Effect of Calcium Additions on N–A–S–H Cementitious Gels

This paper reports a research on the properties of synthetic sodium aluminosilicate hydrate gels as models for the gels arising in alkali‐activated aluminosilicate systems. The interaction between these N–A–S–H gels and aqueous calcium was studied to explore a potential consequence of mixing conventional Portland cements and alkali‐activated systems. The properties of two N–A–S–H gels (with Si/Al=1 and 2) synthesized in highly alkaline media, in the presence of calcium are reported. N–A–S–H gels were synthesized using aluminum nitrate, sodium hydroxide, and a sodium silicate. FTIR, NMR, and TEM/EDX techniques were used to characterize N–A–S–H gels before and after adding calcium. The results obtained show that calcium is uptaken in N–A–S–H gels resulting in a modification of the chemical composition due to the substitution of sodium per calcium.