A seemingly incongruous engineering feat, a tapestry woven by various disciplines, an experience in team building, all bound in unforgettable: the concrete canoe.
Sourcing Our Pumice
Sourcing our pumice aggregate and pozzolans for your competition boat is a two-step process.
1) MIX DESIGN / LAB SAMPLES: Competition teams typically start with small testing samples to zero in on the right concrete mix design. Directly order the testing samples you want to work with and get them on the way. The grades you see available to order are the typical grades (including pozzolan) requested over the years.
2) CANOE CONSTRUCTION SAND, AGGREGATE AND POZZOLAN: When you’re ready to order the pumice pozz and aggregate, send an email to our Fulfillment Center at firstname.lastname@example.org and tell us which grade(s) and how much you need. We are logistics experts: we’ll use all of our resources to get you the best freight rate. Be sure and include all of the information below in your email request.
|EMAIL REQUEST INFORMATION|
|Your Name + Team Name|
|Your Contact Information (cell and email)|
|Pumice Grade(s) wanted and Quantity of each|
|Physical Shipping Address (accessible by LTL truck)|
RECOMMENDED PUMICE GRADES
|Narrow-range graded pumice sand and small aggregate. Grade sizes: #2, #5, #7, #10, and a mine grade, 3/8x#8MN. These grades are used by teams looking for precise control of the aggregate size blend (including the fines).|
|These two aggregate mine grades are screened to grade for top size only and not dried. They include a wider range of particle sizes in the grade range, including extensive fines (sand). Grades include 3/8FinesMN and 1/8FinesMN.|
|Standard Pozz (DS325 - 25 micron APS) and UltraPozz (3 microns APS) grades.|
Order pumice aggregate and pozzolan testing samples directly from the Hess Fulfillment Center via the site Pumice Store.
Working with Pumice Concrete
Preparing and handling lighter pumice concrete is similar to handling normal-weight (heavy) concrete, with a few key differences, as detailed below.
LIGHTWEIGHT AGGREGATES NEED A POZZOLAN
It’s one of concrete science’s ironic truths: lightweight aggregates are reactive, and if used with ordinary Portland cement without the mitigating effects of a reactive pozzolan, the concrete inevitably develops a nasty ASR problem—a reaction between the high silica content in the aggregate and the alkali in the hydrated cement paste. The alkali-silica reaction forms expansive gels that generate a sort of slow-motion explosion, map-cracking and eventually destroying concrete structures from the inside out.
MIXING AND PLACING PUMICE CONCRETE
PREWETTING. All pumice aggregate should be uniformly prewet to reach total saturation, then be allowed to sit while excess water drains out. This will fill the internal voids of the pumice with water. As dry pumice aggregate will aggressively absorb mix water, prewetting the mix will prevent its drying before placement and slump will be uniform throughout the load, and from load to load.
SLUMP. Pumice concrete has about two inches less slump than heavy concrete for the same consistency and workability. Low-slump pumice concrete will flow when vibrated, and finishers can get on it much sooner when the slump is held to two-to-three inches.
AVOID OVERWORKING. Avoid over-vibrating or over-finishing pumice concrete. When using heavy concrete, segregation and over-finishing cause the paste to come to the top. With pumice concrete, it’s the coarse pumice particles that float to the top.
CURE. Pumice concrete is cured in the same method as is heavy concrete.
FORM REMOVAL. Form removal should be delayed for an additional 24 hours for pumice concrete. This applies especially if sharp corners are formed, as they will be softer for a few days.
ABOUT PUMICE and HESS PUMICE
Building (and Racing) Concrete Canoes
An opportunity for students to take engineering principles learned in the classroom and apply them in a challenging, curiously practical effort? Sweet! Stir in competitive components to add flavor? Even better. Heat the competition up with a prove-it race element? It’s on! Hundreds of engineering teams involving thousands of students jump into the months-long Concrete Canoe Competition every year.
A BRIEF HISTORY
Professor Clyde Kesler had an idea: class term projects involving high-strength concrete cylinders and reinforced beams lacked creative and collaborative depth...but a concrete canoe? Now that would stretch ’em out!