Understanding Retardation of Cement Hydration Caused by Zinc

Abstract

Zinc is known to retard the setting and hardening of cement paste/ concrete, and its effects can be very severe depending on the dosage. Research in the past has primarily focused on understanding the effect of zinc on the mechanical and late-age properties of concrete. This study was undertaken with the objective of understanding the chemistry of the cement-zinc mixture and proposing solutions to mitigate the retardation. The real-time evolution of the cement-zinc mixture was studied with 0 to 1% zinc dosage at very early ages with material characterization techniques: Isothermal calorimetry, pore solution analysis through X-ray fluorescence, and pH analysis. The supply of calcium and hydroxide ions were identified as the primary parameters in mitigating the retardation, and a hypothesis has been proposed to explain the observed effects.