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One of the most important properties of a cement is its setting time, as this will regulate how much time the contractor will have to get the concrete placed and finished. In the U.S., setting times are assessed using either a Vicat (ASTM C191) or Gillmore (ASTM C266) needle [1]. These tests basically measure when the hydrating cement paste develops some finite value of resistance to penetration. Within the VCCTL software, setting is assessed using a special percolation algorithm [3,10]. The algorithm measures the fraction of total solids that are linked together by calcium silicate hydrate gel (C-S-H) and ettringite or C3AH6 hydration products. Thus, two touching cement particles do not comprise a percolated structure for setting unless some hydration product bridges them. In this way, the setting behavior of both well-dispersed and flocculated cement pastes can be consistently evaluated. The VCCTL returns the percolated (connected) fraction (0 to 1) for the total solids as a function of either hydration time or degree of hydration.
Figure 9 shows these percolation plots vs. time for cements 135 and 141, both hydrated at a w/c ratio determined by the ASTM Normal Consistency test (ASTM C187 [1]). The initial and final setting times determined by the Vicat and Gillmore needle tests are shown as vertical lines on the graphs as noted in the caption. The initial and final Vicat setting times are seen to approximately correspond to percolated fractions of 0.4 and 0.75, respectively. The Gillmore setting times are always slightly longer, the initial and final setting times corresponding to percolated fractions of 0.6 and 0.8, respectively.
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