Hot Mix Paving after Rain Event

[civil53538]

Any rules of thumb out there when it comes to paving or not paving after a rain storm. In situations when I am asked to inspect a road paving project, and storms have occured the night before or morning of, I have had the paver wait in some cases and gone ahead and paved in other cases. Because the contractor is ultimately responsible and warrantying the pavement, it is typically their call, but just wondering what your thoughts are. I feel that a little excess moisture will aid in compaction, but at what point is excess moisture too much. I have in some situations called for the road to have another proof roll prior to paving to determine if moisture will cause the subgrade to pump during compaction.

 

[cvg]

From our standard specs: "...No asphalt concrete shall be placed when the weather is foggy or rainy, or when the base on which the material is to be placed contains moisture in excess of the optimum. Asphalt concrete shall be placed only when the Engineer determines that weather conditions are suitable..."

 

[Ron]

civil53538....you can experience significant bond problems between the asphalt and base if the base is wet when asphalt is placed.

You can do a quick test to see if the surface is dry enough, though cvg's comment about limiting to optimum is good and works. If you want to do a qualitative test, you can heat a few ounces of roofing asphalt to about 400 degrees and then pour it onto the base. If foaming occurs or if it readily strips back off after cooling...it's too wet. A similar test is used on roof decks before placing a built up roof. The reason I suggest using roofing asphalt vs. asphalt cement for paving is that the roofing asphalt will tolerate higher temperatures which are necessary to do this check.

 

[BigH]

Not sure - Ron??? - but we used to put newspapers on the pavement, press down and if they came up damp, we didn't pave. If dry (or almost dry) we would pave. ???

 

[Ron]

BigH...that's probably better than the hot asphalt test! Cheaper, too!

 

[oldestguy]

Hey guys, don't get all excited about this.

I once worked for Wisconsin DOT and was asked to use the nuke surface gage (original models) to look for re-bars in completed Interstate concrete pavement before it was first opened to traffic at the Illinois border, about 1959.

The Governor was to be there the next day to cut the ribbon and the shoulder paving was not completed.

While there, with a temperature about zero F., snow was plowed off the frozen base course and the pavers went to work. Lots of steam in the air too. Rollers were Johnnie on the spot.

I kept an eye on that area for years to come after that, since this shoulder area also had some traffic at the access ramps.

Never did I see any problem with it.

What is the moral? You figgure it. How'd you like to start up a blacktop plant in the middle of winter?

Oh, yes. The nuke didn't turn out to show the re-bars, but watching the paving was interesting.

 

[Zambo]

this is an interesting topic as this is a problem often encountered, but there doesn't seem to be an easy answer.

firstly from civil53538 my comment would be that although it may be the contractor's call it would be good to have a sound technical opinion to offer - hence good post. I doubt that moisture will "aid in compaction". What happens if you proof roll a primed roadbase, I assume the cutback bitumen is removed in places. If you have to reprime no asphalt will be layed for a few hours.

presumably the prime coat should offer some protection from the rain if there is somewhere for the rain to run off. It would then follow that in accordence with oldestguy's theory the heat of the asphalt will be sufficient to dry out any moisture instantly.

 

[cvg]

suggest it is better not to tempt fate and just wait till it dries out. much more costly to tear ot and redo

 

[VAD]

An old trick that is often used is to pass a broom over the area . This applies to existing ACP. The heat generated does the rest. Has worked well.

Very often when one notices it is going to rain while trucks are hauling, it is very difficult to stop paving before the rain hits the ground. In the meanwhile the Contractor would advise that the plant is shut down. However, you know the trick, another 40 loads ar coming and while they can remain tarped for a while, you soon find out that the paver is working etc etc. As a backup to the observations of the oldest guy, perhaps, I am the second oldest, I have seen many of those pavements perform well. As a result I have my own gauge on the subject. Many Pavements in Western Canada are built during th cold period. It is common practice to sweep off snow immediately before the paver. While this practice is not the general intent, we live in a practical world re construction and we learn from those non text book cases. In the same vein individual experiences and judgements are often not transportable.

[Cheers]

 

[cvg]

as the owners representative / engineer of record for a paving job - it behooves us to advise (the contractor) in the strongest possible way to not schedule paving operations when rain/snow is forecast. If subgrade is wet in the morning, advise again to stop the plant / trucks. Then - if contractor elects to continue anyway, the liability is completely his. You have then done all that you can (short of shutting down the job completely) to protect yourself and the owner from liability.

 

[LCruiser]

So how do you physically make the contractor quit?

 

[Zambo]

LCruiser,

responsible Contractors should/will quit when they are contractually or technically obliged to quit. This thread is a good example where it does not seem clear that there is a technical reason to quit because it has rained. civil53538 has asked if there are good rules of thumb which he can use to determine if there is good reason to instruct the contractor to stop work. So far I do not see any good guidlines posted in the thread.

cvg states that he is concerned that the subgrade may be "wet". The contractor may have a right to ask what the definition of wet is. Furthermore as he is probably laying the asphalt on sub-base or road-base it may not be easy to determine whether the subgrade is indeed wet due to rain.

As I have said earlier this is an interesting thread, but so far there have been no useful rules of thumb provided to assist with a decision on whether to pave or not after rain.

Unfortunately I think this will continue to be a subject that has to be decided on a case by case basis and it will depend on the road-base material involved and the overall control of the quality on the project

 

[BigH]

cvg, et. al.: Try working in monsoon regions. Everyday it is forecasted to rain. We have to be able to jerrymander the paving in those periods when it isn't raining - and rain can come in in a matter of 1/2 hour. When I was in Guyana, I would get off work and not a cloud in the sky. Change into my basketball kit, do some situps (years ago) and head downstairs to walk to town for a little bball. Pouring down rain!

 

[cvg]

obviously, if you are working in a region where you have daily rain or a long monsoon, you need a different specification for "wet" but for the rest of the world which has periodic or seasonal rainfall, it is best to not tempt fate. The specs are quite clear that rain means wet means don't pave. No interpretation is needed by the Engineer. The Contractor can interpret it any way he wants since it is his profit that he will be risking.

 

[LCruiser]

As Zambo points out, "wet" is a subjective term. What is needed is a performance requirement - such as some bonding to the previous lift criteria. Anything out there? One of our very good and experience inspectors used to walk back into the area where it was "wet" and, with a square point shovel, peel up the new lift. Anybody seen that?

 

[DRC1]

I have not seen that if it s well rolled. At oe time I worked for a paving contractor. Never really understod the science of paving, but most of the construction end seemed expierience based. The state specs allowed us to put down what ever was already batched but no more if caught in a rain event. One time I was paving and we were caugt by a hellasious downpou. Comming down in buckets. I called the plant to cancel out the trucks but found out I was too late. I had 13 trailer dumps with 22 tons on each. The cheif inspector did not want to put it down, but at this point thier was little choice, so I paved. We hustled to get rid of the trucks as quickly as possible. That was 20 years ago. The road is still doing fine.

In my humble experience the heart of most problems is loss of heat of the asphalt. If the asphalt can stay warm through the rolling process, it should be okay. If it can not, it may have problems. Most of the asphalt failures I have seen have been from asphalt placed on cold subbase at the end of the paving season.