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

Abstract

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 system of calcium aluminates (CA, CA 2 , C 12 A 7 ) 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.2

Influence of metakaolin on the conversion and compressive strength of quaternary phase paste

“…Calcium aluminate cement (CAC) is a satisfactory alternative to Portland cement (PC) in some special concreting applications such as dam spillways and sewerage pipes, due to its rapid strength gain, high resistance to abrasion, and severe aggressive agents (especially sulfates). [1][2][3] Nevertheless, application of this binder faces two main difficulties, high cost (about 5 times higher than PC) and volumetric instability from hydrates conversion. 4 In CAC, monocalcium aluminate (CA) and Q phase are considered as the major hydratable constituents, though other phases such as mayenite and belite, may also contribute to the strength.…”

Strontium Retention of Calcium Zirconium Aluminate Cement Paste Studied by NMR, XRD and SEM-EDS

“…15 • C, calcium aluminates are hydrated to form metastable CAH 10 . At room temperature, the hydration process proceeds through the formation of other metastable phases C 2 AH 8 and/or C 4 AH [13][14][15][16][17][18][19] (hexagonal hydrates). At higher temperatures (above 28 • C), the metastable hydrates will spontaneously convert to the cubic hydrogarnet C 3 AH 6 .…”

“…Although this approach is unique, there are other approaches to affecting the hydration behavior of aluminates-bearing CACs and related materials. Results from other studies indicate that the metal chloride and nitrate salts are known in CAC science as agents affecting the CAC hydration behavior [15,16]. The exact nature of this behavior is different for alkali metal salts (NaCl, KCl, RbCl, CsCl, LiCl), alkaline earth metal salts ( .…”

“…The effect of alkaline earth metal salts on setting the behavior of CAC is determined by the amount of addition [15]. Another approach in the acceleration effect is the addition of chlorides and nitrates of Li(I), Cr(III), Zn(II) and Cr(VI) (chromate), whereas Pb(II) and Cu(II) retarded the hydration [16].…”

Calorimetry in the studies of by-pass cement kiln dust as an additive to the calcium aluminate cement

“…Different metallic salts, when added to hydrating CAC paste, result in the modification of hydration kinetics in different ways: Acceleration (strong or slight) or retardation of hydration process is observed, depending on the nature of cations and anions, as well as the concentration [8]. The possibility to form the complex compounds is of importance too [8,9].…”