Contaminated Aggregate Base Course

[pantro1977]

I am placing the aggregate base course on a roadway for the Army Corps of Engineers. The ACOE is claiming that the DGA is contaminated because of the silt that traffic has left on the surface. When can we say that the DGA is contaminated? Is there a standard that gives us some parameters? I have been looking but I can find anything.

 

[cvg]

If you want to prove it meets specs, 8% fines or less is acceptable. Otherwise you may need to clean the surface. If the Corps approved the traffic control plan, they should have known it would be contaminated. However, allowing traffic on the base course is sometimes allowed.

SECTION 32 11 23
[ABC shall be free of lumps of clay, organic matter, and other objectionable materials or coatings.]

a. Percentage of material by weight passing the
0.075 mm (No. 200) sieve will not exceed 8.

b. Where local conditions dictate a non-frost-susceptible material, particles passing the 0.02 mm particle size will not exceed 3 percent.

When the [ABC] [or] [GCA] is constructed in more than one layer, clean the ... layer of loose and foreign matter by sweeping with power sweepers or power brooms, except that hand brooms may be used in areas where power cleaning is not practicable.


3.6 TRAFFIC
**********************************************
NOTE: Traffic will not be allowed on any base
course placed for airfield pavements. For roads,
traffic should only be allowed on the base courses
when it cannot be diverted elsewhere; but
precautions should be taken to limit the traffic and
keep heavy equipment off. Any damage caused by
traffic should be repaired to meet these
specification requirements. Designer will choose
the appropriate bracketed information.
***************************************************
[Do not allow traffic on the completed base course]. [Completed portions of the base course may be opened to limited traffic, provided there is no marring or distorting of the surface by the traffic. Heavy equipment shall not be permitted except when necessary to construction, and then the area shall be protected against marring or damage to the completed work.]

 

[pantro1977]

cvg, Thanks for the quick response. This helps me a lot.

 

[BigH]

The problem, though, may not be with the "8% fines" but that the fines are concentrated rather than dispersed homogeneously which is "understood" in a gradation spec - i.e., no segregation. if the fines are at the surface - perhaps a rough brush using mechanical metal brush broom dragged will clean off the dust. Else, you might want to scarify and recompact. The other issue with traffic running on a base course for a length of time is corrugations (which you didn't mention). These will "come" through - I've been there.