(Received 30 May 1989; accepted 11 January 1990)
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Eight generically similar (i.e., rubber base) commercial elastomeric construction adhesives were evaluated to determine the differences in strength and load-slip behavior when wood joints were subjected to lateral (shear) loading. Eighteen joints were made with each of the eight adhesive brands. Ten of these specimens were exposed for various lengths of time (1 to 80 days) to temperatures of 150°F (65°C), before equilibrating to room temperature, then testing. The remaining eight specimens made with each adhesive were used as a control.
Analysis of the control group indicated that not all adhesives of a common chemical base could be considered to behave similarly under lateral loading. At 0.003 inch (0.0762 mm) slip, five of the adhesives carried statistically indistinguishable mean loads which were greater than the other three adhesives, which also showed insignificant differences. At 0.015 inch (0.381 mm) slip, six of the adhesives could not be demonstrated to have different mean load-carrying levels. The remaining two adhesives were similar and significantly inferior.
The results indicated that at low slip levels (0.003 inch), no statistically significant differences in load level was identifiable between treated and control specimens for any of the adhesives. At a significantly higher slip level (0.015 inch), two of the adhesives showed marginally significant differences at the 0.05 level of probability.
When load level was plotted versus duration of exposure to elevated temperature, no relationship between the parameter could be found at either 0.003 or 0.015 inch slip. Therefore, for the elastomeric construction adhesives studied, the issue of whether or not the joints will be exposed to elevated temperatures, not the length of time of exposure, will be more critical.
Associate Professor of Wood Engineering, Colorado State University, Ft. Collins, CO
Stock #: JTE12482J