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Protecting Concrete on the Beijing-Shanghai Railway Bridge

From JPCL, December 2011

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by Huang Weibo, Liu Xudong, Lu Ping, and Ma Xueqiang, Research Institute of Functional Materials, Qingdao Technological University, China.
	The authors give a brief history of polyurea use in China, describe the Beijing-Shanghai High-Speed Railway and the polyurea specification for it, explain the project's major coating challenges, and describe the tests that led to a solution. The authors are with the Research Institute of Functional Materials, Qingdao Technological University, China. ... (Login to read the full article)

Comment from Jerry Trevino, (2/7/2012, 6:02 AM)

It seems that the failures of the polyurea (if I understand this correctly) are attributed to the concrete conditions, temp, humidity, bug holes, etc. Also the incompatibility of the epoxy primers to the Polyurea. Maybe the early failures should be blamed on the characteristics of the Polyurea not the primers or the concrete. The concrete is what it is. If you shot blast or abrasive blast, you will get more profile and more bug holes, that is what you want to remove weak layers of concrete. Maybe the solution is to apply the epoxy at normal curing temps, then spray a thin coat of a aliphatic polyurethane. Polyurea is intriguing, however, it likes to bond to itself more than it likes to bond to concrete. Any moisture on the concrete surface will tend to react with the isocyanates in the curing agents of the polyurea, releasing Co2 and making foam. Polyureas have great potential, I do not think applying them to concrete, especially where there is moisture transmission through the concrete. Most existing structures do not have the luxury of a vapor barrier before they were installed. Just my biased opinion.

Comment from Jerry Trevino, (2/8/2012, 8:25 AM)

I apologize to my overreaction to my first scan reading of this article. Properly due respect should be given to this case study. Obviously, an impressive feat. A lot of questions first came to mind, one is why was a polyurea selected in the first place? What was the decision making process on that, secondly, based on the extreme temperature conditions, how was the concrete placed and cured in those conditions? If not then why is the coating expected to be applied under those conditions, or did the placement happen at better temperature and humidity environments ? Also what was the concrete composition, design, mechanical properties, post tension conditions etc. Could have the original concrete surface be abrasive blasted then coated with a high pozzolanic reactive cement coating, then be coated with a primer and then the polyurea application? Microsilica and other pozzolan cements will reduce permeability of water and thus chlorides and sulfates in the ground into the main concrete structure by at least 10 times. This also allows primers and maybe polyureas to bond better to protect the overall structure. Could have an elastomeric polyurethane, an amine cured epoxy, or polyester resin perform just as well as the polyurea? Just Asking ! Great Article by the way. Congratulations to the publisher.

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