Chloride-induced corrosion is a major cause of degradation of reinforced concrete infrastructure. While the binding of chloride ions (Cl) by cementitious phases is known to delay corrosion, this approach has not been systematically exploited as a mechanism to increase structural service life. Recently, Falzone et al. [, 54-68 (2015)] proposed calcium aluminate cement (CAC) formulations containing NO-AFm to serve as s that are capable of binding large quantities of Cl ions, while simultaneously releasing corrosion-inhibiting NO species. To examine the viability of this concept, Cl binding isotherms and ion-diffusion coefficients of a series of hydrated CAC formulations containing admixed Ca(NO) (CN) are quantified. This data is input into a multi-species Nernst-Planck (NP) formulation, which is solved for a typical bridge-deck geometry using the finite element method (FEM). For exposure conditions corresponding to seawater, the results indicate that Cl scavenging CAC coatings (i.e., top-layers) can significantly delay the time to corrosion (e.g., 5 ≤ ≤ 10, where is the steel corrosion initiation delay factor [unitless]) as compared to traditional OPC-based systems for the same cover thickness; as identified by thresholds of Cl/OH or Cl/NO (molar) ratios in solution. The roles of hindered ionic diffusion, and the passivation of the reinforcing steel rendered by NO are also discussed.

The reasons for the start and end of the induction period of cement hydration remain topic of controversy. One long-standing hypothesis is that a thin metastable hydrate forming on the surface of cement grains significantly reduces the particle dissolution rate; the eventual disappearance of this layer re-establishes higher dissolution rates at the beginning of the acceleration period. However, the importance, or even the existence, of this metastable layer has been questioned because it cannot be directly detected in most experiments. In this work, a combined analysis using nano-tomography and nano-X-ray fluorescence makes the direct imaging of early hydration products possible. These novel X-ray imaging techniques provide quantitative measurements of 3D structure, chemical composition, and mass density of the hydration products during the induction period. This work does not observe a low density product on the surface of the particle, but does provide insights into the formation of etch pits and the subsequent hydration products that fill them.

Disagreements about the mechanisms of cement hydration remain despite the fact that portland cement has been studied extensively for over 100 years. One reason for this is that direct observation of the change in microstructure and chemistry are challenging for many experimental techniques. This paper presents results from synchrotron nano X-ray tomography and fluorescence imaging. The data show unprecedented direct observations of small collections of CS particles before and after different periods of hydration in 15 mmol/L lime solution. X-ray absorption contrast is used to make three dimensional maps of the changes of these materials with time. The chemical compositions of hydration products are then identified with X-ray fluorescence mapping and scanning electron microscopy. These experiments are used to provide insight into the rate and morphology of the microstructure formation.