Extensions of CASH+ thermodynamic solid solution model for the uptake of alkali metals and alkaline earth metals in C-S-H

Porewater compositions of Portland cement with and without silica fume calculated using the fine-tuned CASH+NK solid solution model

“… Sites: DU dimeric unit, BT bridging tetrahedral, IC interlayer cation, IW interlayer water. is the adjustment of endmember value relative to that given in [ 17 ]. The other endmembers of the CASH+NK model and its interaction parameters remain unchanged and are given in Kulik et al and Miron et al [ 16 , 17 ] …”

“…The uptake of K and Na in C–S–H predicted by the initial CASH+ model [ 16 , 17 ] is too strong, when applied to PC, where only little free pore solution is present. The original model was parameterized against several experimental datasets on the uptake of Na and K measured in dilute suspensions at different Ca/Si ratios and has shown a good agreement with the experimental data [ 17 ].…”

“…The uptake of K and Na in C–S–H predicted by the initial CASH+ model [ 16 , 17 ] is too strong, when applied to PC, where only little free pore solution is present. The original model was parameterized against several experimental datasets on the uptake of Na and K measured in dilute suspensions at different Ca/Si ratios and has shown a good agreement with the experimental data [ 17 ]. Nevertheless, the model endmembers with Ca in the BT sites, TCKh and TCNh, that determine the uptake of K and Na in systems with high Ca/Si ratios showed the lowest sensitivity to the experimental data as the alkali uptake is relatively low in C–S–H experiments with high liquid to solid ratio (> 20) leading to a large scatter in the measured alkali uptake, while for hydrated cements this ratio is << 1.…”

“…The calculations were performed using the GEM-Selektor [ 18 ] v.3.9.3 geochemical modeling package and the thermodynamic data for cement phases from the Cemdata18 thermodynamic database [ 19 ], except for the model for C–S–H, where the CASH+ [ 16 , 17 ] was used. The relevant stable phases and solid solutions considered in the calculations are given in Table 2 .…”

“…1 ). The model was then extended to account for the uptake of alkali metals and alkaline earth metals in Miron et al [ 17 ] and work is being carried out to extend it for the uptake of Al and other elements. This CASH+NK model used in the present study is composed of several endmembers belonging to the core CASH+ model, plus those accounting for the uptake of Na and K (Table 1 ) with no account for the aluminum uptake.…”