Chemicals and Concrete: ‘Where’s the Beef?’
This article was contributed by Dan Williams, a retired Highway Maintenance Reviewer from the Montana Department of Transportation
In this last decade, there have been a number of research efforts looking to define the impacts of long-term and repeated chemical applications to concrete. These accelerated tests have determined that there will be damage to concrete over time. So, because of my history with Montana Department of Transportation (MDT) with winter chemicals and maintenance, I went looking for actual damage in the field. (The following images were taken Jan. 19-20, 2011.)
I wanted “old” concrete, 20-year plus concrete that had been exposed to magnesium chloride and road salt. I was not disappointed. Montana, being a rural state, did not get a lot of concrete when the Interstate was being pushed through, but it got some. I-90, from Missoula northwest to Idaho, was a good example of original concrete. This stretch of road gets a lot of snow, freight traffic and winter chemicals. The oldest piece I looked at was 39 years old (milepost 89),and had seen Mg/Cl2 and road salt for the last 18 years. The surface is looking fine and has no plans for immediate work. Closer to the Idaho state line and increased snow fall, is milepost 43, and the concrete is 27 years old and in the same shape, good.
I jumped over to another wintery spot, Kalispell Montana, for another look-see. Main Street in Kalispell is full depth concrete constructed in 1982, and saw magnesium chloride expressly for 16 years as the town is PM-10 non-attainment (air quality status) meaning, no abrasives can be used. Same results – no damage.
I looked at an experimental research ‘white-top’ project also in Kalispell being tracked by MDT on Idaho Street. It’s not old. Constructed in September 2000, this chunk of green concrete got the unthinkable, its first application of magnesium chloride one month after being open to traffic and it continued for the next six years until they switched to salt brine and solid chemical in 2006. Again, no damage.
I went closer to home to Helena where I retired from MDT four years ago. In front of the MDT headquarters runs a four lane piece of concrete (US 12) constructed in 1979 and it got its share of magnesium chloride and salt/sand for 12 years until they switched to salt brine and 75 percent salt/sand three years ago. Again, no damage.
When I say “no damage” I’m saying there is no apparent chemical damage that the lab research indicated would happen – concrete paste disintegrating. There is some studded tire wear, cracking with associated damage, tilted slabs and faulting here and there but not enough to merit anything but an occasional diamond grind to improve ride and a crack seal to keep water out.
These concrete roads are not only meeting their design life but exceeding it in some cases. An exception to this overall performance is a portion of I-90 at the summit of Look Out Pass that
will receive a “crack and seat” with an asphalt overlay on top. Missoula District Administrator is Doug Moeller indicated, “This road may not be in the current condition it is today if water could be reduced from entering the sub-base.” And, he said he “was happy with the length of performance (30 years) of this piece of highway.” Doug’s observation about water damage is a reminder to all of us.
Long term testing of concrete will take 30 to 40 years in actual field conditions. Plus there are a number of variables in the field that can’t be controlled or measured in order to get an objective picture of chemical impacts.
Consequently, methods have been developed to shorten the time of research to as little as two years. If successful, this accelerated approach has the benefit of preventing bad acting chemicals from future years of application to concrete to help ensure its longevity. And who is not for saving money and America’s infrastructure?
In my attempt to gather information about one of these recently completed pooled fund research projects, the South Dakota Study, I spoke with Ron Wright a member of that study and supervisor chemist for Idaho Transportation Department (ITD) as well as chemist for the Pacific Northwest Snowfighters (PNS). Wright noted, “There is no doubt that chloride penetration occurs from chloride based chemical applications, and the infusion depths of chlorides is linked to the quantity and types of materials used in chemical deicing.