In addition, illite (6.5%), gehlenite
(6.3%), dolomite (3.0%), larnite (2.3%), hematite (2.3%), periclase (1.3%), wollastonite (1.0%), merwinite (0.9%), ettringite (0.7%), melilite (0.3%) and calcium aluminate hydrate (0.3%) are present.
As Figure 4 clearly shows, gehlenite is detected after firing the Ca-rich clay.
At the same firing temperature, the mechanical properties are strongly related to the crystalline phases' content and directly related to the percentage of calcium carbonate and calcium silicoaluminates in the matrix : despite the low temperature of firing (850[degrees]C), the presence of crystalline phases, such as gehlenite, provides high mechanical strength (26 MPa, for STD specimens).
The presence of phases such as alite, gehlenite
, calcium silicate, calcium aluminum silicate hydrate, ettringite, silica, calcium hydroxide (portlandite), and calcium carbide can be seen in the concrete.
FA contains quartz, feldspars, anhydrite, maghemite, gehlenite
, cristobalite, zeolites, and carbonates.
The main crystalline phases identified are magnetite ([Fe.sub.3][O.sub.4]), hematite ([Fe.sub.2][O.sub.3]), zinc oxide (ZnO), gehlenite
([Ca.sub.2]Al[AlSi[O.sub.7]]), Mg[Al.sub.2][Si.sub.3][O.sub.10], quartz (Si[O.sub.2]), cyanite ([Al.sub.2]Si[O.sub.5]), lime (CaO), and portlandite (Ca[(OH).sub.2]).
XRD diffractograms show that YFA includes quartz, unburned clay remains (free lime), anhydrite, gehlenite
, hematite, calcite, and sulphide (Figure 6).
Furthermore, as shown in Figure 1, the mineralogical compounds detected in the LF slag could be attributed to mayenite (12CaO x 7[Al.sub.2][O.sub.3], [Ca.sub.12][Al.sub.14][O.sub.33], and [C.sub.12][A.sub.7]), periclase (MgO), gehlenite
(2CaO x [Al.sub.2][O.sub.3] x Si[O.sub.2], [Ca.sub.2][Al.sub.2]Si[O.sub.7]), larnite ([beta]-2CaO x Si[O.sub.2], [beta]-[Ca.sub.2]Si[O.sub.4]), shannonite ([gamma]-2CaO x Si[O.sub.2], [gamma]-[Ca.sub.2]Si[O.sub.4]), and tricalcium aluminate (3CaO x [Al.sub.2][O.sub.3], [Ca.sub.3][Al.sub.2][O.sub.6], and [C.sub.3]A).