How do we decide which materials or coatings to use? The choice involves an examination of at least four factors. These
are 1) whether ice adhesion strength is significantly reduced, 2) the material's durability or longevity, 3) its cost, and 4) its
ease of application. Our research provides the user with actual laboratory and field data on the first two of these factors. This
information, combined with information available from the manufacturer on Factors 3 and 4, allows a project engineer to
estimate the new material's potential benefit. It should be noted that a surface material having before-exposure ice adhesion
qualities that are similar to another coating's after-exposure qualities might be considered equivalently suitable for field use
at a Corps hydro facility, when lifetime benefit/costs are considered.
We have measured in the laboratory the adhesion strength of ice to common paints used by the Corps of Engineers for
protecting steel hydraulic structures as well as that for several candidate icephobic coatings. The test apparatus is a cone con-
figuration, typically used to evaluate the performance of adhesive joints (Anderson et al. 1977). In this configuration, an
adhesive is used to bond concentric cones of variable angle to which an axial load is applied, so that the cones are pulled or
pushed apart. By varying the cone angle, the relative amounts of shear and tension being applied to the adhesive joint can be
controlled. We test using a cone angle of 0 (see concentric cylinders labeled as pile and mold shown in Figure 2), which
predominantly loads the adhesive in shear. In our test, ice is the adhesive, and the inner cylinder (or pile) is either made
entirely of the material to be evaluated, or it is a steel or aluminum pile coated with a candidate icephobic material. Several
examples of test piles are shown in Figure 3.
Approximately 36 hours after the sample freezes and reaches a temperature of 10C, it is loaded at a constant rate of
0.06 mm/min until the icepile bond fails. The measured load at the time the bond fails is used to compute the shear strength
of the bond (the maximum load divided by pileice contact area). This is our indicator of the adhesive strength of the ice
bonded to the material of interest. The adhesion value that we report for each material is typically an average value obtained
from six replicates. This test procedure is fully described in Haehnel and Mulherin (1998).
Because the paints used by the Corps have been developed over many years for their high durability, a selected low-
adhesion coating would be applied over the Corps paints rather than replacing them. Our laboratory test was designed to
simulate this condition, and the coatings were layered over samples that already had the Corps paints applied. Since an
alternate means of protection might be to clad an area with a low-adhesion material, several candidate thermoplastic materials
were evaluated as well. Table 1 lists the paints, low-adhesion coatings, and thermoplastics tested in the laboratory.
Figure 2. Zero-degree cone test configuration (left) and instrumented sample pile and mold in testing machine (right).