Effect of sodium hydroxide on the properties of phosphogypsum based cement

Abstract

The effect of sodium hydroxide (NaOH) amount on phosphogypsum based cement was investigated. The mechanical performances and hydration mechanism of the phosphogypsum-based cement with different proportions of NaOH and steel slag were analyzed based on setting time, volume stability, strength test, XRD and SEM analyses. The experimental results show that, NaOH as an alkali activator significantly reduces the cement setting time and improves the cement early strength. But the acceleration of hydration proces produces coarse crystalline hydration products and the osteoporosis structure of hardened paste, which has a negative effect on later age strength. The combination of 1% NaOH and 5% steel slag as alkali activating agents is optimal with respect to early and later age strengths. Overdose of NaOH not only decreases the cement strength at later age, but also may cause problem of volume stability.

Keywords

phosphogypsum / cement / sodium hydroxide / alkali activator

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