Ettringite and calcium sulfoaluminate cement: investigation of water content by near-infrared spectroscopy

Calcium sulfoaluminate (CSA) cement is a sulfate-based binder whose high-performance hydraulic behavior depends on the rapid formation of ettringite, when grinded clinker is hydrated in presence of gypsum. Ettringite is a calcium aluminum sulfate mineral characterized by high water content, estimated as 32 water molecules per formula unit. Three examples of utilization of near-infrared (NIR) spectroscopy are here shown. First of all, information on water distribution in pure ettringite was deduced and compared with infrared analyses. Then its thermal behavior has been followed up to 400 °C, allowing to improve the knowledge about water loss and thermal decomposition of this hydrated phase. Finally, the obtained results have been employed in order to follow hydration of CSA cement sample, demonstrating thus that NIR spectroscopy, being highly sensitive to water amount and distribution, can be an extremely useful tool for hydration studies.

[1]  P. Schwesig,et al.  Mineralogical Characteristics of Ettringites Synthesized from Solutions And Suspensions , 2006 .

[2]  M. Hartman,et al.  Investigation of the structure of ettringite by time-of-flight neutron powder diffraction techniques , 2006 .

[3]  M. Leone,et al.  Near-i.r. Absorption of H2O and D2O in the liquid and supercooled range , 1983 .

[4]  S. Chandra,et al.  10th International congress on the chemistry of cement , 1997 .

[5]  E. Lachowski,et al.  Metaettringite, a decomposition product of ettringite , 2004 .

[6]  P. Barnes,et al.  On the thermal decomposition of ettringite Ca6[Al(OH)6]2(SO4)3.26H2O , 1996 .

[7]  M. Leone,et al.  Thermal behavior of the near ir absorption of H2O and NaClO4 aqueous solutions , 1977 .

[8]  C. D. Lawrence,et al.  Calcium sulfoaluminate cements—low-energy cements, special cements or what? , 1999 .

[9]  H. Taylor,et al.  Crystal structure of ettringite , 1970 .

[10]  Piero Baglioni,et al.  Hydration water and microstructure in calcium silicate and aluminate hydrates , 2006 .

[11]  J. Pera,et al.  New applications of calcium sulfoaluminate cement , 2004 .

[12]  Piero Baglioni,et al.  Near-infrared spectroscopy investigation of the water confined in tricalcium silicate pastes. , 2006, The journal of physical chemistry. B.

[13]  D. Gastaldi,et al.  The use of Raman spectroscopy as a versatile characterization tool for calcium sulphoaluminate cements: a compositional and hydration study , 2007 .

[14]  P. Monteiro,et al.  Raman scattering and X-ray diffraction study of the thermal decomposition of an ettringite-group crystal , 2003 .

[15]  Paul F. McMillan,et al.  Structure of Calcium Silicate Hydrate (C‐S‐H): Near‐, Mid‐, and Far‐Infrared Spectroscopy , 2004 .