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[117c] - Supercritical CO2 Carbonated Cements - Characterization and Application as Artificial Coral Reefs

Kerry M. Dooley (speaker) Louisiana State University Department of Chemical Engineering, South Stadium Road 110 Chemical Engineering Bldg Baton Rouge, LA 70803 Phone: 2253883063 Fax: 2253881476 Email: dooley@che.lsu.edu		Carl Knopf Louisiana State University Department of Chemical Engineering, South Stadium Road 110 Chemical Engineering Bldg Baton Rouge, LA 70803 Phone: 2253883065 Fax: 2253881476 Email: knopf@che.lsu.edu
Robert P. Gambrell Louisiana State University Center for Wetland Biogeochemistry Baton Rouge, LA 70803 Phone: 2253886426 Fax: Email: gambrell@eatel.net		Bronson Guilbeau Louisiana State University Department of Chemical Engineering, South Stadium Road 110 Chemical Engineering Bldg Baton Rouge, LA 70803 Phone: 2253881416 Fax: Email:

Abstract:

The objective of this research is the efficient fixation of CO₂ by microalgae supported on artificial reefs. These reefs can be manufactured with cement products especially tailored for microalgae attachment. The novel aspect of this work is to use supercritical carbon dioxide (SC-CO₂) to neutralize the cement matrix in a simultaneous molding/curing/carbonation process. Normally the high pH of cement mixes ( pH = 13) requires the use of expensive coatings or extensive underwater aging to generate a surface pH compatible with the marine environment. However, after carbonation with supercritical CO₂, the cement matrix has a near neutral pH, which allows immediate attachment of pH-sensitive marine microalgae to the artificial reef. These attached microalgae are more efficient in the fixation of CO₂ than their unattached counterparts. In addition, the attached microalgae can be concentrated in the vicinity of injection wells or other gas feeder devices. Finally, the pH-neutral cements can be prepared using cement foaming methods, such that additional surface area for marine microalgae attachment is created.

Applications of high-pressure carbonated cements are numerous; however, we are concentrating our efforts on making and testing pH-neutral reef materials, for CO₂ sequestration on a global scale. Manufacture and placement of artificial reefs is already a commercial operation (ReefBall™ Development Corp. Ltd.). Supercritical CO₂ allows controlled but rapid carbonation and therefore neutralization of any cement matrix - several examples will be given. The strength gain accompanying carbonation may allow future reefs to be thinner while still retaining desired flexural and compressive strength. In cured concrete, a carbonated region is typically a few-mm thick layer (generally < 5mm, unless treatment time is excessive). However, we have found that by treating the entire cement matrix with SC-CO₂ as part of a simultaneous molding/curing process, we can carbonate it rapidly, regardless of the thickness. By "rapidly" we mean simultaneous carbonation/curing in a few ks even for large cement forms, compared to typical carbonation times of several days or even years at low pressures.

We have tested the pH-neutral cements as made by the simultaneous molding/curing/carbonation process for attachment of microalgae populations (at both a saltwater and freshwater site), and have studied the CO₂-fixation rates of these attached populations. We have also characterized these novel materials by SEM, TGA, XRD, contact pH measurement, and measurement of uniaxial compressive strength.