Phosphogypsum as a Component of Flowable Fill

Abstract

Phosphogypsum (PG) is a by-product of the production of phosphoric acid, a key ingredient in the manufacture of fertilizers. Large amounts of PG have been stockpiled in Florida, Louisiana, and Texas, as well as other parts of the world. The means of using and disposing of this by-product with minimal environmental impact have been developed in research spanning almost 20 years. A study was conducted to investigate PG as a potential component of flowable fill materials along with Class C fly ash. Both Class F and Class C fly ashes have been used successfully to provide flowability and strength characteristics to flowable fill. A number of mix proportions of PG and fly ash were tested for flowability, time of setting, and unconfined compressive strength in a preliminary test series. Using the results of these preliminary tests, three final design mixtures were developed. These mixtures were then subjected to different physical and engineering property tests, including flowability, time of setting, unconfined compressive strength, flexural strength, dimensional stability, and permeability. Tests were also conducted to evaluate the environmental effects of the individual mixtures. These tests included the toxicity characteristic leaching procedure and radon emission testing. The results of this study indicated that PG can be used successfully as a component of flowable fill.