To produce the new reinforced core, our team placed a layer of C-grid on the mold and cut and contoured it to shape. We used tape and string to hold the splices in place as we positioned the modified flotation frame over this layer. We used tie wires to hold the inner layer of C-grid in place while we removed it and the frame from the mold. Then, we stapled the inner layer of C-grid to the flotation frame and removed the tape, string, and tie wires.
We began our second placement by draping a sheet of plastic over the mold to which we applied turtle wax and a mold release compound. This time, we secured 2.36 mm (0.093 in.) diameter wires across the mold at 15.2 cm (6.0 in.) intervals down the length. Then, our team members used drywall knives to level it to the upper surface of the wires. We left the wires in place to insure that the inner concrete layer would be of uniform thickness as we worked the innermost layer of C-grid and the flotation frame into position. Once this was done, we filled this configuration with concrete that team members leveled to the top of the frame.
After that, we added the outermost layer of C-grid and stapled it to the frame. During this process, we made certain that there were no opposing staples in the same location so that we could accurately compute the reinforcement thickness. After adding the outer layer with the help of the removable spacers, we draped plastic over the configuration. For the purposes of this competition, we placed concrete cylinders (ASTM C31).
Since the latex in our mix coalesced to form a film that coated the aggregate particles and the hydrating cement grains (Biszick and Gilbert 1999), we simply left the canoe and cylinders to dry. From sustainability and cost standpoints, this step saves water, time, and labor.
Our failed attempt forced us to extend the period scheduled for core construction and delayed curing by one week. We made up this time by hand sanding the outer layer of concrete after three days. During this process, we filled voids with the same mix used during the main construction and sanded after dark in soft lighting so that the shadows cast from oblique illumination could help us identify high and low areas. On the bright side, we found that sanding the boat earlier saved materials and the costs associated with them.
We cured the canoe for seven days so that the concrete would have the same flexural strength as that measured in our 7-day testing program. After removing it from the mold, we removed the spacer wires from the inner surface and filled the grooves.
We sanded the interior and applied vinyl lettering and stain to improve the boat’s aesthetics. Then, we placed the splash guard and sealed the surface. Appendix C describes all the materials and products used to produce our canoe. The pie charts shown in Figs. 6 and 7 depict the material costs and person-hours, respectively. We estimated person-hours through project completion; paddling is not included. Overall our costs and man hours stayed approximately the same as compared to last year.
Fig.6. Material costs ($1,482). Fig.7. Project person-hours (1,133).
Impact:During the project, we salvaged materials, and cut waste to a minimum. Our concrete sets up quickly and can be simply left to dry thereby saving cost and labor. Overall, the process can be easily done in the field making it suitable for applications ranging from sidewalks and roadways, to bridges and columns. More importantly, we were able to successfully reduce the weight of an unreinforced canoe by 2.4 kg (5.3lb) while adding a core containing the relatively heavy reinforcement required to sufficiently stiffen and strengthen it.