February 27th, 2010

This daily is for those who were wondering where the concrete canoes go. Here at UW we have several people (me included) whose graduate research centers around recycled concrete aggregate (RCA). So when the canoe competition finishes, the canoe is donated back to the University, and we have a crusher that crushes it down to the appropriate grade/size. Reusing RCA in new concrete requires that it be crushed fairly fine to avoid bond failure (or a failure where the cement shears away from the aggregate due to some pressure). This is a picture showing the finished/crushed result.

Note: Why it's in plastic bags: Any research conducted on the durability performance of using RCA as the main aggregate in new concrete brings up an issue called an Alkali Silica Reaction. Long story short - This is where the alkalinity of either the aggregate or the cement is too high and results in unwanted (and completely uncontrollable) expansion. If any of you have ever observed fairly fresh concrete fail after only a year or even notice that the same stretch of highway keeps being replaced - it's most likely due to an ASR reaction of some degree. For ASR to occur water also needs to be present, hence the need for sealing them.

My daily on the 25th was of the canoe form work, we hadn't actually poured any concrete yet when I took that picture.

recycledconcreteaggregatedaily