base course aggregate compaction

[concretebaby]

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....

Regards

 

[defg]

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.

 

[BigH]

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.

 

[bb29510]

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.

 

[Ron]

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.

 

[defg]

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.

 

[Drumchaser]

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.