Figure 5. Boxplot representation of QXRD, optical microscopy (OM), and round robin (RR) data on phase abundance of alite.
Both microscopical and QXRD methods have been used to estimate phase abundance of clinker and are considered direct methods of analysis. Error in microscopy due to incorrect identification of the constituent phases is considered to exceed the error due to counting statistics [15] as fineness of the constituents may preclude their identification. For the finer-grained clinkers this may be especially problematic for the interstitial phases periclase, free lime, and the alkali sulfates.
X-ray powder diffraction analyses are not limited by crystal size and so are suitable for both clinker and cements. The accuracy of XRD, given careful experimental procedure, is about 2 % to 5 % absolute for alite and belite and 1 % to 2 % for aluminate and ferrite [15]. Limitations of the accuracy lie in the suitability of the reference standards (the structure models), and the ability to identify and control correlations between variables. Generally, one should see good agreement between XRD and microscopy for the silicates and the total interstitial phases.
Alite (Figure 5) shows reasonable comparability among XRD, OM-1 and RR-1, with RR-2 and RR-3 being higher. OM-1 with its 4 points has significantly greater spread (IQ-range) than the more tightly grouped XRD numbers. For belite (Figure 6), the optical points diverge from the XRD yet demonstrate reasonable agreement along themselves, although OM-1 again displays large variance, with only the lowest point comparing favorably with XRD.
Aluminate values (Figure 7) do not demonstrate good agreement among XRD and optical data. Here OM-1 is a lowlier. This may result from the fine crystal size and resulting difficulty in seeing this phase. Ferrite estimates (Figure 8) exhibit reasonable agreement among XRD, OM-1, and RR-1, both in terms of level (mean/median) and spread. Periclase estimates (Figure 9 ) fall into two groupings with respect to the mean/median: XRD/OM/RR-2 versus RR-1/RR-3.
Figure 6. Boxplot on phase abundance of belite.
Figure 7. Boxplots on phase abundance of aluminate.
Figure 8. Boxplot on phase abundance of ferrite.
Figure 9. Boxplot on phase abundance of periclase.
