Mechanism of cement hydration inhibition by zinc and accelerating hardening by sodium aluminate analyzed by XRD

Abstract

Zinc in melting fly ash inhibits cement hydration and makes cement solidification difficult, but the addition of sodium aluminate in equal molar amounts with zinc can accelerate hardening. The mechanism of this phenomenon was analyzed by X-ray diffraction. Zinc exists as zincate in the alkaline atmosphere created by cement, and when mixed with cement, calcium zincate is formed. This reaction is thought to remove calcium from the liquid phase, thereby inhibiting the hydration of calcium silicate, the main component of cement hardening. Normal hydration began after all the zincate had combined with calcium. Sodium aluminate, a cement rapid hardening agent, produced hydrates that incorporated the zincate. Accelerating hardening by sodium aluminate was thought to be due to the formation of hydrocalumite, unlike the normal cement hardening reaction. Hydrocalumite is considered to incorporate zincate, and in the long term, the strength increase due to normal hydration of cement can be expected.