Wash Board

[Nick Abeyta]

What's the general consensus on causes of washboard on asphalt pavement, besides extreme climate temperature and geological chages over time? - Could it be caused by a roller trying to overcorrect an inconsistent HMA laydown during paving?

[Nick Abeyta]

. . . . not that the roller operator was TRYING to achieve an OVERCORRECTION, but that the objective was to correct an inconsistent laydown.

[telescooper]

Nick
what do you mean by wash boarding? Does it look like a wash board or does it feel like one? In the event that looks like it (pushing) , the problem could be caused by vehicle's mostly heavy trucks braking, it could also be caused by a base failure. If The wash boarding is hard to see but can be felt, it could be a paver problem. The screed probably needs some adjustment. Just my .02
Telescooper

[Colorado Digger]

can't you get that from the dozer and blade, you get it going during subgrade and sometimes it's hard to get rid of. i don't know

[telescooper]

can't you get that from the dozer and blade, you get it going during subgrade and sometimes it's hard to get rid of. i don't know

I was thinking more the top and other layers and go all the way down to base also. Sometimes this is caused when heavy trucks slow down. Once you get a ripple then they cause some more.

[Nick Abeyta]

I was wondering if the speed / rate of material laydown could be a possible cause - Seems plausable if certain areas are more dense than others, then when the rollers come through, well maybe we end-up with better compaction in some areas that in others. - Hmmm . . . food for thought.

[Turbo21835]

sounds like a mix issue. I know a lot of mixes are temp sensitive when it comes to compaction

[Raildudes dad]

I'm not sure what the "wash board" is being asked about. At an intersection with a signal or stop sign, loaded trucks will "wash board" the asphalt by shoving it. A number of years ago we had the problem locally but not necessarily at intersections. It was the consensus of the experts that it was due to material overloading in front of the screed. The operator would put so much material in front of the screed and it would try to go up over "the pile". The solution was to keep just enough material on to keep it half way up the augers. I can't remember which one, but one make of paver was more susceptible than the others.

[surfer-joe]

Most likely from improperly prepared base problems, but could be from poor quality mix, cold mix, poor compaction, and high ambiant temperatures and heavy traffic. Maybe a combination of all these things. I've also seen a lot of pavement laid from ten-wheeler end dumps that segregated in the dump bed and in the laydown machine, particularly in the augers. This almost always results in a poor surface condition within a year or two with a lot of larger or course material lying together without much fines in it as a binder. This almost always happens in the loaded portion of the pavement, though I've also seen it clear to the outside.

On the poor quality mix, many times this comes from the first load or two from a batch plant in the morning, or an oil-rich condition, which also is common first thing in the morning.

Something else to consider is base temperature, plus rain or snow sometimes. All will occasionally cause surface problems that don't always show up right away.

Another problem cause is a base surface that hasn't been properly compacted, or one that has a high sand content. The sand tends to migrate under load and given time, will cause surface problems. Then too, I've seen asphaly pavement laid on top of chipseal, which then migrated under heavy loads and high tempertures.

In California, where you are, and in other places too, heavy traffic is sometimes released on top of new laid blacktop too soon before the surface has time to cool off properly. Pavement subject to this stress will compress further unevenly.

If I had all night, I could probably think of a dozen more reasons.

Just thought of another reason. The use of Clarco's will also cause segration of the mix. Frankly, the more a mix is moved around, the more segrated it will become. Clarco's are mostly used with belly dumps, so the bad protions are a bit further apart than with the hauling done by end-dumps.