Effective cation exchange capacity of calcium silicate hydrates (C-S-H)

The binding of alkalis and calcium to silicate hydrate (C-S-H) can be measured by cation exchange using cobalt hexamine solution with adapted pH. effective capacity (CEC) decreased at higher Ca/Si in C-S-H. A maximum chargeexch/Si 0.08–0.10 was = 0.8 decreasing 0.01–0.02 1.6. At high Ca/Si, only a minor fraction Ca present exchangeable sites, while most the Ca2+ interlayer or surface specifically bound thus not exchangeable. In contrast, sodium sites C-S-H, more low than Ca/Si. An increase pH presence 100 mmol/L NaOH increased CEC C-S-H 5–10% indicating limited influence on deprotonation silanol groups.