The Zero-Blanking Band For Rideability
|Editor's Note: In the last five years a new specification for rideability has been in development in a few states across the country. The new measurement, the zero-blanking band, is introducing a new specification for quality concrete roadways. As with all new requirements, it has created some questions in the minds of contractors. What is it? How is it different? Is it fair? This article is going to attempt to answer some of those questions. It is not intended to promote or endorse the use of the zero-blanking band. The article is also presenting basic guidelines for achieving a smooth, chatter-free pavement.
A special thank you is extended to the following people who took the time to be a part of the discussion and expressed their opinions on the zero-blanking band for rideability:
John Geiger, Vice President, Streu Construction Company, Two Rivers, Wisconsin
Michael Hall, Standard Specification Engineer, Wisconsin Department of Transportation
Jay Heinrich, Paving Superintendent, Stanley Johnsen Concrete Contractor Inc., Rapid City, South Dakota
Gary Hoffman, Chief Engineer, Pennsylvania Department of Transportation
Ron McMahon, Concrete Engineer, South Dakota Department of Transportation
John Muir, General Superintendent, Kinsley Construction Company, York, Pennsylvania
Nathan Reede, Project Manager, Upper Plains Contracting, Aberdeen, South Dakota
Also, a special thank you is extended to the following people who took the time to submit information:
Scott Oswald, Estimator, Upper Plains Contracting, Aberdeen, South Dakota
Bill Parcells, Pavement Surface Engineer, Kansas Department of Transportation
Neil Reede, President, Upper Plains Contracting, Aberdeen, South Dakota
Matt Ross, Executive Director, MO/KS Chapter, American Concrete Pavement Association, Overland Park, Kansas
What is the zero-blanking band for rideability and how is it different from the two-tenths band?
The zero-blanking band for rideability is a new specification being developed by some state Departments of Transportation (DOT) across the United States. A profilograph is used to measure the ride for both bands. A two-tenths blanking band does not count any bumps or chatter under two-tenths of an inch against the total ride. The zero-blanking band does not have that cushion. Everything is counted and averaged to determine the ride of the pavement. Incentive/disincentive numbers were adjusted to accommodate the new readings to determine the bonuses or penalties.
Muir: The two-tenths blanking band basically let any deviation less than two-tenths be blanked out. It didn't count against your ride. With the zero-blanking band, you no longer have that tool. All deviations away from a straight line are now registered and incorporated into your ride index.
Why are some states using the new measurement?
Hall: If you look at the response of the profilograph using the two-tenths blanking band, it's a blanking band. It blanks out part of the information. We've had cases where you can see on the trace there was noise and you could feel on the road there was noise, but it was all inside the blanking band.
Hoffman: We had some projects that we paid some pretty significant bonuses on that the driving, motoring public said they didn't like the feel of the road. It rode rough because we had all this chatter in it under two-tenths of an inch.
McMahon: One of the things we compete with is the asphalt industry. It's an area that we, as a concrete industry, need to look at to see what we can do to provide the smoothest pavements we can. I think everybody's really been in tune to that.
What are the guidelines?
Each state has a different set of guidelines for incentive/disincentive. Some pay out a percentage while others offer a flat dollar amount. One consistency with all the states is the disincentive amount is always larger than the incentive.
Hall: I think the easiest way to justify that is, on the incentive side, it's not really a bonus for producing better pavement, it's an incentive to produce better pavement. The disincentive is not just a disincentive to not do that, but it's also a penalty for having done it. We have confidence a smooth ride will make the public happy and will also reduce the impact loads on the pavement. From an engineering point of view, it'll make it last longer, and that's worth a bonus. On the downside, a bad ride is going to have more impact loads. It's going to get the public screaming and we're going to have to do something that is going to cost money. I think it's pretty clear there needs to be a downside.
Is the zero-blanking band something contractors should be afraid of?
Reede: If you're more into quantity versus quality, you probably will be a little afraid of it. You have to pay attention to detail and all of the variables that contribute to good ride and you have to have a quality paver and other instruments and equipment.
Geiger: It's not something you should be afraid of if indeed you are getting a good ride without the zero-blanking band. You should be able to work with this and enhance your ride.
Muir: I wouldn't say afraid. You have to be somewhat prepared for it. You have to take some care in setting up the equipment.
Hall: Frankly, it's something they should be wary of. The reason we're doing it is to spread out the distribution so we can pay bonuses and be able to distinguish between bonus ride and penalty ride.
Hoffman: They should be afraid if it is arbitrarily used and misused. If the specifying agency works with the contractors to make the switch rationally and take some time for everybody to get familiar with the new spec to take out some of the unknown and some of the risk away from the contractor, then I think it can work well.
Is it fair?
Geiger: Yes, it is fair if everybody is under it in our work. That makes it fair. It's a lot tougher to attain the ride. It closes down the parameters, but as far as being fair and equitable, I think it is.
Heinrich: I think it is. We've talked with the state of South Dakota and we're trying to get them to do a little modifying with it but, overall, I think it's fair.
Reede: I think it's a fair determination. You can run into some different constructability issues from state to state but it puts us all on an even playing field. It promotes you to be more innovative as a contractor and it promotes your company to install quality. It forces you to do a good job and it forces you to have the good equipment out there to do it.
Hall: We want an incentive that encourages and pays back the contractors who are paying attention to quality. Some of the contractors are afraid we're just going to continually raise the bar. That's not our intention. We want to try to assure the best of the group continue to have some incentive and the worst of the group continue to have some disincentive to push them toward the quality the industry defines as a standard.
Hoffman: Most of the work in the state last year was in bonus. A good percentage of the work was in the four to six percent bonus range, so the contractors are not only able to give it to us, they are willing to give it to us because they feel that dollar incentive is enough to give us a smooth ride. Plus, they have to be concerned with public perception of the industry. They want the industry to be perceived by the customer as doing a good job, that concrete pavement has value.
What is good ride with the zero-blanking band?
Reede: I think if you can get down to 10 inches per mile (158 mm/km), you're looking at some great pavement and it's tough to get. At 10 to 15 inches per mile (158 to 237 mm/km), you're looking at some really smooth pavement. I think a good average is right around the 20 inch (316 mm/km) mark, 15 to 20 inches (237 to 316 mm/km). We shoot for 15 inches (237 mm/km).
Muir: If you were less than 18 inches per mile (284 mm/km) on a high speed roadway, you could get maximum bonus of 107 percent of whatever your bid price is per square yard for the concrete paving.
Heinrich: We did 13 miles (21 km) of interstate last fall and we averaged right around the upper teens, low 20s, for ride. The numbers earned us bonus and we were pretty pleased with it.
Geiger: Top bonus is 12 inches (300 mm) or less. The next set of bonus is 12 to 16 inches (300 to 400 mm) and that is a real good ride. We just finished 12 miles (19 km) on Highway 29 in Wisconsin and we got bonus on it.
How do you relate to the zero-blanking band measurement five years from now?
Hall: There was a perceived problem with concrete not having as good a ride as it could. The concrete industry has been out in front with the ride spec because of the perceived ride problem and now the asphalt industry is following.
McMahon: We haven't gotten that far yet. I know the industry has really stepped forward and been very innovative in trying to get the best possible ride they can and I think that's a pat on the back.
Why do you need the rideability now, when a year from now the ride will be different?
Hoffman: We want smooth roads right out of the chute because that's what the customers want and that's what the customers are paying for. We can all make the argument that as soon as you put traffic on a road it's going to start to deteriorate and it's eventually going to get rougher. If you start out smoother, it's going to take longer to get rougher.
McMahon: If it's smoother to start with, you're going to end up with less impacting, loadings and things of that sort which can cause problems through deterioration of your pavements. The thought is if it's smoother initially, it will remain smoother.
Hall: We really should be concerned with the ride down the road and we are monitoring the ride as part of our pavement management system but that's a longer term thing. We try to run over our pavements once a year.
How do you achieve good rideability?
The Missouri/Kansas chapter of the American Concrete Pavement Association and FHWA have outlined eight techniques and practices for achieving smoothness. They call them "The Great Eight."
1. Precise Stringline
Stringline is the primary guiding system for most pavers and has the greatest potential to affect smoothness. The stringline must be set precisely and protected from damage during the paving process. Usually, supports for stringline have been placed at 50 foot (15 m) centers, but to reduce the chances for sag, some contractors use 25 foot (7.62 m) spacings between supports. Offsetting the stringline during setup allows it to remain in place through the whole process, from subgrade trimming to mainline paving. Splices in stringline need to be clean and tight because loose ends can wreak havoc on sensors creating a dip or a hump in the pavement.
Geiger: Stringline has to be set every 25 feet (7.62 m). You need to have pins every 25 feet (7.62 m). You can't have 50 foot (15 m) stations and you need to really check your line.
Heinrich: Good ride is a combination of different things and stringline is definitely one of them. We use cable.
Reede: We use cable for stringline now. We've paved with stringline and we haven't been as successful on some urban jobs with our ride.
2. Build From Ground Up
Roads are built from the ground up. It's not possible to attain a smooth riding surface without a solid and smooth foundation. The stabilized base should also be extended two or three feet (.6 to .9 m) outside the pavement edges to support the paving equipment. It will give the paver tracks a firm, smooth riding surface which means a smoother driving surface.
3. Watch Paving Speed and Delivery Rate
The paving train should be kept moving at a consistent speed. It's necessary to have an adequate supply of concrete delivery vehicles matched to the batch plants production capability to maximize paving machine speed and smoothness.
4. Control Concrete Head
The concrete head in front of the paving machine needs to be consistently monitored and controlled to insure it doesn't get too low or too high. Highs and lows affect the slab coming out the back of the paver. Placer/spreaders in front of the paver help deliver a metered and consistent supply of concrete.
5. Strive for Mix Consistency
The mix design needs to be proportioned to assure proper consolidation without excessive vibration. The mix also needs to be monitored for slump and air content consistency. These factors will help produce a mix with a uniform workability increasing smoothness and overall quality.
Reede: The first key for us is the consistency of our concrete. We run about as consistent of mix as I think you can.
Muir: The mix design plays a big factor. The consistency of the concrete is really the biggest obstacle we have to handle.
6. Minimal Hand Finishing
Restraint is the key word for finishing operations. Hand finishing is limited to edging, surface sealing and checking with a straight edge. A surface texture needs to be applied to assure a skid-resistant surface after the finishers. The traveling public prefers a surface that is quiet as well as smooth, and care needs to be taken when texturing. Studies have proven longitudinal tining and random transverse tining reduces the whine associated with uniform transverse tining while providing a safe, skid-resistant surface.
Reede: We run a 16 foot (4.88 m) straight edge and that's all we want on there. We feel our setup and our GHP-2800 is doing the work and we just want to make one pass with the straight edge, broom it and tine it. The more straight edges and floats you have on it, it feels like you disrupt your rideability. We feel it's coming out nice behind the paver so we check it and let it ride.
Heinrich: We try not to give a real rough tining. It doesn't show up anything real big on the measurement with a little rougher tining but you get a lot of little counts and they all add up.
7. Use Good Equipment
There's no substitute for clean, well-maintained equipment. Dirty equipment with old concrete on the finishing pan will affect the smoothness and appearance of the concrete surface. It's also important to know the sensitivity of your equipment. Contractors should experiment with their equipment to determine how it responds to influences like stringline, sensors, and hydraulic head forces.
Geiger: Let's start right away with number one, the right brand of paver.
Reede: We have a GHP-2800 with the 5000 series pan, the bigger frame and bigger tracks. We have experienced some excellent, excellent ride incentive on the zero-blanking band here in South Dakota. We feel, with the bigger tracks and 5000 series pan, this paver is capable of laying some of the best pavement in South Dakota.
8. Motivate Work Force
The work force is a contractor's most important resource. It takes motivated employees working in an atmosphere of cooperation to produce high quality, smooth pavements.
Reede: Upper Plains feels our paving superintendent and the guys that work on the machines are doing an absolutely outstanding job setting up the machines. There's a lot of fine tuning to it, from the stringline to setting the machine, and I feel our crew does an excellent job and because of them, we've experienced excellent, excellent pavement.
Geiger: You have to have good equipment, good finishers and good people.
Reede: At Upper Plains, we took on mainline paving after the zero-blanking band had been implemented. I guess we took it as a challenge and I think that's one of the reasons we went to GOMACO. The type of pavers GOMACO produces has contributed to our success.
Muir: We were concerned about the new spec. We're currently finishing up two projects which were our first two projects with the zero-blanking band as opposed to the two-tenths band. We found that our acceptable pavement was still just as acceptable under the zero-blanking band as opposed to the two-tenths blanking band.
Geiger: We run a GOMACO with IDBI. We've been very successful with it and we're really happy with the rides we've been getting with that machine on the zero-blanking band.
Heinrich: We were skeptical about this at first and it took a couple of jobs to really get the knack of it. It's the refining of your paving process and putting out a better quality product.
McMahon: I think we all have good, quality contractors. The individuals themselves are taking pride in their work and doing the best they can.
Hoffman: Our number one measure that we grade our success by, as a state highway agency, is smoothness. We're doing everything we can to make our roads smoother because our customers tell us in no uncertain terms that's the most important thing they want from us.
Hall: What we're saying to the industry is you decide how smooth our pavements should be. You're competing against asphalt. It's in your best interest to make smoother pavements. If you do, then as an industry and as long as you can remain competitive, we want to put a little extra money in on the smoothness side and take a little out on the roughness side to keep some pressure on the industry to develop smoother pavements. That's our strategy.
Above is an example from a profilograph using the two-tenths blanking band.
Above is an example from a profilograph using the zero-blanking band.