Kinetic analysis and thermodynamic simulation of alkali‐silica reaction in cementitious materials

Abstract

This work aims to study the alkali‐silica reaction (ASR) with incorporated kinetic‐thermodynamic analysis. The model reactant tests were first conducted to study the silica dissolution in the simulated pore solution under different temperatures. Then, the kinetic model for silica dissolution was further improved by considering the influence of effective surface area. The improved kinetic model was also incorporated into the GEMS thermodynamic simulation. The model analysis demonstrated the silica dissolution rate is decreased mainly caused by reduced hydroxyl activity with increased saturation degree. The dissolved silica first reacted with the portlandite phase and formed the Calcium–Silicate–Hydrate (CSH) gel. The ASR gel can only be generated under high silicate ion concentration after the consumption of portlandite.

A 3D reactive transport model for simulation of the chemical reaction process of ASR at microscale

“…In general, non-crystalline phases have a higher solubility than their crystalline compositional equivalents. In available ASR thermodynamic models [39,41,87], magadiite, okenite and kanemite have been used as surrogates for low Ca/Si ASR gel based on their similarities in composition. We have recalculated their equilibrium constants based on the thermodynamic data in [39,41] with H 2 SiO 4 or SiO 2 (aq) and H + transferred to the used ion H 2 SiO 4 2− and OH − in this paper.…”

Application of thermodynamic modelling to hydrated cements

“…The use of thermodynamic models would give the possibility to gain a deeper understanding of the observed phases in model systems and to predict which ASR products could potentially form within concrete. First attempts to use thermodynamic modeling to assess the changes due to ASR have been recently made [204][205][206][207]. Kim [207] used thermodynamic data for magadiite NaSi7O14•4.5H2O as a crystalline surrogate for an alkali-silicate and okenite CaSi2O5•2H2O as surrogate for a high calcium-silicate ASR product, as solubility measurements and solubility products for real ASR products are still missing.…”

Insights in the chemical fundamentals of ASR and the role of calcium in the early stage based on a 3D reactive transport model

“…As a result, the calcium depletion time and the starting time of KSH growth are shortened, making ASR to happen earlier and faster. As stated in our former paper [28] and in [51,58], the silica dissolution rate is proportional to the dissolution constant, the silica surface area, the pH (a power of 0.5), the ionic strength (a power of 0.2) and the undersaturation degree. An increase of the reactive silica fraction in the aggregate or the silica microstructural disorder degree or the aggregate porosity would result in an increase of the silica surface area, the rate constant, and the pH inside the aggregate plus the silica surface area (because the diffusion distance of OH − is increased) respectively.…”