NMR Analysis of Roman cements compared with GEOCISTEM cements.
We found at least two specimens of Roman cement (ROM 4 and OST 7G) whose 29Si NMR Spectrum show the same resonances as those of GEOCISTEM cements. The spectrum for the cement ROM 4 (Opus Signinum) is similar to the spectra of Ca 01/Ca 02 GEOCISTEM cements. These particular GEOCISTEM cements were made of MK-750 (or kandoxi) and zeolithic tuffs Ca01, Ca02 (philipsite type). The spectrum for the cement OST 7G is equivalent to the LA01 GEOCISTEM volcanic tuff cement .
Comparative 29Si NMR spectra for Cements ROM 4/Ca 01,
Ca 02 GEOCISTEM (left), and Cements OST 7G/LA 01 GEOCISTEM (right).
ROM 4 results from the reaction between lime and a special ceramic testa different from plain kaolinitic clay. This chemical reaction yields an alumino-silicate structure with a major resonance at -86 ppm suggesting a structure of the Si(Q3Si,1OH) and Si(Q4) types, or a hydrated felspathoid analogue. In addition, the presence of hydrated gehlinite in ROM 4 cement deducted from 27Al Spectroscopy suggests following final make-up for ROM 4 cement:
- hydrated gehlinite,
- recarbonated lime,
- hydrated feldspathoid,
- fine grained zeolitic volcanic tuff.
The 29Si NMR spectrum of OST 7G cement is equivalent to the one of the LA01 GEOCISTEM volcanic tuff cement. OST 7G mortar results from the reaction between lime and analcime type cretoni. The product of this reaction is an alumino-silicate of type Si(Q3, 1OH) and Si(Q4) (-86 ppm to -94 ppm range) different from those expected with regular pozzolan. There is no hydrated gehlinite in OST 7G cement deducted from 27Al Spectroscopy. The final make-up of OST 7G cement would be:
- recarbonated lime,
- hydrated feldspathoid,
- fine grained zeolitic volcanic tuff.
Hydrated feldspathoid and hydrated gehlinite are X-ray amorph. This explains why the chemical and mineralogical analysis carried out by the GEOCISTEM geologist team at Cagliari University on these ancient mortars, did not provide detailed information on the make-up of the lime-cement.
See also in The Mystery of Roman Concretes unveiled .