Road improvement project 4

May 2014

With the roadbed now properly graded and flattened it was almost ready to pave, but a bunch of little fiddly bits remained to be fixed up first. The pavement layers would build up a specific height to the final surface, so everything had to be planned to match that.

[Thumbnail pictures are linked to larger ones.]

Jackhammering Any existing paved surfaces such as driveways or sidewalk-like structures needed to have a nice edge established, that the new paving would meet in a neat line. Thus, a bunch of jackhammer work was needed.   Ptttbbttthththbbtbtbtbt ...

Easy edge line Deeper edge line
Some of these lines were relatively easy to establish, only needing a couple of inches trimmed back, and others involved much deeper cuts past existing features of residential frontage. The new road would just barely clear someone's stone pillars, for example, but the way things worked out no outright destruction of property was necessary to make the required width.

Removing pavement by sections Where a deep cut was needed, the line was established first and then crosscuts were done to subdivide the rest into easily-removed chunks. All of this was later collected by the bobcat and taken away.

Air-powered or not, jackhammering is a lot of work. I've done some back in the day; the hardest part is lifting the 80-pound object to move it to the next cut point. The guy was totally sweat-soaked after he finished trimming up everything along the roadway. At least someone had brought him lunch today, and left it on the truck liftgate for him.

Intersection grade designed on the fly Although the hump near the intersection had been leveled, the exact profile at the turn hadn't quite been figured out yet. The grader operator spent quite a while down here, going back and forth and playing with blade angles and depths -- later I asked him if he was sort of designing all that on the fly, and he said "uh, yeah, does it look that way?" Evidently there wasn't a specific profile plan for that area but everything had to slope down the right way to the other catch basins that they'd already put on either side of the intersection, and they also wanted to minimize the amount of crown that would carry runoff into the wetland on the right.

Catch basin temporary cover The newer catch basins were dug out and exposed a little more, but still covered up with plates to prevent anything [including water, basically] from dropping into them during more operations. Some temporary berms of fill were put in to ramp up to existing driveways so people could get in and out in the interim. A little final tweaking and smoothing of the overall roadbed grade was done, and things were finally ready for the pavers to arrive.

    Bind me in black

Paving equipment lined up Warm dump trucks
And arrive they did, getting one of the earliest morning starts I'd seen yet on this project -- I heard engines running and basically tumbled out of bed and grabbed the camera. The equipment and supply trucks were lined up on the subdivision road ready to go, and they were already moving.

As I walked past one of the dump trucks I felt quite a bit of heat coming off it, and realized oh, right, paving is a hot operation! Went back and got the infrared camera for more or less the same shot, and it was easy to tell which trucks were loaded with hot asphalt.

Thermal image of asphalt truck The load was not in contact all the way up the sides of the dump, but made for an amusing "whatcha got in there?" profile. Despite the fact that the metal dump freely conducts heat out, one of the drivers told me that a truckload of hop-top can basically stay workably warm "all day" if it has to sit around for a while.

Removing temporary berm Pre-rolling grade base
A quick pass to remove the temporary driveway berms and roll the rest to 90-degrees flat was done, to make sure the substrate would be uniform and at the right level up to the meeting point. Any residents wanting to drive out would have to bump down a four-inch dropoff, but they were about to get trapped in by the paving job for a little while anyway.

Roller water tank They spray-painted a quick guide line up the middle of the roadbed, and then the equipment headed up to the top of the hill where they'd start. As I walked up to follow I spotted fluid leaking out a tank cap on the roller -- just water, though, not anything nasty.

Paving machine in operation The paver was one we typically see on road jobs these days, but I'd never taken a close look at one. It's a Lee Boy 8616, suited for small to medium jobs, and is basically a spreader with a small reserve hopper so it can keep going while supply trucks swap in and out ahead of it. This one also features an electrically powered heater to keep the asphalt up at temperature as it gets distributed.

Underside of paver Not that much to see under the business end of the paver; basically a distribution slot and a heavy flat plate behind it to give an initial tamp to the material being laid down. This is referred to as the screed, and its design and how it attaches to the rest of the machine is significant in how it works to lay a nice level surface in one pass.

Ingestion transport of paver Distribution auger
The other major components are a conveyer to bring asphalt in from the hopper, and a couple of feed augers to spread the stuff out evenly along the screed in both directions. The screed can extend outward on both sides to accomodate varying widths needed, and those pieces adjust in height to maintain a proper crown profile toward the edges. The thing on the coily wire is a "sonic sensor", which determines when the screed is full of material and stops feeding until more is needed.

Feeding paver from dump truck The hopper opens to full width to accept a larger batch of asphalt, and is designed to fit under and around the back end of a typical dump truck. The pair moves along like this until the truck is empty.

The paver pushes the truck along In fact, the paver is designed to be able to push its feed truck along, using little rollers [arrow] to bear on the back wheels. Obviously the truck has to stay in neutral for this, and possibly apply a little resistive braking when the operation is heading downhill.

The things one just doesn't realize about construction equipment until a closer look is taken...

Dumper up at full height The first empty truck pulled away some, then stopped and raised its dump to full height. It was about here when I thought that the paving operation moving along with a raised dump might be another height clearance problem.

Cleaning with diesel The stop and full raise was to drop any remaining bits of asphalt, and so the driver could get in under the tailgate and spray the whole bed down with ... *diesel fuel*. That's what is generally used as a release agent on tools and containers that handle asphalt to prevent it from permanently sticking to surfaces.

This is one of the times nobody worries about dropping petroleum products all over the ground, since that's pretty much what asphalt is anyway.

Ducking the wires again The truck driver explaining the diesel also reassured me that they're used to dealing with low clearances, especially when working in urban environments where they've got to "duck wires every 20 feet" as he put it. Their crews took appropriate care to lower the dumps under the usual problematic spots.

First strip done Thermal view of first strip
The three trucks of asphalt that had arrived with all the paving stuff were enough for a one lane strip about halfway down the stretch, which now sat there baking away, made much more obvious in an IR shot. Spec for asphalt being laid is north of 300 degrees, to give it the flexibility and binding ability needed. In fact there's a whole optimal design cooling profile for the various stages of spreading and rolling.

The trucks then headed off for more asphalt, the supplier of which was conveniently only a couple of miles down the road.

Rolling is a wet process The paver's line was able to run right along this driveway cut and match the line, still leaving a two-inch or so height difference for the final layer later.

Rather than dribbling diesel all over the place, rollers use a water film and scrapers to prevent the material from sticking to them. That's why the water tank on the roller at the start of the operation was topped right up enough to leak a little when sitting on a slant. While diesel is used more like a cleaning solvent, water makes a barrier layer to the hydrophobic asphalt with the idea that it never gets on the roller in the first place. So hot rolling is always a wet operation, and with the pavement still above 220F it steams off pretty quickly.

Second strip starting The trucks soon returned, and they started the second strip down the other half of the road. Basically they were working from the far end of the road back toward the subdivision entrance where they would exit through.

Blending halves The two runs were basically butted together, and any minor mismatches were smoothed across by hand all the way down.

Oops, gap in distribution As they started the third strip, there was apparently some distribution problem -- a lump of stuff that blocked the screed slot in one place. They backed over this and did whatever was needed to clear it, then took another pass which filled in the gap.

Thermal view of fresh pavement A closer IR shot of what emerged from under the paver showed the stuff going down at a nice healthy temperature, not entirely uniform but close enough.

Third strip down Thermal comparison of courses
Looking back thermally at the three runs, it was easy to tell which order they'd gone down in. Between strips there was some amount of hurry-up-and-wait for the supply trucks to get back with fresh loads.

Paver screed extension Deeper driveway cuts were accomodated by extending the screed on the fly to meet the edge. A little bit of hand shoveling by the guys alongside the machine quickly filled in any missing bits.

Paver controls The paver has multiple control positions, and the guys driving it were constantly fiddling with layer depth and profile and screed extension as it moved along.

Working around catch basin They ducked in a little around the catch basins to avoid dumping pavement in on top of the steel plates on top. They still got some on it...

Along the front Other than that it was pretty straightforward running, although they didn't exactly stay 2 feet off the stakes.

Looks like colorful lava The fresh stuff was well above 300F now, looking like colorful lava of some sort in the IR. With the auto-ranging nature of the FLIR, blue doesn't mean anything like "cold" here! This is one of a couple different color map schemes the camera has; the other one we often see is "rainbow" and I think it's less intuitive in terms of how we would "see" hot and cold.

Rollin' rollin' rollin' I tried to grab a detail video of how the asphalt deforms just ahead of the roller, but that mostly failed. Suffice to say that it mashes down nicely but does exhibit just a little elastic rebound afterward.

Water boiling out of asphalt What worked much better was a detail of the roller water boiling back out of the mix; the short video is here and gives an interesting stereo sound-field of the bubbling going on all around. The big-picture is left linked here to show the relative sizes of stone used. This was the "binder" layer, which generally uses a certain proportion of larger stone but still includes the fines to help seal everything together. Its surface winds up a bit rough but that makes it a little more stable, forming a solid base for the final layer which would be finer-grained.

Firewalking The recent runs were still wikkid-hot, that didn't bother some of the guys who walked over it with impunity. With thick shoes on, of course! I was clearly going to stay off them for a while, and for chronicling purposes I had to sort of plan ahead as to which side of the street I was going to be on before the paver came through any one stretch.

Nice driveway approach The conveniently-installed niece of the developer, of course, was going to get a nice approach into her own driveway. The old man was over there to make sure of that.

Filling in intersection paving Finishing by hand
They took a couple more passes across to empty the hopper and fill in the rest of the intersection, and as the paver then departed some of the small details and final leveling had to be done by hand old-school style.

One other significant thing implied by asphalt finally going down was that there would be no more vibrating roller.

Curb box locator bricks The various grading and dirt movement had completely lost my marker for where the water shutoff was, so I dug around to re-locate it. I discovered that it was now under the edge of the asphalt -- the vertical brick showing here was one of two standing on end on top of a third, the other one still hidden behind in the dirt. This little assembly was on top of a layer of plastic and the rather subsided curb box itself, which I'd put in just to make it easier to find and excavate again if needed. I knew they were going to screw this up for me somehow...

Obvious water shutoff marker There was already a stake near the valve box but not in the right place anymore; I left the hole partially open and made a really obvious marker for where this was. We would figure out later what anybody wanted to do about this, be it the developer or the town or whoever.

Go to Part 5: Access and adjustments

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