Page 16 - report P Lemoine feb 2013c

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between phases. Due to the topographic inhomogeneties and brittleness of the

samples, cracking during indentation affects the measured depth h, which affects in
turn the contact depth h c and the contact area A (see annex B). This would affect

1/2
both the E and H value, but more so the H value (ie E varies as 1/A whereas H
varies as 1/A), as observed in this report. Evidence of cracking during indentation
can be seen on figure 9c, but also on the AFM micrographs shown in figure 20 and

21.

Indentation cracking can also be seen in the load-displacement (L-d) and stiffness-
displacement (S-d) curves for the Y asrec and Y fired samples in the matrix region,

shown in figure 22. The important data scatter is again expected considering the

compositional and topographical hetereogenity of the matrix regions. For an
homogeneous material undergoing an elasto-plastic indentation by a Berkovitch

diamond tip, one would expect a linear S-d curve. Pure cracking would give a zero S
value while cracking with elasto-plastic deformation would simply give a reduction in

the S value, which is observed more often for the Y asrec sample than for the Y fired
sample. This observation would need to be corroborated by SEM micrographs of the

indents, nevertheless, if confirmed, this would indicates that the fire treatment

toughen the cement with the RoadCem additive.

Finally, another observation can be put forward in favour of mechanical toughening

mechanisms at interfacial regions, both for the effect of the Y additive on the cement
properties and for the effect of the fire treatment on the properties of the cement with

additive. Examining the two tables (figure 7 and 19), one can see;

· Much larger mean ratio for Y fired/Y asrec, in the case of random positioning (
1.61-3.44 for for random positioning, 1.2-1.5 for individually defined indents).

· Much smaller mean ratio for no Y asrec/Y asrec, in the case of random
positioning (0.11-0.22 for random positioning, 0.3-0.8 for individually defined
indents)

This can be explained if one considers again that cracking affects the indentation

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