By Matt Zeller, Executive Director-Concrete Paving Association of Minnesota (CPAM)
I have been around MnROAD since 1992 when I was a graduate engineer in MnDOT’s Concrete Office while it was being constructed. Since then, many great things have been done at MnROAD … too many to discuss in this short article. MnROAD has been, and continues to be, a treasure for us in Minnesota because it is an experiment in which we are allowed and expected to fail so that we learn what to do and what to avoid. As Tom Burnham once noted, “It is a place for Matt to try his crazy ideas.”
Some of the crazy ideas over the years—all of which have been implemented in one way or another in actual projects in the past few years—have included:
- Thin concrete overlays
- Fiber reinforced concrete (overlays and on grade), and
- Low cementitious concrete mixes
One of the most exciting projects in the past couple years has been the investigation into how strong the concrete really needs to be before opening to traffic. In 2017 a test section was developed to run a 31,000-lb. tandem axle snowplow truck and a 9400-lb. pickup truck down the test section at varying times to evaluate how the concrete responded and to document any premature deterioration due to the early loads. Amazingly, the concrete showed no visible damage after allowing the snowplow to begin driving on the concrete after only three hours. Initial strain on the first day was significant but repetitions on the subsequent days showed very low strain.
YouTube video #1:
Shows the loading: https://www.youtube.com/watch?v=A7n-CaONIwU.
YouTube video #2: Team purposely rutting the concrete by driving the pickup truck across the concrete at an even younger age and then study the ruts over time: https://www.youtube.com/watch?v=ZyNy2UA9mSs
In 2018, we tried a similar experiment on full- and partial-depth concrete repairs as well as some roller compacted concrete (RCC). Again, these repairs were loaded at about three hours after they were placed. The only visual effect was that some of the curing compound was tracked by the vehicle. In both experiments, non-destructive evaluation will continue diligently for a few more years to expose any potential for long-term damage.
YouTube video #3: https://www.youtube.com/watch?v=fn-bd4RVXWQ
During the 2018 construction season we used some of the information we have learned at MnROAD to better serve the traveling public and to better build our pavements.
On at least one project this year, the contractor, in agreement with the contracting agency, (names withheld because there is no spec yet) allowed local traffic and residents to cross the concrete pavement after the joints had been sawed in the concrete pavement (at about eight hours).
On another concrete overlay project, the contractor, in conjunction with the contracting agencies, drove a fully-loaded water truck (approximately 50,000+ lbs.) to help induce the sawed joints to activate. The process was successful in activating more joints, and there was no visible damage to the concrete pavement.
While there is still research to be completed, available observations and an abundance of evidence indicate that we will in the near future be opening concrete pavements earlier to traffic. If designers know they can get their residents home and provide access to their businesses after only a day or so, the benefits of choosing a long-term concrete pavement solution becomes even easier.
NRRA and MnROAD are looking for more ideas to try in 2019. I am sure I will have many more ideas, and I encourage anyone involved in NRRA to submit ideas. You never know how we can change the world!
For Matt Zeller’s article, pease go to: http://www.dot.state.mn.us/mnroad/nrra/newsletter/november2018.html