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KA' <br />■■ i <br />■■ <br />Bead size varied in the test sanples frcm small to large to mixed. There was <br />no indication that bead size had any relationship to rate of absorption. <br />Bead density was once thought to effect absorption, with less absorption in <br />higher density beads. This theory was not evident in tests as shown on the <br />density chart on page 8. Although density may have an effect on absorption <br />into the bead, it has no correlation to absorption between the beads. With <br />exposed foam, the foam which absorbs the most water will be less solid and <br />therefore subject to easier and quicker erosion and deterioration. <br />Most polystyrene foam weighs around 1.0 Ib./cu.ft. but can vary upward and <br />downward. To assure a solid enough mass of foam to backup coatings and <br />coverings, a most cannon specification calls for polystyrene foam to have a <br />mtniimn density of 0.9 Ibs./cu.ft. Specifying this density combined with a <br />requirement of less than 3 Ibs./cu.ft. absor- -.ion at seven days, assures the <br />buyer of getting a high quality polystyrene foam. Do not specify an average <br />density of 1 Ib./cu.ft. because that can get you anything since there are no <br />low limits. Always use minimum densities in the specifications. <br />Polystyrene sanples were tested <br />for effects of freeze/thaw <br />cycles and no difference was <br />found in absorption between <br />sanples continually frozen and <br />thawed and sanples that remained <br />in water without being frozen. <br />(Note: This was not the case <br />with polyurethane.) <br />polystyrene <br />The depth of polystyrene block <br />inmersicn into water affects <br />initial absorption and longer term <br />absorption as shown on the graph <br />to the right. TWo sanples were cut <br />side by side from a block and <br />tested with 1/2” head and 9” head <br />of water over the top of the <br />sanples. Not only did the deeper <br />sanple absorb more water <br />imnediately but absorbed more water <br />with time. <br />Testing was done to see if foam <br />absorbed water by capillary action. <br />This question came up when people <br />found wet and heavy foam above the vjaterline. Testing showed that foam does <br />not take on water by capillary action. My explanation for wet foam above the <br />waterline is the fact that when a liveload is applied to a dock with exposed <br />fo«n, foam nonrally above the waterline goes under water and the voids are <br />imnediately filled with water. Although these voids quickly fill with water, <br />they do not let it out very fast in fact very slowly. This is confirmed by the <br />-9-