Acceleration of cements with phosphogypsum through sodium chloride: analysis of compressive strength and corrosive potential

Resumo

Phosphogypsum, a byproduct of phosphoric acid production in the fertilizer industry, is an environmentally friendly source of calcium sulfate for controlling the setting time in cements, replacing gypsum. However, as it is a waste product, it can contain impurities such as F- and P2O5, which may prolong the setting time beyond the desired duration and reduce initial mechanical strength. A solution to this problem is the use of hydration/strength accelerators, of which several types are available. Considering cost, sodium chloride can be an attractive option. However, it is known that chlorides can cause corrosion in reinforcements. Therefore, the incorporation of these materials as setting accelerators in concrete requires caution regarding the durability of structures. This study aims to analyze the influence of using phosphogypsum in Portland cements and the impact of sodium chloride as an accelerator. Tests were conducted to verify the behavior of the mixtures at early ages, using isothermal calorimetry in pastes, compressive strength, and corrosion potential in concretes. The results confirm that the presence of phosphogypsum delays the setting process but does not significantly affect the final strengths. Additionally, the tested chloride levels did not indicate a high probability of reinforcement corrosion.