reinforced asphalt

[ajk1]

Would placing reinforcing mesh in asphalt adjacent to expansion joint, as shown in attached sketch, help to limit asphalt crack width? This pertains to buried expansion joints...buried to protect the expansion joint seal from snow plough damage (I am aware of a number of proprietary joint systems as well as plate over procedures that are intended to protect from snow plough damage, but my inspection of a number of garages indicates they are not always successful...depends I suppose on how hard the plough driver goes at it). So the buried joint as shown seems to protect the joint seal against damage, but always results in ugly cracking of the asphalt, so I wonder what your thoughts are on reinforcing the asphalt as shown in the attached.

 

[ACtrafficengr]

It doesn't look like your drawing was attached.

I don't have any direct experience, but the maker of GlasGrid, a fiberglass mesh reinforcement for HMA, says it will help control cracking from horizontal movement, but not vertical movement.

 

[Ron]

Add steel fiber to the asphalt mix. The short ductile fibers work better than the long stiffer fibers.

 

[Canuck67]

Typically joints in asphalt that are located over expansion joints are filled with flexible material. I have never seen a reinforced asphalt over an expansion joint. Perhaps look at the steel reinforcing mesh they place in between layers of mastic toppings as a form of reinforcing. You might have to perform some tests as the mastic is typically much more flowable than asphalt and likely has a better ability to fully encapsulate the mesh.

 

[ajk1]

Please let me know if you now have the attached file. I think I did not upload right last time and that is why you did not see it, as noted by ACtrafficengr. I will study up on the reference you give for reinforcement, and may have follow up question if that is OK.

Thanks to all three of you for what seem like good ideas worth looking into.

Ron, do you know of any reference document to which I can refer for adding steel fibres to asphalt? Which steel fibre, what dosage, procedure for mixing into the asphalt? Any concern that they will corrode and stain the asphalt surface, or that they could stick out of the asphalt and be a cutting hazard to any child who fell on the asphalt?

 

[ACtrafficengr]

The attachment worked this time. Since you mention snowplows, I'd stay away from steel reinforcement if it will ever see chloride de-icers.

 

[ajk1]

That is why I said "galvanized" and " mesh". By the time that has significant corrosion I expect that the asphalt may be approaching its 17 year life that some road departments take as the life of asphalt paving. In concrete it has been found that the mesh corrosion products are too small in volume to spall or delaminate the concrete. I take your point though that it is something to consider, because asphalt is much more porous than concrete and would behave differently. Thanks.

 

[jayrod12]

17 years! Must be nice, we're lucky to have it last 2 years in high traffic areas. Our freeze thaw cycles (-30 to +30 celcius annual swings) here just destroy the pavement.

 

[ajk1]

where are you? I am in Toronto. I have not seen any competently installed pavement here destroyed in just 2 years. Cracking usually initiates several years after installation and proceeds from there, but is serviceable. By 17 years it can be in advanced deterioration and breaking up. But you are probably right that after the McGuinty government and now the Wynne government, the corruption is so blatant that maybe they have even corrupted the new paving quality.

By the way, assuming a competent base, the more the asphalt is kneeded by the traffic, the better it is for the asphalt (up to a limit I suppose). That is what an asphalt specialist told me 30 years ago.

 

[jayrod12]

Just a bit further west.

The competent installation and design are where it lacks. I would say more blame lies with the designers than the installers from what I've seen.

 

[ajk1]

ok. I take your point.

 

[ajk1]

ACtrafficengr - there are several different grids and weights for the Glasgrid products. Any idea how I determine which to use? If not, I will have to try to get thru to their engineering department and discuss.

 

[ACtrafficengr]

ajk1, We've looked into it a few times, but as I've said, we've never used it. Sorry.

 

[ajk1]

ok, I will try to contact them.

 

[ajk1]

I found on the web a paper by the Michigan Department of Transportation, where they reported on pavement repairs using Glasgrid and withut it, and monitored for several years. They found that overlay pavements without Glasgrid did better than this with Glasgrid.

 

[ACtrafficengr]

I read that too. The problem was the width of the Glasgrid product sold then was less than the "development length" of the grid. It comes in wider strips now, but you won't be able to get the 2 1/2 feet on the joint side of the crack. Assuming braking forces are causing the cracks, it might work.

 

[ajk1]

To ACtrafficengr - I do not think the brake forces are the main problem. I think that it is that the asphalt bonds to the waterproofing protection board and membrane immediately under it, which in turn is bonded to the suspended structural concrete slab. So when the joint in the slab widens in winter, the waterproofing membrane pulls the asphalt on the other side of the joint along with it, and causes a crack to open in the asphalt. If it were braking forces that caused the cracking, I would not see so much of it in the parking stalls.

I am not quite understanding what the 2 1/2 feet is that you mention. Is that the bond development length of the Glasgrid?

Are you aware of anyone having used the Glasgrid with noticeable beneficial results regarding cracking?

 

[ACtrafficengr]

AJ, would this webcast help?

Using Geosynthetic Interlayers as a Solution for Reflective Cracking]

 

[Ron]

ajk1....contact the company below. I did a research project for them in about 1984 using steel fiber in HMA. Got excellent stability increases and substantial tensile strength increase (thus inhibiting cracks). I did a test section in a parking lot near Orlando, Florida. It has been down since 1988 and has not needed an overlay to my knowledge.

Mitchell Fibercon produced the correct kind of fibers for this. They are still in business. Steel fiber in asphalt never really caught on, but it has excellent potential. I've seen some more recent stuff in the past few years being done in Germany.

I wrote an article on it for Roads and Bridges Magazine in 1985....if I can find a copy I'll post it.

http://www.fiberconfiber.com/