Non-Evaporable Water Content

After achieving the required age, samples for the non-evaporable water content, W_N, determination were ground to a powder using a mortar and pestle and flushed with methanol, using a porous ceramic filter and a vacuum, to stop the hydration. The resultant powder was divided approximately in half and placed in two crucibles of known mass and left overnight (on the order of 20 hours) in an oven at 105 ºC. When removed from the oven, the mass of the crucibles and samples were redetermined before placing them in a furnace at 950 ºC for a minimum of four hours. The non-evaporable water content was calculated as the average difference between the 950 and 105 ºC mass measurements for the two crucibles, corrected for the loss on ignition of the cement powder itself, which was assessed in a separate crucible experiment.

To convert the non-evaporable water measurements to estimated degrees of hydration, $\alpha$, it was necessary to determine the non-evaporable water content for a fully hydrated sample. Cement paste samples at a w/c=3.0 were prepared for each of the two cements. The samples were each continuously ground in a jar mill, containing approximately 50% volume fraction of stainless steel balls, for a period exceeding 28 days. Samples were removed periodically and the non-evaporable water content assessed using the above procedure. Little change in the non-evaporable water content was observed after the first seven days of grinding. For Cement 115, a value of 0.226 g H₂O/g cement was determined at "complete" hydration, which can be compared to a value of 0.240 calculated based on the Bogue composition of the cement and tabulated values for the non-evaporable water content of the major cement phases [9] provided in Table 5. For Cement 116, values of 0.235 and 0.239 were determined using the experimental procedure and direct calculation, respectively.

Table 5: Non-evaporable Water Contents for Major Phases of Cement

Phase	Coefficient g water / g cement	Source
C3S	0.24	[9]
C2S	0.21	[9]
C3A	0.40	[9]
C4AF	0.37	[9]
Free lime	0.33	Direct calculation a

^a Assuming reaction of free lime with water to produce portlandite (CH).