You may hear this phrase often, especially during the summer. 

"Drivers should prepare for some delays on this state highway due to pavement preservation work between this and that milepost."

Maintaining state highways and freeway is a full-time gig for us. In fact, the tentative 2022-2026 Tentative Five-Year Transportation Facilities Construction Program even has $1 billion allocated for pavement preservation over the next five fiscal years. 

But what exactly do we mean when we say "pavement preservation?" 

To answer that question we turned to Andrew Roth, the assistant district engineer for ADOT's Northwest District. He broke down for us the major types of pavement preservation work crews get up to this time of year. In order of ascending cost we have:

Fog seal: This is the most common type of pavement maintenance. As we explained in an earlier blog post, fog seals contain emulsion – remember that's asphalt binders and water – onto a road to rejuvinate the asphalt and restore lost flexibility to the roadway surface. As Roth explained, the sun causes paving to start oxidizing, and fog sealing helps keeps that oxidization from getting into the deeper, structurally significant part of the road. 

Chip seal: We've told you about chip seals before, where aggregate (crush gravel) and an emulsion (asphalt binders plus water) are laid down together to form the new top road surface. Turns out though that there are two different types of chip seal. The first is what we just described. The second is known as a hot application, where different, heavier asphalt binders are sprayed on the roadway surface at temperatures between 350 and 400 degrees Farenheit and covered with chips that are pre-coated in asphalt. 

Slurry seal: This type of pavement preservation involves an emulsion, aggragate and a bit of dry-powder cement which is mixed in a specialized machine. The mix looks like chunky chocolate milk, Roth said, and looks brown on the road until it cures, when it looks like typical black asphalt. A slurry seal is especially good at sealing up cracks and keeping out water.

Micro-seal: Finally we come to the micro-seal, which is a lot like a slurry seal, but here you are getting into some heavy-duty chemistry, as the asphalt binders in the emulsion have different polymers so it acts different. A micro-seal can also be used to fill ruts, which alleviates any issues with water collecting on the road.

There also is something called a "cape seal," which is basically a chip seal covered by a slurry seal or micro seal. 

So those are the different types of pavement work you can expect to see while out on the road this summer. But there's a good reason why you see it while it's summer. Paving needs a specific temperature range that, depending on the work being, done cannot be either too cold or too hot. For example, a chip seal can only be applied when the pavement surface temperature is at least 85 degrees and the air temperature is at least 65 degrees and rising. A chip seal application must stop once the air temperature is 70 degrees or less and falling, while a slurry seal may be applied when both the pavement and air temperatures are above 45 degrees and rising. It has to stop if either the pavement or air are below 55 degrees and falling. And a hot application chip seal can't be done if the daytime air temperature will exceed or are forecast to exceed 110 degrees the day before, the day of or two days after it's applied. 

Furthermore, these treatments cannot be applied if rain is forecast within 24 of the pavement work. The same is true if there is the possibiity of freezing weather forecast, Roth said. 

That means paving work usually has fairly narrow time windows when it can be done, which become more narrow as you rise in elevation. 

As you might expect, one the most important elements for pavement preservation is having the right temperature range and plenty of sunshine. Those help evaporate the water used in the asphalt emulsion, which allows the pavement to cure properly. As we explained in an earlier blog, this is one of the major reasons for doing paving work during the day. While some of this could be done at night, and is under special circumstances, without daytime highs and sunlight, it takes much longer for the road surface to be ready for the driving public again. 

"It's a lot of artwork when it comes to applying these pavement treatments because of all the elements you are trying to monitor that drive construction," Roth said. 

The Greek philosopher Heraclitus of Ephesus, who died in roughly 475 B.C.E., is said to have been the originator of the phrase "the only constant in life is change."

And while that thought seems fine for philosophy books, what does it have to do with transportation? 

Well, it turns out that you can find change and new approaches in even a common task like paving a road.

Let's take ADOT's project on US 60 and State Route 260 at Show Low, for example. The work, which kicked off on June 1, will remove and replace a total of 11 miles along US 60 and SR 260 near Show Low, in addition to curb and gutter, sidewalk and guardrail work. 

So what's so innovative about that? Because, for this project, ADOT is using a relatively new type of pavement that will improve the road life. In layman's terms, the paving is more dense than what has been used in the past, achieved through greater compaction and a reduction in small air bubbles found in the mixture. This in turn makes it more durable and resistant to things such as rutting, cracking and moisture intrusion. 

Bottom line: That could expand the life of the driving surface by years. 

And if you need another reason to get excited about this, we have you covered. Because ADOT is using this new type of paving, it successfully applied for federal innovation funding. With those new dollars, the federal share of the $16 million project went up 5 percent to 99.3 percent. That means roughly an extra $800,000 is being covered by federal funds.

This isn't the first time ADOT has used this new type of paving, and there are more projects scheduled to utilize it moving forward. 

While we're pretty sure Heraclitus wasn't thinking specifically about paving a road when he talked about change, but improvements like what's happening near Show Low still help prove the 2,500-year old thinker right. 

Much like vehicle maintenance, regular road maintenance is needed to keep highways in good functional condition. ADOT continually invests in maintenance of highways and state roads across Arizona that serve countless commercial trucks and passenger vehicles every day.

In fact, ADOT spent more than half a billion dollars (yes, billion with a “B”) on pavement preservation projects alone in a five-year period from 2016 to 2020.

The paving projects during this period covered the state from SR 389 in Fredonia near the Utah state line to SR 92 in Sierra Vista and Business 19 in Nogales; and from SR 95 in La Paz County to US 191 and US 163 in the Navajo Nation and SR 75 in Greenlee County and everywhere in between.

Steve Boschen, director of ADOT’s Infrastructure and Delivery Operations Division, acknowledges the importance of these kinds of maintenance projects saying, “This is an important investment that we make each year to help keep traffic and commerce flowing in and around the state.”

He added how even these basic maintenance projects help achieve ADOT’s True North of safely home for every driver.

And ADOT will continue to invest in maintenance of Arizona’s highway infrastructure. In fact, another pavement project is starting in Show Low this month. This project will repave a total of 11 miles of US 60 and SR 260 in Show Low. For more information on that project, visit azdot.gov/ShowLow.

In addition to state roads, ADOT has also administered dozens of paving projects to help maintain local streets in communities across Arizona.

What do the Loop 202 (Red Mountain, Santan and South Mountain freeways), State Route 347 north of Maricopa and Interstate 40 near Seligman all have in common?

The answer is they have all benefited recently from today's topic: fog sealing. 

Fog sealing is a pavement preservation technique used to add life and extend the longevity of pavement. "Fog" just means a coat, which is how the treatment gets its name, according to Mohammed Elomeri, with ADOT's Central Engineering and Maintenance District.

A fog seal normally contains an emulsifying agent – or diluted asphalt – and a rejuvenator and is designed to seal narrow cracks and restore lost flexibility to the pavement surface, Elomeri said.

You can see the results from these photos taken on State Route 89A last year, and from fog seals done on Loop 101 (Agua Fria Freeway) in Glendale two years ago and many other stretches where fog sealing has been used to extend the life of pavement.

Doing regular pavement preservation such as a fog seal or a chip seal, which we mentioned in this blog from 2018, is an important part of maintaining highways. Mainly because it proves the old saying that an ounce of prevention is worth a pound of cure. It costs $3,000 per lane mile for a fog seal, while to mill down and replace the asphalt surface of the same mile would cost $300,000. 

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!