Potential use of phosphogypsum in paving blocks

Abstract

The present work aims to contribute to finding more recycling routes for phosphogypsum (PG) and its potential uptake in the material construction industry as paving blocks. Laboratory testing was conducted to formulate mixes using PG as fine sand replacement. An optimal 20% substitution rate was proved. Industrially processed paving blocks were made for high-quality experimental investigation. The most interesting testing results of PG paving blocks are the low water absorption coefficient of 5.7% and excellent mechanical properties, including high compressive and flexural strengths at early age (20.7 and 4.65 MPa at 7 days, respectively). Compressive strength evolves with respect to the curing period: 26% increase at 28 days and 36% increase at 90 days; flexural strength evolves from 6% at 28 days to 10% at 90 days. The leaching test showed low levels of heavy metals released, and their concentrations were lower in the mix than in the raw PG. For all the aforementioned results, PG waste from a phosphate plant in Gabès, Tunisia was proved to have high potential for reuse in the manufacturing of paving blocks with low health risks and excellent properties. Reusing PG waste in paving blocks would thus contribute to solving an environmental issue and reduce the use of sand, which is prone to depletion as a non-renewable resource.