100% compaction for aggregate basecourse/sub-base?

[CivilHeadache]

I'm writing an RFI requesting revision of a spec calling for 100% compaction on aggregate basecourses and sub-bases under asphalt paving and PCC paving. Anyone here ever required such a thing for base courses??

The state DOT standard only requires a 95% for all basecourse/sub-base. I'm looking for any other reasonable excuses other than thats just plain silly.

 

[cvg]

City of Phoenix requires 100% for aggregate base and the top 6 inches of subgrade under arterial streets

 

[Ron]

100% for base course is not uncommon. Use 98% minimum....remember, more compaction will be done by traffic if you don't do it during construction! 95% in base course is not enough!

 

[Drumchaser]

Have seen 100% required for aggregate basecourses, and due to frequency of testing and overall quality control of material it is not difficult to acheive with the regional quarries we have in this area.
I agree 98% is reasonable for crushed aggr. base courses that are with-in a pretty rigid spec. base.

As for subbases, not sure of the material(s) you are refereing too.

 

[BigH]

Please advise if you are specifying Modified Proctor (Heavy Tamping for the Brits) or Standard Proctor (Light Tamping). It makes a difference on the level of compaction you will require.

 

[Ron]

Good point BigH...as usual. I was assuming Modified Proctor. If 100% of standard, just do it and don't complain.

 

[fattdad]

vdot requires 100 percent standard proctor (i.e., vdot T-99)

f-d

¡papá gordo ain’t no madre flaca!

 

[CivilHeadache]

We are talking T-180 modified proctor (state of Hawaii).

I've done most my projects out of the state of washington and never encountered a 100% compaction spec.

 

[Ron]

CivilHeadache....I read your original post again. The requirement is not a silly one. There are many reasons to specify 100% compaction. For one, you are practicing in a geographical area outside the one in which you normally practice. There could be a quirk of the local materials that requires that degree of compaction to achieve appropriate stability (such as a CBR). If the compaction level isn't there, then neither is the stability. Some materials have sharply peaked compaction and stability curves.

Compacting to 100% takes out most of the additional compaction that will be done by traffic. Not such a big deal with rigid pavement, but can be significant with flexible pavement. Further, if subbase or subgrade soils require bridging in any fashion, a higher stability and compaction in the base will be necessary.

My point is not to summarily dismiss the compaction requirement. If done for considered reasons, it is a responsible requirement.

 

[BigH]

Interesting fattdad - the specs I have seen and used sometimes allow standard Proctor for subgrade or improved subgrade but always is modified Proctor for granular subbase and base courses.

 

[CivilHeadache]

This is mostly 6-8" reinforced concrete for a pov parking area. There is a very small amount asphalt patching. I think 100% under a parking lot is a bit excessive.

 

[msucog]

one thought: i'd be careful if you saw 95% compaction (standard/modified?). the state DOT here has a line in there about this but it's referring to remedial work...a lot of civils see that and run with it on drawings. when you read further, it requires either 98% or 100% modified depending on the aggregate used. most everywhere here, it's 100% modified for base course and 100% standard for subgrade for DOT work. some local DOTs knock that down a bit. as a matter of practice (here), i recommend 98% standard for all subgrades and 98%-100% modified for base course material. for the base course, it's not that difficult to achieve 100% modified as long as the material is placed/wetted/compacted properly and as long as the underlying materials are satisfactory and well-compacted.

if you think 100% (modified/standard?) is excessive, then recommend something else based on your lab testing, design experience, pavement design criteria, owner's expectations, etc etc. it's your stamp and liability.

 

[grabens]

we use 98 percent of a modified proctor here in FL for FDOT base courses. Not uncommon to see 100 percent of modified proctors on airport pavement subgrades.

 

[darthsoilsguy2]

100% modified in North Carolina. I would like to say the Master-Spec is 100% modified.... but ours has been editted too much to have any confidence in that statement.

 

[CT013]

100% in PA. Can be easily achieved with good material, optimium moisture content, proper lift thickness and also proper compaction equipment.

 

[EXPRESSO]

BigH raises an important question (good job btw). Not familiar with T-180 modified method..can't comment on it. If its similar to the standard proctor, I agree with Ron - give it to them..it won't be too difficult to achieve.

The other aspect of this question that isn't being asked is what is the classification of the subgrade material? CL,..CH?..SP? I know a case where 95% compaction was specified for a CH subgrade and CL. II AB beneath concrete paving..the result was a suit when the subgrade swelled and the concrete cracked. Subgrade material type is important.

I'm surprised both by some of the responses from other states, and in that anyone would specify 100% compaction. Not because its impossible, but rather because it seems impractical. If Std proctor...ok...but still awkward. If modified proctor, why as an engineer or agency would you want to hold the contractor to such a high standard? Also, for aggregate, the range of moisture over which 100% could be achieved would be fairly narrow,on the order of a couple of percent.

I'm curious as to how 100% compaction is monitored; what will be expected from the field engineer under such a spec? For example - when confronted with test results suggesting 104% compaction..or even 99% has been achieved must he fail the lift and advise the contractor to rip it, and do it again until exactly 100% is achieved? In the former case where several tests exceeded 100%, would he properly obtain a bulk sample and run another lab compaction test to determine the new 100% (max dry density value)?..or simply accept the values exceeding 100% as acceptable when clearly the composition of the material has changed...? Or perhaps this is a case where close adherence to such things is not the norm, and testing is performed over an area, the tests averaged and if 100% is achieved the lift passes?

 

[GeoPaveTraffic]

EXPRESSO,

Remember that the max dry density value as determined by the standard or modified proctor is just one such max value, i.e. it is not "the maximum density" of the material. Therefore, it is possible to have over 100% compaction when compared to the proctor.

We typically specify 100% of the standard proctor for aggregate base material. We use the standard proctor for base because we found that the higher energy of the modified proctor test resulted in crushing of some of the aggregate creating a result that did not match field observations for placed material.

Mike Lambert

http://www.shannonwilson.com

 

[Hoaokapohaku]

Aloha from the Big Island CivilHeadache. Since you aren't on a DOT project, and your project has PCC (rare in Hawaii), I assume it is either FAA or a military spec project, which are the only places I have ever seen a 100% of modified proctor requirement in Hawaii. It is not difficult to achieve as long as optimum moisture is also achieved for a long enough period of time to complete the compaction. This is much easier to achieve if the percent passing the #200 sieve is on the high side of the specified range. When it is on the low side, our crushed basalt aggregates are often too free draining to maintain optimum moisture unless the compaction is performed under steady, moderate to heavy rain.