Doctor of Philosophy (PhD)
Civil and Environmental Engineering
The use of limestone as coastal protection devices and as an oyster cultch material has placed a substantial economic burden on the State of Louisiana. Limestone is not locally available in the State of Louisiana and must be transported from out of state which significantly increases the cost of utilizing the material. Placement of limestone on the unconsolidated soils in coastal Louisiana result in significant losses to sinking of the material due to the density of limestone. Therefore, locally available materials with a lower density compared to limestone are needed to reduce the economic burden of protecting and enhancing coastlines.
Previous research has shown that the stabilization of phosphogypsum (PG), a locally available material, with type II Portland cement (PC) and class C fly ash (FA) reduces the dissolution potential enabling PG to be utilized for applications in a marine environment. However, the United States Environmental Protection Agency has defined PG as a technologically enhanced naturally occurring radioactive material and has restricted this material to stockpiling when its radioactivity is greater than 10 pCi g-1. A similar (although non-radioactive) locally available material, fluorogypsum (FG), has been identified as a substitute to PG. The goal of this research is to prove the feasibility of and optimize a composition of FG stabilized with PC and FA for aquatic applications.
The leaching behavior, specifically sulfate and calcium release, was determined for 11 compositions consisting of 60% to 90% FG, 2% to 10% PC, and 0% to 38% FA exposed to synthetic saltwater (30 g L-1), brackish water (15 g L-1), and freshwater (0.5 g L-1) solutions. Sulfate and calcium effective diffusion coefficients (De) were calculated for each composition in each solution. Evidence of rupture development was found in compositions with ≤80% FG and 10% PC. The composition 70% FG, 2% PC, and 28% FA is recommended for saltwater and brackish water applications based on the sulfate and calcium De. Compositions with ≤80% FG and ≤6% PC are recommended for freshwater applications. A model to predict the retained mass based on the composition and time of exposure enables the optimization of the composition based on materials’ cost and retained mass. Comparison of predicted retained mass with the observed retained mass after exposure for 372 days to field conditions indicates the developed model estimates the predicted retained mass within 7% of the observed retained mass.
Lofton, Charles Davis, "Optimizing Stabilized Fluorogypsum to Decrease Dissolution Potential in Aquatic Environments for Construction of Artificial Reefs" (2017). LSU Doctoral Dissertations. 4116.