significance level of 0.05, the differences in Gsa of the natural
sand measured by the four test methods (Modified T 84,
Phunque fine, SSDetect, AASHTO T 84) were not statistically
significant. Since the natural sand was rounded and had a low
P200 content with no clay fines, it was not expected to cause
discrepancies among the four test methods. The differences
in Gsa of the Preston sandstone fine aggregate, except for
Phunque vs. SSDetect, also were not statistically significant.
For other materials, the four test methods generally produced
statistically different Gsa results.
Table 3-14 shows a statistical analysis of Gsb results measured
using the four test methods for fine aggregate. Based
on a significance level of 0.05, the differences in Gsb results
measured using the AASHTO T 84 and Modified AASHTO
T 84 procedures were not statistically significant, except for
the RC limestone fine aggregate, which has a high percentage
(26.5 percent) of P200 material. For the natural sand, the
differences in Gsb measured by the four test methods, except
for Phunque vs. SSDetect, were not statistically significant.
However, for the RC limestone fine aggregate, the four test
methods produced statistically different Gsb results.
Table 3-15 shows a statistical analysis for Gssd results
measured by the four test methods for fine aggregate. The
comparison results of Gssd values were very similar to those
for the Gsb results discussed previously. This observation
was expected because Gsb and Gssd are both dependent on
how the SSD condition and water absorption capacity are
determined.
Tukey’s pairwise comparisons of water absorption values
measured by the four methods for fine aggregate are presented
in Table 3-16. The SSDetect and Phunque flask methods had
the tendency to yield lower and higher absorption values
than AASHTO T 84, respectively. In addition, the Modified
AASHTO T 84 procedure produced higher water absorption
results than the AASHTO T 84 method; however, the difference
was only statistically significant for the RC limestone fine
aggregate.
Figure 3-8 shows graphical comparisons of the means of
Gsa, Gsb, Gssd, and water absorption measured by the four
test methods for fine aggregate. As shown in Figure 3-8(a),
the AASHTO T 84 procedure yielded Gsa results that were
closest to those of the Modified AASHTO T 84 procedure,
then the Phunque method, and finally the SSDetect. Of the
four test methods, the SSDetect is the only one that vacuumsaturates
fine aggregate samples for measuring the Gsa, which
may contribute to the difference of Gsa.