Alkali-activated binders based on ground granulated blast furnace slag and phosphogypsum

Abstract The effect of phosphogypsum (PG) in alkali-activated ground granulated blast furnace slag (GGBFS) on the reactivity, strength development and final matrix properties was investigated, as a function of alkali activator. The results were compared with alkali-activated reference samples from GGBFS. PG completely dissolves and takes part in solid reaction product formation. Upon PG incorporation, portlandite and ettringite are initially formed after dissolution. The hardened binder consists mainly of amorphous hydration products, intermixed with thenardite and minor amounts of secondary gypsum and merwinite. PG incorporation resulted in faster initial and delayed final setting time, while it enhanced the compressive strength and amorphous phase development when sodium hydroxide was used. PG gave rise to a decrease of Al/Si and Ca/Si ratios in the C-A-S-H gels and a higher polymerized network.