Double-Lap Shear Tests
All of the specimens were tested until failure. The shear stress at the bond interface at the time of failure were calculated using
FIG. 6—Tension pull-out specimen testing load setup.
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s = the shear stress at each bond interface (MPa),
P = the recorded ultimate applied load (N),
l = the length of effective bond area (mm), equal to 450 mm for this experiment and,
w = the width of effective bond area (mm), equal to 100 mm for this experiment.
In Table 1 a summary of the experimental results is provided; in addition, the specific side of the specimen that experienced failure is shown as being either east or west, which were defined previously in “Double-Lap Shear Test Specimens." In the case of the specimens using epoxy type A, failure did not occur due to debonding between the GFRP and the UHPC. Instead, shear failure in the GFRP plates at the connection with the steel chair occurred. As can be seen in Table 1, the side of the specimen that experienced failure was not stated for the specimens using epoxy type A. Accordingly, the shear strength at the bond interface was provided as a lower limit, due to the fact that had shear failure not occurred at the connection a higher applied load would have been reached. The failure for the specimens that used epoxy types B or C for bonding of the coarse silica sand aggregates occurred predominantly in the epoxy adhesive layer, though some fracturing of the aggregates were seen along the interface for the specimens that used epoxy type C for aggregate bonding. In conjunction with the values for maximum shear strength, comparison of the failure modes for the specimens with epoxy types B and C shows that the epoxy type B provided greater bonding between the UHPC and the coarse silica sand aggregates, where it maintained a consistent bond strength equal to or greater than the fracture strength of the aggregates. Photographs showing the failure of representative specimens under shear load for all three types of epoxy adhesive used are shown in Fig. 7.
TABLE 1—Experimental results of double shear test specimens.
c) Epoxy Type C
FIG. 8—Distribution and variance of shear strength for different types of epoxy used for coarse silica sand bonding.
The distribution and variance for the shear strength of the individual double shear test specimens are shown in Fig. 8, with the ±r range represented by the box and the actual experimental minimum and maximum values indicated by the capped vertical lines. It can be observed in Fig. 8 that the specimens that used epoxy type A for aggregate bonding at the interface provided the highest shear resistance. In order to ascertain if the results obtained from the specimens with the three different types of epoxy adhesives were statistically different, a single factor ANOVA (analysis of variance) test was performed, with the results shown in Table 2. By comparing the F value with the value for Fcrit, it is evident that F is substantially greater than Fcrit. The result from the ANOVA analysis indicates that the average shear strength provided by the specimens using the three different epoxy adhesive types were statistically different from one another within a 95 % confidence level.