The degrees of reaction of MA in the blended systems are shown in Fig. 6, along with the standard deviations. These degrees of reaction come from a direct point counting measurement. At all ages, slag reacts much faster than fly ash due to its inherent hydraulic and higher pozzolanic reactivity. The standard deviation for fly ash reacted is from ± 4.6 % to ± 5.0 %, while for slag reacted is from ± 3.6 % to ± 4.3 %. The higher standard deviation for fly ash than for slag is due to the lower replacement of fly ash (20 %) in the blended cement pastes than slag (30 %). In Equation (8), similar point counting standard deviations will be divided by smaller numbers, thus giving larger standard deviations for the extents of reaction. These results are comparable with the results from selective dissolution methods as performed by other researchers [2, 3]. For example, with a 20 % fly ash replacement, a 10 % fly ash extent of reaction at 28 d was reported by R. Hardtl et al. [2]. Our work here shows an 11 % reaction extent with a standard deviation of ± 4.8 %. With 30 % slag replacement, J.S. Lumley et al. [3] found a 35 % slag degree of reaction at 28 d, while in our work, a 28 ± 3.9 % reaction extent was measured. Standard deviations for the literature measurements were not given.
Figure 6. Degree of reaction of MA in blended cement systems. Error bars represent point counting standard deviations.