Understanding the workability of alkali-activated phosphorus slag pastes: Effects of alkali dose and silicate modulus on early-age hydration reactions

Understanding the workability of alkali-activated phosphorus slag (AAPS) pastes is fundamental for their efficient application. This study revealed the novel mutual inhibition mechanism through which the alkali dose and silicate modulus affect the workability of AAPS pastes based on the hydration reaction. The slump loss of NaOH-activated phosphorus slag (NAPS) paste was slow, and that of waterglass-activated phosphorus slag (WAPS) paste was faster because the soluble Si in waterglass accelerated the dissolution of the phosphorus slag (PS). At a moderate waterglass modulus, the slump losses of the WAPS pastes were slow because the moderate [Al]/{[Ca]+ [Mg]} ratio in the pore solution minimized the difference in the magnitude of mutual inhibition between Ca, Mg and Al, causing all hydrates to form slowly. However, at higher and lower waterglass moduli, the WAPS pastes exhibited fast slump losses because hydrates with excess elements formed rapidly due to the excessively high or low [Al]/{[Ca]+[Mg]} ratio.

Automated summary

This study reveals how the alkali dose and silicate modulus affect the workability of alkali-activated phosphorus slag pastes. Waterglass accelerates the dissolution of the phosphorus slag, resulting in faster slump loss in waterglass-activated pastes. Moderate waterglass modulus leads to slower slump loss due to the minimized difference in mutual inhibition between Ca, Mg, and Al, allowing hydrates to form slowly. However, higher and lower waterglass moduli result in faster slump loss as a result of the excessive formation of hydrates with excess elements.