Effect of Gypsum on the Early Hydration of Cubic and Na-Doped Orthorhombic Tricalcium Aluminate

Abstract

The tricalcium aluminate (C3A) and sulfate content in cement influence the hydration chemistry, setting time and rheology of cement paste, mortar and concrete. Here, in situ experiments are performed to better understand the effect of gypsum on the early hydration of cubic (cub-)C3A and Na-doped orthorhombic (orth-)C3A. The isothermal calorimetry data show that the solid-phase assemblage produced by the hydration of C3A is greatly modified as a function of its crystal structure type and gypsum content, the latter of which induces non-linear changes in the heat release rate. These data are consistent with the in situ X-ray diffraction results, which show that a higher gypsum content accelerates the consumption of orth-C3A and the subsequent precipitation of ettringite, which is contrary to the cub-C3A system where gypsum retarded the hydration rate. These in situ results provide new insight into the relationship between the chemistry and early-age properties of cub- and orth-C3A hydration and corroborate the reported ex situ findings of these systems.

Influence of Polycarboxylate Superplasticizers with Different Functional Units on the Early Hydration of C3A-Gypsum

“…Regarding this stage, the work of Quennoz et al [1] reported that the remaining site for AFm nucleation on the surface of C 3 A controlled the acceleration part, and the space available for growth was the main factor impacting the slope of the deceleration part. Also, the result of Kirchheim et al [19] proved that only the reaction Equation (3) existed during this stage instead of the concurrence of Equations (1) and (3).…”

Physicochemical effects of nanosilica on C3A/C3S hydration

“…A clear inhibiting effect by nanosilica on C 3 A hydration was found in the above results. To further investigate the probable mechanism of the retarding phenomenon, the first step was to understand the influence of gypsum on C 3 A hydration, which was also shown an inhibiting effect and has been well studied 42‐46 …”

Filler Effect in Shotcrete

“…The high reactivity of this C 3 A-rich cement is not only due to the amount of C 3 A but also to the ratio cubic/orthorhombic C 3 A (0.7%/10.8%), controlled by the alkali content in the raw mix and the cooling rate [56]. In the presence of sulfate the orthorhombic C 3 A is more reactive than the cubic polymorph [57]. The low C 3 A cement, on the other side, forms smaller amounts of ettringite but, more important than that, it also increases strength at a slower pace.…”