Study of the early hydration of calcium aluminates in the presence of different metallic salts

The effect of chlorides and nitrates of Li(I), Cr(III), Zn(II), Cu(II), Pb(II) nitrate and Cr(VI) (chromate) on the early hydration of ternary cement system of calcium aluminates (CA, CA2, C12A7) was reported. Li(I) and Cr(III) caused a strong acceleration of the hydration, while Zn(II) as well as chromate gave rise to a slight acceleration. On the contrary, Pb(II) and Cu(II) retarded the hydration. A clear formation of AFm phases during the first hydration stages was found and related to the acceleration ability. Anions (nitrate or chloride as counterions or even chromate) were able to be incorporated into the interlayer space of AFm, yielding insoluble and stable compounds. A balance between the insolubility of the metal hydroxides (dependant on the low amphoteric character of the compound) and the ability of the formation of AFm hydrates seems to be very important to lean the equilibrium towards the retarding of the hydration or towards the acceleration, respectively.