Valorization of Phosphate Waste Sludge as a Nonhazardous Fire Resistant Material added to Concrete mix.

Abstract

Phosphate waste sludge (PWS) generated from a phosphate unit of an automotive manufacturing plant was investigated by X-ray Fluorescence and total heavy metals content and metal Leachability using Toxicity characteristic Leachate procedure (TCLP). Addition of different percentages of (PWS) to a concrete mix of Portland cement)was used for the solidification and stabilization (S/S) process to immobilize the hazardous contamination of metals within the (PWS) as well as to create a construction matrix capable to be used as fire-resistant material. The Solidification/Stabilization (S/S) concrete mixtures were prepared, then after a molding time of 24 hours, the samples were exposed to curing conditions that had a constant temperature (20 ^oC) and constant relative humidity. Investigation of the obtained specimens containing PWS as an additive ( control specimen,  1% and 3% PWS) after curing in water for 28 days was done by measuring both, compressive strength and fire resistance properties. The fire testing was done up to a temperature of 1000 ⁰C,the results show that concrete mix containing (PWS) of 3% have an excellent Fire resistance compared to the pure concrete, and also higher than specimen with 1 % (PWS). The degree of fire resistance was (around on hour and 15 minutes). Compressive strength of our specimens was decreased by increasing the percentage of PWS added. A noticeable decrease in the value of compressive strength of specimens containing (PWS) comparing to that of control concrete: from 31.2 N/mm² for control sample to a value of 19.8 N/mm² of specimen containing 3 % PWS. The microstructure of our mixes after compression testing was studied using scanning electron microscopy (SEM). Propagation of cracks and micro-cracks was observed for all specimens. Needle-like structure (Ettringite) also was observed in the SEM image.