Zeolite formation in the presence of cement hydrates and albite

Publication date: Available online 21 February 2017 Source:Physics and Chemistry of the Earth, Parts A/B/C Author(s): Barbara Lothenbach, Ellina Bernard, Urs Mäder Zeolite formation caused by interactions between cement hydrates and rock forming minerals was investigated by two sets of batch experiments and supported by thermodynamic modelling. The first set of batch experiments investigated the interaction between calcium silicate hydrates (C-S-H) (Ca0.8SiO2.8·32H2O) and ettringite (Ca6Al2(SO4)3(OH)12(H2O)26) as cement hydrate minerals and albite (NaAlSi3O8) as a rock forming mineral at 20, 50 and 80°C. The dissolution of C-S-H, ettringite and albite led to relatively high calcium and low silicon and sodium concentrations and to the formation of zeolite P(Ca) (Ca2Al2Si2O8·4.5H2O) and natrolite (Na2Al2Si3O10·2H2O). The second set of experiments used ettringite and silica fume as cement phases and NaAlO2 to represent a rock forming mineral. High initial sodium, hydroxide and aluminium concentrations were observed leading to the precipitation of zeolite X (Na2Al2Si2.5O9·6.2H2O) and C-S-H gel at 20 and 50°C where only 40 to 60% of the silica had reacted after 3 years. At 80°C where more silica fume had reacted, the formation of SiO2-rich zeolite Y (Na2Al2Si4O12·8H2O) and chabazite (CaAl2Si4O12·6H2O) was observed. Solubility products for the zeolite P(Ca), natrolite, chabazite, zeolite X and zeolite Y were obtained from the measured concentrations. Comparison with ...
Source: Physics and Chemistry of the Earth, Parts ABC - Category: Science Source Type: research