RTShadow

We opened up a new fitness trail recently at the military facility I work at, it is a one mile concrete oval track. You can run or bike on it.

I wanted to test it out so I did 13 laps, really windy day slowed me down quite a bit but still got a good workout.

I timed my workout to coincide with about a 42 minute long music album I was listening to as I rode.

As I finished I nearly crashed rounding the last corner and realized it was because the rear tire was going flat. This was the first time I've ever had a slow leak on my road bike, as many of you know, a road bike flat is usually "PSHHHHHHHHHH" and you are done in under 10 seconds.

I have Gatorskin tires, because I'm willing to compromise rolling resistance for not getting a flat. When I got home I refilled the back tire to full and dipped it in the tub, and found tiny bits of what I thought was metal in the tire, but as I pulled them out with my leatherman realized it appeared to be tiny shards of concrete?

Then today (2 days later) went out to get started on fixing the rear tire, BOTH tires are flat (again, both have gatorskin).

I don't know much about concrete, what exactly could I be looking at here? I can tell you this much, I won't be riding on that concrete path again.

MoAlpha

New concrete doesn't puncture tires, but the screws used to make the form for it sure can if they're left around by the contractor.

Reflector Guy

"Shards" of concrete? Unlikely.... Small flakes of concrete are more likely to crumble than to do anything else. It doesn't splinter like that.

What area are you in? Is it possible they may have used coral or bones of some sort to make the aggregate for the concrete?

I worked on a project where some of concrete floors had metal shavings mixed into it as additional reinforcement. Now THAT would be something to be leery of.

Bah Humbug

Concrete is glue and sand. It shouldn't cause punctures itself, but as mentioned, Could they have been little shards of flint somehow washed or blown onto the track?

Also, I would have expected the much-beloved Gatorskins to laugh at those, otherwise what are they for?

Mojo31

If the concrete was brush finished, I can see the possibility of the peaks in the concrete causing punctures. If trowel finished, then not likely.

Brushed:



Troweled:

Iride01 

Did you look to find out if it was even a puncture that caused the flat? If the hole in the tube wasn't oriented toward the tread, then you have other issues to look for. Some might just be installation related. Especially since you say they were flat the next day, installation technique is suspect.

Tires flat for more reasons than just a tread puncture.

Andy Somnifac 

New, fresh, traditional concrete? No. That won't cause punctures, neither brushed nor troweled.

New concrete with some kind of additive to strengthen it? That's possible, but since you describe a fitness trail, I cannot imagine that it would contain the types of additives that would cause issues.

Iride01 

If there was sand, grit or other stuff inside the tire, then that might have gotten in there after you flatted and rode on the flat tire for a time.

Or perhaps if you tried to patch it you let the tube touch the concrete or somehow kicked some loose stuff into the tire when the bead wasn't seated.

Zaskar

Concrete is more than glue and sand. It's aggregate, Portland cement and a combination of one or more - fiber, rebar, or wire mesh.

The finish... First off, no one is broom-finishing an area that big. Next, unless they used a rake, no broomed finish should damage a tire.

The likelihood is what MoAlpha said - you're running over some construction debris - could be the drop cuts from the wire-ties from when they laid the wire mesh/rebar. Or, if they did a really bad job and those little ends that are tying the rebar/mesh together were not bent cut/bent down - and they're poking through the surface. My bet is still just lose crap on the surface.

Sounds like a walking tour is in order.

Psimet2001 

Pull the tubes and diagnose the causes. I have a video that can help explain it or give you some tips.

canklecat

That striated concrete can and will trap sharp debris that punctures tires. With smooth finished pavement, motor vehicle traffic tends to blow debris off to the sides, and any remaining debris is easy to spot. But broken glass, etc., can hide in that striated concrete, making it harder to avoid.