| Summary: | The oysterbreak is a method of growing an oyster reef into a wave attenuating device. A study was conducted to determine an optimal material for the oysterbreak. As oysters grow on the oysterbreak, wave energy in the lee of the structure is reduced. It was predicted that more rapid oyster growth would lead to a more rapid reduction of wave energy. Louisiana is losing coastal marshes at an alarming rate. Wave action from storms erodes sediments from Louisiana's shorelines and barrier islands. Structures such as the oysterbreak may be used to protect Louisiana’s fragile shorelines. A material for the oysterbreak may also be used to produce artificial oyster reefs or harvestable oyster cultch.
Concrete makes an excellent structural material and is attractive to oysters. It was hypothesized that adding cottonseed or crushed oyster shell to concrete would stimulate greater oyster growth than on concrete alone. The objectives of this study were to 1) determine whether concrete containing either cottonseed or oyster shell would have a greater increase in cross section due to oyster growth compared to concrete with no biological additive and 2) determine the structural properties of concrete with increasing amounts of cottonseed. Concrete samples were deployed in Caminada Bay near Grand Isle Louisiana in June of 2005. By March of 2006, concrete with oyster shell experienced the most growth (16.2% increase in perimeter of the bar), followed by samples with cottonseed (11.2% increase in perimeter). Samples with no additive had the least oyster growth (7.9% increase in perimeter).
An experiment was also conducted to determine the structural properties of concrete with cottonseed in it. Density ranged from 2.25 g/cc for samples with no cottonseed to 2.05 g/cm3 with samples with a high concentration of cottonseed. Strength ranged from 27 MPa for samples with no cottonseed to 7 MPa for samples with the highest concentration of cottonseed. It was determined that this range of strength was acceptable for use in the oysterbreak. It was also concluded that concrete containing either cottonseed or oyster shell would make a superior material for the oysterbreak, compared to concrete alone.
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