What is acceptable us of Bituminous Slurry Seal? 1

[kashley1229]

Can Bituminous Slurry Seal be effective on old, deteriorated roads and can it be effectively used under asphalt overlay? Also, if it is used on old, fatigued pavement, should it have an applicatioin of tack coat previous to placement because of the dry and raveled condition of the existing asphalt pavement?

I am a 3-yr E.I. with no P.E. working over me. I have limited access to Engineering literature and source materials do I appreciate any input that is offered.

 

[Ron]

I will assume you are referring to an asphalt slurry seal. Coal tar emulsion slurry seals are generally worthless, in my opinion.

The primary purpose of a slurry seal is to provide weathering protection for an otherwise structurally stable pavement surface, and to fill cracks in the surface. It will not be as effective on a structurally deficient pavement and will offer no enhancement.

A primer or tack coat is generally not needed. Yes, an overlay may be applied on top of a slurry seal, once it has weathered a bit.

If you are referring to a coal tar emulsion, I would not put an overlay over one of these until it had completely weathered.

 

[kashley1229]

Thanks, Ron.

The original plan was to mill and fill 1" until I figured out that the subbase is pumping (Desert land with high clay content) and there is minimal asphalt in its existing condition. I am just trying to rehab some roads that are in need of maintenance and the Agency responsible for that has not been doing a very good job. My goal is to add 5 years to the life of these roads.
Now I think we can get the most bang for the buck by doing a slurry seal to fill the smaller cracks and traditional partial and full depth repair for transverse cracks and potholes, then put a 1.5" lift of 3/4"- Superpave over the top. Otherwise, I'm afraid the new pavement will be a complete waste of time and money.
May I ask you for your opinion based on your experience? It would be very much appreciated.

 

[Ron]

kashley1229...I would use a double chip seal over the existing pavement then put the overlay. The chip seal will serve as a crack mitigation layer, to prevent or minimize the number of reflective cracks you'll get into the overlay.

If you don't have a competent base layer, you might consider a "mix-in-place" recycling, using asphalt emulsion injected at the time of mixing to provide a new base material out of the existing surface and base. When you do this and add a wearing course, you'll get much more than 5 years out to of the pavement at a relatively low cost.

 

[tumbleleaves]

Kashley1229's question is very interesting and I hope the experts will comment further.

What are the issues associated with a slurry seal. When is a slurry seal used instead of a chipseal. My understanding is that a chipseal is (more or less) a slurry seal with rock broadcast over the surface to provide friction for safety and as a further wearing surface?

I have seen a slurry seal used on some low speed <25 mph roads and parking lots, but never on any sort of significant road. I assumed a slurry seal would be a safety issue due to reduced friction on anything over 25 mph?

 

[Ron]

A slurry seal is primarily used to seal multiple cracks that would otherwise be too voluminous to seal with a wand for individual crack treatment. It provides some surface protection and does not have to reduce or affect skid resistance or other properties if done properly (Google "microsurfacing").

A chip seal is provided as a protective surface coating to seal cracks and to offer skid resistance for low speed applications. It is also used as a crack mitigation layer to minimize reflective cracking through an overlay.

A slurry seal, in the form of microsurfacing, can be used on high speed pavement sections.

 

[Drumchaser]

No expert here.

It would be beneficial to know what the ADT is, thickness and type of existing pavt. structure (subgrade, base course, and ACP)

I have firsthand knowledge in what is called in my area (south) Microsurfacing. I have seen it used on all types of roadways and speeds. Results have been mixed.

Based on the info. you have provided...it is hard guess what is needed. If the pavt. is in severe distress, removing it (mill and fill) might be the way to go. If the pavt. is in decent shape....a surface treatment (hot AC oil and aggr.) and a 1.5 to 2" surface course of ACP might be what you need, with some acp pavt. repair 6-8" for the worst areas.

A rehab might be what is best (under traffic) to treat the clay with lime, then add some type of aggr. base then a surface treatment on top.

Really hard to guess without typical sections of existing features....and maybe your available ballpark budget.

 

[kashley1229]

Thanks so much for your replies. There are several limiting factors on these projects and it's going to take some imagination to envision these roads.
I work on a Southwestern Indian Reservation. The roads were built in the early - mid 1970's. According to the Feds, there are no as-builts available. We are guessing the ACP to average 3-4 inches thick with another 6-8 inches of base course and have not had maintenance, or at least not like they should have had. Just some scattered pothole repairs.
In addition to that, the ADT's are pretty low (exact numbers unknown), again, it's something that the Feds should have, but don't. There are only about 7000 people scattered over 200 square miles, so these are rural roads with posted speeds of 35 MPH.
The soil composition here is clayey sand and the drainage on the roads is failing. The subbase is supersaturated and the general opinion is that if we mill, we stand a chance of destabilizing the subbase. We would rather just rehab the drainage and let it dry out. That's a solution we can afford and is included in my recommendations.
The pavement has profuse aligator cracking, along with longitudinal and transverse cracks. Some of transverse cracks are 3-4 inches wide. There are also potholes, and places where the CMP's are completely rusted out and the roadway has collapsed and been filled with gravel to keep the road open.
I want to be able to do partial or full depth repair in spots where it's needed, and do a good crack fill under a 2 inch lift of SP-III.

I really appreciate your input and I hope this information gives you a clearer picture of what I'm dealing with.

 

[Ron]

kashley1229...I agree with correcting the drainage first, then you can deal with the pavement. It sounds like your alligator cracking is from weathering, not fatigue failure. The 3-4 inch wide cracks will have to be handled on an individual basis, preferably with a sand-asphalt hot mix compacted into the cracks. I doubt that anything flowable is going to help you there.

After you get that done, I would look at a chip seal for crack mitigation before overlaying. That should get you a pavement that will last a long time with the low traffic you noted.

Good luck. Let us know how it goes. Sorry you don't have a supervising engineer to give you some guidance. You'll need that for your PE exam, so start trying to find someone to work with, even if informally.

Ron

 

[kashley1229]

Thanks for the info. I am doing a cost analysis on chip seal under the ACP now. I am so thankful for this site! What a life saver!