Transportation Defined

Transportation defined: Hydrodemolition and MMC

Transportation defined: Hydrodemolition and MMC

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Transportation defined: Hydrodemolition and MMC

Transportation defined: Hydrodemolition and MMC

June 4, 2014

We have a couple of new terms for you today and they both have to do with concrete...

First up is hydrodemolition. Simply put, it’s a method that uses a high-pressure stream of water to remove concrete, or other types of surfaces.

David Sikes, a resident engineer in ADOT’s Flagstaff District, explains in the video above that using the hydrodemolition tool is much more efficient than other methods for removing concrete.

“We get this machine that’s got about an 8-foot-wide head with nozzles on it that puts out the high-pressure water and we can take off the surface concrete fairly quickly,” Sikes says in the video. “If we had to do it with chipping hammers, it would probably double the work time.”

Besides being efficient, Hydrodemolition can allow crews to control the depth of the cut they’re making (the machine’s pressure can be adjusted and its nozzles can be controlled). Hydrodemolition also helps control any dust – crews use a vacuum hose to suction water and debris as they go along.

The next term we’d like to define is Microsilica Modified Concrete (MMC).

MMC is a type of concrete that’s mixed with microsilica, which according to the FHWA, “is a byproduct of the reduction of high-purity quartz with coal in electric furnaces in the production of silicon and ferrosilicon alloys.” MMC has plastic fibers in the mix, too, as shown in the video above.

The result is a dense and durable concrete that is very appropriate for bridge decks like I-15 Virgin River Bridges 3 and 7, Sikes says.

“Trucks traveling south on I-15 carry salt-laden slush from roadways to the north. As the air temperature warms, the salt mixture drops off of the trucks onto the bridge decks.  If the salt is able to penetrate the concrete down to the rebar, the rebar will corrode, causing the concrete surface to pop off,” he said. “MMC is a very dense concrete that will resist the penetration of the salt mixture. We should have a durable bridge deck for a number of years.”

Transportation Defined is a series of explanatory blog posts designed to define the things you see on your everyday commute. Let us know if there's something you'd like to see explained ... leave a comment here on the blog or over on our Facebook page!

Transportation Defined: Lead Abatement

Transportation Defined: Lead Abatement

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Transportation Defined: Lead Abatement

Transportation Defined: Lead Abatement

February 11, 2014

While it does have a number of valuable uses, lead can be pretty toxic to humans and animals, so it’s best to steer clear the stuff when possible.

But, if you can’t avoid it – say when it’s in paint that was used to coat the surface of a 100-year-old bridge you’ve been charged with rehabilitating – your best bet is to have it safely removed by professionals.

That’s the route ADOT took, as you can see in the video above.

Lead abatement

According to ADOT Hazardous Materials Coordinator Ed Green, any painted surface that’s going to be modified, renovated or demolished by ADOT is always tested for lead.

A before (top photo/Aug. 2013) and after (bottom photo/Jan. 2014) look at the Chevelon Creek Bridge.

If a structure tests positive, as was the case with the Chevelon Creek Bridge, steps are taken to either remove the lead paint or encapsulate it so it’s not a hazard to the environment.

For the Chevelon Creek Bridge, the only option was to completely remove the paint…

Located in Navajo County, about 12 miles southeast of Winslow, the Chevelon Creek Bridge was built in 1913 on the old road that connected Winslow and Holbrook prior to the construction of Route 66.

The bridge, which had been painted and re-painted several times since it was first constructed over 100 years ago, was due for a little rehab that included deck replacement, steel repairs, etc. (we’ll tell you more about the entire project soon).

In order to comply with the National Environmental Policy Act, crews had to figure out how to get the lead paint off the structure without introducing it into the environment and water below.

“What we had to do is what we call lead abatement, which means we’re going to remove all that lead-bearing material and get it out of the environment,” says ADOT Historic Preservation Specialist David Zimmerman in the video above. “We’re going to take it to a special landfill where they’re engineered to deal with these kinds of materials.”

How’d they do it?

Crews built a temporary aluminum deck underneath the bridge. Next, they covered the whole bridge in plastic so that none of the toxic lead paint could fall into the canyon below.

Once the bridge was “cocooned” in plastic, workers sandblasted the lead paint off the structure, contained it and properly disposed of it before repainting the bridge using modern, non-lead based paint.

Fun fact: Since sand is very abrasive and would have degraded the bridge’s metal, crushed walnut shells were used to blast the paint off (baking soda can also be used for a less abrasive “sand” blast).

Transportation Defined is a series of explanatory blog posts designed to define the things you see on your everyday commute. Let us know if there's something you'd like to see explained ... leave a comment here on the blog or over on our Facebook page!

Transportation Defined: Geogrid

Transportation Defined: Geogrid

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Transportation Defined: Geogrid

Transportation Defined: Geogrid

January 9, 2014

You know that there are layers of dirt and rock beneath the surface you drive on, but would you guess that some roads are built on top of a special material (in addition to all the dirt and rocks)?

What we’re referring to is called geogrid, which is a polymer material that is used to reinforce soil.

If the term sounds familiar, we’re glad. Because that means maybe you watched our video from August about the paving of US 89T (we definitely appreciate our devoted blog/YouTube followers!).

In that video, you can see that a geogrid material was used on that project. You can also hear a good explanation of how geogrid works with the dirt and rocks. In case you missed it…

“AB is aggregate base – it’s the gravel that goes down under the asphalt. It helps distribute the weight of the traffic that’s on the asphalt,” Resident Engineer Steve Monroe says in the video. “By using the geogrid, we can cut out two inches of that AB. The geogrid is much less expensive and easier to put down than hauling in all that extra AB.”

A closer look at geogrid on the US 89T project.

How is geogrid installed?

Once the subgrade material (that’s the layer under everything else) is prepared, a geogrid is placed on top (sometimes along with a geotextile filter fabric used to keep fine material from migrating into the aggregate base). The openings in the geogrid are meant to interlock with the granular aggregate base – check out the video above to see what we mean.

After the geogrid goes down, the aggregate base is placed and finally, paving takes place on top of all those layers.

Why does it work?

When testing determines it necessary, geogrid material can improve the ability of the subgrade to carry traffic loads and reduce rutting or pavement failure over weak soils. It does this by providing tensile strength and distributing the load from a vehicle to a wider area.

Transportation Defined is a series of explanatory blog posts designed to define the things you see on your everyday commute. Let us know if there's something you'd like to see explained ... leave a comment here on the blog or over on our Facebook page!

Transportation Defined: Rumble Strips

Transportation Defined: Rumble Strips

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Transportation Defined: Rumble Strips

Transportation Defined: Rumble Strips

September 4, 2013

A center lane rumble strip.

If you’ve ever drifted a little too far outside a travel lane, only to be jolted back to attention with a not-so-subtle shake, you know what rumble strips are.

For the drivers out there who never have encountered a rumble strip, let us explain a little further…

Rumble strips are indentations often placed on the shoulders of highways to alert drivers that the edge of the paved roadway surface is near.

The concept may be simple, but rumble strips aren’t last-minute additions. There’s a lot of thought that goes into installing these safety features.

How they’re made

ADOT’s current standard calls for rumble strips to be ground into the asphalt pavement. A grinding wheel on a special moving vehicle is used to grind (or carve) the rumble strips into the road.

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A close up look at a rumble strip.

Rumble strips are installed after the pavement surface has fully hardened. Previous ADOT rumble strips (used in the 1980s) were installed with a special wheel in hot asphalt, however, this method doesn’t provide the level of rumble feedback (that not-so-subtle shake we mentioned earlier) as do the current designs.

Want to know more?

Rumble strips are ground to a depth of 3/8 inches every 12 inches, with a 10-foot gap every 40 feet to allow bicyclists to cross the rumble pattern without dropping into the depressions (on roads that allow bicyclists). They come in 6-inch, 8-inch and 12-inch widths, depending on the roadway type and shoulder width.

Rumble strips are typically placed about 1 foot to the outside of the edge line, but can be placed under the edge line if the shoulder width is narrow. On divided highways, rumble strips are usually placed on both shoulders (left and right). ADOT is starting to phase in the use of centerline rumble strips to potentially reduce the chances of head-on and sideswipe crashes (see photo above).

Rumble strips are NOT typically placed in urban or suburban areas due to noise considerations.

You can learn more about ADOT’s policies concerning rumble strips (and other pavement markings) by checking out the ADOT website.

Transportation Defined is a series of explanatory blog posts designed to define the things you see on your everyday commute. Let us know if there's something you'd like to see explained ... leave a comment here on the blog or over on our Facebook page!

Transportation Defined: Curing Compound

Transportation Defined: Curing Compound

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Transportation Defined: Curing Compound

Transportation Defined: Curing Compound

August 6, 2013

Workers spraying concrete curing compound.

No, the photo at right isn’t an example of ADOT’s latest design “statement.” Despite how it might look, the cement is not being painted a pale pink hue.

What’s being sprayed on the concrete pavement is a curing compound. It goes on pink so crews can see where it has been applied, but it dries clear.

This curing compound is sprayed on to prevent moisture from evaporating from the freshly placed concrete. It creates a kind of membrane that keeps the water in so the concrete can properly cure to its intended level of strength/hardness (you might remember that we’ve blogged before about the number of factors that can have an impact on concrete pavement).

Once the concrete has properly cured, the compound is sandblasted off portions of the road that will be painted (lane stripes, retaining walls, etc.) because it leaves behind a slight buildup that makes it difficult for paint to adhere.

Transportation Defined is a series of explanatory blog posts designed to define the things you see on your everyday commute. Let us know if there's something you'd like to see explained ... leave a comment here on the blog or over on our Facebook page!

Transportation Defined: Minibenches

Transportation Defined: Minibenches

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Transportation Defined: Minibenches

Transportation Defined: Minibenches

July 9, 2013

Minibenching on the I-10 Marsh Station project.

No, the stair-step design on the slope at right isn’t just for looks…

The “steps” are actually referred to as minibenches and they serve as an erosion and sediment control measure on slopes like the one in the photo (that happens to be the I-10 Marsh Station project, in case you were wondering).

Minibenches are designed to retain soil on slopes that may otherwise be susceptible to erosion due to weather.

They also improve water infiltration and basically work to increase the effectiveness of other temporary or permanent soil stabilization efforts.

How are they made?

They’re created with heavy-duty equipment. The minibenches on the I-10 Marsh Station project were made with an excavator that was used to “dig” out the benches starting from the top of the slope down. Those particular minibenches will get wattles, which will assist in keeping the slopes from eroding. They'll also get seeded in another effort to achieve final stabilization of the slopes.

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A closer look at minibenches.

When are minibenches used?

Minibenching can be implemented on projects in areas that have soils prone to erosion.

Minibenching is also considered in cases where there’s a large, engineered slope that needs to be created or if there’s a particularly steep slope on a project.

Transportation Defined is a series of explanatory blog posts designed to define the things you see on your everyday commute. Let us know if there's something you'd like to see explained ... leave a comment here on the blog or over on our Facebook page!

Transportation Defined: Reclaimed Asphalt Pavement

Transportation Defined: Reclaimed Asphalt Pavement

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Transportation Defined: Reclaimed Asphalt Pavement

Transportation Defined: Reclaimed Asphalt Pavement

June 18, 2013

RAP is old asphalt pavement that's been ground up for use in the production of new asphalt concrete.

You’ve likely recycled plastic, glass, paper, maybe even your old electronics, but did you know ADOT recycles its old asphalt pavement?

Known as Reclaimed Asphalt Pavement (or, RAP if you’re short on time), this material is old asphalt pavement that has been ground up for use in the production of new asphalt pavement.

How it’s used
Once the asphalt pavement has been milled off the old roadway, it goes to an area where it is run through various screens in order to separate out the appropriate sized pieces – this is all done according to the new pavement’s specifications.

When the proper sized pieces are sorted out, the material can be mixed in with the new aggregate (rocks).

Besides being sorted for size, the RAP material also undergoes testing to determine how much asphalt (which is a binder) is still attached to each piece of aggregate because the binder is being recycled, too.

Why recycle?
ADOT allows 15 to 25 percent of some new pavements to be made up of reclaimed material.

By recycling the old asphalt pavement, less new aggregate and binder (asphalt) will be needed. That means the contractor doesn’t have to crush or haul as much new aggregate and since those costs are part of the contractor’s bid, those savings are realized by ADOT (and the taxpayers).

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RAP is being used for the N20 project.

The same goes for the binder (asphalt) that’s used in the new mix. If an asphalt mix design calls for 5 percent binder, and 1 percent of that can come from the reclaimed material, then ADOT only has to pay for 4 percent. Typically, binder costs about $500/ton and some projects can require 2,000 - 3,000 tons of binder (another cost savings!).

RAP on the roads
Right now, RAP is being used for the N20 paving project. About 15 percent of the new pavement mixture will be recycled from asphalt millings off of an I-40 pavement project.

Transportation Defined is a series of explanatory blog posts designed to define the things you see on your everyday commute. Let us know if there's something you'd like to see explained ... leave a comment here on the blog or over on our Facebook page!

Transportation Defined: Time Domain Reflectometry

Transportation Defined: Time Domain Reflectometry

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Transportation Defined: Time Domain Reflectometry

Transportation Defined: Time Domain Reflectometry

April 9, 2013

The TDR cable can be seen above alongside the inclinometer casing.

You might remember that we blogged about inclinometers back in February – they’re the instruments used to measure slope inclination or movement at specific locations.

Well, today we have another technology that we want to tell you about called Time Domain Reflectometry.

Like inclinometers, TDR can help our geotechnical experts and geologists measure movement of a slope or a landslide. However, TDR technology looks and operates a little differently from inclinometers.

How does it work and what is it used for?

TDR technology consists of a coaxial cable (similar to the one that's coming out of your television set – but more heavy duty) that’s embedded or grouted within a vertically drilled hole (it might help if you can recall our milkshake straw analogy from the inclinometer post).

Alternately, a TDR cable can be attached to a grouted inclinometer casing (see photo above). That coaxial cable that's in the ground is then connected to a cable tester that sits outside the drilled hole.

You should know that the cable is installed in a precise way so that the zones of ground movement (shear planes) in the landslide mass are intersected.

Once the cable is in the ground, it will be able to detect ground movement that’s happening within the vicinity of the cable. If there is movement in the landslide mass, the cable becomes kinked, stretched or even sheared.

This damage creates a change in the impedance of the cable, which can be detected by the cable tester, says ADOT Engineering Geologist Nick Priznar.

“The cable tester sends an electronic voltage pulse that is reflected like radar from a damaged location in the coaxial cable,” he said. “The returned signal will show where changes have occurred along the length of the cable and can be compared to the signal obtained originally when the cable was undamaged. This makes it possible to determine the depth, progression and general magnitude of movement of the landslide zone that was intersected.”

TDR technology is often used in conjunction with inclinometers. That’s because the lifespan of the inclinometer casing is limited – slide plane movement can shear or distort the casing, eliminating its stable base or reducing its diameter to a point where the inclinometer probe cannot pass through the casing.

When, or if, that happens, the TDR system can be used to continue to monitor the movement/displacement. That’s because the TDR cable is usually more resilient to displacement than the inclinometer casing.

However the two systems are not equivalent, according to Priznar. While the inclinometer data provides actual measures of deflections the TDR cable tester can only provide depth and relative magnitude of displacement.

How are TDRs being used on US 89?

At this time ADOT engineers are in the process of developing the best strategy for implementing TDR technology for US 89.

In anticipation of utilizing this technology, TDR cables are being be secured along the outside diameter of select slope inclinometer guide casings (again, see photo above).

Transportation Defined is a series of explanatory blog posts designed to define the things you see on your everyday commute. Let us know if there's something you'd like to see explained ... leave a comment here on the blog or over on our Facebook page!

Transportation Defined: Truck Escape Ramps

Transportation Defined: Truck Escape Ramps

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Transportation Defined: Truck Escape Ramps

Transportation Defined: Truck Escape Ramps

March 28, 2013

Unless you drive a big rig, truck escape ramps probably aren’t something you think of too often...

But, you are a reader of the ADOT Blog, which means you're the sort of inquisitive person whose curiosity demands to know what things are and how they work. So, about those truck escape ramps…

There are two primary types – gravity ramps and gravel arrester beds.

A gravity ramp works essentially like this: a truck takes the ramp and experiences an uphill grade that naturally will stop the truck.

A gravel arrester bed works in a completely different way, but the goal is the same. This ramp is on a flat-level grade. Trucks will take the ramp and run into a bed that’s full of small, round gravel. The friction from the wheels going through the gravel is what slows the truck down to a stop.

An ADOT roadway design manager explains that the type of ramp used depends on the spot in which it is being built.

Ramp or no ramp
Roadway design guidelines help engineers decide whether or not a truck escape ramp is necessary at a certain location. But other factors are looked at, too, including the grade of the highway and whether or not there are curves or a stop at the end of the grade. Observation also plays a part – if ADOT district employees, DPS officers or truck drivers notice a lot of the big trucks are experiencing hot brakes at a certain location, an escape ramp may be considered.

Getting out
Trucks typically can maneuver off the gravity ramp fairly easily, but because the gravel arrester beds are pretty deep, a towing vehicle has to pull trucks out of those.

There are service roads next to the ramps, so a tow truck can drive alongside and get into position. There also are concrete anchors spaced along the service road that assist with towing the vehicle out of the gravel arrester bed.

One more thing
We thought maybe you’d like an explanation of why these ramps are necessary in the first place. Here’s the answer, according to ADOT’s Roadway Design Guidelines:

The combination of heavy trucks and steep highway downgrades presents a potential safety hazard... Defective or incorrectly adjusted braking systems on trucks or trailer, among other things, can contribute to brake overheating and failure resulting in the driver's inability to control vehicle speeds on downgrades.

Truck escape ramps offer an opportunity for out-of-control trucks to exit the highway and come to a controlled stop.

But we can’t forget…
Brake check areas are just as important as the truck escape ramps. You’ll find these areas at the top of a summit or just ahead of a long downhill grade – they give truck drivers the chance to check their brakes before heading down.

Transportation Defined is a series of explanatory blog posts designed to define the things you see on your everyday commute. Let us know if there's something you'd like to see explained ... leave a comment here on the blog or over on our Facebook page!

Transportation Defined: Pavement Design Life

Transportation Defined: Pavement Design Life

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Transportation Defined: Pavement Design Life

Transportation Defined: Pavement Design Life

March 20, 2013

Road Pavement

After 300-plus blog posts, you’d think that by now we’d have covered everything there possibly is to know about pavement...

But you’d be wrong.

Certainly, it’s not from a lack of trying – we’ve blogged about quiet pavement, pavement at airports, pavement materials testing, pavement markers and even the impact weather and climate can have on pavement. Oh, and remember when we explained how our crews are able to make sure pavement is as smooth as it can be (bonus points if you can recall how a profilograph works)?

It’s just that there’s so much to know about pavement (we’re not kidding – there really is) that we haven’t even scratched the surface.

Which brings us to today’s topic: pavement design life.

Pavement design life is a term that engineers use when they’re planning to build a new road or maintain an existing roadway. They’ll also use a number of years to go along with it, for example: 10-year pavement design life, 20-year pavement design life, etc.

The phrase should not be taken to imply that a road is only being built to survive for a set number of years. What it does represent is the road’s age at which some preventative maintenance or reconstruction will be considered so the road can continue to be durable and useful for the traffic it’s serving.

“For a typical highway, we generally will design an asphalt pavement for 20 years,” said ADOT Pavement Design Group Manager Paul Burch. “It does not mean that the road’s going to be falling apart and rubble in 20 years.”

A little more on pavement design…

Burch says that when engineers want to build a road, they take a lot into consideration, including soil condition, location, expected traffic levels and the area’s climate. Once those factors are determined – and the engineers know the pavement design life they want to build for – design begins.

All those conditions play a role in how the pavement is designed. Say, for example, the road’s being built in an area that gets very cold weather. If that’s the case, engineers will adjust the asphalt pavement mix to account for the temperature extremes.

Now, what if there’s a road that was constructed decades ago that’s not serving the traffic levels very well … can it be built up to a 20-year pavement design life?

Of course it can!

“What we would do if we were to inherit a road like that is we’d start by getting soil samples to test so we can determine what the strength of the soil is. Or, we could do Falling Weight Deflectometer testing so we could determine the strength of the existing roadway and the underlying soils through a method called 'Back Calculation.' From there, we would estimate what our traffic level would be and what design life we would want to design for,” said Burch, adding that the next step would be to create a design that takes all those important factors into account.

For more on pavement, check out our previous blog posts. And, stay tuned – we promise there are more pavement posts to come!

Transportation Defined is a series of explanatory blog posts designed to define the things you see on your everyday commute. Let us know if there's something you'd like to see explained ... leave a comment here on the blog or over on our Facebook page!