Substituted Tobermorites: ²⁷Al and ²⁹Si MASNMR, Cation Exchange, and Water Sorption Studies

Abstract

A1 and 29Si magic angle spinning nuclear magnetic resonance spectroscopy revealed that the maximum amount of Al that can be substituted for Si in the tobermorite structure is 15 to 20 mol%. Powder X-ray diffraction and cation exchange studies corroborate the above finding. Anomalous tobermorite structures resulted in all cases, and hydrogarnet appeared beyond the 15 to 20 mol% A1 substitution limit for Si. The sorption of water molecules by synthetic [A13+ + Na+]-substituted tobermorites and their cationexchanged forms heated at 200°C under vacuum (>lo-' torr) was measured at 25°C in order to probe the nature of the ion-exchange cavity. Samples with 530 mol% of Al substitution for Si showed isotherms of Brunauer, Demming, Demming, Teller (BDDT) type 1 and gave better linearity with the Langmuir plot than with the BET plot. Samples with 2 3 5 mol% of A1 substitution for Si showed BDDT type I1 isotherms and gave better linearity with the BET than with the Langmuir equation. The Langmuir monolayer capacity was found to depend on the Al content and on the cationic form. The Li+-and Na+-exchanged tobermorites with about 20 mol% of Al substitution for Si showed the highest Langmuir monolayer water sorption capacity. The Cs+-exchanged tobermorites showed a smaller capacity than the Li+-or Na+-exchanged samples, which can be ascribed to clogging of the ion-exchange cavity by the large Cs+ ions.[

Unlocking the secrets of Al-tobermorite in Roman seawater concrete

“…8a) indicates that the alumina tetrahedra occur in silicate chain [Q 2 (1Al)] and branching [Q 3 (1Al), Q 3 (2Al)] positions within the (002) interlayer (Komarneni and Roy 1983;Komarneni et al 1985;Tsuji et al 1991;Skibsted et al 1994;Sun et al 2006). The high intensity of Q 2 (0Al) and Q 2 (1Al) peaks relative to the Q 1 peak indicates long chain lengths in the b [020] crystallographic direction.…”

“…The poorly crystalline C-A-S-H binders of these concretes improve chemical stability relative to C-S-H, the "glue" of conventional Portland-type cement concretes, whose model basis is the ideal composition of tobermorite, Ca 5 Si 6 H 2 O 18 ·4H 2 O (Taylor 1992;Sun et al 2006). C-A-S-H and 11 Å Al-tobermorite hold great potential as cementitious binders for high-performance concretes and concrete encapsulations of hazardous wastes (Komarneni and Roy 1983;Komarneni et al 1987;Komarneni and Tsuji 1989;Tsuji et al 1991), but the long-term performance of C-A-S-H is unknown and neither pure tobermorite nor Al-tobermorite occur in moist air-cured conventional concretes. Although laboratory syntheses of Al-tobermorite typically require high temperatures, 120 to 240 °C (Diamond 1966;Komarneni and Roy 1983;Komarneni and Tsuji 1989; Barnes and Scheetz 1991;Shaw et al 2000;Sun et al 2006;Houston et al 2009), occasional syntheses have been achieved at 80 °C with amorphous silica and zeolites (Komarneni and Roy 1983;Komarneni et al 1985), reactants similar to zeolitized alkaliand alumina-rich Flegrean ash pozzolan (de'Gennaro et al 2000).…”

Vapor hydration of SON68 glass from 90°C to 200°C: A kinetic study and corrosion products investigation

“…The presence of this phase was confirmed with micro-Raman analysis. If Al 3+ is substituted for Si 4+ then tobermorite has a high absorption capacity for Cs, Sr, and other alkaline and alkaline-earth elements through ion exchange [8,21]. This phase has also been extensively studied because it incorporates Eu(III), which is oftentimes used as a surrogate for the trivalent actinides [22].…”

Microstructure and characterization of aluminum-incorporated calcium silicate hydrates (C–S–H) under hydrothermal conditions

“…metakaolinite, 8,11 kaolinite, 1 zeolite, 6 newsprint recycling residue 12 and y ash [14][15][16][17] ) and the optimization of its ion exchange performance. 4 It has also been reported that aluminum could inuence the formation of tobermorite to form Al-substituted tobermorite, in which Al substitution occurred at the Q 2 or Q 3 sites (the symbol Q represents one SiO 4 tetrahedron and the superscript indicates the number of other Q units to which it is bonded), 7 as illustrated in Fig.…”