(deep swooshing sound) (booming sound)
- [Narrator] Years ago, micro cracks were discovered
on the surfaces of unused bridge girders,
located at the state's precast concrete plants.
Those same cracks were also found on some of the bridges
where the girders had been installed,
but why?
And could this lead to more cracking
and shortened surface life of the bridges?
- It didn't look like there was necessarily a pattern
to when this cracking occurred and when it didn't.
And so we looked at different seasons,
we looked at time of day, we looked at temperatures,
we looked anything you can imagine.
Finally got to the point I was like,
well, just looking and trying to figure out the pattern
wasn't gonna resolve it.
So we started needing to take some cores,
get some, study what's exactly going on.
- So one of the main questions we had is that
we know if it just had a single micro crack
that is not really going to cause an issue,
but what happened when you have many cracks?
So what is the effective crack density
when you're looking at micro cracks?
So we did the field studies in which we're monitoring
in service girders over time.
And then we also augmented that with some laboratory studies
in which we cast concrete mixtures,
we subjected those concrete specimen
to accelerated weathering tests
by subjecting it to moisture,
as well as simulating a marine environment.
And we developed a model to predict what,
how these cracks would grow over time
and more importantly,
how they may impact the strength
as well as the corrosion resistance of the concrete.
- So if these cracks get deep enough
or wide enough to allow water in and chlorides
and things like that,
and it gets to the reinforcing steel,
that's gonna quickly deteriorate the bridge.
And so, that's the biggest thing we're trying to avoid.
- We found that depending on the nature of the micro cracks,
that it could impact the surface life
between 2 to 13 years.
So that means a 2 to 13 year reduction
in the overall service life of the bridges.
So our major recommendation for TxDOT is that
in terms of monitoring, additional monitoring is needed,
particularly towards the very end of the service life
of the bridges.
- We believe the cause of the cracking
was related to shrinkage.
Now, why it's shrinking more than what it had prior
to that period?
We're not quite certain of that.
We think it may have been coincidental
with the big drought we had from 2010 to 2015,
because towards the end of that sort of drought
is when we started noticing some of this cracking.
And so, you've believed that played a role
the environment.
In fact, what we should said,
was environmental impact does play a significant role
in how much cracking is going to occur.
- We've already have really good specifications
about how a single crack is going to impact strengthened,
it's going to impact corrosion resistance.
What we didn't know is how many small cracks
are going to affect it.
That's really where we had this gap in the research,
the gap in the science.
And what this project really showed is that,
yes if you had one little micro crack,
that's not going to make a difference,
but if you do have many micro cracks,
the density of those micro cracks
can actually exacerbate the problem
and impair long-term durability.
- [Narrator] For more information,
and to find the publications for this project,
please visit the TxDOT Research Library
at the link shown below.