Activation of fly ash–lime systems using calcined phosphogypsum

Experiments were performed to determine the effect of calcined phosphogypsum on the strength of fly ash–lime binders. Significant strength increases compared to binders without calcined phosphogypsum were observed due to the activation. But lowering the lime to calcined phosphogypsum ratio of blends with the same fly ash content yielded a relatively lower compressive development at late ages. Strengths of samples cured first at 45 °C in over 90% R.H. for 12 h and then at room temperature were better than those cured at room temperature all the time. X-ray analysis suggests that the activation of calcined phosphogypsum to the systems was due to the formation of ettringite and dihydrate calcium sulfate during the hydration process.