Pavia Systems: The Gravel Pit Blog

Constructing a porous asphalt pavement is no more challenging than constructing a dense graded pavement, but is different in that more attention must be paid to keeping the air voids open. Some tips for the field:

• First, excavating must be done with tracked or lightly loaded equipment in order to prevent subgrade compaction.
• Geotextiles must go down immediately after fine grading of the subgrade.
• Single-sized base aggregate must be clean and washed, and only lightly compacted – don’t use vibration!
• A choker course is recommended, as it will provide a more stable base for paving.
• After these crucial steps, paving can be done much as usual, but consider a tracked paver and make sure to keep equipment off the aggregate base as much as possible.

Open graded, washed aggregate base with keys for scale

To learn more about construction or techniques for designing your mix, check out:

• NAPA’s Porous Asphalt Pavements for Stormwater Management: Design Construction, and Maintenance Guide (IS-131),
• Pavement Interactive article on Permeable Pavements, or
• The Pennsylvania Stormwater BMP.

The Smoothness Playbook was the topic in the most recent RoadReady newsletter. An additional best practice add to the Smoothness Playbook is to maintain the proper head of material behind the screed. Here is a slide from our Paver Operations course to help illustrate the impacts of not maintaining proper head of material.

In addition to our Paver Operations course, we would recommend that you check out the following resources for more information on smoothness:

• The Pavement Interactive article on Roadway Roughness.
• Everything You Wanted to Know About IRI, But Were Afraid to Ask! describes the history of roughness measurement and helps explains the physical meaning of IRI.
• Smoothness Matters is a publication put out by the Asphalt Pavement Alliance and looks in depth at the correlation between smooth roads and decreased vehicle fuel consumption.

Let us know if you have any additional resources on smoothness as we’d love to include them here on our blog!

Constructing high quality longitudinal joints was the topic in the most recent RoadReady newsletter . One of the critical steps to constructing a quality joint is compacting the joint properly. Below is an animation illustrating proper placement of the roller.

1. BEST PRACTICE: Rolling from the hot side 6 inches (150 mm) away from the joint. The first roller pass is done in vibratory mode with the entire roller wheel on the hot lane about 6 inches (150 mm) from the joint.  This compaction technique pushes the material between the roller and joint towards the joint during the initial roller pass, which crowds the mix at the joint yielding a an opportunity to achieve better density during the 2nd pass when the roller compacts the joint directly.
2. Rolling from the hot side.  NOT RECOMMENDED. The first roller pass occurs in vibratory mode with the majority of the roller wheel on the hot lane and overlapped onto the cold lane by about 6 inches (150 mm). Because part of the weight of the roller is supported by the previously compacted cold lane, it can cause a situation where the roller “bridges” over the joint or leaves it only partially compacted.
3. Rolling from the cold side.  NOT RECOMMENDED. The first roller pass occurs in the static mode with the majority of the roller wheel on the cold lane and overlapped onto the hot lane by about 6 inches (150 mm). This technique is believed to pinch the joint together.  The reason this is not a recommended technique is because the timing in this type of rolling is critical.  When the roller is operated on the cold side of the joint, the hot side undergoes cooling which makes it difficult to achieve the desired compaction level before the hot side reaches cessation temperature.

Here are some additional resources if you want to learn more about longitudinal joint construction, performance data and best practice:

• The Pavement Interactive Longitudinal Joint Construction article gives lots of practical construction solutions.
• NCAT’s Evaluation of Eight Longitudinal Joint Construction Techniques for Asphalt Pavements in Pennsylvania has performance data on joints in roadways constructed in several popular ways.
• We mentioned that we don’t recommend using handwork unless you have well trained and experienced crews. Here are some resources to help get your crews the knowledge they need: the Pavement Interactive HMA Placement Considerations article and our Paving Handwork course.

In our most recent newsletter, we discussed longitudinal joints and why they fail (if you aren’t subscribed to our newsletters – sign up here).

A great example of distress because of a non-uniform joint is illustrated in the image used courtesy of WSDOT below.

In our next newsletter, we’ll discuss joint construction methods and the best practices that, when properly performed, will alleviate many of the problems identified when constructing longitudinal joints, but in the meantime if you wanted to learn more about joint construction, check out the following:

• The Longitudinal Joint Article on Pavement Interactive.
• Our Components of Compaction course, that discusses joint compaction techniques and best practices.

If you have any additional joint construction resources, let us know and we’ll add them to the list. Until next time, drop us a line if you have any questions or suggestions for topics that you’d like to see us cover.

Are you applying tack coat properly?  As we learned in our newsletter on tack coats, the height of the spray bar and nozzle spray patterns have a significant effect on tack coat coverage.  Click on the interaction below to see how various combinations of spray bar height and nozzle pressure produce different coverage patterns. 

Want to learn more about tack coats, application rates, laydown timing, specs? Check out the following resources:

• A Pavement Interactive article on Tack Coats that describes the basic aspects and application considerations.  It also contains additional resources describing emulsions to help you understand how tack works. 
• Summary results from a Tack Coat Survey of all 50 states that shows how the state DOT’s use tack coat in their specifications.

Got other tack resources or links to share? Please let us know and we’ll add it to the list above.

In our most recent newsletter, we talked about Milling as a technique to level existing surfaces prior to paving. Below is an animation from our Construction course that shows the parts and processes of a typical milling machine. This course also provides an overview of all the construction activities associated with asphalt mix paving including also asphalt mix production, transport, placement, and compaction.

There is also a great article we’d reccomend looking at in Pavement Interactive, Existing Surface Preparation for Overlays, that covers all the common ways to prepare existing pavements for overlays. (Notice the familar milling animation? It’s from our Construction course!)

Building roads and highways can be dangerous work. Dangers in the work zone come from many sources, but we focused on Blind Spots in our most recent newsletter and wanted to provide more information as well as a preview from our newly updated Work Zone Safety course.

We’ve also found these two websites extremely helpful for aggregating information like policy, best practice and additional resources:

• WorkZoneSafety.org – clearinghouse for tools, resources and status related to Work Zone Safety and they do just that! This is a great place to get answers (or at the very least, the direction where to get answers) to any of your questions about work zone safety.
• FHWA Work Zone Safety Site - dedicated to Work Zone Safety, this FHWA site presents some staggering facts about the complexities around Work Zones as well a wealth of other information like best practices or updates from different agencies and states about what they are doing to make work zones safer.

As we mentioned earlier, Pavia Systems offers an online course on Work Zone Safety that takes folks through common work zone hazards, how to avoid them, other work zone safety practices and traffic control in the work zone.

There are several considerations and best practices when transporting asphalt pavement mixes that we discussed about in our most recent RoadReady newsletter, but we also wanted to provide some additional resources on our blog.

Here’s an animation from our End Dump Truck Exchange course that highlights how to properly back into the paver:

There are two articles on Pavement Interactive on transporting asphalt mix that we think provide great supplemental information:

• Ashphalt Mix Transporting (we really like the close up video of the truck loading):
  http://pavementinteractive.org/index.php?title=HMA_Transport
• Material Trasfer Vehicles, which provides a great overview of the types of MTV’s and when/why they are used:
  http://pavementinteractive.org/index.php?title=Material_Transfer_Vehicles

HMA Temperature Differentials were the topic of our most recent newsletter and we’ve heard feedback from some of you that you like to see additional resources listed here on our blog. For anyone interested in learning more about temperature differentials, segregation and how to manage the impacts, check out the following:

• Pavement Interactive article on Temperature Differentials (we especially like the “sequence of events” graphic): http://pavementinteractive.org/index.php?title=Temperature_Differentials.
• Pavement Interactive article about Segregation During Transport (including a short video of roads showing the effects of temperature differentials): http://pavementinteractive.org/index.php?title=Segregation_in_Transport.
• Pavia Systems Trucking Course, which highlights many best practices, including how to prevent  temperature segregation: http://training.paviasystems.com/catalog/view.php?id=34 (we also talk more about this course in our blog post on Aggregate Segregation from last August).
• Pavia Systems Components of Compaction Course, which covers compaction and cessation temperatures as well as many other best practices for compaction: http://training.paviasystems.com/catalog/view.php?id=3. 
• WSDOT Materials Lab “tech notes” about Temperature Differentials: http://www.wsdot.wa.gov/biz/mats/Pavement/Technotes/TemperatureDifferentials.pdf.

The HMA industry is doing some great things in the area of sustainability.  We’ve sent a couple of newsletters on the topic , available here, and wanted to include a list of resources as well as introduce our newest introductory course on Sustainability.

• What is sustainability in the context of the HMA Industry? (Pavia Newsletter)
• Sustainability and Paving.  Free 15 minute online training course. www.paviasystems.com/sustainability
• Recycled Asphalt Pavement. Free 15 minute online training course. Visit www.paviasystems.com/rap.
  • You’ll learn the history of RAP, its benefits and the key things you should consider for your business.
• Warm Mix Asphalt. Free 15 minute online training course. Visit www.paviasystems.com/warmmix.
  • You’ll learn what Warm Mix is, how it’s produced and why it matters for your business.
• Also, check out a new rating system created to measure sustainable practices at the University of Washington called GreenRoads.