2% of Optimum Requirement
2% of Optimum Requirement
(OP)
Several DOTs have the standard requirement, that aggregate base course be placed with a moisture content within 2% of optimum. Was discussing the reason for that requirement, with a co-worker recently. So, why is the standard set at 2%? Why not 1.5%, 2.5%, or 3%?





RE: 2% of Optimum Requirement
Since the density-moisture curve for a given sample, is only based on a few data points, the majority of the curve is an extrapolation. Isn't it possible that even peak of the curve could be an approximation, however small? IOW, the information on the curve is to one degree or another theoretical. So, how strict is the 2% requirement really? What if an aggregate is 3% wet of optimum, but with a dry density of 97% or 98%? Is that really unacceptable construction? How could one be sure?
RE: 2% of Optimum Requirement
For a road bed, the percent above or below optium shouldn't really matter. However, the further you are away from optium moisutre, the more energy required to reach your compaction requirement.
Mike Lambert
RE: 2% of Optimum Requirement
Now what's wet or dry of optimum? The reason I ask this rhetorical question is the industry is confused on this matter. Ask yourself, what the optimum moisture content to acheive 95 percent compaction? It's not the same value as the optimum moisture content for 100 percent relative compaction. Bear in mind running parallel to the ZAV is the LOO (Line of Optimums). It's not a vertical line, but that's how the industry perceives optimum moisture!
Outside of the technical answer to your question, I'll also say if you make compaction moisture content a specification requirement, you are a bit more likely to have the technician select the approprate proctor (or you are more likely to see in a forensic evaluation where the technical got off track.
f-d
ípapß gordo ainÆt no madre flaca!
RE: 2% of Optimum Requirement
RE: 2% of Optimum Requirement
RE: 2% of Optimum Requirement
Holding the compaction requirement to within 2% of optimum allows a direct comparison to the stability design values, thus a better assessment of in-place stability than just density alone.
RE: 2% of Optimum Requirement