AN EXAFS STUDY OF CEMENTITIOUS PHASES

Local environment around calcium and aluminium in high-alumina cement hydrates is investigated by X-ray absorption spectroscopy at the Ca an d Al K-edge. This technique is first validated for reference compounds CH and C(3)AH(6); the hydrates C(2)AH(8) and CAH(10), for which many doubts exist concerning the structure, are then studied. Ca K-edge EXA FS confirms that C(2)AH(8) is an AFm phase. A location is given for th e interlayer atoms, especially for the interlayer aluminium atoms, whi ch are in a tetrahedrally coordinated hydrated site. The structural mo del proposed for CAH(10) is based on two rings of six edge-sharing [Al (OH)(6)](3-) octahedra, with Ca2+ cations linking them together.