Non-evaporable Water Content Determination

One method of quantifying the degree of hydration of a portland cement is via measurement of its non-evaporable water content, after any hydration time of interest [8]. For the non-evaporable water content determinations, cement pastes were prepared with a water-to-cement ratio (w/c) of 0.4. The cement powder and necessary mass of water were mixed together by kneading by hand in a sealed plastic bag for two to three minutes. Samples were then removed and stored in capped plastic vials. After placing the cement paste sample (typically 10 g to 15 g in mass) in its container, the vials were either capped to maintain sealed curing conditions, or about 1 mL of water was added on top of the cement paste to maintain saturated curing conditions throughout the experiment. The samples were stored at 25 ºC until their evaluation. Evaluations were typically made after the following hydration times: 8 h and (1, 3, 7, 14, and 28) d.

After achieving the required age, samples for the determination of non-evaporable water content, w_n , were ground to a powder, using a mortar and a pestle, and flushed with methanol, using a porous ceramic filter and a vacuum, to halt the hydration. The resultant powder was divided approximately in half and placed in two crucibles of known mass, which were left overnight (about 20 h) 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 1000 ºC for a minimum of 4 h. The non-evaporable water content was calculated as the average difference between the 105 ºC and 1000 ºC mass measurements for the two crucibles, corrected for the loss on ignition of the cement powder itself, which was assessed in a separate experiment.

To convert the non-evaporable water content measurements to estimated degrees of hydration, $\alpha$, it was necessary to determine the non-evaporable water content for a fully hydrated sample. Based on the compositions of the two cements [3], values of 0.235 g H ₂O/g cement and 0.243 g H ₂O/g cement were determined for cements 135 and 136, respectively.