Chemicals and Concrete: ‘Where’s the Beef?’
“Research has studied the rapid effects of many chemical deicer composition,” Wright continues.” The rapid lab tests are conducted on concrete with poor mix designs to produce data quickly that can be extrapolated to what will potentially occur in the field. The problem is in identifying the life cycle of a durable concrete exposed to chemical deicers. Researchers have reported that some of the most destructive lab results will take many years, perhaps beyond the life span of the concrete, to show any negative effects on the chemical paste matrix and strength of a durable concrete place in the field. This fact has been confirmed by comparing rapid lab test results to actual field samples exposed to many years of exposure from the field.”
I think we know intuitively that chemicals don’t improve concrete performance or add to longevity. On the other hand, eliminating chemical applications for winter safety is not a realistic option at this point in time. We should avoid, if possible, excessive and prolonged use of chemicals. And, when conditions allow, flush our structures and water proof them every three or four years to prevent chemical intrusion. Bridges take a pounding from heavy freight and increased freeze/thaw cycling causing them uncommon distress.
As Ron mentioned, accelerated concrete testing relies in part on producing test sample bricks of poor quality such as reduced air voids and high water/cement ratios. Submit them to accelerated freeze/thaw cycling, wetting/drying cycles, high temperatures and an abundance of chemicals and you get “results.”
Those results, perhaps, go beyond simulating actual exposure of concrete to actual winters in Montana and actual usage of magnesium and sodium chlorides.
At the 2011 APWA North American Snow & Pacific Northwest Snowfighters Conference, held in mid-April in Spokane Wash., Purdue University Professors Jan Olek and Jason Weiss presented their concrete/chemical study results.
Their study confirmed some damage was caused by magnesium and, to a greater degree, calcium chlorides to concrete but to a much smaller degree than previously published studies have indicated. A portion of their research included the addition of fly ash to the concrete which nearly eliminated all damage from magnesium chloride. Their study went on to show why previous studies provided invalid results because of some accelerated test methods. From what I heard at this session, the greatest culprits to concrete damage are, and continue to be, poorly constructed concrete and the presence of water.
My personal advice to winter maintenance providers is to develop realistic and attainable Levels of Service (LOS) guidelines for your highway systems.
- Educate all of your employees involved and consider sharing these LOS guidelines with your customers as well.
- Select appropriate chemicals from an approved listing, such as the PNS, that will provide the kind of performance your winter conditions require.
- Select, calibrate and maintain quality equipment that will enable your crews to appropriately “place” the “correct” amount of chemical to meet their needs.
- Establish a variety of reliable weather information sources – use them.
- Construct your bridges with the best possible modern materials (including fly ash), and methods and then clean and dry.
- Crack seal ALL your roads to keep water out.
All too often, we look for a single cause for a failure when experience tells us it is likely a combination of factors. There is no substitute for common sense. Build it right, take care of it, and you will likely experience the same life cycle for concrete roadways that Montana is experiencing.
About the author: After 22 years, Dan Williams is a retired Highway Maintenance Reviewer with statewide responsibility to ensure quality work and methods and new technology. His focus was as the winter maintenance specialist and noxious weed manager. Williams represented MDT at the Pacific Northwest Snowfighters (PNS) Conferences and was one of the founding fathers. He also provided training and oversaw winter chemical use for most of the state as well as a public relations component. After retiring from Montana Department of Transportation, Williams spent several years as a senior research consultant with the Western Transportation Institute in Bozeman, Mont., at Montana State University working under Dr. Xianming Shi.
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