous experience with pervious concrete pavements reported, however, that the mixtures would have been considered too “wet” if evaluated by visual inspection only.
Fresh and hardened properties
ACI 522.1-08 Section 1.6.2.1 requires that the unit weight of fresh concrete is within +-5 lb/ft3 (+-80 kg/m3) of the specified fresh unit weight. ACI 522.1-08 Section 1.6.5.2.1.b requires that the unit weight of the hardened concrete is within +-5% of the approved hardened unit weight measured in test panels.
As indicated previously, the specified in-place air void content was 17.5%. Extending ACI 522.1-08 in-place density requirements to air void content, the allowable range would be from 12.5 to 22.5%. Air void contents measured using cores ranged from 13.4 to 21.6%- well within the allowable range. A comparison between estimated and in-place void contents is shown in Table 1. Even though the estimated in-place unit weight test is highly operator dependant, the mean of the test results was within 3% of the mean of the values measured using cores (Fig. 5).
Table 2 compares the air void contents of the fresh concrete (measured using ASTM C1688) and hardened concrete (measured using core samples). For all five cores, the void contents measured per ASTM C1688 were lower than the void contents found using the core samples.
Figure 6 shows the general relationship between void contents, as determined per ASTM C1688, and permeability, as determined per ASTM C1701. Permeability tests were not performed directly on the cores, as that ASTM standard is under development. Because the same equipment and methods were used to consolidate all pavement sections, Fig. 6 implies that initial workability, which influences compaction, also influences hardened permeability. The largest infiltration rate measured per ASTM C1701 was 2016 in./hour (51,200 mm/hour) and the lowest was only 62 in./hour (1600 mm/hour). While our observation of an exponential increase in permeability with increased void content is consistent with observations made by others, the multi-operator reproducibility of the test method is under evaluation.1,6 INDICATIONS
Our work for the MCC pavement project (Fig. 7) indicates that:
* Air void and unit weight tests per ASTM C1688 can be used to predict in-place air void content;
* The inverted slump cone test is a good predictor of mixture workability and provides a rapid method for culling mixtures that will have unacceptably low unit weights; and
* A requirement that the in-place unit weight is within +-5% of the specified unit weight (as per ACI 522.1-08) is appropriate and achievable.
For workable mixtures that passed the inverted slump cone test, estimated in-place unit weights correlated well with measured in- place air void contents. Mixtures that met the specified unit weight of 133.5 lb/ft3 (2140 kg/m3) were very workable, although they might have been considered too “wet” if evaluated by visual inspection only.
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