Title : Moroccan Phosphogypsum recycling in road applications.
Abstract:
Morocco produces annually an important quantity of phosphogypsum, a byproduct of the phosphoric acid industry by the wet process, consisting mainly of calcium sulfate dihydrate (CaSO4.2H2O) in association with low amounts of silicon (Si), phosphorus pentoxide (P2O5), organic matter and traces of rare earth elements (REE). Storing phosphogypsum in stockpiles brings about technical and financial problems, due to the fact that they occupy large land areas and cause serious environmental damage. This presentation aims to suggest novel alternative to recycle PG in road applications in a circular economy approach. In order to evaluate this option, we first identified and characterized the phosphogypsum produced in the industrial area of Jorf Lasfar. Then, our experimental approach focused on an optimal mixture between phosphogypsum and sand, treated with cement , which meets the mechanical requirements of a road pavement. A mathematical model was developed so as to obtain the dry density of any mixture using the percentage of PG, sand, cement and moisture. The target was to rise the strength up to a threshold allowing the use of the stabilised mixture as a material in road pavement, while neutralizing acidity generated by PG. The criteria detailed in SETRA’s guides were used to identify the needed responses which were then modelized by experiments design approach, and in particular mixing designs. Two optimal mixtures were reached, one for the subgrade layer of the pavement, the other for the base layer.
A cost comparison for the PG-SC-C mixes in different pavement structure types were carried out, resulting in the conclusion that pavement structure with a hydraulically bound base is the most economic type. Then, a comparative rational design using ALIZE software showed a significant cost gain compared to an equivalent road structure made up of conventional gravel.
What will audience learn from my presentation?
- The audience will be able to characterize what phosphogypsum is, and then discover new recycling horizons of this byproduct in road application.
- The presentation will help the audience understand what a mixture design with constraints is, and how far it is helpful to save time having the same or rather clearer results.
- It provides a practical solution to stockpiles problem, occupying large land areas and causing serious environmental damage.
- It is a practical solution to building materials shortage.
