and energy savings
By Andy Bateman
Keynote speaker Gerry Huber began the 2008 seminar’s presentation session by noting how sensitive the public has become to environmental issues, beginning with environmental concern taught at school and frequent doomsday media reaction to environmental stories.
Despite difficult weather conditions, the annual Ontario Hot Mix Producers Association Fall Asphalt Seminar attracted over 450 attendees and retained its title as one of the largest industry seminars in the country.
| The 2008 Ontario Hot Mix Producers Association Fall Asphalt Seminar attracted over 450 attendees.|
Keynote speaker Gerry Huber began the 2008 seminar’s presentation session by noting how sensitive the public has become to environmental issues, beginning with environmental concern taught at school and frequent doomsday media reaction to environmental stories. At the same time, everyone including ourselves tends to cling to the past, so the goal of our industry is to look for opportunities to reduce environmental impact, reuse waste and recycle without restraining existing lifestyles. The ethic of environmental stewardship involves the responsibility to care for our natural resources to ensure they are sustainably managed for current and future generations, including recycling, conservation, regeneration and restoration. For anyone who might be thinking environmental stewardship is not applicable to their own situation, Huber cited the experience of British Petroleum. BP was forced to shelve a $US 3.8 billion expansion of its Whiting Refinery in Chicago until a pledge had been made not to increase discharges into Lake Michigan, despite having all necessary approvals in place. Many agencies have now embraced the concept of stewardship including federal government, provincial government, the industry and other institutions such as universities Huber reviewed the LEED program which has a pavement component but is primarily targeted at buildings. (LEED is an acronym for the Leadership in Energy and Environmental Design program, administered by various Green Build Councils in 28 countries worldwide.) Under the program’s criteria, points are awarded and a project attains one of four award levels: certified, silver, gold or platinum. Pavements can contribute nine possible points out of 69 for new construction and 10 out of 92 for existing buildings. Huber also pointed out that the pavement component is much higher under a relatively new points system called Greenroads. Here, the pavement can contribute 51 out of 62 (82 per cent) of total points and Huber recommends a road system be used to define its contribution if an applicant’s product is used primarily in roads.
|Warm mix asphalt is generating strong industry interest.|
|A Sasobit warm mix asphalt trial in King Street Hamilton.|
|LEFT: A trench section on Highway 25 near Denver CO., revealed that segregation not visible at the time of construction was caused by the paver.|
RIGHT: A detail of the longitudinal cracking on Highway 25.
Using U.S. data, Huber demonstrated that roads consume a lot of materials in their construction, as well as a lot of energy. A typical hot mix asphalt road requires 3.0 Terra Joules (TJ) of energy to construct, over 90 per cent of which is used in the manufacturing phase. A Portland cement concrete pavement uses even more energy, 3.7 TJ, with manufacturing consuming 94 per cent of that total due to the energy intensive cement production process. By comparison, 100 U.S. homes consume about 4.0 TJ each year.
The Greenroads rating system is designed to distinguish more sustainable roads and awards credits for approved sustainable choices and practices, although as Huber pointed out, the system is project oriented and does not deal with operations. For instance, two credits are awarded where the recycle content is a minimum of 30 per cent in the hot mix asphalt or Portland cement concrete and 50 per cent of the total material if base course fill or structures are included in the project. Recycle content can earn up to four credits depending on the percentage of recycled content, with differing certification levels based on the number of credits received.
Recycled hot mix asphalt is the number one recycled material at (in the U.S.) some 72 million tonnes, beating out second placed scrap steel with 63 million tonnes. But, as Huber notes, we can do better, with some 20 per cent of recovered hot mix asphalt and a similar percentage of recovered Portland cement concrete still going to landfill. Each tonne of RAP used conserves 220,000 BTUs of energy not consumed in aggregate mining processing and delivery as well as asphalt refining and delivery. Energy saving from using 1 million tonnes of RAP per year is equivalent to 6.5 million litres or the gasoline consumed annually by 1,650 Ford Expeditions. Recycle materials include shingles, both the tabs from the manufacture of new shingles as well as “tear offs” from shingle replacements.
Other environmentally friendly initiatives include porous pavements that allow water to flow into the soil and so reduce the disruption to natural flows. Going even further into ways to reduce our environmental impact, Huber noted that old paint and even hazardous waste may have potential. In the first step of the paint recovery process, the paint is recovered and crushed cans sold for scrap. The paint is then mixed with coarse aggregate in a unit somewhat resembling an aggregate log washer. The resulting paint coated aggregate has lower absorption than the virgin material and therefore requires less asphalt cement (AC) to achieve the same AC content in the final asphalt mixture.
Huber concluded that such approaches recognize the need to seek opportunities to improve the environment, to make new sellable products and create win-win solutions.
Warm mix solutions
Second speaker of the day Vince Aurilio presented “Meeting Difficult HMA Challenges with Warm Mix Asphalt Solutions”. Aurilio reported strong industry interest in warm mix as demonstrated by a recent (U.S.) National Asphalt Pavement Association conference in the U.S. which broke all previous attendance records for association topics, Superpave included. This level of interest in warm mix has been spurred by a powerful combination of a high cost of fuel, high cost of asphalt cement, greenhouse gas reduction, the advent of carbon tax, “ the movement to green specifications”, hot mix asphalt construction constraints and, perhaps most important, the relationship between quality and sustainability. The benefits of warm mix asphalt include reduced emissions, reduced fumes, reduced fuel consumption, improved workability, an extended paving window and cold weather paving.
Aurilio reviewed the various methods of producing warm mix now available including two stage processes that involve the use of a hard and soft binder, the introduction of moisture to create a foaming process, viscosity reduction, flow enhancer and emulsion/ chemical packages. An extensive list of warm mix projects has already been completed across the country using these methods, with all delivering good durability and performance to date. Although warm mix is rapidly gaining acceptance, there are still industry concerns with respect to the potential impact on baghouses, any required plant modifications and the availability of binder storage tanks, for example. Human factors include changing behaviours or the mindset with respect to utilizing the warm mix technologies, an enhanced appreciation of paving and compaction procedures, costs and acceptance by department of transportation, with concerns by those departments including relative costs, suitable testing procedures and long term pavement performance. Overall, Aurilio believes that the market for warm mix will grow, driven by emissions reduction, worker safety, the increased use of RAP, density specifications, higher fuel costs, the extended paving window, cold weather paving and last but not least, the need to improve quality. Warm mix asphalt makes sense environmentally with its combination of reduced greenhouse gases, reduced or eliminated fumes, reduced fuel consumption and technically – by achieving improved density.
Hot mix and the environment
In “Carbon Tax, Carbon Footprint and LEED”, Sandy Brown of OHMPA began by explaining the various carbon tax regimes currently in use. Under the direct tax method, a carbon tax is paid by the one who burns the carbon. This approach affects all aspects of our industry: not only the extraction, processing and transportation of aggregates and the extraction, refining and transportation of asphalt cement, but also the production of hot mix asphalt and its placement. The units of measurement used by the direct tax method are (metric) tonnes of carbon equivalent or carbon dioxide. The B.C. model, currently the only one in force in Canada, applies a $10/ tonne tax of carbon equivalent to petroleum fuels adding $0.0267 to each litre of diesel fuel, $0.0241 to each litre of gasoline and $0.0171 to each m3 of natural gas. For each tonne of hot mix asphalt produced using 10m3 of natural gas, this tax would add $0.17 to each tonne of product.
The cap and trade model is another carbon tax approach where a cap value is set for each industry sector and emissions are monitored. If a producer’s emissions are below the cap, the producer has credits to trade. Similarly if emissions are above the cap, credits have to be bought or a fee is payable.
Brown also described a method that has been used to calculate the carbon footprint of transportation projects. Here, the quantity of carbon dioxide or equivalent green house gases (GHG) produced during the project is calculated and used to establish offsets. As an example, the estimated GHG emissions of a roadbuilding project in Australia were offset by the planting of 4,500 trees. Brown took the concept a step further by comparing the carbon footprint of a number of designs of flexible and rigid pavements. In the first example, the carbon footprint of a 7.5 m wide a rigid pavement utilizing concrete and granular base was some four and a half times bigger than an equivalent flexible pavement design section consisting of hot mix asphalt and granular base. Similar results were obtained with a 15 m wide collector and a six driving lane highway, with the carbon footprint of the concrete road more than four times the hot mix asphalt road in each case. Other greenhouse gas reduction strategies include the use of RAP and warm mix asphalt. If all the hot mix asphalt placed in Ontario contained 20 per cent RAP the resulting greenhouse gas reduction would offset 5,000 cars while every 9 lane km of warm mix asphalt placed at a thickness of 40 mm will offset the GHG emissions from a typical county inspection vehicle.
Brown concluded with an overview of the LEED program. LEED is an acronym for Leadership in Energy and Environmental Design and is administered by various Green Build Councils in 28 countries worldwide. Canada’s LEED program is administered by the Canada Green Build Council and the system consists of a scoring system used to rank the environmental impact of various construction technologies. Hot mix asphalt appears in a number of places in the current spreadsheets and the NAPA has generated a guide to help applicants gain LEED credits on projects.
Ministry of Transportation concepts
Becca Lane of the Ministry of Transportation of Ontario (MTO) presented some current conceptual thinking within the ministry for the advancement of sustainable design and construction. Among ideas being considered is the inclusion of a green rating system in the MTO’s life cycle costing model and LEED-type certification for roads. Lane reminded attendees of the definition of sustainability and a sustainable pavement. The MTO’s current sustainable pavement initiatives include in-place pavement recycling, optimising the use of recycled materials, the use of innovative recycled materials, long life and perpetual pavements, warm mix asphalt, quiet pavements, permeable pavements and low VOC (volatile organic compound) pavement markings.
Lane provided a historical summary of the development of green initiatives. Recycling efforts by MTO have been made in three distinct areas: the reuse and recycling of existing roadway materials, the incorporation of alternative recycled materials into the roadway and full scale in-place pavement recycling. MTO specifications allow the use of reclaimed aggregates, reclaimed concrete, reclaimed asphalt pavement and industrial by-products such as crushed glass, ceramics, and blast furnace slag in granular base and sub-base. Roof shingles (cut off tabs from shingle manufacture) are now being used in hot mix asphalt as a partial replacement of asphalt cement and aggregates. Rubber asphalt trials have incorporated recycled rubber into pavements as an additive to asphalt cement or as an aggregate substitute. For almost 30 years, MTO has been using industrial by-products such as finely powdered blast furnace fly ash and silica fume as partial replacements for Portland cement in concrete mixes. Further green pavement initiatives include warm mix asphalt trials which reduce plant greenhouse gas emissions and particulate emission by 35 per cent to 60 per cent, permeable pavements, quiet pavements and perpetual pavements. When looking at the criteria for a sustainable pavement, in-situ recycling technologies address the main criteria by optimizing the use of natural resources, reducing energy consumption, reducing greenhouse gas emissions, limiting pollution and ensuring a high level of user comfort and safety.
The Road Rehabilitation Energy Reduction Guide for Canadian road builders compares the energy used per tonne of material placed for hot mix asphalt, cold mix, hot in-place recycling, central plant recycling and cold in-place recycling, detailing the energy use during binder manufacture, aggregate production, material processing, transportation and placement. Cold in-place recycling, for example, can provide energy savings of up to 80 per cent compared to traditional hot mix asphalt. The report concludes that recycling technologies are the most promising tool to assist in the selection of environmentally friendly flexible pavements. The MTO’s primary pavement design and rehabilitation goal is to provide safe durable roads that maximize the use of recycled materials. To demonstrate some of these findings, Lane referred to an Ontario Case study estimating the environmental benefits of in place recycling with mill and overlay. The impact was evaluated using PaLATE, a comprehensive software package that assists decision makers in the evaluating the use of recycled materials in highway construction, both in terms of life cycle costing and environmental impacts. In the example, the PaLATE program was used to calculate the greenhouse gas emissions for a typical 7 m wide, 2-lane km section of Ontario highway, comparing 100 mm of CIR/CIREAM (cold in-place recycling/cold in-place recycling expanded asphalt mixture) with a 50 mm overlay on 100 mm of milling plus a three lift, 130 mm thick overlay. The results indicated a 52 per cent reduction in carbon dioxide emissions versus traditional rehabilitation techniques, as well as a 54 per cent reduction in nitrogen oxide emissions and a 61 per cent reduction in sulphur dioxide emissions. With environmental benefits such as these in mind, the MTO is considering the addition of a “green” component to its existing life cycle costing models to promote green pavement alternatives. The component will utilize the PaLATE software to calculate green house gas emissions and energy savings. Possible next steps include the developments of a “green points system” for the MTO to use on pavements. There are numerous existing green points systems and the goal would be to maintain the general framework but focus on pavement components. Next steps may also include the development of typical sustainability values for different pavement materials based on parameters such as typical emission values and recycling contents. According to Lane, current green road rating systems are limited insofar as they are still under development and are not focused on the pavement itself but rather on other road aspects such as route planning and transportation alternatives. The goal of any rating system is to create an understandable and quantifiable system to promote sustainable development technologies for the design and construction of new pavements, rehabilitation, reconstruction and preservation management of pavements.
Lane concluded that the implementation of sustainable pavement management principles is critical to addressing infrastructure investment requirements and providing environmental stewardship over the long term.
Asphalt cement price trends
Eric Sigurdson of Imperial Oil – Canada kicked off the seminar’s afternoon session with “Asphalt Review with Customers”. Presentation topics included an overview of the Canadian and Ontario asphalt (cement) market; trends in the crude oil industry and their impact on the asphalt business. Sigurdson also summarized today’s crude oil supply and refining environment, adding a supplier’s perspective on likely future price trends for buyers of asphalt cement.
The Great Lakes basin is a net importer of asphalt cement, a factor which impacts its supply and pricing in the North American market. Within the context of the global crude oil supply and demand, the increase in U.S. refining coking capacity has been a significant factor in the availability of asphalt cement in the North American market.
Cokers have the ability to significantly shift the refinery yield as percentage of crude intake and, of special interest to asphalt cement consumers, is the ability of a coker to produce high value products such as gasoline from the heavy crude fractions. The coker therefore gives oil refiners much more flexibility in their choice of refinery products. This increased flexibility is in sharp contrast to the output of a traditional simple refinery where asphalt cement was an inevitable by-product of gasoline production. Put another way, asphalt cement is rapidly moving from a “waste” refinery product to a discretionary product whose production is optional and based on commercial decisions. This flexibility does not come cheaply to refiners. Cokers cost some $1 billion each, but with the resulting incremental revenue streams running at about $1 million a day, a coker project will typically have a viable payback period of about three years.
Looking forward to future trends, Sigurdson notes that more heavy crudes are being produced and processed, with Canadian based heavy crude displacing conventional and Middle East supply. Recognizing this trend, cokers are being built to handle the changing crude diet available.
Overall, the message to frazzled asphalt cement buyers seeking relief from 2008’s supply and price gyrations was hardly comforting. On the contrary, asphalt cement price will have to trend faster with crude oil price than in the past and be competitive with light products such as gasoline, diesel and jet fuel. Asphalt cement buyers can expect continued or increased price volatility and higher prices relative to both crude oil price and historical asphalt prices.
How are asphalt cement users to respond? No punches were pulled here either, with Sigurdson stressing the need to understand and manage price volatility using mechanisms such as the indexing of the asphalt cement component of paving jobs. Buyers should also recognize that retention of any “fixed price forward” environments entails greater risk to the asphalt cement supplier, who in turn charges the increased risk premium that accompanies increased price volatility. Paving contractors’ financial viability is the key to survival in a high cost and highly volatile environment. Sigurdson also predicted industry consolidation with fewer larger players and increased emphasis on improved quality of work and innovation. The increased privatization of paving construction and the expansion of public private partnership (P3) projects, with longer term tenders and proposals are also expected.
Pavements under the microscope
The seminar’s afternoon session included a team effort by Tony Tuinstra of the MTO, Sandy Brown and Gerry Huber. Tuinstra kicked off with the “Good”, describing the MTO’s Paver of the Year process. This award has been in place since 1992 and has eleven evaluation considerations. These include end result specifications (ERS), smoothness, segregation, other surface defects, workmanship, innovation, length of paving, total tonnage, type of mix placed, traffic volume and conditions and night paving. Characteristics shared by successful contractors include a commitment to quality throughout the process, together with sound mix considerations and good mix production and supply practices. On site, good practice includes careful paver operation to avoid mid lane streaks or end of load segregation, the proper set up of longitudinal joints, the proper construction and take off from transverse joints as well as good alignment and thickness control. Good compaction is achieved by establishing and maintaining appropriate rolling patterns, properly maintaining rolling equipment and avoiding roller or pick up marks.
Looking at the “Not so good”, Sandy Brown looked at causes and solutions for some pavement problems. These include thermal cracks which appear as regularly spaced transverse cracks typically 3.5 to 5 m apart. The solution is to pick the proper Performance Grade (PG) of asphalt cement for the environment.
Poor patch performance is not necessarily the caused by the hot mix asphalt. During patch repair, the subgrade and granular subbase must be adequately repaired to support the HMA patch and it is often a good idea to overcut after the repair to allow better compaction of the granular base.
Polishing, another pavement defect, leads to low friction and can be a cause of accidents. The solution here is to use aggregates as specified in OPSS 1003. Pavement segregation, open texture and loss of fines are defects which can have several causes including mix design, compaction or stripping. In theses cases, some investigation should be completed to determine the cause and suggest remedial action.
Pavement shoving and tearing can be caused early in asphalt life by too little or too much tack coat although similar symptoms later on in a pavement’s life may be caused by changes in traffic pattern.
Longitudinal deformation and pavement flushing are most likely caused by using the wrong mix for the traffic density. These problems can normally be prevented by using the right Superpave category for the mix with the correct PG grade (bumping the high temperature grade were necessary) and referring to the new Table 3 of AASHTO M320.
Pavement rutting can take several forms including consolidation rutting or densification in wheel paths, plastic flow rutting where material flows and humps on either side of the wheel path and subgrade rutting caused by inadequate pavement thickness. The solution to rutting problems Like deformation and flushing, rutting problems can normally be avoided by using the right Superpave category for the mix with the correct PG grade (bumping the high temperature grade were necessary).
Scuffing is caused by allowing access to the road before the surface has cooled and can be avoided by respecting the pavement surface.
Last but not least, longitudinal joints have been under scrutiny by an MTO-OHMPA Task Group, with the MTO producing a guide for designers looking at issues that must be addressed. OHMPA will be producing a best practice guide for joint construction and one outcome of the task group was the new ramp down specification that the MTO will implement on selected projects in 2009.
Huber’s “Not So Obvious” presentation described a forensic investigation on Interstate Highway 25 just north of Denver. Here, the pavement had been milled and overlaid three years earlier. Photos show the amount of longitudinal cracking that occurred in three years. Many potential causes were theorized, but a trench section across a lane showed the problem to be segregation caused by the paver that was not visible at the time of construction. As a result, the Colorado DOT performed an investigation across the state and worked with industry to develop a specification for pavers to prevent segregation from happening.