A study on self-terminating behavior of sodium-concrete reaction (2)

Fundamental experiments were carried out to investigate the self-termination behavior of sodium–concrete reaction (SCR). In the reference experiment, the reaction time was controlled to investigate the distribution change of Na and the reaction products in the pool and around the reaction front. The measured concentrations at the reaction front were 18–24 wt.% for Na, 22–18 wt.% for Si, and 4–3.4 wt.% for Al and Ca after the self-termination. From the thermodynamics calculations, stable materials at the reaction front comprised more than 90 wt.% solid products such as Na₂SiO₃ and no Na. Furthermore, in two sensitivity experiments with additional heating or using mortar, the concrete-ablation behavior depended strongly on the reaction at the reaction front. It was concluded that SCR termination was caused by the lack of Na at the reaction front.

The distribution of Na and reaction products could be explained by a steady-state sedimentation–diffusion model. At the early stage of SCR, the reaction products were suspended as particles in the Na pool because of the high H₂-generation rate. As the concrete ablation proceeds, they start settling down due to the decreased H₂-generation rate, thereby allowing SCR termination.