Use of a low-cost concrete-like fluorogypsum-based blend for applications in underwater and coastal protection structures

This research aims to develop a concrete-like material for underwater construction applications by using fluorogypsum (FG, an industrial by-product of hydrofluoric acid production), class C fly ash, and type II Portland cement. Two Response Surface Models (RSMs) were derived based on compressive strength tests and expansion measurements on FG-based blend cylindrical samples after 28-day curing. The developed RSMs allow accurate prediction of the compressive strength and volumetric expansion as functions of the relative content in weight of different components in the FG-based blend material. Using these RSMs, a composition with promising strength and durability properties was identified. Additional mechanical and physical properties that are significant for structural applications were also investigated experimentally for this composition, confirming that the select composition could be a promising substitute for ordinary concrete and/or limestone. The effects of environmental actions on the mechanical and durability properties of the FG-based blend were investigated by immersing samples in seawater for a period of one year. The results of this experimental investigation suggest that the developed FG-based blend is a promising material for underwater applications (e.g., as oyster cultch) and coastal protection structures (e.g., for the construction of artificial reefs and breakwaters), at a significantly lower cost than other materials commonly used for the construction of these structures. Additionally, the unit weight of the proposed material is significantly lower than that of ordinary concrete and limestone, which contributes to a longer life span of the underwater structure by reducing its sinking rate into the soft soil typically found, e.g., in the US Gulf Coast region.