| July 28, 2008 | Volume 44, Number 6 |
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The Art and Science of Pavement Optimization |
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Technology is all around us and is an integral part of virtually everything we do. It's in your most recent cell phone conversation, the news report you may have seen at the gas pump, the automated toll you just paid, or the debit card you just swiped for your lunch purchase. Yes, technology is all around us, and generally made available through machines and software. Technology is increasingly prevalent in concrete pavement design, construction, and rehabilitation. The Mechanistic-Empirical Design Guide, or ACPA's own StreetPave and AirPave software, are just a few ways technology is helping make pavements more efficient and cost-effective than ever before. Pavement optimization often involves software solutions, but always involves the human elements of experience, training, and expertise. It's that combination of art and science that we |
 Pavement optimization often involves software solutions, but always involves the human elements of experience, training, and expertise. (Photo: ACPA) |
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| in the concrete pavement industry believe produces the highest quality, most durable and cost-effective pavements in the world. It's in this spirit that we bring you this issue of CONCRETE PAVEMENT PROGRESS, which presents information about software and technological solutions, as well as some good old fashioned tips and techniques designed to help optimize concrete pavements. |
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Industrial Concrete Pavements Bear the Load |
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With the rising price of oil and fuel, there's never been a more important time for efficient distribution centers to assist with the flow of goods from manufacturers to markets. |
 Industrial facilities such as regional distribution centers support the operations of not only trucks, but other heavy-load vehicles. (Photo: Getty Images) |
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Taking time for frequent pavement maintenance or repairs can result in lost time and money. |
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| Concrete pavements offer a durable, low-maintenance, and cost-effective choice for these facilities. | ||||
And, while concrete pavements' life cycle cost benefits have been well documented historically, a growing number of agencies and business leaders are realizing that first costs between concrete and asphalt are increasingly competitive. While the cost of PG-58 asphalt has risen 7.3% in the past year, cement prices have remained relatively stable, rising only 0.5%, according to ENGINEERING NEWS-RECORD's June 2 cost indices. Even more alarming is that the price of PG-58 is more than 250% of what it was in 1996. Software Solution Given these trends, concrete is demonstrating better value than ever. Concrete pavements are engineered structures, but engineering for industrial facilities may be easier than people believe. ACPA's StreetPave software helps engineers design the proper thickness and other associated pavement details without over-design. The software uses fatigue and erosion as the primary design failure criteria to provide recommendations for thickness design, dowel bars, and joint spacing. To do this, users input the following information: • Design period, or the theoretical life of the pavement before it requires either major rehabilitation or reconstruction. • Expected traffic loads, including truck configurations and the frequency of operations for each section of the facility. | ||||
 Ben E. Keith Foods chose concrete pavement for its Oklahoma Distribution Facility. (Photo: ACPA) |
•Type of facility, such as streets providing access to the facilities, or arterials that bring traffic to and from expressways. • Truck traffic loadings and axle-load distributions. ACPA is in the production stages for a guide to designing concrete pavements for industrial facilities using StreetPave later this year. CONCRETE PAVEMENT PROGRESS will announce details as they are finalized.For more information on using StreetPave or designing concrete industrial facilities, contact Scott Haislip at 219-629-3194. |
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| ___________________________________________ (1) American Road & Transportation Builders Association, 01/18/08 |
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Ten Things to Know About Proper Joint Layout |
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| Proper joint layout is an essential, but often overlooked aspect of concrete pavement design and construction. To that end, ACPA encourages designers to follow some simple "do's" and "don't's" when designing pavements. "Thickness may be the top consideration when designing a concrete pavement," said Robert Rodden, ACPA's Director of Technical Services, "but without an effective joint layout plan, even the most solid concrete pavement may be susceptible to distress." Transverse and longitudinal joints are necessary to control cracking in concrete pavement. By effectively choosing a joint layout appropriate for the application and spacing joints properly, engineers can avoid many pavement distresses. Typical maximum joint spacings are 15 ft. for transverse joints and 12 ft. for longitudinal joints, although the maximum joint spacing for any project is dependent on concrete thickness and subgrade/subbase type. In addition to these guidelines, ACPA technical staff also recommends the following general joint layout rules: |
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Five Things to Do |
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Some Things to Avoid 1. Slabs less than 2 ft. wide. 2. Slabs more than 15 ft.-wide. |
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| 3. Angles less than 60 degrees. These angles can be avoided this by dog-legging joints though curve radius points. 4. Creating interior corners. 5. Odd shapes–be sure to keep slabs near-square or pie-shaped. |
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Newly constructed, typical roadways should have transverse joint spacing of approximately 15 ft. and lane widths of approximately 12 ft. (Photo: ACPA) Additional considerations must be made for more difficult geometries and applications, such as intersections, roundabouts, and utility cuts, said Robert Rodden, E.I.T., ACPA's Director of Technical Services. Advice on joint layout for these situations can be found in the following resources: |
Uniformity the Key to Subbase, Subgrade Design |
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Strength is not necessarily the key focal point when it comes to designing subbases and subgrades for concrete pavements. Instead of building an exceptionally strong subbase, engineers should focus on uniformity, according to ACPA. This prevents high materials costs from over-design, while ensuring long-term performance and smoothness of the finished pavement. The underlying structure for a concrete pavement typically consists of: • The subbase, or layer(s) of select or engineered material of planned thickness placed between the subgrade and a concrete pavement to perform one or more functions. These can include: preventing pumping, distributing loads, providing drainage, minimizing frost action, or facilitating pavement construction. The subbase is an optional component. • The subgrade, or the natural ground, graded and compacted on which a pavement structure is built. Concrete pavements do not require subgrades to be exceptionally strong. Heavier loads are distributed over large areas of the subgrade because of the rigidity of the concrete pavement, and thus do not cause high subgrade pressures. It's important that the subgrade and subbase contain no abrupt changes or isolated weak or stiff spots. Performance surveys show that pavements resting on uniform, low-strength soils have provided longer service than pavements on stronger soils lacking uniformity. |
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| In fact, adds Robert Rodden, E.I.T., ACPA's Director of Technical Services, increasing subbase thickness too much may potentially lead to faulting. It also may lead to mid-slab cracking if other design details are not changed to compensate for the increased rigidity of the subbase. |  Asphalt (left) requires stronger base layers closer to the surface, compared to concrete pavement's need for more uniformity in its foundation. (Image: ACPA) |
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This runs counter to the principle of design for asphalt pavements. Asphalt requires successively stronger base layers closer to the surface to distribute the much higher pressure transmitted by wheel loads through each layer and ultimately to the subgrade. For more information on subbase/subgrade design, see ACPA's EB204P: Subgrades and Subbases for Concrete Pavement. Click here to order a copy from ACPA's online bookstore or call Customer Service at 1-800-868-6733. Be sure to reference "EB204P." |
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Advertisement |
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Three Tools You Can't Live Without for Pavement Design |
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| Here's an update on some of the state of the art software available to pavement designers: | ||||
| • AirPave:
ACPA is finalizing the latest upgrade to its AirPave design software for airport runways and other airfield infrastructure. With the new version, engineers will be able customize pavement thicknesses to accommodate an entire fleet of aircraft. AirPave users follow three easy steps: 1. Input specific characteristics about the pavement to be constructed, including a thickness value; 2. Choose from a list of more than 25 popular aircraft with more than 59 configurations, including the A300, B777, and military aircraft, as well as other vehicles that travel on airfields. 3. Finally, run a report that calculates fatigue life and stress ratios for pavements bearing loads. The new version is slated for release later this summer. |
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| For more information, contact Gary Mitchell, P.E., ACPA's Director of Airfields, at 704-948-8988. | Mechanize concrete pavement airfield design using AirPave. (Photo: Getty Images) | |||
| • StreetPave:
ACPA's updated StreetPave design software program makes pavement comparisons more objective, while also allowing a higher degree of |
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pavement optimization for local and highway applications. |
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ACPA
Concrete Pavement Progress is published 12 times per year and covers current
practices and case histories in the concrete pavement industry. ACPA Concrete
Pavement Progress is distributed free of charge to public officials, ACPA
members, executive committee, board of directors, and affiliated chapter/state
paving associations. |
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American Concrete Pavement Association |
2008 Chairman,
ACPA Board of Directors |
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