Steel wheel 3/4-0 sandy AB?

[jacks4u]

I work for a grading and paving company that does curb to curb paving. Recently, on an infrastructure road (3" asphalt over 8" sandy AB, rolled in with a 9 wheel roller in 3 lifts.) I was asked to steel wheel, with vibration, the AB while it was still prety sloppy. I was told not to wory about the material sticking to the wheels, even though it was tracking severely, and to 'hammer the daylights out of it'.

The steel wheel roller is an Ingersol DD-110. There are several options for vibration - high or low frequency, vibrate front, both, or rear wheel, vibration intensity - a 1 to 8 setting at the wheel. There is also a guage that varies inversely with speed, I think it reads vibs per minuite or perhaps vibs per foot.

I have several questions: on wet 3/4-0 sandy AB, is high or low frequency vibration more beneficial? is it possible to reduce compaction by using the wrong combination of settings and speed? Does this even help meet compaction specs, given that this base was rolled in 2 to 3 inch lifts with a 9 wheel roller?

Any information would be greatly appreciated.

jacks4u

 

[Ron]

jacks4u....vibratory compaction will work on AB, but if the frequency is too high it will be less effective, because the viscosity of asphalt is higher than water. The best way to gage this is to try a few sections (test strips) using varying frequencies the doing in-place density tests to see the results. This doesn't take long and you'll get a good idea of the appropriate range of vibration.

The fact that it had already been rolled with a traffic roller suggests that perhaps it was either pumping or otherwise unstable from a poor mix control. Vibratory compaction won't usually help that. Sounds like you were trying to correct a few ills after the fact.

If the base was set with emulsion, just letting it sit for a while would have helped. If hot mix, well....not much you can do for a bad mix other than compact and hope the tenderness goes away as the asphalt hardens. Might be "tear out and replace" time.

 

[jacks4u]

Thanks for the information. I will use the lower frequency vibration settings if I encounter this situation again.

jacks4u

 

[bcallagan]

If it is "sloppy", it's possible the voids are completely filled with water, and no method of compaction would work. Is the water above optimum and do you have a curve for it?

 

[jacks4u]

Thank you both for your thoughts.

You both have hit upon the issue that drives me nuts.I've worked on: commercial pads, both standard and over ex, curb to curb residential and infrastructure, and larger excavations. I've operated several types of compation equipment (sheeps foot, steel wheel, 9 and 7 wheel pneumatic) water truck, and grading tractor. Only once, on a small over-ex job for a commercial pad was there a soils technician available that actually was working with us, giveing meaningfull data as we hydrated and compacted the sub-grade. On all the other jobs I've worked on, the soils tech showed up just before the job was inspected. What I'm saying is, there is little or no information available to us while we are working a job.

I've found relatively coarse and non-standard measures for compaction, by watching where a water truck or other heavy equipment leaves tracks. Are the tracks indented, and if so, by how much? Was the water truck full or empty?

But I have no quick measure for moisture, except to watch for standing or puddled water, mud, or "pumping" as a machine drives by.

Some types of material are quite forgiving, such as lime treated AB, which seems to tollerate or even require excessive amounts of moisture. while others turn from dirt to mud in a blink.

Some times it's possible to add moisture or density in the hour or so that the soils tech is on site. Other times it is not. One over-ex job I worked on excavated 24 inches below the footer, and backfilled with imported material at 14 percent moisture and compacted in 6 inch lifts. Soils testing was a week after the job was finished.

I feel that it would be nice to have instruments on-site, daily if needed, but think many crews would claim that they 'just know' when it's right.

 

[civilperson]

AB can be aggregate base or asphalt base depending on the location and standard abbreviations used. Both meanings have been used in these discussions. For clarity, please distinguish your specific meanings.
A proctor of the material being used is a required first step to knowing the relative compaction achieved by the method under discussion. Large amplitude low frequency has given me the best results on sand and gravel materials but can pump water from subgrade below.

 

[jacks4u]

Oh my! I appologize! In my area, AB is the abreviation for Agregate Base,or Agregate Base Compound (ABC), and AC is Asphalt/Concrete.

My appologies!