A question was raised regarding how to test reinforcement to comply with Rule IIC.6.b of the 2002 national rules and regulations. Here's how we tested ours.
The rule in question states that:
" Solid mats or plates for reinforcing are not permitted. Solid mats and plates are described as reinforcing materials that require additional bonding agents or post-manufacture perforations to keep the reinforcement from delaminating from the concrete composite (i.e., lack of open space between the reinforcement sufficient for mechanical bonding to the concrete composite). To test for acceptance under this rule, a 102 by 203 mm (4" by 8') cylinder mold should be filled with one cup of "Graded Standard Sand" as described in ASTM C 778 (Ottawa sand). The reinforcement should be placed over the cylinder in the same configuration (layers, layer orientation, and spacing) that will be used in the canoe. When the cylinder is inverted, it should take less than 10 seconds for the sand to pass through the reinforcement scheme. Any used combination and single layer of reinforcement must comply."
According to a communication received from the Committee on National Concrete Canoe Competitions (CNCCC) on February 22, 2002:
"The intent of this rule is to assure that the canoe has strength through composite interaction between the reinforcing and the concrete by making sure that the concrete can form a mechanical bond with the reinforcing.
The reinforcing should be tested at the same spacing expected when the reinforcing is in place in the walls of the canoe. Reinforcement that passes the test as written will certainly not be questioned on this point by the judges."
On April 9, 2002 the CNCCC followed up with the statement, "The cylinder may be tilted it in whatever direction needed as many times as needed** to get the sand to fall through the reinforcement into the bottom of the cylinder. The cylinder may not be shaken or tapped.
** It is up the judges to determine if a team has had sufficient time to prove that the sand will go through."
As illustrated in the figure below, we employed three layers of graphite mesh to reinforce our composite cross section. The separation between layers is 2.8 mm (0.11 in.).
We prepared for our compliance test by cutting 10.2 cm (4 in.) diameter holes in 15.2 cm (6 in.) x 15.2 cm (6 in.) cardboard squares. The cardboard was 1.4 mm (0.055 in.) thick, equal to half the spacing between the layers in our cross section. Three different coupons were made by sandwiching one layer of graphite mesh between two layers of cardboard. Then, we conducted 30 tests.
Each test began by our filling 10.2 cm (4 in.) diameter, 20.3 cm (8 in.) long cylinder mold with one cup of Ottawa sand. After one layer of reinforcement was placed over the open end of the mold, the cylinder was inverted. This test was repeated 10 times. In every case, it took less than 2 seconds for the sand to pass through the mesh.
The procedure was repeated 20 times for the three-layer configuration used in the canoe. The results of these tests varied somewhat depending upon the relative orientation of the fibers. In the worst case scenario, where the fibers in one layer of reinforcement were intentionally positioned between the gaps created by the fibers in a lower layer, it took slightly less than 5 seconds for the sand to pass through the reinforcement scheme.