December 29, 2009

2009 is coming to a close and the mix design team is nearing completion of the concrete mix for the 2010 canoe.  We have had a lot of trouble with the new rules requiring two recycled aggregates and we can't say we're particulary excited about this rules change (especially the negative effects on our unit weight).  Regardless, we are pushing forward with the mix and we hope to have a near complete design by today.

The team began the year with the typical goals of a unit weight less than water and a concrete strength to resist all of our static and dynamic demands.  To keep the unit weight of the mix relatively low, the team decided to use Praver Siscor spheres once again as our primary aggregate.  The trouble came with selecting the second aggregate.  First, we tried using cork, but it was too fine and too light (25% by weight equates to about 75% by volume, which obviously won't woek).  The second choice was to use cenospheres, but they were also too fine and too light to make up 25% of the total aggregate weight.  The thrid and less desirable choice was recycled tumbled glass, but batches ended up around 65 pcf.  As we started running out of time, we finally settled on using recycled tile as our second aggregate.  We placed an ad on Craig's List and obtained the tile from a lady who just remodeled her bathroom and wanted to discard her used tile.  We hauled it back to Reno and crushed it ourselves in the materials laboratory.  Then, the material was sorted and sieved for use in the concrete mixture.  Of course, the bulk specific gravity of the tile is still fairly high (2.291), but we haven't found anything outside the box to use as a lightweight recycled agg.  We ran material tests on the tile yesterday, and we are batching our first mix with it today.  In an ideal world, the concrete unit weight would stay around 60 pcf, but we may just have to accept heavier concrete and add some bulkheads to the canoe.

Workability is also an area where we had trouble this year (as every other year).  To mitigate this, we attempted to use latex for the first time, but we're unsure how successful this has been.  The team purchased a new concrete mixer (actually, it's a mortar mixer) and it may not be entraining air well as we hoped.  We will have to further investigate this to determine if the application of latex is working within our concrete mix.

Overall, this year's mix design is steadilly moving along, and we hope to have a final mix in the next couple weeks.  It looks like we we be using the following constituents in this year's mix: Type I white cement, Type K (), Vcas (a recycled pozzolan), Daravair (AEA), Adva 170 (HRWRA), VMar 100F (VMA), Poraver Siscor spheres (sizes ranging from 0.1 mm - 2.0 mm), recycled tile (sizes raging from 2.0 - 4.5 mm) and PVA fibers (6 mm and 12 mm sizes).  We'll post an update as soon as we get our final mix with the properties and some photos.