Influence of alternative accelerators on the hydration and strength of Portland cement with phosphogypsum

Influência de aceleradores alternativos na hidratação e resistência do cimento Portland com fosfogesso

Abstract

Phosphogypsum (PG), a byproduct of phosphoric acid production, shows potential as a substitute for traditional gypsum in cement formulations. However, the fluorides and phosphates in its composition can delay setting time and reduce early strength in Portland cement. The use of hydration and strength accelerators can counteract these effects, but the literature lacks sufficient information on the subject. This research evaluates the influence of alternative accelerators on the hydration of cement with phosphogypsum. Sodium chloride (NaOH), calcium chloride (CaCl₂), sodium hydroxide (NaCl), and sodium silicate (Na₂SiO₃) were analyzed. Isothermal calorimetry and compressive strength tests were conducted on cement pastes. NaOH showed the highest 24-hour compressive strength and cumulative heat, suggesting its potential as a strength accelerator. Na₂SiO₃ exhibited the lowest performance compared to the reference sample (REF). The strengths and reaction rates of CaCl₂ were similar to those of the REF. NaCl displayed higher strengths and cumulative heat than the REF, indicating its effectiveness as an accelerator.

Keywords
Phosphogypsum; Alternative accelerators; Hydration