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base course aggregate compaction

base course aggregate compaction

base course aggregate compaction

Dear All,

How many passes a 14 Tonne vibratory roller should make to achieve 100% compaction for base course aggregate? The MDD is 2.315 T/cum, OMC = 7%. Please help as the site is facing serious delays because of less compaction achieved even after 5-6 full passes. The maximum compaction achieved is only 85%!!

Hope somebody can help me out of this anamoly....


RE: base course aggregate compaction

better go back and check your numbers, but why 100% and not 95%? and is this standard or modified proctor? or is it a relative density test?

RE: base course aggregate compaction

i'd suggest against 95% modified...use at least 98% or 100% modified...not standard Proctor on base course material.

was the subgrade tested/proofrolled? what was the requirements for that? also as cvg asks, you referring to standard/modified Proctor or relative?

RE: base course aggregate compaction

also what was the in-situ density and moisture as tested?

RE: base course aggregate compaction

What is your base course, thickness, processing methods?

RE: base course aggregate compaction

The short answer is that no one can tell you how many passes of the roller will be required.  It depends on the water content of the material and the stiffness of the subgrade that you are compacting against.

RE: base course aggregate compaction

1.  Whenever compaction of pavement structure is presented, it is always a good idea to identify CLEARLY (a) the type of material (i.e., crushed stone aggregate, river gravel, etc) (b) the compaction method used (i.e., standard or modified Proctor (light or heavy tamping for our British friends).  This establishes facts that anyone making a reply will want to know - and lessens confusion.

2. Normally, in my experience, base courses are compacted to 98 to 100% of the maximum dry density (MDD) Modified Proctor.

3. GeoPaveTraffic indentifed several aspects that are important.

4.  7% OMC (optimum moisture content) seems a bit on the high side for pavement base courses I have used.  It would suggest that you are not using crushed stone aggregate and that your base course material is a bit on the sandy side - or, forbid, the base course has significant fines that might be clayey in nature (high PI).

5.  85% is very much on the low side - especially since end dumping into a pile will be in the order of 85% (standard proctor).  So any passes you are making should improve considerably this number.  Sands I have used in the past would gain 95% standard Proctor under 4 passes.  

6. I would doubly check your proctor values if after all those passes you are getting such low results.  I might suggest that you carry out a relative compaction check using the old Ontario's Ministry of Transportation and Communication (MTC)-or whatever they call themselves these days. I've explained it fully in previous threads - but basically, you dig a hole, use a sand cone or rubber balloon to determine the volume of the hole.  you take ALL the material from the hole and compact, on site, into a proctor mould at "about" the optimum moisture content(depends on how good your field tech is - but if they do this a lot, they would have a good feel).  Adjustments in the number of blows per layer are made for holes that are not of the "standard" volume. You then determine the volume of the compacted material in the mould.  Compare the volume in the dug hole with the volume in the compacted mould to get the approximate relative compaction.  It is a good test - takes time but as a check on the lab proctor values would be reasonable.

Sorry it is long reply . . . Cheers

RE: base course aggregate compaction

Another point.

How are you determining the density in the field?  That is the first thing to check when you are that far off of what might be expected.  Do you have equipment to do the test by old stand-by methods such as the sand cone (large enough size also).  A 2 mm loosening error on hole sides even for that method can make a major goof in the result.  Is sand calibrated in the lab?

 Accumulating errors in the wrong direction also may be your problem.

If you are using nuke methods, there can be some big errors present due to technique and  no on-site calibration (not a lab calibration).

Then comes the proof of the pudding.  What does a full load of heavy vehicle tire load cause in the way of visual appearance of the job?  Any ruts?  Deflection in the base?

RE: base course aggregate compaction

BigH...interesting that you consider the 7% to be high...it is very low compared to the materials we see here in the SE US.  For a modified proctor on crusher run granite or river rock, we see slightly higher than the 7%....8.5 to 10.  For limerock, we see about 9 to 11.  The sandier the material is, the higher the optimum moisture will generally be.

This material has a MDD of about 142 pcf, so 7% is not out of the ballpark.  I would expect that the shape of the proctor curve is steep and therefore the material is very moisture sensitive.  Maybe they're not controlling the moisture well enough to achieve compaction. If they are on the dry side, then they can pound on it forever and not get anywhere.

GPT, BigH, and oldestguy have laid it out nicely...no point in repeating.

RE: base course aggregate compaction

Ron - the crushed stone I've been using for road base over the years (Laos, India) had OMC values in the order of 5% plus or minus a couple of points.  Interesting to see how such values do vary over the many regions of the world and country. . . Why we must all be somewhat cautious about correlations. Agree that the sandier, the higher the OMC.

RE: base course aggregate compaction

BigH...you're right...difficult to correlate to a variety of locations.  Most of our base materials will care a MDD of 115 to 125 pcf, with optimum in the range of 9 to 11%.  Stabilities are good with CBR in the 80+ range.

RE: base course aggregate compaction

The lab proctor value needs to be achieved in the field with a plus minus moisture.  If the lab proctor moisture is 7% make sure that u are using +\-7%.  u have indicated 85% but u have not shown at what moisture.  The compaction is always a function of moisture.  The right time to start compaction in the field is to take hand full of earth and pressing it.  If it retains its shape then start compacting it.

A thorogh mixing is very important.

Next time please check compaction and see the corresponding moisture.  What is the gap in moisture against lab moisture.

If you do not achieve compaction with 7% moisture, u need to request a recheck on proctor density and moisture

RE: base course aggregate compaction

"you", not "u" please, por favor, tolong!

RE: base course aggregate compaction

Which type of a roller is required to compact a crushed stone base(CRR)specified norminal degree of compaction is 104%by the use of BS-Heavy.Also Iwould like to know how many passes will be required to achieve the spcified degree of compaction?The maximum dry densities achieved from that crushed rock by proctor testing ranges from 2220kg/cum to 2230kg/cum.In addition to this the specification specified two method of Acceptance limits in respect of field density,which are Aggregate apparent density(88) and BS-Heavy(104)which is appropriate and the best among the two methods?Please assist on this.

RE: base course aggregate compaction

assuming the subgrade is stiff under a proofroll...
and the material is a crushed stone mix with fines...

85% sounds like you're not getting it wet enough, or at least that's what would be the case if what you described happened in my regional area. Most paving contractors i know inundate the stone with water right before compaction.  The excess water is squeezed out to the top and evaporates after a day or two. Road base done right looks like concrete around here.

5-6 passes of a 14 ton smooth drum roller should get much better than 85% of either the Standard or the Modified Proctor. but don't count the passes... keep compacting until it feels and looks right.  Rolling patterns are appropriate for asphalt paving construction.

i get 144.5 pounds per cubic feet for the conversion... 7% does seem a little high, but there is no telling that you don't have parent bedrock with a higher specific gravity than i'm used to.

if your crew is wet-setting the stone and you're still getting less than 95% Modified Proctor...i'm guessing your soil subgrade may not be as stiff as you need.

RE: base course aggregate compaction

With respect to the above post, you might want to be careful about inundating depending on the makeup of the fines.  I have seen many cases where a bit too much water was used and the material wet.  The vibration compaction forced the water to the surface which also included some fines.  The fines prevented further water from escaping.  As a result, the surface became spongy - a layer of trapped water just below a very thin surface layer of fines.

RE: base course aggregate compaction

Please also consider the lab proctor may not have considered the presence of oversize materials.  The onus during field compaction testing is to evaluate the percent oversize materials (refer to the method A or C criteria) and adjust the results accordingly. There are several methods to do this and the point of my post is not to get into these details, but that could be where the body is buried.

Then again, the problem could be as also described.


¡papá gordo ain't no madre flaca!

RE: base course aggregate compaction

i notice the compaction of base course above 100% relative to maximum density in the proctor test ,Although it's same material .
is that normal or not ?
& why ?   

RE: base course aggregate compaction

You can achieve more than 100 percent compaction; however, if the value is more than about 103 to 105 percent, I would suspect that you are working in a material to which that Proctor does not apply.  At the least do a check point on the Proctor with that material to see if it falls on the curve.  If not, run another Proctor.

RE: base course aggregate compaction

To add to Ron's comment, 103 to 104 percent "standard" proctor is achievable with the heavy vibrators - but would by about 98 to 99 percent "modified" proctor.  emad84 - you need to understand that 100% maximum dry density is related to the compactive energy in carrying out the lab test.

RE: base course aggregate compaction

In fact six pasess for the use of 14tonnes vibratory roller is adequate to achieve 100%compaction effort required for the crushed stone base.What is to check and make followup are the followings:
a) are the roller operatory putting the roller in a high gear(vibrating gear)during this operation?High gear normally uses more diezel,most probably they may use a low gear to serve or to sell diezel.By using a lower gear you will not achieve the compaction required.It will be just as rolling the base coarse material.Remember the crushed stone base are cohesionless materials and inorder to bring the particles close require vibration gear.
b)Yuo should use a lot of water after spreadingand greading the materials prior to compaction.So you need to have a lot of water buozer on site.Similarly you need to slush thhe section after compaction to bring all fines to the surface.Hopefully if you follow cosely this procedure you shall achive the required compaction not more than six passess.

RE: base course aggregate compaction

Why do you want to bring the fines to the surface???  Seems you like too much water . . .  As I indicated in my earlier post, when the material was too wet, it became to spongy - the fines at the surface wouldn't let the water escape during the compaction process.

RE: base course aggregate compaction

100 % compaction on rock is very normal, in fact the Alabama Highway dept requires 100% of modified.

BMP's on rock. I found that by flooding the rock, we use a lot of limstone, and then vibration heavy, it will go to pumping. This movement is needed with the lubication of the extra water to bring the fines to the surface and interlock with the large aggregates. yes it will be wet, pumping and soggy, but a day later after the water has evaporated out it will be over 100%. Rock is only going to absorb so much water, You cannot get rock too wet. the excess water is surface saturated water, it be gone in couple hours.

so knock to grade, flood it, vibrate it and cut to grade. If you cut after the water drys the dozer will not cut the rock, it will slide on top.

RE: base course aggregate compaction

Trying to vary the gradation of material after it is placed is a poor practice (such as "bringing fines to the surface).  The gradation of the material should remain and it should be compacted at or slightly above optimum, but not to the point of pumping.

If you are routinely achieving 100% of modified with pumping, I'd question your tests.

RE: base course aggregate compaction

In principle the crushed stone base after the compaction finish the section must be slushed by a pneumatic or tyred roller inorder to bring all fines to surface.All the fines must be broomed prior to primming.This will enable the primer to penetrate into the base for at least (3-10)mm.This will make good bonding between the pavement layers(base course)to receive the surface dressing works.Rember crushed stone materials required more water during compaction as the materials are cohesionless materials.

RE: base course aggregate compaction

Crushed Stone Base....comes in many flavors.
The method(s) of setting it up, finishing it, curing it, and continuing with the next layer is I think very dependent on the local availability (spec's are usually tailored to weed out the bad "local" sources) or pits.

Where I have worked (SW US) some materials that meet specifications cannot be slushed and others can.

If the type of material can be slushed I prefer it, as it produces a more homogeneous/smoother course. I have seen folks bring up the (very fine) fines using a vib. stl. whl. compactor, and have also seen them "make" fines with a small windrow and the same stl. whl. compactor.

  I disagree that the bringing of fines to the surface is a poor practice....it has be a good method of helping to seal off the surface so as to properly cure and prime the base course. It has been a proven practice for years around my areas.  

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