Sorption and electrokinetic properties of ASR product and C-S-H: A comparative modelling study

Alkali-silica reaction (ASR) is one of the most important concrete durability issues worldwide. ASR products formed at high temperature have a structure similar to the natural mineral shlykovite. Reactive Grand Canonical Simulations were used to investigate sorption of K+, Cl− and Ca2+ on C-S-H and ASR products at different pH (10.0 to 13.0) and pore water chemistry. Divalent ions can overcompensate for the negative surface charge, in particular for C-S-H, which leads to a co-adsorption of negative species such as Cl−. At high K/Ca in solution, monovalent K+ can desorb calcium from C-S-H and shlykovite surface. The calculated Ca/K partition coefficient shows a higher affinity of ASR product for K+, while C-S-H favours Ca2+. The uptake of K+ by ASR products lowers the alkali concentration in the solution and could thus slow down the rate of ASR.