The impact of zirconium oxide radiopacifier on the early hydration behaviour of white Portland cement

Zirconium oxide has been identified as a candidate radiopacifying agent for use in Portland cement-based biomaterials. During this study, the impact of 20 wt.% zirconium oxide on the hydration and setting reactions of white Portland cement (WPC) was monitored by powder X-ray diffraction (XRD), 29Si and 27Al magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR), transmission electron microscopy (TEM) and Vicat apparatus.The presence of 20 wt.% zirconium oxide particles in the size-range of 0.2 to 5 μm was found to reduce the initial and final setting times of WPC from 172 to 147 min and 213 to 191 min, respectively. Zirconium oxide did not formally participate in the chemical reactions of the hydrating cement; however, the surface of the zirconium oxide particles presented heterogeneous nucleation sites for the precipitation and growth of the early C-S-H gel products which accelerated the initial setting reactions. The presence of zirconium oxide was found to have little impact on the development of the calcium (sulpho)aluminate hydrate phases.

► This is the first study of Portland cement-based biomaterials by 27Al and 29Si NMR.
► 20 wt.% ZrO2 radiopacifier accelerates the early cement hydration reactions.
► Extent of hydration after 6 h is increased from 5.7% to 15% in the presence of ZrO2.
► Initial and final setting times are reduced by 25 and 22 min, respectively.
► ZrO2 provides nucleation sites for the precipitation of early hydration products.